Many undergraduates seem to think molecules like to hang around rather than moving on
Keith S. Taber
A representation of a small part of a layer of molecules in a solid substance – with one molecule highlighted by colour. If the solid were melted, and then refrozen, where would the highlighted molecule be?
If you are a science teacher: what would your students think?
In this article I offer my own version (actually two versions, see below) of a question I saw used in a published study (Smith & Villarreal, 2015a). As I no longer have any students, I cannot easily try this out, but perhaps a reader who is currently teaching science might be tempted to see what their pupils or students might think? (If you do, I would apreciate hearing about what you find!)
The two versions of the question can be downloaded from the links below.
The question could be given to individual learners, or as the basis of small group discussion, or perhaps just projected onto the screen for a 'show of hands' for each response option. (Exploring student thinking to detect misconceptions is known as diagnostic assessment.)
Alternative conceptions abound
I am very familiar with the extensive evidence which shows that is very common for learners, at all levels, and in any topic, to hold alternative conceptions ('misconceptions') at odds with canonical science and the target knowledge set out in the science curriculum. So, I am seldom surprised when I read about a study which reports finding learners demonstrating such conceptions.
Yet one study I read which reported learners commonly holding an alternative conception did surprise me. I would have not been surprised if the respondents had been secondary levels students, and a minority of them had demonstrated this particular conception, but I would not have expected how the study found a high incidence of the alternative conception among undergraduates studying chemistry.
The research asked about what happens when a solid is either dissolved, or melted, and then returns to the solid state. It used an instrument that presented a figure representing the particles in a small section of a solid, with one particle marked out, and asked the learners to draw the equivalent images after the solid had either dissolved and then been recrystallised, or melted and then been refrozen.
I an going to limit myself to the easier context (melt, then freeze – no solvent molecules involved). According to the researchers, the results suggested that a large proportion of the undergraduates indicated that the atom that had been marked out would be found in the same position in the solid at the end of the process: the exact proportion shifted in two versions of the study (65%, 50%) but a very rough gloss was that at least half of the learners located the marked particle back at its original point.
"These results indicated that a large proportion of the students viewed the [marked] molecule as being near to the same position after melting as it was before melting, and being in the position it was originally in after the liquid froze back to the solid."
Smith & Villarreal, 2015a: 277-278
Perhaps this should not have surprised me – I have been told by very bright A level students that on homolytic bond fusion each atom would always get its own electrons back, and this seems something of a parallel notion.
Now there was some questioning of the methodology and instrument used here (Langbeheim, 2015; see also Smith & Villarreal, 2015b) – as there often is in educational research – but it seemed a substantial proportion of learners thought the solid would reform with particles in their original positions, and this suggests a rather limited understanding of the level of molecular motion in the dissolved or molten state. I would not have been so surprised if this work had been carried out with, say, twelve year olds – but such a high level of misconception among undergraduates did surprise me as it reflects a failure to imagine the nature of the molecular world, and that surely makes learning high level (e.g., degree level) chemistry very difficult.
Now there are serious challenges in representing the nanoscale (thus the questioning of the representations used in the study) simply because molecules, ions, electron, atoms – are not the kinds of things we can draw realistically – they are fuzzy objects with no surfaces that somewhat blend into their neighbours. This raises a possible defence for students in such studies
'yes, your honour, I did show the particle as having returned to the same position, but as the focal figure had been drawn unrealistically as a set of circles I did not think authenticity was being asked for!'
It seems unlikely any learner really did think that – and the researchers did ask learners about their reasoning. The most common type of explanations were (Smith & Villarreal, 2015a: 278):
In the molten state: The molecule doesn't move far from its original position
After resolidification: The molecule ends up near where it was positioned in the liquid
Representing quanticles
Molecules, ions, atoms are 'quantum objects' which do not have the properties of familiar macroscopic objects. The nanoscopic particles in a lattice or liquid are not like the particles in table salt (grains) or sugar (granules) which each have a definite volume and surface, and which cannot be made to overlap their neighbours.
The following is my representation of a section of a layer of molecules in a solid substance. I have shown them round as that is simpler. Most molecules are not round (but 'molecules' of, say, neon or argon, are.) I have tried to show them as being fuzzy rather than as if ball-bearings with definite surfaces as the 'substance' of atoms, ions and molecules is largely electric fields and electron 'clouds' (a rather appropriate metaphor) rather than anything 'solid'. (And, of course, the word solid loses its meaning for a single molecule. We might, figuratively, suggest the atom is like a tiny liquid drop surrounded by an immense volume of gas – but it is probably best to avoid using such comparisons with learners becasue of the potential for them taking the terms literally.)
Should the molecules be touching in the solid? That is a problematic question as how do we decide whether things are touching when the things concerned do not have distinct surfaces but rather fade away to infinity? (If the gas giants Jupiter and Saturn were to ever come together, how would we decide at what point they had actually physically collided?)
Often in science teaching we cheat and show molecules touching in solids when teaching about the differences between condensed and gaseous states; but then hope students have forgotten this by the time we want to teach about thermal expansion of solids.
My diagram shows a layer of the regular crystal structure, so if you think my 'molecules' should touch then you can imagine that they would once the adjacent layers were drawn in.
The image I have used might suggest too much space between molecules…
…adding another layer might help give the appearance of close packing, but if a different colour is used this may suggest some physical difference…
yet making both layers the same colour makes the figure more dificult to interpret.
It is a problem of scale
The real issue for the novice learner here is one of scale. The scale of atoms is far beyond our ready grasp. My figure shows a much more extended section of material than that in the original study – but still, a tiny, tiny, tiny fraction of a solid we could readily see and manipulate. If the solid substance melted, then (e.g., around room temperature) we would expect molecular speeds of the order of hundreds of metres per second. In the gas phase that might be somewhat reflected in how far some molecules get (but diffusion is still much slowed by collisions), but in a condensed phase, so in a liquid, the molecules are not going to get very far at all before colliding with a 'neighbour' and being deflected off course.
The so-called 'random walk' of any molecule in a liquid will reflect mean speeds orders of magnitude less than the hundreds of metres per second instantaneous speed (as it is constantly being shifted to a new direction, and is just as likely to be sent back in the direction it originated).
But then, given the size of the sample represented, the distance from one end of the image to the other is of the order of maybe 0.000 000 001 metres. If a molecule with an instantaneous speed of hundreds of metres per second only has to travel of the order of perhaps 0.000 000 000 1m before colliding with the next molecule, it is going to have an awful lot of collisions each second – many billions. So, a molecule bumping around at say 300 m/s would not take very long to move 0.000 000 001 m (and so off the region of lattice shown in my figure) even with all those restrictive collisions!
Two versions of the diagnostic question for use in class
Even if the solid melts and is a liquid for only a few minutes (that is, a few hundred seconds), and even if we have placed the original solid in a tightly constricting container such that the liquid does not change overall shape, what are the chances of the molecule ending up in the same lattice position? Or even being in the frame when we represent such a small section of the lattice?
If we are only representing one layer of molecules, then what are the chances of the molecule even ending up in the same layer (it is likely to have moved 'up'/'down' just as much as laterally along the plane represented whilst in the liquid state).
Each of the options (in both versions of the question) are possible outcomes.
Given that the section of the latice shown is so limited, all the positions shown are pretty much local to the starting point, so I would argue the molecule could almost equally likely end up in any of the lattice positions in the figure (so: A, C and D are, in effect, equally likely – as would be any other lattice position you selected from the image).
What about Option B?
Option B reflects all the possibilities where the molecule ends up outside the small section of lattice layer illustrated, including all the options where it has moved to a different layer. There will be billions and billions of these options, including, at least, many thousands of options close enough for the molecule to have easily moved there in the number of 'random walk' steps feasible in the time scale.
So, the answer to the question of which option is most likely (in either version of the question) is easy – option B is by farmost likely.
But I wonder if most students who have been taught about particle models and states of matter would agree with me? If Smith and Villarreal's undergraduate sample is anything to go by, then I guess not.
Work cited:
Smith, K. C., & Villarreal, S. (2015a). Using animations in identifying general chemistry students' misconceptions and evaluating their knowledge transfer relating to particle position in physical changes [10.1039/C4RP00229F]. Chemistry Education Research and Practice, 16(2), 273-282. https://doi.org/10.1039/C4RP00229F
Langbeheim, E. (2015). Reinterpretation of students' ideas when reasoning about particle model illustrations. A Response to "Using Animations in Identifying General Chemistry Students' Misconceptions and Evaluating their Knowledge Transfer Relating to Particle Position in Physical Changes" [10.1039/C5RP00076A]. Chemistry Education Research and Practice, 16(3), 697-700. https://doi.org/10.1039/C5RP00076A
Smith, K. C., & Villarreal, S. (2015b). A Reply to "Reinterpretation of Students' Ideas when Reasoning about Particle Model Illustrations. A Response to 'Using Animations in Identifying General Chemistry Students' Misconceptions and Evaluating their Knowledge Transfer Relating to Particle Position in Physical Changes' by Smith & Villarreal (2015)" [10.1039/C5RP00095E]. Chemistry Education Research and Practice, 16, 701-703. https://doi.org/10.1039/C5RP00095E
I was recently listening to a podcast of an episode of a science magazine programme which included two items of astronomy news, one about a supernovae, the next about a quasar. I often find little snippets in such programmes that I think work making a note of (quite a few of the analogies, metaphors and similes – and anthropomorphisms – reported on this site come from such sources). Here, I went back and listened to the items again, and decided the discussions were rich enough in interesting points to be worth taking time to transcribe them in full. The science itself was fascinating, but I also thought the discourse was interesting from the perspective of communicating abstract science. 1
I have appended my transcriptions below for anyone who is interested – or you can go and listen to the podcast (episode 'Largest ever COVID safety study' of the BBC World Service's Science in Action).
Space, as Douglas Adams famously noted, is big. And it is not easy for humans to fully appreciate the scales involved – even of say, the distance to the moon, or the mass of Jupiter, let alone beyond 'our' solar system, and even 'our' galaxy. Perhaps that is why public communication of space science is often so rich with metaphor and other comparisons?
When is a star no longer a star (or, does it become a different star?)
One of the issues raised by both items is what we mean by a star. When we see the night sky there are myriad visible sources of light, and these were traditionally all called stars. Telescopes revealed a good many more, and radio telescopes other sources that could not detected visually. We usually think of the planets as being something other than stars, but even that is somewhat arbitrary – the planets have also been seen as a subset of the stars – the planetary or wandering stars, as opposed to the 'fixed' stars.
At one time it was commonly thought the fixed stars were actually fixed into some kind of crystalline sphere. We now know they are not fixed at all, as the whole universe is populated with objects influenced by gravity and in motion. But on the scale of a human lifetime, the fixed stars tend to appear pretty stationary in relation to one another, because of the vast distances involved – even if they are actually moving rather fast in human terms.
Wikipedia (a generally, but not always, reliable source) suggests "a star is a luminous spheroid of plasma held together by self-gravity" – so by that definition the planets no longer count as stars. What about Supernova 1987A (SN 1987A) or quasar J0529-4351?
"This image, taken with Hubble's Wide Field and Planetary Camera 2in 1995, shows the orange-red rings surrounding Supernova 1987A in the Large Magellanic Cloud. The glowing debris of the supernova explosion, which occurred in February 1987, is at the centre of the inner ring. The small white square indicates the location of the STIS aperture used for the new far-ultraviolet observation. [George Sonneborn (Goddard Space Flight Center), Jason Pun (NOAO), the STIS Instrument Definition Team, and NASA/ESA]" [Perhaps the supernova explosion did not actually occur in February 1987]
Supernova 1987A is so-called because it was the first supernova detected in 1987 (and I am old enough to remember the news of this at the time). Stars remain in a more-or-less stable state (that is, their size, temperature, mass are changing, but, in proportional terms, only very, very slowly2) for many millions of years because of a balance of forces – the extremely high pressures at the centre work against the tendency of gravity to bring all the matter closer together. (Imagine a football supported by a constant jet of water fired vertically upwards.) The high pressures inside a star relate to a very high temperature, and that temperature is maintained despite the hot star radiating (infra-red, visible, ultraviolet…) into space 3 because of the heating effect of the nuclear reactions. There can be a sequence of nuclear fusion reactions that occur under different conditions, but the starting point and longest-lasting phase involves hydrogen being fused into helium.
The key point is that when the reactants ('fuel') for one process have all (or nearly all) been reacted, then a subsequent reaction (fusing the product of a previous phase) becomes more dominant. Each specific reaction releases a particular amount of energy at a particular rate (just as with different exothermic chemical reactions), so the star's equilibrium has to shift as the rate of energy production changes the conditions near the centre. Just as you cannot run a petrol engine on diesel without making some adjustments, the characteristics of the star change with shifts along the sequence of nuclear reactions at its core.
These changes can be quite dramatic. It is thought that in the future the Earth's Sun will expand to be as large as the Earth's orbit – but that is in the distant future: not for billions of years yet.
Going nova
Massive stars can reach a point when the rate of energy conversion drops so suddenly (on a stellar scale) that there is a kind of collapse, followed by a kind of explosive recoil, that ejects much material out into space, whilst leaving a core of condensed nuclear matter – a neutron star. For even more massive stars, not even nuclear material is stable, as there is sufficient gravity to even collapse nuclear matter, and a black hole forms.
It was such an explosion that was bright enough to be seen as a 'nova' (new star) from Earth. Astronomers have since been waiting to find evidence of what was left behind at the location of the explosion – a neutron star, or a black hole. But of course, although we use the term 'nova', it was not actually a new star, just a star that was so far away, indeed in another galaxy, that it was not noticeable – until it exploded.
Dr. Olivia Jones (from the UK Astronomy Technology Centre at The Royal Observatory, Edinburgh) explained that neutron stars form from
"…really massive stars like Supernova 1987A or what it was beforehand, about 20 times the mass of a Sun…
So, what was SN 1987A before it went supernova? It was already a star – moreover, astronomers observing the Supernova were studying
…how it evolves in real time, which in astronomy terms is extremely rare, just tracing the evolution of the death of a star…
So, it was a star; and it died, or is dying. (This is a kind of metaphor, but one that has become adopted into common usage – this way of astronomers talking of stars as having births, lives, careers, deaths, has been discussed here before: 'The passing of stars: Birth, death, and afterlife in the universe.') What once was the star, is now (i) a core located where the star was – and (ii) a vast amount of ejected material now "about 20 light years across" – so spread over a much larger volume than our entire solar system. The core is now a "neutron star [which] will start to cool down, gradually and gradually and fade away".
So, SN 1987A was less a star, than an event: the collapse of a star and its immediate aftermath. The neutron star at is core is only part of what is left from that event (perhaps like a skeleton left by a deceased animal?) Moreover, if we accept Wikipedia's definition then the neutron star is not actually a star at all, as instead of being plasma (ionised gas – 'a phase of matter produced when material is too hot to exist as, what to us seems, 'normal' gas) it comprises of material that is so condensed that it does not even contain normal atoms, just in effect a vast number of atomic nuclei fused into one single object – a star-scale atomic nucleus. So, one could say that SN 1987A was no so much a star, as the trace evidence of a star that no longer existed.
And SN 1987A is not alone in presenting identity problems to astronomers. J0529-4351 is now recognised as being possibly the brightest object in the sky (that is, if we viewed them all from the same distance to give a fair comparison) but until recently it was considered a fairly unimpressive star. As doctoral researcher Samuel Lai (Research School of Astronomy and Astrophysics, Australian National University) pointed out,
this one was mis-characterised as a star, I mean it just looks like one fairly insignificant point, just like all the other ones, right, and so we never picked it up as quasar before
But now it is recognised to only appear insignificant because it is so far away – and it is not just another star. It has been 'promoted' to quasar status. That does not mean the star has changed – only our understanding of it.
But is it a star at all? The term quasar means 'quasi–stellar object', that is something that appears much like a star. But, if J0529-435 is a quasar, then it consists of a black hole, into which material is being attracted by gravity in a process that is so energetic that the material being accreted is heated and radiates an enormous amount of energy before it slips from view over the black hole's event horizon. That material is not a luminous spheroid of plasma held together by self-gravity either.
This video from the European Southern Observatory (ESO) gives an impression of just how far away (and so how difficult to detect) the brightest object in the galaxy actually is.
These 'ontological' questions (how we classify objects of different kinds) interest me, but for those who think this kind of issue is a bit esoteric, there was a great deal more to think about in these item.
"A long time ago, in a galaxy far, far away"
For one thing, it was not, as presenter Roland Pease suggested, strictly the 37th anniversary of the SN 1987A – at least not in the sense that the precursor star went supernovae 37 years ago. SN 1987A is about 170 000 light years away. The event, the explosion, actually occurred something like 170 000 years before it could be detected here. So, saying it is the 37th anniversary (rather than, perhaps, the 170 037th anniversary4) is a very anthropocentric, or, at least, geocentric take on things.
Then again, listeners are told that the supernova was in "the Large Magellanic Cloud just outside the Milky Way galaxy" – this is a reasonable description for someone taking an overview of the galaxies, but there is probably something like 90,000 light-years between what can be considered the edges of our Milky Way galaxy and this 'close by' one. So, this is a bit like suggesting Birmingham is 'just outside' London – an evaluation which might make more sense to someone travelling from Wallaroo rather than someone from Wolverhampton.
It is all a matter of scale. Given that the light from J0529-4351 takes about twelve billion years to reach us, ninety thousand light years is indeed, by comparison, just outside our own galaxy.
But the numbers here are simply staggering. Imagine something the size of a neutron star (whether we think it really is a star or not) that listeners were informed is "rotating…around 700 times a second". I do not think we can actually imagine that (rather than conceptualise it) even for an object the size of a pin – because our senses have not evolved to engage with something spinning that fast. Similarly, material moving around a black hole at tens of thousands of kilometres per second is also beyond what is ready visualisation. Again, we may understand, conceptually, that "the neutron star is over a million degrees Celsius" but this is just another very big number way that is outside any direct human experience.
Comparisons of scale
Thus the use of analogies and other comparisons to get across something of the immense magnitudes involved:
"If you think of our Sun as a tennis ball in size, the star that formed [SN] 87A was about as big as the London Eye."
"A teaspoon of this material, of a neutron star, weighs about as much as Everest"
the black home at the centre of the quasar acquires an entire Sun worth of mass every single day
the black hole at the centre of the quasar acquires the equivalent of about four earths, every single second
the quasar is about five hundred trillion times brighter than the Sun, or equivalent to about five hundred trillion suns
Often in explaining science, everyday objects (fridges, buses – see 'Quotidian comparisons') are used for comparisons of size or mass – but here we have to shift up to a mountain. The references to 'every single day' and 'every single second' include redundancy: that is, no meaning is lost by just saying 'every day' and 'every second' but the inclusion of 'single' acts a kind of rhetorical decoration giving greater emphasis.
Figurative language
Formal scientific reports are expected to be technical, and the figurative language common in most everyday discourse is, generally, avoided – but communication of science in teaching and to the public in journalism often uses devices such as metaphor and simile to make description and explanations seem more familiar, and encourage engagement.
Of course, it is sometimes a matter of opinion whether a term is being used figuratively (as we each have our own personal nuances for the meanings of words). Would we really expect to see a 'signature' of a pulsar? Not if we mean the term literally, a sign made by had to confirm identify, but like 'fingerprint' the term is something of a dead metaphor in that we now readily expect to find so-called 'signatures' and 'fingerprints' in spectra and D.N.A. samples and many other contexts that have no direct hand involvement.
Perhaps, more tellingly, language may seem so fitting that it is not perceived as figurative. To describe a supernova as an 'evolving fireball' seems very apt, although I would pedantically argue that this is strictly a metaphor as there is no fire in the usual chemical sense. Here are some other examples I noticed:
"we have been searching for that Holy Grail: has a neutron star formed or has a black hole been left behind"
"the quasar is not located in some kind of galactic desert"
there is a "storm, round the black hole"
"the galaxies are funnelling their material into their supermassive black hole"
"extraordinarily hot nuclear ember"
"a dense dead spinning cinder"
"the ultimate toaster"
Clearly no astronomer expects to find the Holy Grail in a distant galaxy in another part of the Universe (and, indeed, I recently read it is in a Museum in Ireland), but clearly this is a common idiom to mean something being widely and enthusiastically sought.5
A quasar does exist in a galactic desert, at least if we take 'desert' literately as it is clearly much too hot for any rain to fall there, but the figurative meaning is clear enough. The gravitational field of the black hole causes material to fall into it – so although the location, at the centre of a galaxy (not a coincidence, of course), means there is much material around, I was not sure how the galaxy was actively 'funnelling' material. This seems a bit light suggesting spilt tea is being actively thrown to the floor by the cup.
A hot ember or cinder may be left by a fire that has burned out, and one at over a million degrees Celsius might indeed 'toast' anything that was in its vicinity. So, J0529-4351 may indeed be the ultimate toaster, but not in the sense that it is a desirable addition to elite wedding lists.
Anthropomorphism
Anthropomorphism is a particular kind of metaphor that describes non-human entities as if they had the motivations, experiences, drives, etc., of people. The references to dying stars at least suggest animism (that the stars are in some sense alive – something that was once commonly believed 6), but there are other examples (that something is 'lurking' in the supernova remnant) that seem to discuss stellar entities as if they are deliberate agents like us. In particular, a black hole acquiring matter (purely due to its intense gravitational field) was described as feeding:
quasars are basically supermassive black holes just swallowing up all the stars and rubbish around
a quasar is feeding from the accretion disc
a monstrous black hole gobbling up anything within reach
just sat [sic] there, gobbling up everything around it
it has to have been feeding for a very, very long time
it will eat about four of those earths, every single second
in a particularly nutritious galaxy
a quasar that has been declared the hungriest object in the universe
There is clearly some kind of extended metaphor being used here.
Feeding frenzy?
The notion of a black hole feeding on surrounding material seems apt (perhaps, again, because the metaphor is widely used, and so familiar). But there seems a lot more 'negative analogy' than 'positive analogy: that is the ways in which (i) a black hole acquires matter, and (ii) an organism feeds, surely have more points of difference than similarity?
For advanced animals like mammals, birds, fish, snails and the like, feeding is a complex behaviour that usually involves active searching for suitable food, whereas the black hole does not need to go anywhere.
The animal has specialist mouth-parts and a digestive system that allows it to break apart foodstuff. The black-hole just tears all materials apart indiscriminately:"it's just getting chopped up, heated up, shredded".
The organism processes the foodstuff to release specific materials (catabolism) and then processes these is very specific ways to support is highly complex structure and functioning, including the building up of more complex materials (anabolism). The black hole is just a sink for stuff.
The organism takes in foodstuffs to maintain equilibrium, and sometimes to grow in very specific, highly organised ways. The black hole just gets more massive.
A black hole surely has more in keeping with an avalanche or the collapse a tall building than feeding?
One person's garbage…?
Another feature of the discourse that I found intriguing was the relative values implicitly assigned to different material found in distant space. There is a sense with SN 1987A that, after the explosion, the neutron star in some sense deserves to be considered the real remnant of the star, whilst the other material has somehow lost status by being ejected and dispersed. Perhaps that makes sense given that the neutron star remains a coherent body, and is presumably (if the explosion was symmetrical) located much where the former star was.
But I wonder if calling the ejected material – which is what comprises the basis of "an absolutely stunning supernova [which is] beautiful" – as 'debris' and 'outer debris"? Why is this material seen as the rubbish – could we not instead see the neutron star as the debris being the inert residue left behind when the rest of the star explored in a magnificent display? (I am not suggesting either should be considered 'debris', just playing Devil's advocate.)
Perhaps the reference to being able to "isolate the core where the explosion was from the rest of the debris" suggests all that is left is debris of a star, which seems fairer; but the whole history of the universe, as we understand it, involves sequences of matter changing forms quite drastically, and why should we value one or some of these successive phases as being the real product of cosmic evolution (stars?) and other phases as just rubbish? This is certainly suggested by the reference to "supermassive black holes in the middle of a galaxy … swallowing up all the stars and rubbish".
Let's hear it for the little guys
Roland Pease's analogy to "the muck at the bottom of your sinkgoing down into the blender" might also suggest a tendency to view some astronomical structures and phenomenon as intrinsically higher status (the blender/black hole) than others (clouds of dust, or gas or plasma – the muck). Of course, I am sympathetic to the quest to better understand "these guys"(intense quasars already formed early in the universe), but as objectively minded scientists we should be looking out for the little guys (and gals) as well.
Appendix A: "the star hidden in the heart of [the] only supernova visible from Earth"
"If you are listening to this live on Thursday, then you're listening to the 37th anniversary of the supernova 1987A, the best view astronomers have had of an exploding star in centuries, certainly during the modern telescope era. So much astrophysics to be learned.
All the indications were, back then, that amidst all the flash and glory, the dying star should have given birth to a neutron star, a dense dead spinning cinder, that would be emitting radio pulses. So, we waited, and waited…and waited, and still there's no pulsing radio signal.
But images collected by the James Webb telescope in its first weeks of operation, peering deep into the ejecta thrown out by the explosion suggest there is something powerful lurking beneath. Olivia Jones is a James Webb Space Telescope Fellow at Edinburgh University and she helped in the analysis."
"87A is an absolutely stunning supernova , it's beautiful, and the fact that you could see it when it first exploded with the naked eye is unprecedented for such an object in another galaxy like this.
We have been able to see how it evolves in real time, which in astronomy terms is extremely rare, just tracing the evolution of the death of a star. It's very exciting."
"I mean the main point is the bit which we see when the star initially explodes , we see all the hot stuff which is being thrown out into space, and then you've got this sort of evolving fireball which has been easiest to see so far."
"Yes, what see initially is the actual explosion of the star itself right in the centre. What happens now is then we had a period of ten years when you couldn't actually see very much in the centre. You needed these new telescopes like Webb and JWST to see the mechanics of the explosion and then, key to this is what was left behind, and we have been searching for that Holy Grail: has a neutron star formed or has a black hole been left behind at the centre of this explosion. And we've not seen anything for a very long time."
"And this neutron star, so this is the bit where the middle of the original star which at the ends of its life is mostly made of iron, just gets sort of crushed under it's own weight and under the force of the explosion to turn itself entirely into this sort of ball of neutron matter."
"Yeah, it's the very, very core of the star. So the star like the Sun, right in the centre is a very dense core, but really massive stars like Supernova 1987A or what it was beforehand, about 20 times the mass of a Sun.
If you think of our Sun as a tennis ball in size, the star that formed 87A was about as big as the London Eye. So it's a very massive star. The pressure and density right in the centre of that star is phenomenal. So, it creates this really, really, compact core. A teaspoon of this material, of a neutron star, weighs about as much as Everest. So, it's a very, a very dense, very heavy, core that is left behind."
"These were the things which were first detected in the 1960s, because they have magnetic fields and they rotate, they spin very fast and they cause radio pulsations and they're called pulsars. so When the supernova first went off I know lots of radio astronomers were hoping to see those radio pulsations from the middle of this supernova remnant."
"Yes. So, we know really massive stars will form a black hole in the centre, 30, 40, 50 solar masses will form a black hole when it dies. Something around 20 solar masses you'd expect to form a neutron star, and so you'd expect to see these signatures, like you said, in the radiowaves or in optical light of this really fastly rotating – by fastly rotating it can be around 700 times a second – but you would expect to see that signature or some detection of that. But even with all these telescopes – with the radio telescopes, X-ray observatories, Hubble – we've not seen that signature, before and so we are wondering, has a black hole been formed? We've seen neutrinos, so we thought the neutron star had formed, but we've not had that evidence before now."
"So, as I understand it, what your research is doing is showing that there's some unexplained source of heat in the middle of the debris that's been thrown out, and that's what your associating which what ought to be a neutron star in the middle, is that roughly speaking the idea?"
"So, the wonderful thing thing about the Webb telescope, you can see at high resolution both the ring, the outer debris of the star, and right at the very centre where the explosion was, but it's not just images we take, so it's not just taking a photograph, we also have this fantastic instrument or two instruments, called spectrographs, which can break down light into their individual elements, so very small wavelengths of light, it's like if you want to see the blue wavelength or the red wavelength, but in very narrow bands."
"And people may have done this at school when they threw some salt into a Bunsen burner and saw the colours, it's that kind of analysis?"
"Yes. And so what we see where the star was and where it exploded was argon and sulphur, and we know that these needed an awful lot of energy, to create these, and I mean a lot, of energy. And the only thing that can be doings this, we compared to many different kinds of scenarios, is a neutron star."
"So this is basically an extraordinarily hot nuclear ember, that's sort of sitting in the middle."
"Yes, right in the middle and you can see this, cause Supernova 1987A is about 20 light years across, in total, and we can isolate the core where the explosion was from the rest of the debris in this nearby galaxy, which I think is fantastic."
"Do you know how hot the surface of this star is and is it just sort of the intense heat, X-ray heat I imagine, that's coming off, that's causing all this radiation that you're seeing."
"I hope you are ready for a very big number."
"Go on."
"The neutron star is over a million degrees Celsius."
"And so, that's just radiating heat, is it, from, I mean this is like the ultimate toaster?"
"Yes, so what eventually will happen over the lifetime of the universe is this neutron star will start to cool down, gradually and gradually and fade away. But that'll be many, many billions of years from now.
What we currently have now is one of the hottest things you can imagine, in a very small location, heating up all its surroundings. I would not want to be anywhere nearby there."
Roland Pease interviewing Dr. Olivia Jones (Edinburgh University)
Appendix B: "possibly the brightest object in our universe"
"Now 1987A was, briefly, very bright. Southern hemisphere astronomy enthusiasts could easily spot it in the Large Magellanic Cloud just outside [sic] the Milky Way galaxy. But it was nothing like as bright as JO529-4351 [J0529-4351], try memorising that, its a quasar twelve or so billion light years away that has been declared the brightest object in the universe and the hungriest. At first sight, it's an anonymous, unremarkable spot of light of trillions on [sic] an astronomical photo. But, if you are an astronomer who knows how to interpret the light, as Samual Lai does, you will find this is a monstrous black hole gobbling up anything within reach. Close to the edge of all that we can see."
"So this quasar is a record breaking ultra-luminous object, in fact it is the most luminous object that we know of in the universe. Its light has travelled twelve billion years to reach us, so it's incredibly far object, but it's so intrinsically luminous that it appears bright in the sky."
"And as I understand it, you identified this as being a very distant and bright object pretty recently though you have gone back through the catalogues and its was this insignificant speck for quite a long time."
"Yes, indeed. In fact we were working on a survey of bright quasars, so we looked at about 80% of the sky using large data sets from space satellites. Throughout our large data sets, this one was mis-characterised as a star, I mean it just looks like one fairly insignificant point, just like all the other ones, right, and so we never picked it up as quasar before. Nowadays we are in the era of extremely astronomical, pardon the pun, data sets where in order to really filter thorough them we have these classification algorithms that we use. So, we have the computer, look at the data set, and try to learn what we are looking at, and pick out between stars and quasars."
"Now, is it also interesting, they were discovered about sixty years ago, the first quasars. These are basically supermassive black holes in the middle of a galaxy that's just swallowing up all the stars and rubbish just around it, and that's the bit that for you is quite interesting in this instance?"
"Yes, exactly, and the quasar owes its luminosity to the rate at which it is feeding from this accretion disc, this material that's swirling around, like a storm, with the black hole being the eye of the storm."
"I mean, I think of it as being a bit like the muck at the bottom of your sink going down into the blender at the bottom, it's just getting chopped up, heated up, shredded, and, I mean what sort of temperatures are you talking about? What, You know, what kind of energy are you talking about being produced in this system?"
"Yes ,so the temperatures in the accretion disc easily go up to tens of thousands of degrees, but talking about brightness, the other way that we like to measure this is in terms of the luminosity of the Sun, which gives you are sense of scale. So, this quasar is about five hundred trillion times brighter than the Sun, or equivalent to about five hundred trillion suns."
"And it's been doing this sort of constantly, or for really for a long time, I mean it's just sat there, gobbling up everything around it?"
"Yeah, I mean the mass of the quasar is about 17 billion solar masses, so in order to reach that mass it has to have been feeding for a very, very long time. We work it out to be about one solar mass per day, so that's an entire Sun worth of mass every single day. Or if you like to translate that to more human terms, if you take the Earth and everybody that's on it, and you add up all of that mass together, it will eat about four of those earths, every single second."
"I suppose what I find gob-smacking about this is (a) the forces, the gravitational forces presumably involved in sweeping up that amount of material, but (b) it must be an incredibly busy place – it can't be doing this in some kind of galactic desert."
"Yes, indeed, I mean these quasars, these super-massive black holes are parts of their galaxies, right, they're always in the nuclear regions of their host galaxies, and in some way the galaxies are funnelling their material into their supermassive black hole."
"But this one must be presumably a particularly, I don't know, nutritious galaxy, I guess. It is so far away, you can't make out those kinds of details."
"We can however make out that some of that material moving around, inside the storm, round the black hole, their dynamics are such that their velocities reach up to tens of thousands of kilometres per second."
"Why are you looking for then? Is it because you just want to break records – I'm sure it's not. Or is it, that you can see these things a long way away? Is it, it tells you about the history of galaxies?"
"I mean we can learn a lot about the universe's evolution by looking at the light from the quasars. And in fact, the quasar light it tells you a lot about not just the environment that the quasar resides in, but also in anything the quasar light passes through. So, you can think of this, lights from the quasar, as a very distant beacon that illuminates information about everything and anything in between us and the quasar."
"I mean the thing that I find striking is, if I've read the numbers right, this thing is so far away that the universe was about a billion years old. I mean I suppose what I'm wondering is how did a black hole becomes so massive so early in the universe?"
"Ah see, I love this question because you are reaching to the frontier of our current understanding, this is science going as we speak. We are running into an issue now that some of these black holes are so massive that there's not enough time in the universe, at the time that we observe them to be at, in order for them to have grown to such masses as they are seen to be. We have various hypotheses for how these things have formed, but at the moment we observe it in its current state, and we have to work backwards and look into the even older universe to try to figure out how these guys came to be."
Roland Pease interviewing Dr. Samuel Lai (Australian National University)
Notes
1 Having been a science teacher, I find myself listening to, or reading, science items in the media at two levels
I am interested in the science itself (of course)
I am also intrigued by how the science is presented for the audience
So, I find myself paying attention to simplifications, and metaphors, and other features of the way the science is communicated.
Teachers will be familiar with this. Curriculum selects some parts of science and omits other parts (and there is always a debate to be had about wither the right choices are made about what to include, and what to omit). However, it is rare for the selected science itself to be presented in 'raw' form in education. The primary science literature is written by specialists for other specialists, and to a large extent by researchers for other researchers in the same field – and is generally totally unsuitable for a general audience.
Curriculum science is therefore an especially designed representation of the science intended to be accessible to learners at a particular stage in their education. Acids for twelve years olds or natural selection for fifteen year olds cannot be as complex, nuanced and subtle as the current state of the topic as presented in the primary literature. (And not just because of the level f presentation suitable for learners, but also because in any live field, the work at the cutting edge will by definition be inconsistent across studies as this is just where the experts are still trying to make the best sense of the available evidence.)
The teacher then designs presentations and sequences of learning activities to engage particular classes of learners, for often teaching models and analogies and the like are needed as stepping stones, or temporary supports, even to master the simplified curriculum models set out as target knowledge. Class teaching is challenging as every learner arrives with a unique nexus of background knowledge, alternative conceptions, relevant experiences, interests, vocabulary, and so forth. Every class is a mixed ability class – to some extent. The teacher has to differentiate within a basic class plan to try and support everyone.
I often think about this when I listen to or read science journalism or popular science books. At least the teacher usually knows that all the students are roughly the same age, and have followed more-or-less the same curriculum up to that point. Science communicators working with the public know very little about their audience. Presumably they are interested enough in the topic or science more generally to be engaging with the work: but likely of a very diverse age, educational level, background knowledge: the keen ten year old to the post-doctoral researcher; the retired engineer to the autistic child with an intense fascination in every detail of dinosaurs…
I often find myself questioning some of the simplifications and comparisons used on science reports in the media – but I do not underestimate the challenge of reporting on the latest findings in some specialist area of science in an 'academically honest' way (to borrow a term from Jerome Bruner) in a three minute radio slot or 500 words in a magazine. So, in that spirit, I was fascinated by the way in which the latest research into Supernova 1987A and J0529-4351 was communicated, at least as much as the science itself.
2 That is, the flux of material emitted by our Sun, for example, is quite significant in human terms, but is minute compared to its total mass. Our sun has cooled considerably in the past few billions of years, but that's long time for it to change! (The Earth's atmosphere has also changed over the same time scale, which has compensated.)
3 Some very basic physics (Isaac Newton's law of cooling) tells us that objects radiate energy at a rate according to their temperature. Stars are (very large and) very hot so radiate energy at a high rate. An object will also be absorbing radiation – but the 'bath' of radiation it experiences depends on the temperature of its surroundings. A hot cup of coffee will cool as it is radiating faster than it is absorbing energy, because it is hotter than its surroundings. Eventually it will be as cool as the surroundings and will reach a dynamic equilibrium where it radiates and absorbs at the same rate. (Take the cooled cup of coffee into the sauna and it will actually get warmer. But do check health and safety rules first to see if this is allowed.)
The reference to how
"what eventually will happen over the lifetime of the universe is this neutron star will start to cool down, gradually and gradually and fade away. But that'll be many, many billions of years from now"
should be understood to mean that the cooling process STARTED as soon as there was no internal source of heating (form nuclear reactions or gravitational collapse) to maintain the high temperature; although the process will CONTINUE over a long period.
4 That weak attempt at humour is a variant on the story of the museum visitors who asked the attendant how old some ancient artefacts were. Surprised at the precision of the reply of "20 012 " years, they asked how the artefacts could be dated so precisely. "Well", the attended explained, "I was told they were twenty thousand years old when I started, and I've worked here for twelve years."
Many physics teachers will not find this funny at all, as it is not at all unusual for parallel mistakes to be made by students. (And not just students: a popular science book suggested that material in meteors can be heated in the atmosphere to temperatures of up to – a rather precise – 36 032 degrees! (See 'conceptions of precision').
5 The Holy Grail being the cup that Jesus is supposed to have used at the last supper to share wine with his disciples before he was arrested and crucified. Legend suggests it was also used to collect some of his blood after his execution – and that it was later brought to England (of all places) by Joseph of Arimathea, and taken to Glastonbury. The Knights of King Arthur's Round Table quested to find the Grail. It was seen as a kind of ultimate Holy Relic.
6 Greek and Roman cultures associated the planets (which for them included the Sun and Moon) with specific Gods. Many constellations were said to be living beings that have been placed in the heavens after time on earth. Personification of these bodies by referring to them in gendered ways ('he', 'she') still sometimes occurs.
In his cosmogony, Plato had the stars given a kind of soul. Whereas Aristlotle's notion of soul can be understood as being something that emerges from the complexity of organisation (in organisms), Plato did imply something more supernatural.
Alternative conceptions underpin some, but not all, learning difficulties
Keith S. Taber
I recently wrote here about a paper published in a research journal which used a story about the romance between two electrons, Romeo and Juliet, as a context for asking learners to build models of the atom. (I thought the approach was creative, but I found it quite dificult to decode some aspects of the story in terms of the science).
But something else I noticed about that study (Aquilina et al., 2024) was that the authors listed a number of 'misconceptions' that their teaching approach was meant to address (see the Table reproduced above). These were:
Students, after studying planetary and Bohr's atomic models, cannot move beyond them easily.
Students rarely reflect on and/or understand the need for the development of new atomic models.
Students find it difficult to associate spectral lines with transitions between energy levels.
Students do not describe photon emission processes properly.
Students do not clearly understand the concept of an orbital.
Students find it difficult to understand atomic quantum-mechanical models.
But none of these actually seemed to be misconceptions.
To be clear, I think
all of these points are pertinent to the research; and they reflect
challenges to the teacher, and
learning difficulties experienced by many learners.
But they are not misconceptions.
What is a misconception?
There is a very large literature reporting student misconceptions, or alternative conceptions, in science subjects.1 A misconception, or alternative conception, is a conception that is judged to be inconsistent with the scientific account (or the version of the scientific account presented in the curriculum). The points listed in Aquilina and colleagues' table are not conceptions, so cannot be alternative conceptions – just as a postbox cannot be a red car, because it is not a car; and nor can Boyle's law be a refuted theory, because it is not a theory; and a mushroom cannot be a leafless plant, because it is fungi not plant.
So, what is a conception?
We might understand a conception to be one facet of a concept (Taber, 2019). Consider a student has some ideas about atoms. We might consider the learner's concept of the atom to be the collection of all those ideas about atoms. Imagine a learner thinks:
atoms are very small
an atom contains a nucleus
atoms contain electrons arranged in shells
there are many different types of atoms
gold atoms are gold coloured
everything is made of atoms 2
an exploding atom can destroy a city
If this was the full extent of their ideas about atoms, we might collectively see this list as comprising their atom concept. We could represent it by drawing a concept map showing how the learner sees 'atom' to be linked to other concepts such as 'nucleus', 'electron', etc.
But we might consider each one of these separate statements to be a conception.
Our conceptions vary across a number of dimensions (after Figure 2.3 in Taber, 2014)
There are complicatons:
A person may have (implicit / tacit) 'conceptions' that they could not easily put into words to express as statements. (A researcher might elicit what a learner is thinking and represent it as a sentence, but for the learner it may be more a vague intuition that they only put in words in response to the researcher's questions.)
A person may also show different levels of commitments to conceptions – perhaps our hypothetical learner is pretty certain that atoms are very small, but only has a hunch that gold atoms are gold coloured. Perhaps the learner was told by a friend that an atom bomb that is powerful enough to destroy a city is based on exploding a single atom at its centre – and our learner remembers this, but is actually very sceptical.
We usally say a learner has an alternative conception when they hold a conception which is inconsistent with (so alternative to) the scientific account. A great many such alternative conceptions have been elicited in research that explores people's thinking about science. Much of this work has been undertaken with science learners, but some simply with people in the general population (when alternative conceptions may be termed as 'folk science' or 'urban myths'). Here are just a few of the examples discussed elewhere on this site:
These are 'alternative' because they are contrary to the scientific account, and they are significant to science teachers because they are contrary to the target knowledge the teacher is expected to teach to students.
One reason to perhaps prefer the term 'alternative conception' to 'misconceptions' is that the latter term may seem to imply the outcome of misunderstanding teaching. Alternative conceptions certainly can be linked to misunderstanding teaching, but often this occurs because the learner already has an intuitive idea that is contrary to the science, and this leads to them misinterpreting teaching. But consider this example:
an atom of an element in the first period has a full shell with two eletrons, all other atoms would need to have eight electrons in the outer shell for it to be a full shell
This is an alternative conception that learners sometimes do hold, whereas eight electorns only counts as a full shell in period 2 (Li, Be, B, C, N, O, F, Ne) and not for any of the other elements. So, a chloride atom (electronic configuration 2.8.7) does not have a full outer shell when it joins with an electron to become a chloride ion (2.8.8).
But I have seen school textbooks aimed at secondary levels learners (c.14-16 year old students) that actually state quite clearly that all atoms, apart from H and He have a full outer shell with eight electrons. If a learner had read that in the textbook issued by the school, and so believes it to be so, then they have not misconceived what they read – they have accurately understood the intended meaning. But it is still an alternative conception ('misconception').
Learning blocks and misconceptions
So, something cannot be an alternative conception (misconception), unless it is both a conception, and counter to the scientific account. But there are other reasons a learner may struggle to understand the science in the curriculum.
A learner may lack specifc prerequisite background knowldge needed to make sense of a new idea; or the learner may not appreciate that cetain prior knowledge is meant to be applied in understanding the new material. Learners may indeed misinterpet teaching due to an existing alternative conception, but they may also sometimes make an unhelpful association with unrelated prior learning. (That is, they interpet teaching in terms of some prior learning that they think is related, but which from the scientific perspective is not relevant.) Sometimes that may relate to how scientific terms may be understood through the learner's language resources (such as assuming a 'neturalisation' reaction will always lead to a neutral product becasue that's exactly what a reasonable person might expect 'neutralisation' to mean!) or it may relate to not appreciating the limitations of a teacher's model, or to how an analogy or metaphor (e.g., electron shell) is intended to be figurative, not literal.
Learners may not always understand teaching as intended
So, alternative conceptions are indeed very relevant to the challenge of teaching science, but not all learning difficulties are due to alternative conceptions; and certainly not all learning dificulties should be labelled as 'misconceptions'.
Beyond misconceptions
So, what about Aquilina and colleagues' list of supposed 'misconceptions'?
Students, after studying planetary and Bohr's atomic models, cannot move beyond them easily.
Students rarely reflect on and/or understand the need for the development of new atomic models.
Students find it difficult to associate spectral lines with transitions between energy levels.
Students do not describe photon emission processes properly.
Students do not clearly understand the concept of an orbital.
Students find it difficult to understand atomic quantum-mechanical models.
There are a number of well-recognised issues here. Two in particular stand-out.
The unfamiliar abstract
For one thing the subject matter is unfamiliar and abstract. People can only understand teaching if they can link it to existing experience or prior learning. Teachers have to find ways 'to make the unfamiliar familiar'. (This is why Aquilina and colleagues devised a narrative based on a tragic love story that they expected the students to be familiar with.)
But learning about the abstract in terms of the familiar only moves a learner so far when the familiar is only a little like the target. Learners know about shells, so can imagine electrons in shells – but electron shells are not really like more familiar shells (such as those that protect snails and cockles or bird's eggs). Learners can imagine electrons spinning like spinning topics, but electron spin is not like that – the electron does not spin.
The behaviour of quanticles, quantum objects, is quite unlike the behaviour of familiar objects. An orbital is not really an object at all, but more a description of the solution of a mathematical equation – those diagrams showing the different atomic or molecular orbitals are a bit like the map of the London underground: schematic representations that are useful for some purposes, but not realistic images of the orbital/rail line.
Acquiring model nous (epistemologial sophistication)
The second issue relates to epistemological niavety, which comes from not appreciating the subtle nature of science. If we teach students that an atom is like THIS (say, electrons orbitting a central nucleus like planets orbiting the sun), why shoud we then be surprised that students think that is what an atom is like – and so then struggle to understand why we are now teaching them the atom is quite different from this? The defence that we did point out this was a model is only convincing if we are sure the students understood what a scientific model is.
We might describe thinking that electrons in atoms have definite trajectories as being a 'misconception' – but if we have taught such a model then the learner's real misconception is in thinking that such a model is meant to be a realistic representation. If we never taught them that the model was something other than a scale replica of an atom, then this is a 'pedagogic learning impediment'. That is, the student is only guilty of learning what they have been taught!
Perhaps more attention to this aspect of the nature of science throughout school science might avoid this problem. Imagine that from a young age learners had regularly been asked in their science lessons to:
devise different models and representations of various scientific phenomena
identify the strength and limitations of different models (both those produced by learners, and mulitpile representations presented by the teacher)
discuss why having several different (imperfect) models might sometimes be useful
be asked to choose between alternative models/representations for different specified purposes
In contexts where science has tended to be taught as though it offers a single, realistic account of phenomena, then we should not be surprised
that students do not see the need to move beyond the models they have been taught (they consider them as more like scale replicas than theoretical models)
nor indeed when they complain they have put a lot of effort into learning models they now feel they are being taught were wrong all along!
Learners' alternative conceptions are a major impediment to learning school and college science. However, learning of abstract ideas requires learners to make sense of teaching in terms of the interpetative resources they have available – and that is often challenging enough even when they have no existing alternative conceptions in a topic.
Aquilina, G.; Dello Iacono, U.; Gabelli, L.; Picariello, L.; Scettri, G.; Termini, G. "Romeo and Juliet: A Love out of the Shell": Using Storytelling to Address Students' Misconceptions and Promote Modeling Competencies in Science. Education Sciences, 2024, 14, 239. https://doi.org/10.3390/educsci14030239
Taber, K. S. (2014). Student Thinking and Learning in Science: Perspectives on the nature and development of learners' ideas. New York: Routledge.
Taber, K. S. (2019). The Nature of the Chemical Concept: Constructing chemical knowledge in teaching and learning. Cambridge: Royal Society of Chemistry.
Notes:
1 There are a number of other related terms used in the literature, such as intuitive theories and preconceptions. Sometimes these different terms refect subtle distinctions (so preconceptions refers to alternative conceptions a learner has prior to being taught anything about a topic). But, in practice, there is no real consisitency in how various terms are used across different authors.
I try to reserve the term alternative conceptual framework for more large scale conceptual structures than discrete alternative conceptions. (But again, the terms are sometimes used interchangeably) So, for example, the 'octet' framework is a network of related conceptions built around the core alternative conception that chemical change is driven by atoms needing full electron sells or octets of electrons:
2 A teacher might want to ask students what they means by their words. If a student suggests they believe that everythings is made of atoms, or everything is made from atoms, then this may be a canonical understanding, or an alternative conception:
motto
is a short-hand way of suggesting
alternative conception
everythings is made of atoms
all material substances found under normal conditions can be shown to contain atomic cores surrounded by electrons
if we could examine all materials we would find they are comprised of lots of discrete atoms just stuck together
everything is made from atoms
we can envisage that any substance could be built up by chemiclly joining together a certain number of atoms of various elements – all molecules and other structures can be imagined as being built up from atoms
chemical reactions produce different substances by starting with lots of atoms of the relevant elements
Do plants deceive insects by deliberately pretending to be rotting meat? (Spoiler alert. No, they do not.) [Image credits: Rafflesia – Maizal, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons; Amorphophallus titanum – ailing moose, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons; fly and beetle – by Clker-Free-Vector-Images from Pixabay]
Mysterious plants
Earlier this week I heard an episode of BBC Radio 4's 'Start the Week' programme entitled 'Mysterious Plants' 1 (which can be heard here). It is always good to hear science-related episodes of series such as this. The mysterious plants included Amorphophallus titanum2 believed to have the largest un-branched inflorescence of any plant in the world; and the parasitic genus Rafflesia, one species of which is thought to have the largest individual flowers in the world. 3
I could not help notice, however, that according to the guests, some plants are sentient beings, able to reflect on their circumstances, and to deliberately act in the world. Botanist Dr Chris Thorogood (of University of Oxford's Oxford Botanic Garden and Arboretum) described the parasitic plant Rafflesia as being 'pretty sneaky'. This is anthropomorphic, because – if taken literally – it implies deliberate behaviour.
No insects were deceived in the making of this programme
He was outdone, in this sense though, by evolutionary chemical ecologist Dr Kelsey Byers (of The John Innes Centre, Norwich) who told listeners,
"So these flies and beetles like to lay their eggs on rotting meat', and the flower goes 'oh, what if I also looked and smelled like rotting meat', or like the Amorphophallus titanum you might see at Kew Gardens for example, 'what if I also emitted heat, just like a pile of rotting meat?' …
So, what it's attracting are flies and beetles that essentially are going 'Ooh, that smells like food, that looks like food, I'm going to lay my eggs here, it's going to be great, my babies will have a great chance to survive'.
But there's, there's no food, it is deceiving them, it's basically saying 'I'm, mimicking the food, come and stay'."
Dr Kelsey Byer speaking on Radio 4
Now, I assume that Dr Byers does not intend this as a literal account of the biology discussed. In strict scientific terms, it is rather misleading
"flies and beetles like to lay their eggs on rotting meat"
I get a little uneasy when non human entities are described as liking things, as this does not reflect the subjective human experience of liking, say chocolate or Pink Floyd. But this unease probably links to the common alternative conception that students acquire in chemistry that atoms 'like' or 'want' full shells of electrons. Dr Byers could quite reasonably suggest that "flies and beetles tend to lay their eggs on rotting meat"; that their behaviour reflects a preference; and that is what 'likes' means. Fair enough.
"the flower goes 'oh, what if I also looked and smelled like rotting meat' … 'what if I also emitted heat, just like a pile of rotting meat?'…"
Now, flowers do not express themselves in language, and in any case (I'm fairly certain) do not have thoughts to potentially be expressed in language. Plato (2008) has his spokesperson Timaeus suggest that plants were "the kind of living being that…knows nothing of belief, reasoning, and intelligence". 4 So, no, plants do not do this – at least not literally.
"flies and beetles essentially are going 'Ooh, that smells like food, that looks like food, I'm going to lay my eggs here, it's going to be great, my babies will have a great chance to survive'…"
So insects are animals, and I can be less sure they do not have any kind of thought processes. (But it seems likely conscious thought requires a much more complex nervous system than that of any insect.) The 'essentially' means that Dr Byers is not suggesting they are directly expressing these ideas, but only indirectly (perhaps, those behavioural preferences again?) But I am pretty sure that even if insects could be said to 'think' at some level, they do not have formal concepts of food. I do not doubt that the fly experiences something when it eats that is different to when it is not eating, but I really doubt it is meaningful to suggest a fly has any concept of eating or can be said to 'know' when it is eating.
Surely, a fly feeding is pure instinct. It responds to cues (smell much more than sight I should think given the fly's compound eye {perhaps excellent for spotting movement, but – identifying potential meals?}, and the likely distance away that food might be found) to approach some material (without thinking, 'oh good, that smells like food!') and then further cues (greater intensity of the smell, perhaps; texture underfoot?) trigger eating, or egg laying. To be honest, I think even as a human I have sometimes behaved this way myself when distracted by a problem occupying all my conscious attention! (To clarify, that's when eating, not laying eggs.)
I do not think flies or beetles have any concept of 'babies'. I am pretty sure they do not know that egg laying is a reproductive function (even if they can be said to have any awareness that they are laying eggs), and will lead to offspring. I'm also pretty sure they are not aware of the issue of infant mortality, and that that they have a greater chance to be a grandparent if they choose the right place to lay their eggs.
The plant is deceiving the insects, it's basically saying 'I'm, mimicking the food, come and stay'.
Again, the plant is not saying anything. If does not have a notion of mimicry, and is not aware it is mimic. It does not have any notions. It is not deliberately deceiving the flies or beetles. It does not know there are flies or beetles in the world. It does not do anything deliberately.
I am not even sure it is right to say the plant deceives. You can only deceive an entity capable of being deceived. Insects are not deceived, just following instincts. The plant does not do anything to deliberately attract or entice the insects – their attraction to the plant is just a consequence of a match of the animal's instincts (not under the control of the insect), and the plant's evolved anatomy, physiology and biochemistry.
Now, as I suggested above, I am pretty sure Dr Byers knows all this (much better than me!) Perhaps this is just a habitual way of talking she has adopted to discuss her work, or perhaps she was deliberately using figurative language on this occasion to help communicate the science to a diverse radio audience. To 'make the unfamiliar familiar' the abstract concepts of science need to be related to more familiar everyday experiences. The narrative here helps to humanise science.
This type of figurative language is anthropomorphic. That is, it treats non-humans (flowers, whole plants, insects, clouds, atoms…) as if they were human – with human cognition (concepts, deliberate conscious thinking) and motivations and emotions. Humans are part of the natural world, and the extent to which anthropomorphism distorts scientific accounts surely varies. An atom cannot be jealous. Nor a bacterium. But I would think a chimp can be.5 What about a fish?
This is a serious issue for science educators because learners often use anthropomorphic language in science lessons, and it is less clear they are doing so figuratively. They may mean this literally – and even if not, may come to habitually use this kind of language and so feel that in doing so they really they can explain phenomena 'scientifically'. But from a technical scientific perspective these are only pseudo-explanations (Taber & Watts, 2000).
So, sodium reacts with chlorine because the atoms want to fill their shells (Taber & Watts, 1996). So wrong, on so many levels, but so many students think that is the scientific account! Bacteria want to infect us, and seek to become resistant to antibiotics. And so many more examples.
The canonical biological explanation is that living things are the way they are because they have evolved to be so, through natural selection. It is natural selection that has led to insects laying eggs in conditions where they are likely to hatch – such as in rotting meat. It is natural selection that has led to some plants attracting insect pollinators by becoming similar to rotting meat – similar, that is, in how those plants are perceived within the insect's unwelt.
But lay people often tend to prefer teleological explanations because they appeal more to our own instincts. It seems that things are the way they are for a purpose: as if a plant was guided towards a new structure because there is an end point, identified from the outset, of becoming attractive to insects that will fertilise the flowers.
As humans behave deliberately and work towards goals, it is easy to transfer this familiar scheme to non-human species. Because human artefacts (the Eiffel Tower, the Pyramids, the iPhone, the international space station) have been designed and built with purposes in mind, it is easy to also see the intricate and effective structures and mechanisms of the living world as also designed with purpose in mind.
Of course, some of these biological structures can seem so unlikely to have evolved through 'chance' or 'trial and error' that many people find the canonical scientific account non-feasible. (And, it is very hard for people to conceptualise the sheer number of generations over which species have evolved.) Of course, although chance is involved, at each step there is feedback into the system: there is preferential selection of some outcomes. What 'works' is selected not so much because it works, but by virtual of it working.
Evolution is contingent – natural selection can only select the features that are 'in play' at a particular time. But which features remain in play is not just down to chance. 6 So, to adopt an analogy, natural selection is not simply a matter of chance, like a number coming up on a roulette wheel. It is more like a game of poker where the cards dealt may be at random, but one can then select which cards to keep, to build up a winning hand. 7
Darwin's book on 'various contrivances'
Darwin was very aware of this general problem, and the specific example of how it came to be that some plants need to be fertilised in very particular ways, by particular insects – and would seem to have structures so specific and well matched to their pollinators that it seems incredible they could have evolved rather than had been deliberately designed.
Darwin knew that many people found his account of evolution unconvincing in the face of the subtlety and intricacies of natural forms. He chose to study the orchids in some detail because they showed great diversity in flower structures and often seemed especially well 'designed' (with 'various contrivances') for their particular animal fertilisers. Darwin argued that all these odd structures could be understood to have slowly evolved from a common ancestor plant by myriad small modification of ancestral structures that collectively led to the wide diversification of forms (Darwin, 1862)
A difficult balance for science communicators
So, science communicators – whether teachers or journalists or scientists themselves – have a challenge here. The kind of language that is most likely to engage an audience and make science seem accessible can actually come to stand in the way of genuine understanding of the scientific principles.
I do not think that means figurative language should be completely avoided in discussing science, but it is very important to remember that an account which is intended to obviously be metaphorical may be understood literally because anthropomorphism and teleology seem to make perfectly good sense to most people.
These kinds of pseudo-explanations may not score any credit in science exams, but this way of thinking is perhaps as instinctively appealing to many humans as, say, laying eggs in rotting meat is to some insects.
Work cited:
Darwin, C. (1862) On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. London: John Murray
Plato (2008) Timaeus and Critias (Translator: Robin Waterfield).Oxford University Press, 2008.
Taber, K. S. and Watts, M. (1996) The secret life of the chemical bond: students' anthropomorphic and animistic references to bonding, International Journal of Science Education, 18 (5), pp.557-568. (Download this paper)
Taber, K. S., & Watts, M. (2000). Learners' explanations for chemical phenomena. Chemistry Education: Research and Practice in Europe, 1(3), 329-353. (Download this paper)
Notes:
1 The enticing episode description is:
"The plant Rafflesia has the world's largest flowers and gives off one of the worst scents; it's also something of a biological enigma, a leafless parasite that lives off forest vines. For the botanist Chris Thorogood, an expert in parasitic and carnivorous plants at the Oxford Botanic Garden and Arboretum, Rafflesia is also an obsession. In his book, Pathless Forest, he goes in search of this mysterious plant in some of the last wildernesses in South East Asia.
Dr Kelsey Byers is an evolutionary chemical ecologist who specialises in floral scent and its influence on the evolution of flowering plants. In her laboratory at the John Innes Centre in Norwich she studies how flowers use different smells to attract their pollinator of choice. From sweet aromas to the stink of rotting flesh, she explores how plants use con-artistry and sexual deception to thrive.
The ethnobotanist William Milliken from Kew Gardens has spent much of his career working with indigenous people in the Amazon to preserve traditional plant knowledge. Now he's focused on collecting folklore about the use of plants to treat ailments in animals in Britain. From wild garlic treating mastitis in cows, to cabbage for flatulence in dogs, he hopes to uncover a cornucopia of plant-based veterinary medicines."
2 Dr Thorogood helpfully explained that what Amorphophallus titanumactually means is 'giant distorted penis'.
Does a sunflower have large flowers?
3 Some plants have a great many flowers on the same 'head' or inflorescence. Consider the sunflower. From a distance it seems each of the flowers are large, but, on closer inspection, each inflorescence has a great many tiny individual flowers – each one able to produce pollen and be fertilised.
A bee on a sunflower collecting nectar and pollen. Each of the tiny structures is an individual flower.
A photo-essay showing sunflowers at different stages of development including close-ups of the structures can be seen here.
4 Although, to be fair, he went on to suggest that a plant "is aware only of the pleasures and pains that accompany its appetites". I would suggest, not.
5 Am I over-cautious? We assume all normal humans beings can potentially feel anger, jealousy, love, fear, etc. But actually no one really knows if anyone else has the same subjective experiences when two people report they are envious, or in love. People could be experiencing something quite different and still using the same label. (This is the qualia issue – e.g., how do I know if the experience I have of red is what you experience? This is something quite different from agreeing on which objects are red.) After all, some people find odours and flavours attractive that others find unpleasant, and the same mode of tickling can lead to quite different responses from different patients.
I think a dog could be sad, and a rabbit can be scared. But I doubt [sic, I mean really doubt] an earthworm could be proud. Unless we can decide where to draw the lines, we really have to wonder if these terms meaningfully transfer across species.
6 At the level of an individual's survival and reproduction, there is a lot of chance involved. Being in the right, or wrong, place when a mate, or a predator, appears; or when a flood, or a forest fire, happens, may have little to do with the variations in features within a population. But a slight advantage in attracting the mate or escaping the peril means that over a large population, across many generations, some features will be preferentially passed on.
7 Strictly these processes are not random, but 'near enough' for human purposes. A roulette ball is large enough to be a classical object (that is we can ignore the indeterminacy that seems to be part of quantum mechanics) so given the spin of the wheel, and the initial trajectory and entry point of the ball (and such factors as the fiction produced due to the materials involved) it is in principle possible to consider this a deterministic process. That is, particular, precise, starting conditions will lead to distinct, in principle predictable, outcomes. In practice though, no human could control the wheel and ball precisely enough to manufacture a specific outcome. It may as well not be deterministic.
Much the same is true of a pack of cards. Given the original order of the deck and a finite number of specific moves to shuffle the deck, only one new order is possible. It is however again difficult to deliberately shuffle a deck and control the new order (though perhaps not quite impossible – which is why often the person shuffling the deck invites other players to choose cuts within the process).
Sometimes in research, the methodology adopted requires randomisation (for example of individual participants to different experimental conditions) and usually such process as rolling dice or drawing blind ballots are 'good enough' even if not strictly random, as no person could control the outcomes obtained.
A new study reports a creative approach to modelling the atom motivated by a love story
Keith S. Taber
Perhaps it would be better not to introduce an orbital model until we feel learners are ready to appreciate the quantum jump from concentric orbits to fuzzy, overlapping, infinitely-extended patterns of electronic probability, and the associated complex patterns of energy levels they generate.
"Grade: B-. Comment: Your model of the heteronuclear molecule of Romeo-Juliet was creative and aesthetically pleasing, but it was inconsistent because you used rope to stand for the covalent bond when you are representing electrons with apples." (Image by Николай Оберемченко from Pixabay)
The science curriculum contains a good deal of abstract material that is both challenging, and – sadly – not always found intrinsically interesting, to many learners. The teacher has to find what can 'make the unfamiliar familiar', something I have written quite a lot about on this site.
One such abstract topic is the structure of 'the' atom1 – an area where learners will likely come across multiple models and diverse representations, and where what is being modelled and represented (as a quanticle – a quantum object) simply cannot be adequately represented concretely. Given that, it is hardly surprising that often even keen and capable learners show alternative conceptions in this topic (Taber, 2002 [Download paper]).
I was therefore intrigued by a recent research paper that described an approach to progressing learners' ideas about atomic structure by asking them to engage with a story. Narrative is a recognised way of helping make the unfamiliar familiar, and here a story was referenced that is familiar to many people: that of Shakespeare's 'star-crossed lovers': Romeo and Juliet.
So, in the storyline, electrons were named after characters from the tragic tale. It is common to relate abstract chemical ideas to social relations (chemistry uses such metaphors as 'sharing electrons', 'nucleus loving' species, reagent species that 'attack' other molecules, and substances that 'compete') – but this does risk the anthropomorphism (that is, treating non-human entities as if they have human qualities) actually confusing learners.
That is, molecules and ions, and nuclei and electrons are not like people, and do not think or have desires, and so they do not act from motivations such as love or hate or jealousy…
Perhaps this seems SO OBVIOUS that only the weakest student could possibly get confused and think otherwise?
But I know from my own research (e.g., Taber & Watts, 1996 [download paper]) that actually even studious, intelligent learners can come to habitually use anthropomorphic language without noticing that they are explaining chemistry in terms that would only make sense if atoms and molecules and ions and electrons did have preferences, and could think for themselves, and did actaccordingly!
Atoms can not care about anything – so they do not care about how many electrons they have, and they never deliberately do anything in order to obtain full shells or octets (as they cannot act under their own volition, of course). But many generally successful, hard-working, intelligent, learners in chemistry classes all over the world seem to think otherwise (Taber, 1998 [Download paper]).
Likewise, electrons do not care if they are in an atom or not, or whether they are spin-paired or not (and if so, which other, indistinguishable, electron they are paired with), or which energy level of a system they populate.
The authors of the recent paper (which is open access, so freely available for anyone who wishes to download/read it) claim that students found the story-related activity engaging (which certainly seems likely) and that it helped address some misconceptions about atomic structure. They note that:
"Students do not clearly understand the concept of an orbital" (Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024)
This is a topic that has long interested me so I took a look at the activity the researchers had devised. The learners were
"10th-grade classes, with the participants' average age being between 15 and 16, attending a technical computer science high school 1…[who] had already studied the atomic model in their chemistry classes during the first half of the year."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
I have taught a basic (planetary) model of atomic structure to students at this age, and also more advanced models to 16-19 year old learners (on A level courses), so I was keen to read about the activity. The authors did not include an explicit statement of the curriculum content which was being treated as target knowledge, although they did include a discussion of their rationale for the story, as well as comments on student work, from which some features could be deduced or inferred. (I would have found it useful to have read an explicit statement of just what the learners were expected to know – what the 'correct' model was meant to be – at the outset of the paper.)
I approached the paper thinking it was ambitious to teach an orbital model of the atom to students of this age. My reading of the story (reproduced below) reinforced that initial impression (I admit, I was challenged in places!) – although the authors certainly felt the students in their research coped well with the challenge.
Although I felt I struggled interpreting some features of the narrative,
A student with a specific learning disorder (SLD), mentioned, "The connection of a fairly complicated topic with such a simple story"
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
It is important to note that the teaching scheme adopted a dialogic approach, where class discussions were included at two points after the students had worked in groups on parts of the activity. The activity was also conceptualised as being part of an enquiry-based learning cycle. So, the material below should be read accordingly, as it does not reflect this wider classroom context.
The story is broken into four parts, each leading to a task for the learners (working in groups) to engage in.
Prologue
"Romeo is a bold and dynamic electron found in an atom with seven energy levels. He is at the 4s energy level, together with the faithful Mercutio, his companion on raids. Always upside down compared to him, but then there is no place for two equal electrons in their crew. The two are part of the Montague family, known for being particularly lively.
Juliet is an electron in 2s, she is more tied to her nucleus and in fact she is a Capulet, a rival family to that of the Montagues and decidedly more calm. Juliet is always accompanied by her nurse; they too are turned upside down with respect to each other.
There is a grand ball to which everyone is invited, and, to better organize their arrangement, there is a need to schematize their position."
[Instructions to learners: "Discuss with your classmates what should be the design of the atom where the two families «are» and build a model"]
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Chapter 1 – part 1
"At one point during the dance, Romeo notices Juliet in her orbital, and, even if he occasionally gets close to her, he is unable to stay there permanently: quivering with love, he asks who knows her and what her tastes are in terms of radiations (electrons are well known to be romantics). He discovers that Juliet is obsessed with color harmony and that the color she prefers is purple "486 nm". To get noticed he wants to perform his famous photon–spectroscopic serenade and jump to emit a purple trail.
[Instructions to learners: "Discuss with your teammates to help Romeo understand how far he will have to jump and whether or not he would have gotten closer to Juliet in this way."]
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Chapter 1 – part 2
"The two are deeply in love and would like to spend the rest of their days together. But Juliet's family hinders them, crying scandal: a Montague cannot be so tied to the nucleus! What to do? The nurse offers Romeo the chance to take her place, but, for her, this would mean losing her place next to Juliet. Romeo and Juliet, very hesitant, then decide to move towards the orbitals occupied by the Montagues. But how to get up there?
While the couple is tormented by this problem, an enlightened friar, Lory, arrives to their rescue with two THz 457s, offering to give them a lift. Despite this help, Romeo and Juliet are unable to reach the Montague orbital, so they loudly invoke another friar, Enzo, asking for new help.
[Instructions to learners: Discuss with your teammates to understand how far they will jump thanks to the first photons and which photons Fra Enzo will have to carry for the two lovers to reach the Montague orbital."]
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Chapter 2 and epilogue
"Juliet's escape has thrown the entire atomic balance into crisis, forcing some Montagues to change levels in order to maintain overall stability. Then, when the couple comes to the Montagues, they cry out for revenge, and the couple is then forced to flee again.
The Montagues set out in search of Romeo and Juliet but fail because it is not possible to reconstruct the trajectory followed by the two lovers.
The story unfortunately ends in tragedy: the two do manage to free themselves from the influence of their families, but they still understand that they cannot be together. Now condemned to separation, the two lovers decide to draw up a schema of the place (the atom) where they met to remember it forever.
[Instructions to learners: "Discuss with your teammates why this trajectory cannot be reconstructed. End the story with a tragic ending, explaining the reasons for the separation sentence.
EPILOGUE Construct with your teammates a possible model of the scheme realized by Romeo and Juliet."]
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Interpreting the narrative
Reading the account I had a very mixed response. I am very keen on approaches that use the familiar everyday as ways into teaching complex, abstract ideas; but subject to two provisos:
these everyday analogies are interim supports ('scaffolds'), to be withdraw as soon as they are no longer needed;
teaching needs to focus on the 'negative analogy' (things that do not map across) as well as the 'positive analogy' (the aspects of the comparison that 'work').
The approach here seemed somewhat different. The learners had already been taught a model of the atom earlier in the year, and this activity was intended to be an opportunity to review this prior learning and apply it – and an opportunity for teachers to identify any alternative conceptions elicited by the activity.
Metaphorical meanings?
Romeo and Juliet are not the lovers in the stage play, but electrons. Therefore, in reading the story I identified scientific information (electron Romeo is in a 4s orbital in an atom) and material that seemed to be metaphorical (the electrons Romeo and Mercutio go on 'raids'). I therefore saw the task of reading the story as being in part a decoding of the metaphors that were used.
So, the idea of Romeo and Mercutio being relatively "upside down" was not to be taken literally (electrons do not have ups or downs) but to be a metaphor for spin +1/2 and spin –1/2, often referred to metaphorically as 'spin up' and 'spin down'. Going on raids was more tricky: in some chemical reactions electron pairs are considered to shift during bond formation (or bond breaking, but that would not refer to an atomic species), but 'raid' suggests a temporary excursion.
I could not understand in what sense Mercutio (the electron, not the fictional character) could be said to be faithful. Electrons respond to physical forces, not personal attachments. Perhaps, I was over-thinking this, and not all the narrative elements did map onto the atomic system? Perhaps that was meant to be part of the challenge for the learners?
A fundamental concern with this kind of comparison is that all electrons are inherently identical, and are only distinguished by the accidental features they acquire in a particular system.
A 2s electron is on average closer to the nucleus, and experiences a greater effective core charge (it is not shielded as much from the nucleus as a 4s electron is) – so the 'tie' (bond) to the nucleus can be understood as analogous to the attractive force operating between the electron and nucleus. 2
The reference to being more calm perhaps refers to how the 2s level is at a 'lower' energy so the 'particularly lively' 4s electrons can be more dynamic?
If Romeo and Mercutio, or even Romeo and Juliet, were swapped it could make absolutely no difference and no one could tell. By giving electrons personal identities they seem to be more like us and less like electrons. Electrons cannot be bold or calm. Romeo and Juliet behave differently because they are in different orbitals at different energy levels, not because they are different electrons. Could learners miss this critical point? If Juliet (or Romeo) moved to a different energy level then she (or he) would change 'personality' – but that would undermine the narrative.
I was not sure how the two families related to anything. Within an atom we could class some electrons alike because they are in the same 'shell' (have the same principal quantum number) – so perhaps the two families were in the n=2 and n=4 levels (the L and N shells being their metaphorical 'houses'). I also could not understand where the ball was meant to be held:
were the electrons to be moved to a new set of orbitals (requiring promotion)
were the electrons meant be moved to outside the atom (requiring ionisation), or
was the ball to take place with the electrons in their current orbitals (but for some reason behaving differently than when no dance was taking place?)
The attraction between Romeo and Juliet (the electrons, not the fictional lovers) was difficult to understand. Certainly, if we adopt a model of electrons moving about in different orbitals 3 then they could sometimes be nearer to each other as atomic orbitals interpenetrate – and if so they would influence each other more (due to their charge and spin) at these times: but this would primarily be a repulsion.
Interpenetrating fields of play. If two sports pitches were marked out overlapping on the same ground, then there would be places that were part of both fields of play.
(Consider a school with very limited space for sports pitches. Perhaps they mark up a soccer pitch and a field hockey pitch overlapping. If both soccer and hockey players train at the same time there will be places that are part of both pitches, and players from the two sports can come close together in those areas. {This is just an analogy. The two sports would need to schedule practice at different times to avoid accidents!})
It seemed to me that the learners were being asked to read the account at two levels – some features of the story were metaphors (such as when the lovers left the atom only to find they had separate indeterminate trajectories) when other features seemed to be simply plot devices to provde an engaging narrative. I thought that the students were being asked to work out which bits of the story they should take seriously as corresponding to part of an atomic model, and which just moved the narrative on. I though this might be challenging for the 14-15 year old learners (as I was struggling!)
Orbitals and transitions
Some features of the story seemed potentially likely to encourage alternative conceptions. Juliet's preference for light of wavelength 486 nm risks the association of a spectral line with an electron or an energy level, rather than with a transition.
The specific references to 486 nm and 457 THz radiation seemed to suggest that a quantative model was needed – where an atom would actually show spectral lines reflecting transitions associated with radiation of these specific characteristics.
The rationale
Unlike the students, I had access to some of the resource designers' thinking as the paper included a rationale for the storyline. This acknowledged that
The specific location of the grand ball remains implicit [?], as it is challenging to conceive of electrons dancing outside the metaphorical context of "moving swiftly". However, all the other character details are essential for initiating the story and allowing mathematical and physical problems and situations to emerge."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
This seemed to confirm that the learners were expected to build a quantitative model. This was reiterated later in the rationale
"Through calculations of energy transitions and the resulting orbital distances, students gain insight into the quadratic proportionality that underlies these phenomena [?], prompting a gradual reshaping of their personal notions regarding orbital distances."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
I was not sure what was mant by 'orbital distances', and return to this point below. I was also not sure how quadratic proportionality underlay energy transitions.
This was only one of the points in the paper where I got the impression that in the teaching model adopted, energy levels and orbitals were not only being associated, but at times almost seen as equivalent and interchangeable.
A diagnostic assessment opportunity
The rationale seemed to confirm that the activity was deliberately testing whether students associated spectral lines with energy levels rather than transitons between levels,
"To elucidate the intriguing connection between emission and electron transitions to different energy levels, we introduce a romantic-comedic twist, employing Juliet's passion for color harmony as a plot device. Juliet's preference for the color purple is strategically chosen to align with her energy level, prompting students to contemplate the intriguing relationship between spectroscopy lines and electron energy transitions."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
On the other hand, my suspicion that I had been reading too much into the narrative, and trying too hard to interpret plot twists was ratherundermined by being told,
"Take, for instance, Romeo's desire to gain Juliet's attention and their joint pursuit of a life away from their feuding families. This narrative intricately parallels the fundamental interplay of orbitals within the model, establishing a direct and compelling link between the characters' human drama and the pivotal role of orbitals in the model."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Indeed? I was struggling to map across some of the story, even when (unlike the students) I had access to the rationale:
"At the outset, the consequences of Romeo and Juliet's choices become apparent: the voids within the nucleus [?] are replenished with new electrons [?], ultimately disturbing the equilibrium of the two feuding families. This disruption leads them to share orbits [sic], not fueled by anger but by fate. The Montagues seek revenge, yet they grapple with the inability to reconstruct the electrons' orbitals due to the uncertainty principle."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
A lot of this went over my head.
The uncertainty principle would not interfere with characterising orbitals, only with being able to posit specific electron trajectories. The orbitals do not belong to electrons ("the electrons' orbitals") but are characteristic of an atomic system with its configuration of charges.
A hybrid model?
Perhaps, in part, my confusion was due to my not being clear about what the target knowledge was- exactly which kind of model was it hoped the students would produce?
"After studying the planetary and Bohr atomic models, students cannot easily move beyond them"
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
It seemed clear from the paper that the learners were expected to have moved beyond a model with planetary orbits, to a model with orbitals, and so from the idea of electrons moving on definite trajectories, to being found somewhere within the orbitals. 3
There was historically a range of models of the atom (even 'the Bohr model' was actaully a series of models), and long ago Rosaria Justi and John Gilbert (Justi & Gilbert, 2000) pointed out that often in teaching we end up presenting 'hybrid' models – that is, models which have features drawn from across several of the different scientific models. Did the curriculum these students followed set out such a hybrid model for students to learn? 4
An atom with seven energy levels?
At the start of the story, the students were told "Romeo is …found in an atom with seven energy levels". I am not sure any real atom could only have seven energy levels. My understanding is that any atom has in principle an infinite number of energy levels, but the the spacing of the levels gets successively smaller, so they converge on a limit (which makes ionisation feasible). Even the hydrogen atom has an infinite number of energy levels, but only one is populated with an electron.
So, I wondered if possibly this was meant to be read as "Romeo is …found in an atom with seven populated energy levels"?
A sensible starting point for a student is to assume the atom is initially in its ground state (as under normal circumstances they usually are). If the reference to seven energy levels means populated energy levels, and students are to assume the atom starts in the ground state then presumably learners are meant to assume the atom they need to model is one of the first transition series (i.e., elements with electronic configurations from 1s2 2s2 2p6 3s2 3p6 4s2 3d1 to 1s2 2s2 2p6 3s2 3p6 4s2 3d10: that is an atom from one of the elements scandium to zinc).
However, later there is a reference to electron Romeo wanting to "jump to emit a purple trail". But he needs to jump 'down' (to a lower energy level) both to get closer to Juliet and indeed to "emit a purple trail" (i.e., for Romeo to be promoted, light would need to be absorbed not emitted) – which is only possible if the atom is NOT initially in its ground state, so that there will be an orbital at a lower energy level not fully occupied. That potentially complicates the model to be built.
For one thing, if the atom is not in its ground state, then atoms of elements of lower atomic mass than scandium might be the target atom to be modelled? Indeed, any atom from the element nitrogen (in the highly excited configuration 1s1 2s1 2p1 3s1 3p1 4s1 3d1 ) on to zinc could theoretically have seven occupied energy levels. It did not help that there seemed to be no information on how many electrons were in this atom – four were specified, and we are told unspecified other 'family' members lived there, and two other characters were name-checked without it being explicit if they were also in the atom or just passing (from the local Abbey perhaps – would that be an atom of a noble gas?)
Interorbital distances?
As noted above, the authors refer to how they "delve into the concept of interatomic orbital distances", but this seems an oxymoron.
"From the analysis of the drawings, it emerges that the students' final drawings can be traced back to three different types of atom representation (R):
R1: orbits/orbitals represented at varying distances to convey the concept of energy levels more effectively;
R2: orbits/orbitals represented at correct distances according to the radius;
R3: attempt to depict the concept of orbitals and the correct distances between them."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
The authors refer to how in a figure assigned to category R3, "The distances between the spheres reflect the correct distances according to n2", but this does not strictly relate to an orbital model.
Orbitals do not have edges, so it is not possible to measure how far they are from anything. Strictly, every orbital reaches to infinity (even if the electron density soon gets so rare that it becomes effectively zero). The point is that this is a gradual falling-off and there is no sudden drop that we might think of as an edge.
Commonly orbitals are represented either with
probability contour lines, or
colour or shading showing differnt levels of electron density (i.e., the relative probabilities of an electron in the orbital being 'found' at different regions of the orbital), or
more simply with probability envelopes.
Those envelopes show where, say, 90% or 95% of the electron density is located – which means 10% or 5% of the electron density (that is inside the orbital) lies outside the envelope drawn. So, these lines are to soem degree arbitrary, conventional and do not correspond to anything physical ('real').
One could measure the distance between the centres of two different orbitals, but this would be a trivial issue when the orbitals are in the same atom. (That is, the atomic orbitals are all centred on the nucleus, so the centres have no distance between each other.)
This is different to a planetary type model where electrons are considered to be a certain distance from the nucleus, so the orbits have quantifiable radii. In moving to an orbital model we have to think of fuzzy overlapping volumes of space, and the notion of there being set distances between orbitals just does not work in this model.
Imagine being asked to report the distance between the soccer pitch and the hockey pitch.
And then imagine having that task when there are no marked out edges to the pitches.
The energy levels associated with the orbitals can be considered to have specific values, and so there are definite differences ('distances'?) between the levels in that sense – but these would be energy gaps: analogical 'distances' on an energy scale, not actual distances.
The authors suggest that,
Despite their discussion about orbitals, [for the students' final drawings] all groups drew orbits, representing them as lines depicting the trajectories of electrons
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
But that is not so clear from the diagrams of the models and the students' own comments.
Student 1: "In a circle, we drew lines. But we know that electrons don't follow that precise path; they exist in orbitals, which are regions where electrons are more likely to be found. So, we don't know the precise radius because it's a region. Therefore, in my opinion, since the radius can always vary, you can't use the radius to depict the atomic model; it's more accurate to use energy levels."
…
Teacher: "Here you have drawn the distances increasingly closer. Why?"
Student 2: "Because it represented differences in energy levels."
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Some groups of students seem to have drawn concentric circles representing energy levels rather than orbits or shells or orbitals. Normally, energy level diagrams are not drawn like that, but this seems a perfectly reasonable form of representation providing it is explained.
Spherical orbitals
We also have to bear in mind that only s-orbitals have spherical symmetry. (A 'shell' of orbitals in an atom would be spherically symmetrical only if each orbital was singly or fully occupied. But it was not clear how many electrons were in this atom.)
The first seven energy levels in any atom or ion with more than one electron will be associated with p- and d-orbitals as well as s-orbitals. So, even if orbitals were represented with probability envelopes, and these were treated (incorrectly) as if the edges of the orbitals, then there would be no fixed 'distances' between the edges of any comparisons involving these non-spherical orbitals.
Not all orbitals have spherical geometry (Image by Smiley _p0p from Pixabay)
At this point it is interesting to examine the samples of student models represented in the paper. All of them are drawn with circles. The authors of the paper seemed satisfied with this aspect of the models.
Making sense of 486 nm and the 'THz 457s'
I pointed out above that my reading of the information given about the atom that it seemed the target atom could be from one of a wide range of elements. It seems I got this completely wrong,
We conclude this paper by highlighting a limitation of the story we have designed from a physical point of view. Our story does not fit the real atomic structure. Indeed, we chose to consider a hydrogen atom with multiple electrons because we thought it was easier for the students to manipulate. We are aware of the fact that this may represent a critical point of our story, but in the classes where we experienced the activity it has not created problems, since the students noticed this inconsistency and talked about it with the teacher.
Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024
Now, by definition, a model is never quite like what is modelled – or it ceases to be a model and becomes a perfect replica. But "a hydrogen atom with multiple electrons" is not an atom at all, but an ion. I am not clear why this is "easier to manipulate" than an atom of a different element, as in models of this kind the nucleus is in effect just a minute point charge – so its composition does not complicate the model in any significant way. If that nuclear charge is +7, say, rather than +1, it makes a difference, certainly (to energy levels), but that does not add any further complexity.
Perhaps the authors chose to retain a hydrogen nucleus because they wanted students to use data from hydrogen spectra? (But if so, this was a little naughty.)
The Balmer series
Again, it did not help that I did not know what the target knowledge set out in the curriculum was.4 But, knowing now that hydrogen was the target atom led me to suspect 486 nm and 457 THz radiation linked to lines in the hydrogen spectra – lines in the Balmer series associated with transitions between n=3 and n=2 (656 nm) and n=4 and n=2 (486 nm).
That was all very well, but those transitions referred to the hydogen atom and not to a hydrogen ion. The extra electrons repelling each other in the ion (assuming the ion could be considered stable, which is itself problematic) mean the energy levels (and so the energy gaps; and so the spectral lines) would all be different.
But, if we pretended the ion was stable, and if we pretended that the additional electrons did not change the energy levels (what is what I meant by being somewhat naughty), then the numbers made sense.
A sleight of hand?
Indeed, if we were to adopt the hydrogen atom as the model for our ion, then I sensed I understood why the orbitals were all drawn as circles. In the hydrogen atom, the energy levels are only associated with the principle quantum number. The 2p orbital is at just the same energy level as the 2s orbital. A transition from the N shell to the L shell has the same energy associated with, and so the same frequency of radiation, regardless of whether it involved 2s-4s or 2p-4s or 2s-4p or 2p-4p or 2s-4d or 2p-4d (or indeed 2s-4f or 2p-4f)5. That is a considerable simplification, that would make the task much easier for learners.
So, if we are modelling the hydrogen atomic energy levels, we only need to worry about the principle quantum number as there is one level for each value of n. The student diagrams reproduced in the paper suggested all the students understood the reference to an atom with seven energy levels to mean n (that is the principle quantum number related to 'shell') = 1-7.
But an energy level is not an orbital. The n=2 energy level in a hydrogen atom is associated with 4 orbitals, only one of which has spherical symmetry. The n=3 level is associated with 9 orbitals, only one of which has spherical symmetry.
Moreover, this assumption that all the orbtials in a shall are at the same energy level ('degenerate') only applies to a hydrogenic species (H, He+, Li2+, etc.) – that is, atom-like species with a single electron. The 'atom' (ion) with Romeo and Juliet and Mercutio and the nurse and the rest of the Capulets and Montagues (and possibly some clergy) would not have 2s and 2p orbitals that were degenerate. The presence of interacting electrons (repelling each other, that is, not lusting after each other and "quivering with love") would raze the degeneracy- so the 2s and 2p orbitals would actually be at different energy levels. And so also with 3s and 3p and 3d.
It is not the presence of a hydrogen nucleus which leads to degeneracy between the orbitals within each value of n (each shell), but a system of one nucleus and one electron. So if this 'atom' (ion) had seven energy levels, these would not equate to seven shells of electrons.
The model
So, it looks like the target model was an ion with a hydrogen nucleus, and 7 energy levels occupied by an unspecified number (>4) of electrons, which has the same energy structure and levels as a hydrogen atom, but where each energy level only contained an s orbital.
Models simplify, and in modelling we deliberately leave aside some complexity and nuance. However, we have to balance the gain in simplicity with the loss of authenticity.
A highly charged hydrogen ion could not exist (unless maintained by some very powerful external field)
Atoms have an infinite number of energy levels (but there is no harm in asking learners to ignore most of them for the time being when working on a task)
A hydrogen atom has orbitals of different types (s, p, d…) not all of which are of spherically symmetrical.
The electronic transitions in an ion would not be those found in the related atom, as energy levels of the system depend on the configuration of charges that are interacting. The ion would have many more potential transitions than a single-electron system (such as a hydrogen atom), and these would not have the same energies/frequencies/wavelengths as in the hydrogen atom.
Orbitals do not have edges, and they interpenetrate, so the concept of interatomic orbital distances does not correspond to anything 'realistic' in the orbital model of the atom.
So, the model seems to put aside a lot of the subtlety of the science. But then are these nuanced ideas suitable for treatment with most 15-16 year olds? I would have suspected not (which is why I started from a position of thinking this whole activity was somewhat ambitious), and that may well be why compromises were made in the teaching model adopted in this study.
But perhaps it would be better not to introduce an orbital model until we feel learners are ready to appreciate the quantum jump from concentric orbits to fuzzy, overlapping, infinitely-extended patterns of electronic probability, and the associated complex patterns of energy levels they generate. (But, again, the teaching model used may simply have been reflecting the target knowledge set out in the school curriculum in this particular national context? 4)
After all, as the authors had noted,
"Students do not clearly understand the concept of an orbital" (Aquilina, Dello Iacono, Gabelli, Picariello, Scettri & Termini, 2024)
Encouraging a new alternative conception?
To take one point. The 486 nm and 457 THz radiation is associated with transitions between n=3 and n=2 (656 nm) and n=4 and n=2 (486 nm) in the hydrogen atom, but NOT in the 'atom' populated with Montagues and Capulets.
Does this matter? After all, the point of the exercise is not to remember these specific values, but to be able to link radiation emitted or absorbed to electronic transitions – so, the particular values of 486 nm and 457 THz are irrelevant. True, but what students are potentially learning here is that the values of energy levels are not affected by the number of electrons repelling each other (here we have an ion with many electrons, but we can simply use the values for a hydrogen atom) – which is an alternative conception.
I also know that this is an alternative conception that learners are likely to readily develop. When students study ionisation energies, and make comparisons between different atoms, they often fail to allow for how the same designation of orbital does not imply an equivalence between differently populated electronic structures.
So, for example, a 2p orbital in an oxygen atom is not only not equivalent to a 2s orbital in the same atom: nor is it equivalent to a 2p orbital in a nitrogen atom. Nor, for that matter, is it entirely equivalent to a 2p orbital in the o2- anion.
This is not the most serious alternative conception that students can acquire, but given the complexity and challenge of this whole topic area, it might be wise to avoid risk misleading students when possible.
Or am I just being over-critical because I myself found the task too challenging? ☹️
To see through an orbital clearly?
This was an interesting project, and I hope the authors explore the idea further, and perhaps use their experiences with this implementation to further refine the activity. But I am not sure it is helpful in the long term to encourage learners to work with a model that is so constrained that it is likely to encourage new alternative conceptions.
But would that be the case? If the activity is part of a dialogic teaching sequence and the catalyst for engaging students in a discussion of these abstract ideas – a discussion that the teacher carefully steers towards the canonical account – then perhaps the outcome can be more productive. I guess we can only conjecture about this, until someone investigates the long-term effects of learning from the activity.
As usual, it is fair to say "more research is needed".
Aquilina, G.; Dello Iacono, U.; Gabelli, L.; Picariello, L.; Scettri, G.; Termini, G. "Romeo and Juliet: A Love out of the Shell": Using Storytelling to Address Students' Misconceptions and Promote Modeling Competencies in Science. Education Sciences, 2024, 14, 239. https://doi.org/10.3390/educsci14030239
Justi, R., & Gilbert, J. K. (2000). History and philosophy of science through models: some challenges in the case of 'the atom'. International Journal of Science Education, 22(9), 993-1009.
Taber, K. S. (1998) An alternative conceptual framework from chemistry education, International Journal of Science Education, 20 (5), pp.597-608. [Download paper]
Taber, K. S. (2002) Conceptualizing quanta – illuminating the ground state of student understanding of atomic orbitals, Chemistry Education: Research and Practice in Europe, 3 (2), pp.145-158 [Download paper]
1 Of course there are many atoms, and indeed many kinds of atoms – so the use of the definite article ('the') is strictly inappropriate. But, this is common usage,
What seems potentially more problematic is the use of the definitive article when the referent is not a specific individual specimen. Chemistry teachers will say things like "the ammonia molecule is pyramidal" when no ammonia molecule is either specified directly or can be inferred to be the case in point from the context. This probably does not seem problematic for the simple reason that it does not matter which ammonia molecule is being referred to: they are all pyramidal. So, statements such as the ammonia molecular is pyramidal; the chlorine atom readily accepts an electron; the K shell is nearest the nucleus; and the iodide ion is a good leaving group; etcetera, will be true regardless.
These statements 'work' in a way that some apparently parallel statements from outside of chemistry would not: the house has a blue door, the man walks with a limp, the baby sneezed all night, the bicycle has squeaky brakes, etcetera. Some houses have blue doors – many do not…So, we should not say 'the house has a blue door' unless we have made it clear which house we are referring to. Yet, we do not need to say which particular water molecule is polar, as they all are (i.e., it may be considered an essential quality of a water molecule). So, the question here is why a teacher would say 'the ammonia molecule is pyramidal' when they are not actually referring to a particular specimen, and the point they are making is actually that (all) ammonia molecules are pyramidal.
Taber, 2019, p.128
And, even if we can refer to 'the carbon atom' when we mean any and all carbon atoms, to simply refer to 'the atom' seems a slight to the periodic table – surely we need to say which (kind of) atom we are modelling? That point certainly proved to be critical in the context of the modelling task discussed in this article!
2 The force is symmetrical – the same magnitude force acts on the nucleus and the electron, with each being pulled towards the other. Students commonly have alternative conceptions about this such as thinking the force only acts in one direction (from nucleus to electron) or that the force on the electron is greater.
3 In the planetary model of the atoms, electrons moved in orbits. In the orbital model we can think of electrons moving about the orbital, and the 'electron density' as a kind of average over time of where they have been. However, it may be more in keeping with the quantum model of the atom to suggest the electrons do not actually move around but rather have probabilities of being located at different points under conditions of observation. (According to a very common interpretation of quantum theory, the notion of an electron being somewhere specific only makes sense at the point of observation.) This is pretty difficult to appreciate (especially for most school-age learners), and I suspect most chemists are happy enough most of the time to think of the electrons moving around in their orbitals.
4 Five of the six authors, including the corresponding author, were based in Italy (the other author gave an affiliation based in Canada), so I assume the schools from which the work is reported is in Italy. The paper reports the task set and the student responses in English, so it is not clear if English was used as the language of instruction in the school (this seems unlikely unless this was an International School, but the paper does not report that material has been translated into English).
5 4f orbitals are not usually relevant to atomic structure till we consider cerium, element 58. But the familiar order of filling orbitals as we imagine we are building up atoms (1s < 2s < 2p< 3s < 3p < 4s < 3d < 4p… *) refers to species with more than one electron. For a hydrogen atom, a 4f orbtial is at the same energy level as the 4s orbital, as when occupied the atom's electron, neither would be sheilded at all from the nucleus by other electrons.
(* Ironically, the familiar descriptions of the discrete orbitals designated in this way are based on calculations for a hydrogen atom and do not strictly apply to multi-electron atoms. However the moodel generally works well, and is widely used.)
I would like to pose a simple quiz question. I think (?) the answer may be obvious to many science teachers, and advanced chemistry learners – but I wonder…
Consider the table below:
List 1
List 2
acid
alcohol
alkane
ether
metal
salt
protein
sugar
Two classes of chemical vocabulary?
The table contains some terms used in science, and especially in chemistry. But I have separated them into two lists, and I would suggest that there is a valid reason to class them into two separate categories in this way.
The ordering in the list is simply alphabetical – they are not intended to be paired (acid-alcohol, etc.): just in two categories.
This is not intended as a comprehensive classification – there are other examples (alkali, alkene, etc.) that could be added to the table.
The question is simple – what is the basis for this discrimination; what is different about the items in list 1, compared with those in list 2?
Too easy?
(As a bonus question: one of the entries, in one of the lists, might be considered to reflect the quality associated with the entries in that list in a more extreme form. Can you spot which item this is?)
I will post my reasoning in due course. But perhaps I will not need to (if you think you know the answer, please comment below).
The World Economic Forum has been compared to a chemical reaction between disparate molecules. (A group of Kenyans in traditional dress, Apple's co-founder Steve Jobbs, former UK minister Rachel Maclean, musician and activist will.i.am, and journalist Gillian Tett – includes images accessed from Pixabay)
Analogy is a key tool in the teacher's toolbox when 'making the unfamiliar familiar'. Science teachers are often charged with presenting ideas that are abstract and unfamiliar, and sometimes it can help if the teacher can point out how in some ways a seemingly obscure notion is just like something already familiar to the learner. An analogy goes beyond a simile (which simply suggests something is a bit like something else) by offering a sense of how the structure of the 'analogue' maps onto the structure of the 'target'.
Apologies are useful well beyond the classroom. They are used by science journalists reporting on scientific developments, and by authors writing popular science books; and by scientists themselves when explaining their work to the public. But analogies have a more inherent role in science practices: not only being both used in formal scientific accounts written to explain to and persuade other scientists about new ideas, but actually as a tool in scientific discovery as a source of hypotheses.
Sometimes, however, one comes across an analogy from a scientific concept or phenomenon to something else – rather than the other way round. The logic of using analogies is that the source analogue needs to already be familiar to a reader or listener if it is to help explain something that is novel. So, an analogy between the concept of working memory capacity and fatty acid structure might be used
to explain something about working memory to a chemist – but could also be used
to explain fatty acid structureto a psychologist who already knew about working memory.
So, the use of a scientific idea as the source analogue for some other target idea suggests the user assumes the audience is also familiar with the science. Therefore I deduce that Gillian Tett, journalist at the Financial Times presumably is confident that listeners to BBC Radio 4 will be familiar with the concept of chemical reactions.
Tett was discussing her experience of the annual World Economic Forum meeting that has just been held in the snow of the Swiss skiing resort of Davos, and suggested that the mixing of various politicians and industry and media and lobbyists had the potential to lead to interesting outcomes – like some kind of chemistry experiment,
"I got jammed into a room with will.i.am, the rapper, who was talking about his views for A.I., and suddenly you've got these activists standing next to somebody from some of the big tech. companies, and a government minister, and a group from Kenya, all talking about whether A.I. could actually be a tool to reduce social inequality, rather than increase it. So, it is a bit like a chemistry experiment where you take all of these ambitious, self-selecting, hustling molecules from around the world, shove them into one test-tube, apply maximum pressure, and force them to collide with each other at close quarters with no sleep, and see what kind of compounds arise."
An experiment (by definition) has uncertain results, and Tett used the analogue of the chemistry experiment to imply that the diverse mixes of people collected together at Davos could lead to unexpected outcomes – just like mixing a diverse range of substances might. Tett saw the way such diverse groups become 'jammed' into rooms in arbitrary combinations as they make their ways around the meeting as akin to increasing the pressure of a reaction mixture of arbitrary reagents. This reflects something of the popular media notion of dangerous 'scientific experiments', as carried out by mad scientists in their basements. Real scientific experiments are carried out in carefully controlled conditions to test specific hypothesis. The outcome is uncertain, but the composition of the reaction mixture is carefully chosen with some specific product(s) in mind.
The figure below represents the mapping between the analogue (a rather undisciplined chemistry experiment) and the reaction conditions experienced by delegates in the melting pot of Davos.
the World Economic Forum at Davos is like a chemical experiment because…
Inspection of my figure suggests some indiscipline in the analogy. The reaction conditions are to "apply maximum pressure, and force [the molecules] to collide with each other at close quarters with no sleep". Now this phrasing seems to shift mid-sentence,
from the analogue (the chemical experiment:"apply maximum pressure, and force [the molecules] to collide with each other")
to the target (being jammed into a room at the conference: "at close quarters with no sleep").
One explanation might be that Gillian Tett is not very good at thinking though analogies. Another might be that, as she was being interviewed for the radio, she was composing the analogy off-the-cut without time to reflect and review and revise…
Either of those options could be correct, but I suspect this shift offered some ambiguity that was deliberately introduced rhetorically to increase the impact of the analogy on a listener. Tatt ('an anthropologist by training' and Provost of King's College, Cambridge) had described the molecules anthropomorphically: just as molecules do not sleep,
they cannot be 'ambitious', as this is a human characteristic;
they are not sentient agents, so cannot be 'self-selecting'; and
nor can they 'hustle' as they have no control over their movements.
But the journalists, politicians, activists and industrialists can be described in these terms, reinforcing the mapping between the molecules and the Davos delegates. So, I suspect that whilst this disrupted the strict mapping of the analogy, it reinforced the metaphorical way in which Tett wanted to convey the sense that the ways in which the Davos meeting offered 'experimental' mixing of the reacting groups had the potential to produce novel syntheses.
Richard Feynman was special. Any one who wins the Nobel prize has to be pretty special, but physics laureate Feynman was even more remarkable as he was an exceptionally high achieving research physicist also known for his…teaching. No one gets a Nobel for being a good teacher, and it is often considered in Academia that teaching (that is, if one tries to give teaching the time and energy required to do it well – as students deserve) distracts from research to such an extent that it is rare to excel in both.
Feynman had something a lot of scientists do not not: great charisma. (That is no insult to fellow scientists – most plumbers and greengrocers and bus drivers and accountants and hairdressers do not – that is what makes it notable). He might be considered the Albert Einstein of the second half of the twentieth century, and because of that timescale we are lucky to have quality recordings of him talking and teaching in a way that could not have happened with previous generations. (A great shame in many cases: if perhaps a blessing with some – Isaac Newton's lectures were apparently avoided by most of his own students.)
Like many people, I find Feynman bewitching – he had a sparkle about him – almost a permanent mischievous twinkle in the eye – and an ability to somehow express the excitement of science (of working out why things are as they are) whilst being able to talk in ways that could be understood by people that lacked his expertise. That is perhaps one trait of a great teacher – being able to talk at the level of the audience, despite personally understanding at a higher, more complex and subtle, level.
That is by way of preamble – as I want to consider an explanation Feynman once offered of surface tension.
Screenshot of Richard Feynman explaining why water forms into drops.
Why does it rain in drops?
The extract I am discussing is taken from a 1983 BBC series of short episodes in a series called 'Fun to Imagine'. Although, at the time of writing, the episodes are "not currently available" from the BBC site, there is a compilation on YouTube. One of the topics Feynman discusses is the origin of surface tension – although he only introduces the technical term after explaining the phenomenon that water forms into droplets,
"you see a little drop of water, a tiny drop And the atoms [sic, molecules] attract each other, they like to be next to each other They want as many partners as they can get Now the guys that are at the surface have only partners on one side here, in the air on the other side, so they're trying to get in And you can imagine…this teeming people, all moving very fast all trying to have as many partners as possible and the guys at the edge are very unhappy and nervous and they keep pounding in trying to get in, and that makes it a tight ball instead of a flat and that's what, you know, surface tension When you realise when you see how sometimes a water drop sits like this on a table then you start to imagine why it's like that because everybody is trying to get into the water"
Richard Feynman speaking in 1983
Is this a good explanation?
Well, we might suggest Feynman makes a schoolchild error – water is not an atomic substance, but molecular. It does not contain discrete atoms, so he should be referring to the molecules attracting each other. But I do not think this is an error in the sense that Feynman was mistaken, simply that although the distinction is of great importance in chemistry, physicists sometimes use the term 'atom' generically to refer to the individual particles in a gas, for example. That might be unhelpful to a secondary school student studying for examinations, but if Feynman thought of his television audience for the recording as lay people, the general public, then perhaps the distinction between atoms (arguably a more familiar term in everyday discourse) and molecules would be considered an unhelpful detail? I am certainly prepared to give him that. I think it was the wrong choice, but not that Feynman was in error.
But what about the overall argument here. The 'atoms' want to have partners all around them 2 so they try to get inside the volume of the liquid. The overall effect of everyone, including these guys at the edge, trying to get inside the water is that it forms a sphere-like shape: "a tight ball instead of [something more] flat". Is that a convincing explanation – and is it a valid one?
What makes for a good explanation?
If anything is central to both science and science teaching, it is explanation.
"Explanation would seem to be central to the essence of science. A naïve view might claim that science discovers knowledge about the World, although it might be more accurate to suggest that science creates knowledge through the development of theories. The theories are used in turn to understand, predict and sometimes control the world, and in these activities, scientific explanations play the key role. We might consider theories and models to be the resources of science, but explanations to be the active processes through which theory is applied to contexts of interest…
An explanation is an answer to a 'why' question: but that in itself neither makes for a good explanation, nor for a scientific one. There is no simple answer to what does count as a good explanation, in science or elsewhere. Explanations have audiences, and to some extent, a good explanation is one that satisfied its audience – in other words it meets the explainee's purpose in seeking an explanation. Additionally, it has been known since at least Aristotle's time that we can talk of different kinds of causes, which suggests that many 'why questions' might have different types of acceptable responses, depending on the type of cause being sought."
That passage is taken from a chapter where I described some activities used with secondary school students to help teach them about the nature of scientific explanation. (Read about the classroom activities here.) In that context, working with learners who were about 14 years of age, students were told that a good scientific explanation would be logical, and would draw upon scientific theory,
"pupils were told that scientific explanations needed to take into account logic and theory, i.e., that the explanation needs to be rational, and the explanation needs to draw upon accepted scientific ideas. As the notion of 'theory' is itself known to be difficult for students, they were also told that scientific theories are ideas about the world which are well supported by evidence; are internally consistent; and which usually fit with other accepted theories."
In that regard, Feynman's explanation can be considered logical, even if it omits (i.e., he takes as assumed) an important step* that is needed to explain the (approximately) spherical shape of the water drop.
If water quanticles (let's leave aside whether they are atoms or molecules) want to have many partners 2, and so try to get inside the volume, then we can understand* that the water drop will tend to the smallest surface area possible, so as few quanticles end up at the surface (with the tenuous air, rather than congregating water partners, on one side) where they will be nervous, and as many quanticles as possible are in the interior of the drop where they will be happy.
* The missing step is to state that a spherical drop will have a smaller surface area than any other shape with the same volume and so fewest quanticles at the surface. Perhaps Feynman assumed everyone would know/see that. Probably there is no such thing as a totally complete explanation.
So, is this a good explanation?
Explanations can have different purposes. Scientific explanations allow us to make effective predictions (and so often to control situations – the application of science through technology). But, in everyday life, explanations have a more subjective purpose ("explanations have audiences, and to some extent, a good explanation is one that satisfied its audience").
If, as a result of hearing Feynman's explanation, the viewers of the BBC televison programme
felt they now understood why sphere-like drops of water form, and
considered they had made sense of some science, and so
appreciated the value of science in explaining everyday phenomena,
then perhaps the explanation achieved its purpose?
Was Feynman's explanation scientific?
Of course, if I am being my usual pedantic self, I could point out that although Feynman's explanation was logical, that does not make it scientific unless it also drew upon accepted scientific principles. It was logical because the explicandum (what was to be explained – here, the drop shape) followed from the premise (i.e., ifwater quanticles want to have many partners, and act accordingly, then…)
But, in science, quanticles are not understood as sentient actors, but as inanimate entities that are not (and cannot be) aware of their situation and cannot act deliberately to work towards personal goals. Therefore, no matter how convincing someone may have found this explanation, it does not qualify as a scientific explanation as it is not based on accepted scientific principles (…or at least, not directly).
An anthropomorphic explanation
Feynman's explanation uses anthropomorphism, which from a scientific perspective makes it a pseudo-explanation. A pseudo-explanation takes the form of an explanation in that it is presented as if an answer to a why question, but does meet the requirements for a formal explanation (e.g., it does "not logically fit the phenomenon to be explained into a wider conceptual scheme", Taber & Watts, 2000.)
There are various kinds of pseudo-explanations such as tautology (circular explanations that rely on the conclusions as premises) and simply offering a label for the explicandum (e.g., water absorbs a lot of heat for a small change in its temperature because it has a high heat capacity – this is a kind of disguised tautology, as a 'high heat capacity' is a way of characterising something that absorbs a lot of heat for a small change in its temperature).
Anthropomorphism explains by assuming that the entities involved can be considered to be like people, and, so, to be sentient, have feelings and opinions and preferences, and be able to plan and carry out actions that are intended to being about desired consequences.
It relies on an analogy that may not be appropriate:
if people were in a situation like this, they are likely to behave in a certain way
if we treat these entities as if they were people then we might expect them to behave as people would, therefore…
It is an open question to what extent we can assume animals (chimpanzees, dogs, birds, etc.) can be considered to share aspects of human-like experiences, emotions, thoughts, etcetera. Perhaps it is reasonable to suggest a dog can be sad or a chimp can be jealous. It may not be stretching credibility to suggest that members of some species of animals want to be in large groups, like to be in large groups, and perhaps may even get nervous when isolated? However, it stretches credibility when we are told that viruses are clever or that a bacterium can be happy.
And, there is a pretty strong scientific consensus that at the level of individual molecules there is no possibility of emotions, opinions, desires, thoughts, or deliberate actions. Atoms do not want to fill their electron shells, and genes cannot be selfish, except in a figurative sense.
So, in order to accept Feynman's explanation as valid, we would have to assume that the quanticles in water, water molecules,
like to be next to each other
want as many partners as they can get 2
can be unhappy and nervous
try to have as many partners as possible 2
try to get into the inside of the volume
So, to find this explanation convincing, we have to accept (contrary to science) that something like a water molecule is able to
have desires and preferences,
be aware of the extent to which is current situation matches its preferences, and,
deliberately act to bring about desired outcomes
[Feynman does not explicitly state that the quanticles know about their situation (point 2), but clearly this is implied as otherwise they would have no reason to be nervous and unhappy, nor to act to bring about change.]
These requirements are clearly not met. A being with a central nervous system as complex as a human can meet these requirements, but there is no conceivable mechanism by which molecules can be considered sentient, or to be deliberate agents in the world.
So, even if Feynman's explanation of surface tension satisfies viewers of the recording (i.e., is is subjectively an effective explanation) it fails as an objective, scientific, explanation. Feynman may indeed have been a 'genius' (Gleick, 1994), and a great physicist, but his explanation here is invalid and simply fails as good science.
Now a reader may suspect I have gone after a 'straw man' target here. Surely, Feynman was speaking figuratively, and not literally. Of course he was, but figurative language cannot support a logical explanation, except through an analogy we suspect to hold.
Consider the following hypothetical claim and two possible consequences if the claim was true
Claim
Consequence 1
Consequence 2
"I managed to get tickets for Toyah and Fripp's sold out concert in Bury St Edmunds, and these tickets are gold dust."
"I could sell these tickets at quite a mark up"
"I could put a sample of these tickets in a mass spectrometer and would find they had an atomic mass of 197."
If the claim was literally true, then consequence 2 would follow. But of course, it is meant as a figurative claim, where 'gold dust' is a metaphor for something of high value because it is rare. So, actually consequence 1 might follow, but not consequence 2.
In the same way, if water particles do not have likes, and do not try to do things, Fenyman's argument seems to fall apart…
A teaching model?
Now I would not presume to know better than Richard Feynman, and I am pretty sure (i.e., about as certain as I can be of anything) that Feynman would not have fallen into the mistake of thinking that atoms or molecules actually act like humans and want things, or try to do things. He surely knew this was not a scientific explanation, but he clearly thought this was a useful way of explaining (to his audience) why water forms into a drop.
Now, I suggested above that Feynman's narrative account of the origin of surface tension "is not based on accepted scientific principles (…or at least, not directly)". But near the outset of this account Feynman states that the water particles "attract each other":
"the [molecules] attract each other, they like to be next to each other"
Feynman was not only a researcher, but a teacher, and teachers use teaching models. I think this is what Feynman is doing here:
"[according to science] the [molecules] attract each other [and we can think of this as if] they like to be next to each other"
Affinity in the sense of human experience is used as a kind of analogy for the affinity between water molecules (which leads to hydrogen bonding and dipole-dipole interactions). Once we model inter-molecular forces as being like attractions between people, we can extend the analogy in terms of how people feel when they do not get what they want, and how they respond by acting in ways that they hope will get them what they want.
Looked at this way, Feynman is doing something that good teachers often do when they judge a scientific model is too abstract, sophisticated, complex, subtle, for their audience; they simplify by substituting a teaching model which represents the scientific model in terms more familiar and accessible to the learners.
From this perspective, Feynman's explanation may not have been a valid scientific explanation, but we might ask if it was an effective intermediate explanation set out in terms of a teaching model. That is, perhaps Feynman's explanation may have satisfied viewers, and also potentially acted as a possible foundation for building up to a more technical, scientifically acceptable explanation.
Teachers and other science communicators often use anthropomorphism as a way of offering accounts of complex scientific topics that will appeal and make sense to learners of a public audience.
This can be effective to the extent that it engages learners, leaves the audience with a subjective sense of making sense of the science, and provides accounts that are often remembered later.
Of course that is not so helpful if the audience is studying a science course, and think they have learnt an account which will get them credit in formal examinations! I know from my own teaching career that learners often find anthropomorphic explanations readily come to mind, even when then they have been taught more technical accounts they are expected to apply when assessed.
In public science communication, then, anthropomorphic accounts may be valuable in offering people some sense of the science. But in formal education we need to be careful as even if anthropomorphism offers a useful way of getting learners familiar with some abstract topic (what might be called 'weak' anthropomorphism: Taber & Watts, 1996), we need to avoid them learning and committing to that metaphoric 'social' account thinking it is a valid scientific account ('strong' anthropomorphism).
Mapping Feynman's explanation
If we see Feynman as offering an analogy as a teaching model then we might seek to 'translate' his terms into more scientific concepts. He tells us that attraction is 'liking', and we can perhaps think of 'wanting' and being 'nervous' as indicating a higher (excited) energy state, 'pounding' as being subject to unbalanced forces, and 'trying to get in' as tending to evolving toward a lower energy configuration. At least, someone who already understood the scientific account could suggest such mappings. It seems unlikely any one who did not appreciate the science already could interpret it that way without a knowing and careful guide.
And like all anthropomorphic explanations, it 'suffers' from the very quality that it offers a narrative which is likely to be more easily understood, better related to, and more readily recalled, than the scientific account. This is why I have very mixed feelings about the use of anthropomorphism in formal science teaching, as even when it (a) does a great job of engaging learners and offering them some level of understanding, this may be at the cost of (b) offering an account which many students will find it hard to later let go of and progress beyond.
Screenshot of Richard Feynman explaining why water forms into drops.
As a good teacher, Feynman would know to pitch his teaching for particular audiences depending on their likely level of background knowledge. The explanation discussed here was not how Feynman taught about surface tension in his undergraduate classes at the California Institute of Technology (Feynman, Leighton & Sands, 1963). We can imagine that had he told students at Caltech that water formed into spherical drops because all the molecular guys are trying to get into the water, he might indeed had heard the retort: Surely you are joking, Prof. Feynman? 1
Work cited:
Feynman, R. P., Leighton, R. B., & Sands, M. (Eds.). (1963). The Feynman Lectures on Physics (3 Volumes). Addison-Wesley Publishing Company.
Gleick, J. (1994) Genius: Richard Feynman and Modern Physics. Abacus.
1 My subtitle is a reference to the book 'Surely you're Joking Mr Feynman: Adventures of a Curious Character' in which Feynman tells anecdotes from his life.
2 Water was perhaps a poor example to choose as there is extensive hydrogen bonding in liquid water,
"I suspect even some experienced chemists may underestimate the extent of hydrogen bonding in water. According to one source…, in liquid water at the freezing point, the typical water molecule is at any time bonded by three or four hydrogen bonds – compared with the four bonds in the solid ice structure."
Taber, 2020, p.98
So, in Feynman's analogy, a water molecules does not become happy (lower energy state) when it is surrounded by as many other water molecules as possible, but when it is aligned with 3 or 4 other molecules to hydrogen bond, if only transiently. Without the hydrogen bonding, the drop would still be approximately spherical, but it would be smaller and denser as the molecules could get even closer together, but it would evaporate away more readily.
Does the medieval notion of the human body as a microcosm of the wider Cosmos – in which is played out an eternal battle between good and evil – still influence our thinking?
Keith S. Taberwants to tell you a story
Are you sitting comfortably?
Good, then I will begin.
Once upon a time there was an evil microbe. The evil microbe wanted to harm a human being called Catherine, and found ways for his vast army of troops to enter Catherine's body and damage her tissues. Luckily, unbeknown to the evil microbe, Catherine was prepared to deal with invaders – she had a well-organised defence force staffed by a variety of large battalions, including some units of specialist troops equipped with the latest anti-microbe weapons. There were many skirmishes, and then a series of fierce battles in various strategic locations – and some of these battles raged for days and days, with heavy losses on both sides. No prisoners were taken alive. Many of Catherine's troops died, but knowing they had sacrificed themselves for the higher cause of her well-being. But, in the end, all of the evil microbe's remaining troops were repelled and the war was won by the plucky defenders. There was much rejoicing among the victorious army. The defence ministry made good records of the campaign to be referred to in case of any future invasions, and the surviving soldiers would long tell their stories of ferocious battles and the bravery of their fallen comrades in defeating the wicked intruders. Catherine recovered her health, and lived happily ever after.
There is a myth, indeed, perhaps even a fairy story, that is commonly told about microbial disease and immunity. Disease micro-organisms are 'invaders' and immune cells are 'defenders' and they engage in something akin to warfare. This is figurative language, but has become so commonly used in science discourse that we might be excused for forgetting this is just a stylistic feature of science communication – and so slip into habitually thinking in the terms that disease actually is a war between invading microbes and the patient's immune system.
Immunity is often presented through a narrative based around a fight between opposed sentient agents. (Images by Clker-Free-Vector-Images and OpenClipart-Vectors from Pixabay.)
Actually this is an analogy: the immune response to infection is in some ways analogous to a war (but as with any analogy, only in some ways, not others). As long as we keep in mind this is an analogy, then it can be a useful trope for talking and thinking about infectious disease. But, if we lose sight of this and treat such descriptions as scientific accounts, then there is a danger: the myth undermines core biological principles, such that the analogy only works if we treat biological entities in ways that are contrary to a basic commitment of modern science.
In this article I am going to discuss a particular, extensive, use of the disease-as-war myth in a popular science book (Carver, 2017), and consider both the value, and risks, of adopting such a biological fairy-tale.
Your immune system comprises a vast army of brave and selfless soldiers seeking to protect you from intruders looking to do you harm: an immune response is a microcosm of the universal fight between good and evil?
A myth is a story that has broad cultural currency and offers meaning to a social group, usually involving supernatural entities (demons, superhuman heroes, figures with powerful magic), but which is not literally true.
Carver's account of the immune system
I recently read 'Immune: How your body defends and protects you' (henceforth, 'Immune') by Catherine Carver. Now this is clearly a book that falls in the genre 'popular science'. That is, it has been written for a general audience, and is not meant as a book for experts, or a textbook to support formal study. The publishers, Bloomsbury, appropriately describe Carver as a 'seasoned science communicator'. (Appropriately, as metaphorical dining features strongly in the book as well.)
Carver uses a lot of contractions ("aren't", "couldn't", "doesn't", "don't", "isn't", "it's", "there's", "they're", "we've", "what's", "who'd", "wouldn't", "you'd") to make her writing seem informal, and she seems to make a special effort to use metaphor and simile and to offer readers vivid scenes they can visualise. She offers memorable, and often humorous, images to readers. A few examples offer an impression of this:
"…the skin cells…migrate through the four layers of the epidermis, changing their appearance like tiny chameleons…"
"Parietal cells dotted around the surface of the stomach are equipped with proton pumps, which are like tiny merry-go-rounds for ions."
"a process called 'opsonisation' make consuming the bacterial more appealing to neutrophils, much like sprinkling tiny chocolate chips on a bacterial cookie."
"The Kupffer cells hang around like spiders on the walls of the blood vessels…"
In places I wondered if sometimes Carver pushed this too far, and the figurative comparisons might start to obscure the underlying core text…
"…the neutrophil…defines cool. It's the James Dean of the immune system; it lives fast, dies young and looks good in sunglasses."
Carver, 2017, p.7
"The magnificence of the placenta is that it's like the most efficient fast-food joint in the world combined with a communications platform that makes social media seem like a blind carrier pigeon, and a security system so sophisticated that James Bond would sell his own granny to the Russians just to get to play with it for five minutes."
Carver, 2017, p.113
When meeting phrases such as these I found myself thinking about the metaphors rather than what they represented. My over-literal (okay, pedantic) mind was struggling somewhat to make sense of a neutrophil in (albeit, metaphoric) sunglasses, and I was not really sure that James Bond would ever sell out to the Russians (treachery being one of the few major character faults he does not seem to be afflicted by) or be too bothered about playing with a security system (his key drives seem focused elsewhere)…
…but then this is a book about a very complex subject being presented for an audience that could not be assumed to have anything beyond the most general vague prior knowledge of the immune system. As any teacher knows, the learner's prior knowledge is critical in their making sense of teaching, and so offering a technically correct account in formal language would be pointless if the learner (or, here, reader) is not equipped to engage at that level.
'Immune' is a fascinating and entertaining read, and covers so much detailed ground that I suspect many people reading this book would would not have stuck with something drier that avoided a heavy use of figurative language. Even though I am (as a former school science teacher *) probably not in the core intended audience for the book, I still found it very informative – with much I had not come across before. Carver is a natural sciences graduate from Cambridge, and a medical doctor, so she is well placed to write about this topic.
Catherine Carver's account of the immune system is written to engage a popular readership and draws heavily on the disease-as-war analogy.
My intention here is not to offer a detailed review or critique of the book, but to explore its use of metaphors, and especially the common disease-as-war theme (Carver draws on this extensively as a main organising theme for the book, so it offers an excellent exemplar of this trope) – and discuss the role of the figurative language in science communication, and its potential for subtly misleading readers about some basic scientific notions.
The analogy
The central analogy of 'Immune' is clear in an early passage, where Carver tells us about the neutrophil,
"…this cell can capture bubonic plague in a web of its own DNA, spew out enzymes to digest anthrax and die in a kamikaze blaze of microbe-massacring glory. The neutrophil is a key soldier in an eternal war between our bodies and the legions of bacteria, viruses, fungi and parasites that surround us. From having sex to cleaning the kitchen sink, everything we do exposes us to millions of potential invaders. Yet we are safe. Most of the time these invaders' attempts are thwarted. This is because the human body is like an exceedingly well-fortified castle, defended by billions of soldiers. Some live for less than a day, others remember battles for years, but all are essential for protecting us. This is the hidden army that we all have inside of us…"
Carver, 2017, p.7
Phew – there is already a lot going on there. In terms of the war analogy:
We are in a perpetual war with (certain types) of microbes and other organisms
The enemy is legion (i.e., has vast armies)
These enemies will invade us
The body is like a well-protected fort
We have a vast army to defend us
There will be battles between forces from the two sides
Some of our soldiers carry out suicide (kamikaze) missions
Our defenders will massacre microbes
We (usually) win the battles – our defences keep us safe
Some of these specific examples can be considered as metaphors or similes in they own right when they stand alone, but collectively they fit under an all-encompassing analogy of disease-as-war.
But this is just an opening salvo, so to speak. Reading on, one finds many more references to the 'war' (see Boxes 1 and 2 below).
The 'combatants' and their features are described in such terms as army, arsenals, assassins, band of rebels, booby-traps, border guards, border patrol force, commanders, defenders, fighting force, grand high inquisitors, hardened survivor, invaders, lines of defence, muscled henchman, ninjas, soldiers, terminators, trigger-happy, warriors, and weapons.
Disease and immune processes and related events are described in terms such as alliance, armoury, assassination campaign, assault, assault courses, attack, battlefield, bashing, battles, boot camp, border control, calling upsoldiers, chemical warfare, cloaking device, craft bespoke weaponry, decimated, dirty bomb, disables docking stations, double-pronged attack, exploding, expose to a severe threat,fight back, fighting on fronts, friendly fire, go on the rampage, hand grenades, heat-seeking missiles, hold the fort, hostile welcome, instant assault , kamikaze, killer payload, massacring, patrolling forces, pulling a pin on a grenade, R & R [military slang for 'rest and recuperation'], reinforcing, security fence, self-destruct, shore updefences, slaughters/slaughtering, smoke signals, standing down, suicidal missions, Swiss army knife, taking on a vast army on its home turf, throwing dynamite, time bomb, toxic cloud, training camp, training ground, trip the self-destruct switch, Trojan horse, victories, war, and wipe out the invader.
Microbes and cells as agents
A feature of the analogue is that war is something undertaken by armies of soldiers, that are considered as having some level of agency. The solder is issued with orders, but carries them out by autonomous decision-making informed by training as well as by conscience (a soldier should refuse to obey an illegal order, such as to deliberately kill civilians or enemy combatants who have surrendered). Soldiers know why they are fighting, and usually buy into at least the immediate objectives of the current engagement (objectives which generally offer a more favourable outcome for them than for the enemy soldiers). A soldier, then, has objectives to be achieved working towards a shared overall aim; purposes that (are considered to) justify the actions taken; and indeed takes deliberate actions intended to bring out preferred outcomes. Sometimes soldiers may make choices they know increase risks to themselves if they consider this is justified for the higher 'good'. These are moral judgements and actions in the sense of being informed by ethical values.
An extensive range of terminology related to conflict is used to describe aspects of disease and the immune response to infection. (Image sources: iXimus [virus], OpenClipart-Vectors [cell], Tumisu [solders in 'Raising the Flag on Iwo Jima'-like poses], from Pixabay.)
Now, I would argue that none of this applies to either disease organisms nor components of a human immune system. Neither a bacterium nor an immune cell know they are in a war; neither have personal, individual or shared, objectives; and neither make deliberate choices about actions to take in the hope they will lead to particular outcomes. No cell knowingly puts itself at risk because it feels a sacrifice is justified for the benefit of its 'comrades' or the organism it is part of.
So, all of this might be considered part of what is called the 'negative analogy', that is, where the analogy breaks down because the target system (disease processes and immune responses) no longer maps onto the analogue (a war). Perhaps this should be very obvious to anyone reading about the immune system? At least, perhaps scientists might assume this would be very obvious to anyone reading about the immune system?
Now, if we are considering the comparison that an immune response is something like a nation's defence forces defending its borders against invaders, we could simply note that this is just a comparisonbut one where the armies of each side are like complex robotic automatons pre-programmed to carry out certain actions when detecting certain indicators: rather than being like actual soldiers who can think for themselves, and have strategic goals, and can rationally choose actions intended to bring about desired outcomes and avoid undesired ones. (A recent television advertising campaign video looking to recruit for the British Army made an explicit claim that the modern, high-tech, Army could not make do with robots, and needed real autonomous people on the battlefield.)
However, an account that relies too heavily on the analogy might be in danger of adopting language which is highly suggestive that these armies of microbes and immune cells are indeed like human soldiers. I think Carver's book offers a good deal of such language. Some of this language has already been cited.
Immune cells do not commit kamikaze
Consider a neutrophil that might die in a kamikaze blaze of microbe-massacring glory. Kamikaze refers to the actions of Japanese pilots who flew their planes into enemy warships because they believed that, although they would surely die and their planes be lost, this could ensure severe damage to a more valuable enemy resource – where the loss of their own lives was justified by allowing them to remain at the plane's controls until the collision to seek to do maximum damage. Whatever we think of war in general, or the Kamikazi tactics in particular, the use of this term alludes to complex, deliberate, human behaviour.
Immune cells do not carry out massacres
And the use of the term massacre is also loaded. It does not simply mean to kill, or even to kill extensively. For example, the Jallianwala Bagh massacre, or Amritsar massacre, is called a massacre because (British) soldiers with guns deliberately fired at, with intent to kill or seriously injure, a crowd of unarmed Indians who were in their own country, peacefully protesting about British imperial policies. The British commanders acted to ensure the protesters could not easily escape the location before ordering soldiers to fire, and shooting continued despite the crowd trying to flee and escape the gunfire. Less people died in the Peterloo Massacre (1819) but it is historically noteworthy because it represented British troops deliberately attacking British demonstrators seeking political reform, not in some far away 'corner of Empire', but in Manchester.
Amritsar occurred a little over a century ago (before modern, post-Nurenmberg, notions of the legality of military action and the responsibility of soldiers to not always follow orders blindly), but there are plenty of more recent examples where the term 'massacre' is used, such as the violent clearing of protesters in Tiananmen Square in 1989 and the Bogside 'Bloody Sunday' massacre in 1972 (referenced in the title of the U2 song, 'Sunday Bloody Sunday'). In these examples there is seen to be an unnecessary and excessive use of force against people who are not equipped to fight back, and who are not shown mercy when they wish to avoid or leave the confrontation.
'Monument in Memory of Chinese from Tiananmen in Wrocław, Poland' commemorating the massacre of 4th June 1989 when (at least) hundreds were killed in Beijing after sections of the People's Liberation Army were ordered to clear protesters from public places (Masur, Public domain, via Wikimedia Commons)
The term massacre loses its meaning without this sense of being an excessively immoral act – and surely can only apply to an action carried out by 'moral agents' – agents who deliberately act when they should be aware the action cannot be morally justified, and where they can reasonably see the likely outcomes. (Of course, it is more complicated that this, in particular as a soldier has orders as well as a conscience – but that only makes the automatic responses of immune cells towards pathogens even less deserving of being called a massacre.)
The term moral agent does not mean someone who necessarily behaves morally, but rather someone who is able to behave morally (or immorally) because they can make informed judgements about what is right and wrong – they can consider the likely consequence of their actions in terms of a system of values. An occupied building that collapses does harm to people, but cannot be held morally responsible for its 'behaviour' in the way a concentration camp guard or a sniper can be. A fox that takes a farmer's chickens has no conception of farming, or livestock, or ownership, or of the chickens as sentient beings that will experience the episode from a different perspective, but just acts instinctively to access food. Microbes and cells are like the building or the fox, not the guard or the sniper, in this respect.
Moreover, in the analogue, the massacred are also moral agents: human beings, with families, and aspirations for their futures, and the potential for making unique contributions to society… I am not convinced that bacteria or microbes are the kinds of entities that can be massacred.
Anthropomorphic references
Carver then writes about the immune system, or its various components, as well as various microbes and other pathogenic organisms, as though they are sentient, deliberative agents acting in the world with purposes. After all, wars are a purely human phenomenon.1 Wars involve people: people with human desires, motives, feelings, emotions, cunning, bravery (or not), aims and motivations.
Anthropomorphism is describing non-human entities as if they are people. Anthropomorphism is a common trope in science teaching (and science communication) but learners may come to adopt anthropomorphic explanations (e.g., the atom wants…) as if they are scientific accounts (Taber & Watts, 1996).
Bacteria, body cells and the like are not these kinds of entities, but can be described figuratively as though they are. Consider how,
"Some bacteria are wise to this and use iron depletion as an indicator that they are inside an animal. Other bacteria have developed their own powerful iron-binding molecules called 'siderophores' which are designed to snatch the iron from the jaws of lactoferrin. Perhaps an even smarter strategy is just to opt out of the iron wars altogether…
…tear lipocalin, whose neat structure includes a pocket for binding a multitude of molecules. This clever pocket allows tear lipocalin to bind the bacterial siderophores…neutralising the bacterium's ability to steal iron from us…"
Carver, 2017, pp.20-21
Of course, bacteria are only 'wise' metaphorically, and they only 'develop' and 'design' molecules metaphorically, and they only adopt 'smarter strategies' or can 'opt out' of activities metaphorically – and as long as the reader appreciates this is all figurative language it is unproblematic. But, when faced with multiple, and sometimes extended, passages seeming to imply wise and clever bacteria developing tools and strategies, could the reader lose sight of this (and, if so, does that matter?)
If bacteria are not really clever, nor are pockets (or 'pockets' – surely this is a metaphor, as actual pockets are designed features not evolved ones). Stealing is the deliberate taking of something one knows is owned by someone else. Bacteria may acquire iron from us, but (like the fox) they do not stealas they have no notion of ownership and property rights, nor indeed, I suggest, any awareness that those environments from which they acquire the iron are considered by them[our]selves as 'us'.
That is, there is an asymmetrical relationship here: humans may be aware of the bacteria we interact with (although this has been so only very recently in historical terms) but it would be stretching credibility to think the bacteria have any awareness – even assuming they have ANY awareness in the way we usually use the term – of us as discrete organisms. So, the sense in which they "use iron depletion as an indicator that they are inside an animal" cannot encompass a deliberate use of an indicator, nor any inference they are inside an animal. There is simply a purely automatic, evolved, process that responds to environmental cues.
I have referred in other articles posted here to examples of such anthropromorphic language in public discourse being presented apparently in the form of explanations: e.g.,
My focus here is Catherine Carver's book, but it is worth bearing in mind that even respectable scientific journals sometimes publish work describing viruses in such terms as 'smart', 'nasty', 'sneaky' – and, especially it seems, 'clever' (see 'So who's not a clever little virus then?'). So, Carver is by no means an outlier or maverick in using these devices.
'Immune' is embellished throughout with this kind of language – language that suggests that parasites, microbes, body cells, or sometimes even molecules:
act as agents that are aware of their roles and/or purposes;
do things deliberately to meet objectives;
have preferences and tastes.
The problem is, that although this is all metaphorical, as humans we readily interpret information in terms of our own experiences, so a scientific reading of a figurative text may requires us to consciously interrogate the metaphors and re-interpret the language. Historians of chemistry will be well aware of the challenge from trying to make sense of alchemical texts which were often deliberately obscured by describing substances and processes in metaphoric language (such as when the green lion covers the Sun). Science communicators who adopt extensive metaphors would do well to keep in mind that they can obscure as well as clarify.
For example, Carver writes:
"…the key to a game of hide and seek is elementary: pick the best hiding place. In the human body, the best places to hide are those where the seekers (the immune system) find it hard to travel. This makes the brain a very smart place for a parasite to hide."
Carver, 2017, p.132
'There is a strong narrative here ("the eternal game of hide and seek [parasites] play with us")- most of us are familiar with the childhood game of hide and seek, and we can readily imagine microbes or parasites hiding out from the immune cells seeking them. This makes sense, because of course, natural selection has led to an immune system that has components which are distributed through the body in such a way that they are likely to encounter any disease vectors present – as this increases fitness for the creature with such a system – and natural selection has also led to the selection of such vectors that tend to lodge in places less accessible to the immune cells – as this increase fitness of the organism that we2 consider a disease organism. Thus evolution has often been described, metaphorically, as an arms race.
But this is not really a game(which implies deliberate play – parasites can not know they are playing a game); and the disease vectors do not have any conception of hiding places, and so do not pick where to go accordingly, or using any other criterion; the immune cells are not knowingly seeking anything, and do not experience it being harder to get to some places than others (they are just less likely to end up in some places for purely naturalistic reasons).
So, a parasite that ends up in the brain certainly may be less accessible to the immune system, but is not deliberately hiding there – and so is no more 'smart' to end up there than boulders that congregate at the bottom of a mountainside because they think it is a good place to avoid being sent rolling by gravity (and perhaps having decided it would be too difficult to ascend to the top of the mountain).4
It is not difficult to de-construct a text in the way I have done above for the hide-and-seek comparison- if a reader thinks this is useful, and consequently continually pauses to do so. Yet, one of the strengths of a narrative is that it drives the reader forward through a compelling account, drawing on familiar schemata (e.g., hide and seek; dining; setting up home…) that the reader readily brings to mind to scaffold meaning-making.
Another familiar (to humans) schema is choosing from available options:
"…the neutrophil's killer skills come to the fore…It only has to ask one question: which super skills should be deployed for the problem at hand?"
Carver, 2017, p.27
So, it seems this type of immune cell has 'skills', and can pose itself (and answer) the question of which skills will be most useful in particular circumstances (perhaps just like a commando trained to deal with unexpected scenarios that may arise on a mission into enemy-held territory?) Again, of course, this is all figurative, but I wonder just how aware most readers are of this as they read.
Carver's account of Kupffer cells makes them seem sentient,
"The Kupffer cells hang around like spiders on the walls of the blood vessels waiting to catch any red blood cells which have passed their best before date (typically 120 days). Once caught, the red blood cell is consumed whole by the Klupffer cell, which sets about dismantling the haemoglobin inside its tasty morsel."
Carver, 2017, p.27
Kupffer cells surely do not 'hang around' or 'wait' in anything more than a metaphorical sense. If 'catching' old red blood cells is a harmless metaphor, describing them as tasty morsels suggests something about the Kupffer cells (they have appetites that discriminate tastes – more on that theme below) that makes them much more like people than cells.
Another striking passage suggests,
"Some signals are proactive, for example when cells periscope from their surface a receptor called ULBP (UL16-binding protein). Any NK cell that finds itselfshaking hands with a ULBP receptor knows it has found a stressed-out cell. The same is true if the NK cell extends its receptors to the cell only to find it omits parts of the secret-handshakeexpected from a normal cell. Normal, healthy cells display a range of receptors on their surface which tell the world 'I'm one of us, everything is good'. Touching these receptors placates NK cells, inhibiting their killer ways. Stressed, infected cells display fewer of these normal receptors on their surface and in the absence of their calming presence the trigger-happy NK cells attack."
Carver, 2017, p.27
That cells can 'attack' pathogens is surely now a dead metaphor and part of the accepted lexicon of the topic. But cells are clearly only figuratively telling the world everything is good – as 'telling' surely refers to a deliberate act. The hand-shaking, including the Masonic secret variety (n.b., a secret implies an epistemic agent capable of of knowing the secret), is clearly meant metaphorically – the cell does not 'know' what the handshake means, at least in the way we know things.
If the notion of a cell being stressed is also a dead metaphor (that is 'stressed' is effectively a technical term here {"the concept of stress has profitably been been exported from physics to psychology and sociology" Bunge, 2017/1998}), a stressed-out cell seems more human – perhaps so much so that we might be subtly persuaded that the cell can actually be placated and calmed? The point is not that some figurative language is used: rather, the onslaught (oops, it is contagious) of figurative language gives the reader little time to reflect on how to understand the constant barrage of metaphors…
"…it takes a bit of time for the B cells to craft a specific antibody in large quantities. However the newly minted anti-pollen antibodies are causing mischief even if we can't see evidence of it yet. They travel round the body and latch on to immune cells called masts anywhere they can find them. This process means the person is now 'sensitised' to the pollen and the primed mast cells lie in wait throughout the body…"
Carver, 2017, pp.183-184
…so, collectively the language can be insidious – cells can 'craft' antibodies (in effect, complex molecules) which can cause mischief, and find mast cells which lie in waitfor their prey.
Sometimes the metaphors seemed to stretch even figurative meaning. A dying cell will apparently 'set its affairs in order'. In humans terms, this usually relates to someone ensuring financial papers are up to date and sorted so that the executors will be able to readily manage the estate: but I was not entirely sure what this metaphor was intended to imply in the case of a cell.
Animistic language
Even a simple statement such as "First the neutrophil flattens itself"(p.28) whilst not implying a conscious process makes the neutrophil the active agent rather than a complex entity subject to internal mechanisms beyond its deliberate control. 3
So, why write
"Finally, the cell contracts itself tightly before exploding like a party popper that releases deadly NETs [neutrophil extracellular traps] instead of streamers."
Carver, 2017, p.27
rather than just "…the cell contracts tightly…"? I suspect because this offers a strong narrative (one of active moral agents engaged in an existential face-off) that is more compelling for readers.
Neutrophils are said to 'gush' and to 'race', but sometimes to be slowed down to a 'roll' when they can be brought to a stop ("stopping them in their tracks" if rolling beings have tracks?). But on other occasions they 'crawl'. Surely crawling is a rather specific means of locomotion normally associated with particular anatomy. Typically, babies crawl (but so might soldiers when under fire in a combat zone?)
There are many other examples of phrases that can be read as anthropomorphic, or at least animistic, and the overall effect is surely insidious on the naive reader. I do not mean 'naive' here to be condescending: I refer to any reader who is not so informed about the subject matter sufficiently to already understand disease and immunity as natural processes, that occur purely through physical and chemical causes and effects, and that have through evolution become part of the patterns of activity in organisms embedded in their ecological surroundings. A process such as infection or an immune response may look clever, and strategic, and carefully planned, but even when very complex, is automatic and takes place without any forethought, intentions, emotional charge or conscious awareness on the part of the microbes and body cells involved.
There are plenty of other examples in 'Immune' of phrasing that I think can easily be read as referring to agents that have some awareness of their roles/aims/preferences, and act accordingly. And by 'can easily be read', I suspect for many lay readers (i.e., the target readership) this means this will be their 'natural' (default) way of interpreting the text.
So (see Box 3 , below), microbes, cells, molecules and parasites variously are in relationships, boast, can beckon and be beckoned, can be crafty, can be egalitarian, can be guilty, can be ready to do things, can be spurred on, can be told things, can be treacherous, can be unaware (which implies, sometimes they are aware), can dance choreographed, can deserve blame, can find things appealing, can have plans, can mind their own business, can pay attention, can spot things, can take an interest, can wheedle (persuade), congregate, craft things, dare to do things, do things unwittingly, find things, get encouraged, go on quests, gush, have aims, have friends, have goals, have jobs, have roles, have skills, have strategies, have talents, have techniques, insinuate themselves, know things, like things, look at things, look out for things, play, outwit, race, seek things, smuggle things, toy with us, and try to do things.
Microbes moving in
One specific recurring anthropomorphic feature of Carver's descriptions of the various pathogens and the harmless microbes which are found on and in us, is related to finding somewhere to live – to setting up a home. Again, this is clearly metaphorical, a microbe may end up being located somewhere in the body, but has no notion, or feeling, of being at home. Yet the schema of home – finding a home, setting up home, being at home, feeling at home – is both familiar and, likely, emotionally charged, and so supports a narrative that fits with our life-experiences.
A squatter among pathogen society? Images by Peter H (photograph) and Clker-Free-Vector-Images (superimposed virus) from Pixabay
Viruses and bacteria are compared in terms of their travel habits (in relation to which, "The human hookworm…[has] got quite an unpleasant commute to work…"),
"…viruses are the squatters of pathogen society. Unlike bacteria, which tend to carry their own internal baggage for all their disease-making needs, viruses pack light. They hold only the genes they need to gain illegal entry to our cells and then instruct our cells' machinery to achieve the virus's aims. The cell provides a very happy home for the virus, and also gives it cover from the immune system."
Carver, 2017, p.35
These pathogens apparently form a society (where there is a distinction between what is and what is not legal 5) and individually have needs and aims. A virus not only lives in a home, but can be happy there. Again, such language does have a sensible meaning (if we stop to reflect on just what the metaphors can sensibly mean), but it is a metaphorical meaning and so should not be taken literally.
The analogy is however developed,
"…the human microbiota is the collective name for the 100 trillion micro-organisms that have made us their real estate. From the tip of your tongue to the skin you sit on, they have set up home in every intimate nook and cranny of our body…The prime real estate for these microbes, the Manhattan or Mayfair equivalent inside you and me, is the large intestine or colon. If you had a Lonely Planet or Rough Guide to your gut, the colon would have an entry something like this: 'The colon is a must-see multi-cultural melting-pot, where up to one thousand species of bacteria mingle and dine together every second of every day. In this truly 24/7 subterranean city, Enterococcirub shoulders with Clostridia; Bacteroides luxuriate in their oxygen-depleted surroundings and Bifidobacteria banquet on a sumptuous all-you-can-eat poo buffet. It's the microbe's place to see, and be seen'. ….[antibiotic's] potential to kill off vast swathes of the normal gut flora. This creates an open-plan living space for a hardy bacterium called Clostridium difficile. This so-called superbug (also known as C. diff) is able to survive the initial antibiotic onslaught and then rapidly multiplies in its newly vacated palace."
Carver, 2017, p.76-78
This metaphor is reflected in a number of contexts in Immune. So, the account includes (see Box 4, below) break ins, camps, communities, homes, lounging, palaces, penthouses, playgrounds, preferred places to live, real estate, residents, shops, squatters, suburban cul-de-sacs, and tenants .
What is for dinner?
The extracts presented above also demonstrate another recurring notion, that microbes and body cells experience 'eating' much like we do ('tasty morsel', 'dine together', 'banquet…buffet'). There are many other such illusions in 'Immune'.
We could explain human eating preferences and habits in purely mechanistic terms of chemistry, physics and biology – but most of us would think this would miss an important level of analysis (as if what people can tell us about what they think and feel about their favourite foods and their eating habits is irrelevant to their food consumption) and would be very reductive. Yet, when considering a single cell, such as a Kupffer cell, surely a mechanistic account in terms of chemistry, physics and biology is not reductionist, but exhaustive. Anything more is (as Einstein suggested about the aether) superfluous.
One favoured dining location is the skin:
"The Demodexdine on sebum (the waxy secretion we make to help waterproof our skin), as well as occasionally munching on our skin cells and even some unlucky commensal bacteria like Propionibacterium acnes…like many of us, P. acnes is a lipophile, which is to say it adores consuming fat. The sebum on our skin is like a layer of buttery, greasy goodness that has P. acnessmacking its lips. However, when P. acnes turns up to dine it has some seriously bad table manners, which can include dribbling chemicals all over our faces…[non-human] animal sebum lacks the triglyceride fats that P. acnes [2 ital] loves to picnic on." p.82
Carver, 2017, pp.81-82
It is hopefully redundant, by this point, for me to point out that Propionibacterium acnes does not adore anything – neither preferred foodstuffs nor picnics – but has simply evolved to have a nutritional 'regime' that matches its habitat. Whilst this extract immediately offers a multi-course menu of metaphors, it is supplemented by a series of other semantic snacks. So 'Immune' also includes references to buffet carts, chocolate chips, cookies, devouring, easy meals, gobbling up, making food appetising, making food tastier, munching, a penchant for parma ham and rare steak, soft-boiled eggs, tasty treats and yummy desserts.
Can you have too much of a metaphorical good thing?
I am glad I bought 'Immune'. I enjoyed reading it, and learnt from it. But perhaps a more pertinent question is whether I would recommend it to a non-scientist* interested in learning something about immunity and the immune system. Probably, yes, but with reservations.
Is this because I am some kind of scientific purist (as well as a self-acknowledged pedant)? I would argue not: if only because I am well aware that my own understanding of many scientific topics is shallow and rests upon over-simplifications, and in some cases depends upon descriptive accounts of what strictly need to be appreciated in formal mathematical terms. I do not occupy sufficiently high ground to mock the novice learner's need for images and figures of speech to make sense of unfamiliar scientific ideas. As a teacher (and author) I draw on figurative language to help make the unfamiliar become familiar and the abstract seem concrete. But, as I pointed out above, figurative language can sometimes help reveal (to help make the unfamiliar, familiar); but can also sometimes obscure, a scientific account.
I have here before made a distinction between the general public making sense of science communication in subjective and objective terms. Objective understanding might be considered acquiring a creditable account (that would get good marks in an examination, for example). But perhaps that is an unfair test of a popular science book: perhaps a subjective making-sense, where the reader's curiosity is satisfied – because 'yes, I see, that makes sense to me' – is more pertinent. Carver has not written 'Immune' as a text book, and if readers come away thinking they have a much better grasp of the immune system (and I suspect most 'naive' readers certainly would think that) then it is a successful popular science book.
My reservation here is that we know many learners find it difficult to appreciate that cornerstone of modern biology, natural selection (e.g., Taber, 2017), and instead understand the living world in much more teleological terms – that biological processes meet ends – occur to achieve aims – and do so through structures which have been designed with certain functions in mind.
So, microbes, parasites, cells, and antibodies, which are described as though they are sentient and deliberate actors – indeed moral agents seeking strategic goals, and often being influenced by their personal aesthetic tastes – may help immunity seem to make sense, but perhaps by reinforcing misunderstandings of key foundational principles of biology.
In this, Catherine Carver is just one representative of a widespread tendency to describe the living world in such figurative terms. Indeed, I might suggest that Carver's framing of the immune system as a defence force facing hostile invaders makes 'Immune' a main-stream, conventional, text in that it reflects language widely used in public science discourse, and sometimes even found in technical articles in the primary literature.
A myth is a story that has broad cultural currency and offers meaning to a social group, usually involving supernatural entities (demons, superhuman heroes, figures with powerful magic – perhaps microbial aesthetes and sentient cells?), but which is not literally true. e.g., Your immune system comprises a vast army of brave and selfless soldiers seeking to protect you from intruders looking to do you harm: an immune response is a microcosm of the universal fight between good and evil?
My question, then, is not whether Carver was ill-advised to write 'Immune' in the way she has, but whether it is time to more generally reconsider the widespread use of the mythical 'war' analogy in talking about immunity and disease.
Notes
1 Even if, for example, some interactions between groups of ants from different nests {e.g., see 'Ant colony raids a rival nest | Natural World – Empire of the Desert Ants – BBC'} look just as violent as anything from human history, their 'battles' are surely not planned as part of some deliberate ongoing campaign of hostilities.
2 The bacteria infecting us, if they could conceptualise the situation (which they cannot), would have no more reason to consider themselves a disease, than humans who 'infected' an orchard and consumed all the fruit would consider themselves a disease. Microbes are not evil for damaging us, they are just being microbes.
3 If my rock analogy seems silly, it is because we immediately realise that rocks are just not the kind of entities that behave deliberately in the world. The same is true of microbes and body cells -they are just not the kind of entities that behave deliberately in the world, and as long as this is recognised such metaphorical language is harmless. But I am not sure that is so immediately obvious to readers in these cases.
4 Such an issue can arise with descriptions about people as well. If I want to share a joke with a friend I may wink. If a fly comes close to my eye I may blink. Potentially these two actions may seem indistinguishable to an observer. However, the first is a voluntary action, but in the second case the 'I' that blinks is not me the conscious entity that ascribes itself self-hood, but an autonomous and involuntary subsystem! In a sense a person winks, but has blinking done to her.
5 If entry to our cells was 'illegal' in the sense of being contrary to natural laws/laws of nature, it would not occur.
* A note on being a scientist. Any research scientists reading this might scoff at my characterisation of the readers of popular science books as being non-scientists with the implied suggestion that I, by comparison, should count as a scientist. I have never undertaken research in the natural sciences, and, although I have published in research journals, my work in science education would be considered as social science – which in the Anglophile world does not usually count as being considered 'science' per se. However, in the UK, the Science Council recognises science educators as professional scientists. Learned societies such as the Royal Society of Chemistry and the Institute of Physics will admit teachers of these subjects as professional members, and even Fellows once their contributions are considered sufficient. This potentially allows registration as a Chartered Scientist. Of course, the science teacher does not engage in the frontiers of a scientific research field in the way a research scientist does, however the science teacher requires not only a much broader knowledge of science, but also a specialist professional expertise that enables the teacher to interrogate and process scientific knowledge into a form suitable for teaching. This acknowledges the highly specialised nature of teaching as an expert professional activity which goes far beyond the notion of teaching as a craft that can be readily picked up (as sometimes suggested by politicians).
Work cited
Bunge, M. (2017/1998). Philosophy of Science. Volume 1: From problem to theory. Routledge. (1967)
Carver, C. (2017). Immune. How your body defends and protects you. Bloomsbury Sigma.
"neutrophil is a key soldier" "the human body is like an exceedingly well-fortified castle, defended by billions of soldiers" "…the incredible arsenal that lives within us…" "the hidden army" "…our adaptive assassins, our T and B cells" "The innate system is the first line of defence…" skin: "…an exquisite barrier that keeps unwanted invaders out." "…your airways are exceedingly well booby-trapped passages lined with goblet cells, which secrete a fine later of mucus to trap dirt and bacteria." "Initially it was seen as a simple soldier with a basic skills set …Now we know it is a crafty assassin with a murderous array of killing techniques." "…ninja skill of neutrophils…", "ninja neutrophils" "macrophages are stationed at strategic sites…what an important outpost the liver is for the immune system" "NK cells [have] killer ways" "trigger-happy NK cells" "Ever neat assassins, NK cells" "vicious immune cells" compared to "a pack of really hungry Rottweilers" interleukins are "pro-inflammatory little fire-starters" "neutrophils, macrophages and other immune system soldiers" "T cells…activate their invader-destroying skills." "…a weapon with a name worthy of a Bond villain's invention: the Membrane Attack Complex" "miniature mercenaries" "a system whose raise d'etre is to destroy foreign invaders" "everything we do exposes us to millions of potential invaders." "…all invaders need an entry point…" "these tiny sneaks [e.g., E. coli]" "the dark-arts of pus-producing bacteria…" Neisseria meningitidis: "this particular invader" "foreign invaders" "an aggressive border patrol" 'Tregs are the prefects of the immune system…" "…the parasite larva has more in common with a time bomb…" "T cells…are the grand high inquisitors of the immune system, spotting and destroying infected cells and even cancer…these assassins" "imagining you have to make a Mr Potato Head army, and you know that the more variety in your vegetable warriors the better" "this process is about …making a mutant army." "they form a fighting force that rivals Marvel Comic's Fantasic Four" "each antibody molecule released as a single soldier" "The pancreas … acts as the commander-in-chief when its comes to controlling blood sugar levels." "our tiny but deadly defenders" "cells in the spleen with a specialised killer-skill" "wears a mask that conceals its killer features from its would-be assassins" "the microbiological mass murderers…the serial killers" "PA [protective antigen] is the muscled henchman" "the murderous cast of immune cells and messengers…this awe-inspiring army" "a microscopic army, capable of seeking out and destroying bacteria" "the terminators are targeted killers" "weaponised E. coli
Box 1: References to the immune system and its components as a defence force
"a kamikaze blaze of microbe-massacringglory" "an eternal war between our bodies and the legions of bacteria, viruses, fungi and parasites that surround us" "these invaders' attempts are thwarted" "battles" "all my innate defences would essentially hold the fort and in many instances this first line would be enough to wipe out the invader before the adaptive system gets a chance to craft bespoke weaponry." "the tears we shed [are] a form of chemical warfare." "…allowing the neutrophils to migrate through the blood vessel and into the battlefield of the tissue beyond" "the cell contracts itself tightly before exploding" "their friendly fire contributed to the death of the victim." "spewing microbe-dissolving chemicals into the surround tissue. This allows the neutrophil to damage many microbes at once, a bit like fishing by throwing dynamite into the water." "NK [natural killer] cells target the microbes that have made it inside our cells." "NK cells attack" "…the initial hole-poking assault…" "all part of the NK cell's plan to kill the cell." "…they trip the cell's self-destruct switch" "expose a cell to a severe, but not quite lethal threat…transform the cell into a hardened survivor" immune cells have an "ability to go on the rampage" "call up … immune system soldiers to mount a response" "leukaemia … has decimated a type of white blood cells called T cells" "it behaves like a Trojan horse [as in the siege of the City of Troy]" "telling our soldier cells to kick back and take some R & R" "the smoke signals of infection" "…like a showing of tiny hand grenades on the surrounding cells." "the donor cells would be vastly outnumbered and it would be like a band of rebels taking on a vast army on its home turf" "the recipient's own immune system is in a weakened state and unable to fight back" "…the antibodies …are therefore able to give a hostile welcome to alpha-gal-wearing malaria parasites." "…our gut bacteria effectively provide a training ground for the immune system – a boot camp led by billions of bacteria which teaches us to develop an arsenal of antibodies to tackle common foreign invader fingerprints…" "fighting on certain fronts" "edgy alliance" "shore up the intestinal defences by reinforcing the tight junctions which link the gut cells together" "our gut's security fence" "a self-cell that should be defended, not attacked" "this mouse-shaped Trojan horse" "the scanning eyes of the immune system" "a form of border control, policing" "…the bacteria-bashing brilliance…" "…the IgA effectively blocks and disables the invaders' docking stations…" "B cells and their multi-class antibody armoury have the ability to launch a tailored assassination campaign against almost anything" "the exquisitely tailored assassination of bacteria, viruses and anything else that dares enter the body" "One of the seminal victories in our war on bugs" "Some bacteria have a sugar-based cloaking device" "…tripped by the pollen attaching to the IgE-primed mast cells and, like pulling a pin on a grenade, causing them to unleash their allergy-inducing chemicals." "The almost instant assault of the immediate phase reaction occurs within minutes as the dirty bomb-like explosion of the mast cell fill the local area with a variety of rapidly acting chemicals." "..the battle against infectious diseases." "teaching the patrolling forces of the immune system to stand down if the cell they're interrogating is a healthy cell that belong to the body. It's a bit like a border patrol force wandering through the body and checking passports" "like a training camp for the newly created border guards". "ordering those that react incorrectly to self-destruct" "These bacteria have a sugar-based polysaccharide outer shell, which acts like a cloaking device" "the [oncolytic] viruses have a Swiss army knifeselection of killer techniques" "This approach slaughters these foot soldiers of our immune system…" "they [macrophages] have picked up a time bomb" "antibodies that act like heat-seeking missiles" "Kadcyla …has a double-pronged attack." "we are setting up easy antibiotic assault courses all over the place" "His suicidal minions were engineered to seek out a pneumonia-causing bacterium by the name of Pseudomonas aeruginosa and explode in its presence releasing a toxic cloud of a Pseudomonas-slaughtering chemical called pyocin." "it could secrete its killer payload" "stimulate the little terminators to produce and release their chemical warfare."
Box 2: References to disease and immune processes as war and violent activity
"The macrophage's … job as a first responder…" " osteoclasts and osteoblasts" are "Carver refers to "the bony equivalent of yin and yang…osteoblasts are the builders in this relationship" (said to be "toiling") …osteoclast, whose role is the constant gardener of our bones" "…a white blood cell called the regulatory T cell, or 'Treg' to its friends…" "…this biological barcode lets the T cell know that it's looking at a self-cell …" "…the ball of cells that makes up the new embryo finishes bumbling along the fallopian tube and finds a spot in the uterus to burrow into…" "By using this mouse-shaped Trojan horse the parasite gets itself delivered directly into the cat's gut, which is where Toxoplasma likes to get it on for the sexual reproduction stage of its lifecycle." "It's as if the trypanosome has a bag of hats that it can whip out and use to play dressing-up to outwit the immune system." "proteins… help smuggle the ApoL1 into the parasite" "Some parasites have a partner in crime…" "the chosen strategy of the roundworm Wuchereria bancrofti…uses a bacterium to help cloak itself from the immune system." "the work of a master of disguise…precisely what Wuchereria bancrofti is." "…its bacterial side-kick" "parasites that act as puppet masters for our white blood cells and direct our immune response down a losing strategy" "parasites with sartorial skills that craft themselves a human suit made from scavenged proteins" "parasites toy with us" "B cells have one last technique" "Chemical messengers beckon these B cells" "what AID [activation induced deaminase] seeks to mess with" "Each class [of antibody] has its own modus operandi for attacking microbes" "in terms of skills, IgG can activate the complement cascade" "…one of its [IgA] key killer skills is to block any wannabe invaders from making their way inside us." "the helper T cell and the cytotoxic T cell, which take different approaches to achieve the same aim: the exquisitely tailored assassination of bacteria, viruses and anything else that dares enter the body." "B cells, cytoxic T cells and macrophages in their quest to kill invaders" "T cells interact with their quarry" "add a frisson of encouragement to the T cell, spurring it on to activation." "the brutally egalitarian smallpox" "Polio is another virus that knows all about image problems." "the guilty allergen" "IgE and mast cells are to blame for this severe reaction [anaphylaxis]" "…The T regulatory cells identify and suppress immune cells with an unhealthy interest in normal cells." "the skills of a type of virus well versed in the dark arts of integrating into human DNA" "The spleen is a multi-talented organ" "to get rid of the crafty, cloaked bacteria" "Even once cells are able to grow despite the chemical melting pot they're stewing in telling them to cease and desist…" "It is believed that tumour cells bobbing about in the bloodstream try to evade the immune system by coating themselves in platelets…" "the cancer's ability to adorn itself" "They [oncolytic viruses] work by …drawing the attention of the immune system" "when the replicating virus is finally ready to pop its little incubator open" "…anthrax, which lurks in the alveoli awaiting its cellular carriage: our macrophages…" "The macrophages are doing what they ought … Completely unaware that they have picked up a time bomb…" "the microbial thwarting talents of interferons" "…your mAbs will do the legwork for you, incessantly scouring the body for their target destination like tiny, demented postal workers without a good union." "One of the tumour techniques is to give any enquiring T cells a 'these aren't the cells you're looking for' handshake that sends them on their way in a deactivated state, unaware they have let the cancer cells off the hook. Checkpoint inhibitor mAbs bind to the T cell and prevent the deactivating handshake from happening. This leaves the T cell alert and able to recognise and destroy the cancer cells." "A third neutrophil strategy…" "all part of the NK cell's plan to kill the cell." "…a majestic dance of immune cells and messengers, carefully choreographed…" "So my immune system's bag of tricks might not currently include a smallpox solution, but if I were to contract the disease my adaptive immune response would try its hardest to create one to kill the virus before it killed me." "Thus earwax can catch, kill and kick out the multitude of microbes that wheedle their way into out ears…" "Up to 200 million neutrophils gush out of our bone marrow and into the blood stream every day. They race around the blood on the look-out for evidence of infection." "a process called 'opsonisation' make consuming the bacterial more appealing to neutrophils" "the same siren call of inflammation and infection that beckoned the neutrophils." "…a set of varied and diverse circumstances can prompt multiple macrophages to congregate together and, like a massive Transformer, self-assemble into one magnificent giant cell boasting multiple nuclei." "The cell responds to the initial hole-poking assault by trying to repair itself…At the same time that it pulls in the perforin holes, the cell unwittingly pulls in a family of protein-eating granzymes…" "the gigantosome is more than just a pinched-off hole-riddled piece of membrane; its creation was all part of the NK cell's plan to kill the cell." caspases in cells "play an epic game of tag" Arachidonic acid: "Normally it just minds its own business" "The interferon molecule insinuates itself into the local area" "The chemokines …their ability to beckon a colourful array of cells to a particular location…they can call up neutrophils, macrophages and other immune system soldiers to mount a response to injury and infection…" "chemicals that can tell these cells where to go and what to do. These crafty chemicals…" "…the triad of goals of the complement system…" "It's the T cell's job to spot infected or abnormal cells." "Microbes aren't easy bedfellows" "…the 'lean' microbes won out over the 'obese' ones." "IgD is the most enigmatic of all the immunoglobins" "the parasite larva …treacherous"
Box 3: Examples of phrasing which might suggest that microbes, cells, etc., are sentient actors with human motivations
"Bifidobacterium infantis, a normal resident of the healthy infant gut" "trillions of microbes that make us their home" "…a much more diverse community of inner residents…" "Entamoeba … just happened to prefer to live in a multicultural colon." "…the mouth had the least stable community, like the microbial equivalent of transient squatters, while the vagina was the quiet suburban cul-de-sac of the map, with a fairly fixed mix of residents." "that's where they [Mycobacteria] set up home" "Neisseria meningitidis "sets up shop inside our cells…it breaks in…" "…Heliocobacter pylori (a.k.a H. pylori), a bacterium that makes its home in the sticky mucus that lines the stomach. While the mucus gives H. pylori some protection from the gastric acid, it also employed a bit of clever chemistry to make its home a touch more comfortable." Dracunculus medinensis will "seek out a mate, turning the abdominal wall into their sexual playground." "…plenty of creepy crawlies have been known to to call the human brain home, lounging among our delicate little grey cells…" the tapeworm Spirometra erinaceieuropaei : "…this particular tenant ensconced in their grey matter." "the worm…wriggled up through his body to reach its cranial penthouse where it could enjoy the luxury of a very special hiding spot." "There are flatworms, roundworms hookworms, whipworms, fleas and ticks, lice and amoeba. They're all queuing up to get a room at the palace of parasites" Clostridium tetani "can often set up camp in soil", "About 75 million people worldwide are thought to carry the dwarf tapeworm in their small intestine, where it lives a fairly innocuous life and causes its host few if any symptoms." "Though it may not seem like it, our nostrils are prime real estate and rival bacteria fight each other for resources, a fight which includes chemical warfare." "…we'll meet the creepy critters that like to call us home and the ways our immune system tries to show them the door."
Box 4: Microbes and cells described as the kind of entities which look for and set up homes.
"an all-you-can-eat oligosaccharide buffet for B. infantis [Bifidobacterium infantis]" "…complement's ability to make these bacteria seem tastier to our macrophages…" "Mycobacteria… actually want to be gobbled up by our macrophages…" "sprinkling C3b on the surface of bacteria makes them much more appetising to microbe-munching cells" macrophages 'devour' the remains of dead cells "…Salmonella, which likes a soft-boiled egg, and Toxoplasma gondii, which shares my penchant for parma ham and rare steak." Dracunculus medinensis "looks like an easy meal for a peckish water flea. Sadly for the water flea the parasite larva has more in common with a time bomb than a tasty snack ever should, and the treacherous morsel spends the next 14 days inside the flea…" "…flagging a microbe as munchable for macrophages…" "IgG …can mark targets as munchable. Thus any bacterium, virus or parasite coated in IgG finds itself the yummiest dessert on the buffet cart and every hungry macrophage rushes to get itself a tasty treat." "…from our brain to our bones, we are riddled with munching macrophages…" opsonisation: "much like sprinkling tiny chocolate chips on a bacterial cookie" "Demodex dine on sebum…as well as occasionally munching on our skin cells" "P. acnes is a lipophile, which is to say it adores consuming fat. The sebum on our skin is like a layer of buttery, greasy goodness that has P. acnes smacking its lips." "when "P. acnes turns up to dine it has some seriously bad table manners" " P. acnes loves to picnic."
Box 5: References to the culinary preferences and habits of entities such as microbes and immune cells
I have designed a simple concept cartoon. Concept cartoons are used in teaching, usually as an introductory activity to elicit students' ideas about a topic before proceeding to develop the scientific account. This can be seen as 'diagnostic assessment' or just part of good pedagogy when teaching topics where learners are likely to have alternative conceptions. (So, in science teaching, that means just about any topic!)
But I am retired and no longer teach classes, so why am I spending my time preparing teaching resources?
Well, I was writing about dialogic teaching, and so devised an outline lesson plan to illustrate what dialogic teaching might look like. The introductory activity was to be a concept cartoon, so I thought I should specify what it might contain – and so then I thought it would help a reader if I actually mocked up the cartoon so it would be clear what I was writing about. That led to:
A concept cartoon provides learners with several competing ideas to discuss (This can be downloaded below)
What happens, and why?
In my concept cartoon the focal question is what will happen when some NaCl is added to water – and why? This is a concept cartoon because there are several characters offering competing ideas to act as foci for learners to discuss and explore. Of course, it is possible to ask learners to engage with a cartoon individually, but they are intended to initiate dialogue between learners. So by talking together learners will each have an audience to ask them to clarify, and to challenge, their thinking and to ensure they try to explain their reasoning.
Of course, there is flexibility in how they can be used. A teacher could ask students to consider the cartoon individually, before moving to small group discussions or whole class discussion work. (It is also possible to move from individual work to pairing up, to forming groups from two pairs, to the teacher then collating ideas from different groups.) During this stage of activity the intention is to let student make their thinking explicit and to consider and compare different views.
Of course, this is a prelude to the teacher persuading everyone in the class of the right answer, and why it is the right answer. Concept cartoons are used where we know student thinking is likely to make that stage more than trivial. Where learners do already have well-entrenched conceptions at odds with the scientific models, we know simply telling them the target curriculum account is unlikely to lead to long-term shifts in their thinking.
And even if they do not, they will be more likely to appreciate, and later recall, the scientific account if the ground is prepared in this way by engaging students with the potential 'explanatory landscape' (thinking about what is to be explained, and what explanation might look like). If they become genuinely engaged with the question then the teacher's presentation of the science is given 'epistemic relevance'. (Inevitably the science curriculum consists of answers to the questions scientists have posed over many years: but in teaching it we may find we are presenting answers to many questions that simply have never occurred to the students. If we can get learners to first wonder about the questions, then that makes the answer more relevant for them – so more likely to be remembered later.)
Is there really likely to be a diversity of opinion?
This example may seem fairly straightforward to a science teacher. Clearly NaCl, sodium chloride (a.k.a. 'common salt' or 'table salt') is an ionic solid that will dissolve in water as the ions are solvated by the polar water molecules clustering around them. That should also be obvious to advanced students. (Should – but research evidence suggests not always.)
What about students who have just learned about ionic bonding and the NaCl crystal structure? What might they think?
Surely, we can dismiss the possibility that salt will not dissolve? Everyone knows it does. The sea is pretty salty, and people often add salt to the water when cooking. And as long as learners know that NaCl is 'salt' there should be no one supporting the option that it does not dissolve. After all, there is a very simple logical syllogism to be applied here:
common salt dissolves in water
common salt is NaCl
so NaCl dissolves in water
Except, of course, learners who know both that salt dissolves in water and that it is NaCl still have to bring both of those points to mind, and coordinate them – and if they are juggling other information at the same time they may have reached the 'working memory capacity' limit.
Moreover, we know that often learners tend to 'compartmentalise' their learning (well, we all do to some extent), so although they may engage with salt in the kitchen or dinner table, and learn about salt as NaCl in science lessons, they may not strongly link these two domains. And the rationale offered here by the student in red, that NaCl is strongly bonded, is a decent reason to expect the salt to be insoluble.
Now as I have just made this cartoon up, and do not have any classes to try it out on, I may be making a misjudgement and perhaps no learners would support this option. But I have a sneaking suspicion there might be a few who would!
The other two options are based on things I was told when a teacher. That the solid may dissolve as separate atoms is based on being told by an advanced student that in 'double decomposition' reactions the precipitate was produced when atoms in the solution paired up to transfer electrons. The student knew the solutions reacting (say of potassium iodide and lead nitrate) contained ions, but obviously (to my informant) the ions changed themselves back into atoms before forming new ionic bonds by new electron transfers.
I was quite shocked to have been told that, but perhaps should not have been as it involves two very common misconceptions:
(Moreover, another advanced student once told me that when bonds broke electrons had to go back to their 'own' atom as it would be odd for an atom to end up with someone else's electron! So, by this logic, of course anions have to return electrons to their rightful owners before ironically bonding elsewhere!)
So, I suspect a fair number of students new to learning about ionic bonding might well expect it to dissolve as atoms rather than ions.
As regards the other option, that the salt dissolves as molecules, I would actually be amazed if quite a few learners in most classes of, say, 13-14-year-olds, did not select this option. It is very common for students to think that, despite its symmetrical crystal structure (visible in the model in the cartoon), NaCl really comprises of NaCl units, molecule-like ions pairs – perhaps even seen as simply NaCl 'molecules'.
It becomes the teacher's job to persuade learners this is not so, for example, by considering how much energy is needed to melt NaCl , and the conductivity of the liquid and the aqueous solution. (In my imaginary lesson the next activity was a 'Predict-Observe-Explain' activity involving measuring the conductivity of a salt solution.)
A challenge to science teachers
Perhaps you think the students in your classes would not find this a challenging task, as you have taught them that NaCl is an ionic solid, held together by the attractions between cations and anions? All your students know NaCl dissolves, and that the dissolved species will (very nearly always) be single hydrated ions.
Perhaps you are right, and I am wrong.
Or perhaps you recognise that given that in the past so many students have demonstrated alternative conceptions of ionic bonding (Taber, 1994) that perhaps some of your own students may find this topic difficult.
As I no longer had classes to teach, I am uploading a copy of the cartoon that can be downloaded in case you want to present this to your classes and see how they get on. This is primary for students who have been introduced to ionic bonding and taught that salts such as NaCl form solids with regular arrangements of charged ions. If they have not yet studied salts dissolving then perhaps this would be a useful introductory ability for that learning that content?
If you have already taught them about salts dissolving, then obviously they should all get the right answer. (But does that mean they will? Is it worth five minutes of class-time to check?)
And if you work with more advanced students who are expected to have mastered ionic bonding some years ago, then we might hope no one in the class would hesitate in selecting the right answer. (But can you be sure? You could present this as something designed for younger students, and ask your students how they would tutor a younger bother or sister who was not sure what the right answer was.)
If you do decide to try this out with your students – I would really like to know how you get on. Perhaps you would even share your experience with other readers by leaving a comment below?
Analogies are thinking tools as well as communication tools.
Keith S. Taber
Analogy is very familiar to science teachers as a tool for communicating ideas (one way to help 'make the unfamiliar familiar'), but analogies have also been important to research scientists themselves. Analogy can be a useful thinking tool for scientists, as well as a means of getting across novel ideas.
Indeed we might suggests that analogies have roles that might be described as exploratory, autodidactic, and pedagogic:
I wonder if it is like this? A creative source of ideas generating hypothesis to test out;
Ah, I see, it is like this! A tool for making sense of something that seems unfamiliar to us;
You see, it is somewhat like this… A tool for helping others to make sense of some novel or unfamiliar notion.
On this site, I have given quite a lot of attention to the pedagogic, communicative role of analogies as used by teachers – and also by other communicators of science such as journalists, and indeed sometimes also scientists themselves when writing for their colleagues. As well as discussing some teaching analogies in detail in blog postings, I've also compiled some examples I have come across from my reading and other sources (such as radio items).
I was recently using an analogy myself to communicate an idea as part of a talk I had been asked to give. I set up an analogy to illustrate four categories in a model of 'bugs' that can occur in teaching-learning when students either do not understand, or misunderstand (misinterpret), teaching. I was trying to explain an educational model to science teachers, so used some science (that I assumed would be familiar to the audience) as the analogue.
An analogy involves a comparison between the structures of two systems where there is an explicit mapping to show similar structural features between the two systems – the analogue being used to explain and the target being explained. (If that sounds a bit obscure, there is an example presented in the table below).
Analogy as a thinking tool
I readily found 'mappings' for my four categories, so my analogy 'worked' (for me!) But, in working out the analogy, I realised that there was an additional option, a variation on one of the categories, that I had not fully appreciated. That is, by thinking about an analogy, I discovered a potential mapping back to my model that I had not expected, so the act of developing an analogy (meant to communicate the idea) actually deepened my own understanding of the model.
This is just the kind of thinking that analogy as an exploratory tool can offer (even if that was not how I was intending to use the analogy). This did not lead to a drastic rethinking of my model, but I thought it was interesting how working with the analogy could offer a slightly different insight into the original model.
Accommodating concepts
This puts me in mind of how concepts can both grow and then be modified by analogical thinking in science. For example, when (the substance that was to be named as) potassium was first discovered it had a combination of properties quite unlike any previously known substances. It seemed to share some – but not all – properties with the group of known substances referred to as metals, so it could be considered a metal by analogy with them. But for potassium (and then sodium) to be accepted as actual metals (not just partial analogies of metal) it was necessary to modify the set of properties considered essential to a substance that was classed as a metal (Taber, 2019).
(Of course, it seems 'obvious' to us now that potassium and sodium are metals – but that is with the benefit of hindsight, as the metal concept we learnt about in chemistry had long since been adapted to 'accommodate' the alkali metals.)
Types of learning blocks
The 'target' material in my talk was the typology of learning impediments which is meant to set out the types of 'bugs' that can occur in a 'teaching learning system'. That is, when
"there is a teacher who wishes to teach some curriculum material that has been prepared for the class; and a learner, who is present; willing, and in a fit state, to learn; who is paying attention in class; and where there is a good communication channel, which will normally mean that the learner and teacher can see and hear each other clearly… even when this system exists, we cannot be confident the learner will always understand what is being taught in the manner intended"
The teacher-learner system – a learner, motivated to study, able to see and hear the teacher, and paying attention to the teacher's clear explanation of a scientific idea: "even when this system exists, we cannot be confident the learner will always understand what is being taught in the manner intended"
The model has four main categories of system 'bugs', organised in two overarching classes:
A null learning impediment meant the student failed to associate teaching with prior learning – that the teaching did not lead to the learning bringing to mind something that helped them make sense of the teaching. This could be because the expected prior learning had never happened, called a deficiency learning impediment; or because the relevance of prior learning was not appreciated (i.e., not associated), a so-called fragmentation learning impediment.
The two main types of substantive learning impediments involve the learner making sense of teaching in a way that does not match that intended, either because the relevant prior learning includes alternative conceptions, and so the learning is distorted by being understood within a conceptual framework that does not match the science; or through the teaching being understood in the context of some other prior learning that seemed relevant to the learner, but which, from the teacher's perspective, was not pertinent. These are referred to in the model as grounded learning impediments and associative learning impediments, respectively.
A typology of learning impediments: things that go wrong even when the teacher explains the concepts clearly, and the learner wants to learn and is paying attention.
The analogy that came to mind was from biochemistry (perhaps because I had recently been thinking about the metaphors and analogies in a book on that subject?) As meaningful learning requires teaching to be related to (fit into, anchor in, make sense of in terms of) some prior learning available to the learner, I envisaged learning as being analogous to some small molecule that in metabolism became bound to a protein (an enzyme perhaps) which was only possible because there was a good fit between the molecular configurations of the protein (a component of the learners' existing conceptual structure) and the metabolite (the information provided in teaching).
An analogy for learning – a metabolite will only bind to a protein if there is a good 'fit' between the structures.
So in my analogy, the mapping was:
analogue
maps to
target concept
binding of a metabolite to a protein
⟷
conceptual learning
protein
⟷
an aspect of the learner's existing conceptual structure
metabolite
⟷
a 'quantum' of information presented in teaching
metabolite-protein complex
⟷
new information understood in terms of prior learning – new information assimilated to develop conceptual understanding
So, in my talk I represented learning, and the possible 'bugs' in learning, through simple animations, using the following signs:
Dramatis personae for the analogue…
These signs were somewhat arbitrary symbols, except that they had an iconic feature – a complicated shape representing the molecular conformation that could indicate the presence or absence of a binding site capable of leading to complex formation.
Learning was modelled as the binding of the metabolite (information presented in teaching) with the protein (an existing feature of conceptual structure) into a new complex (new information from teaching assimilated into prior learning).
Learning was seen as analogous to the binding of a metabolite to a protein…
Each of my four main types of learning block seemed to have a parallel in scenarios where the metabolite would not become tightly bound to the protein in the molecular analogue.
Impediments to assimilating the metabolite
The learner can only relate new information to prior learning if they have indeed learnt that material. If the teacher assumes that students have already learnt some prerequisite material but the learner has not (perhaps a previous teacher ran out of time and missed the topic; or the learner was off-school ill at the time; or the learner attended a lesson on the material, but made no sense of it; or the student attended a lesson on the material which made sense at the time, but the material was never reinforced in later lessons, so was never consolidated into long-term memory…) then this will be as if the target protein is missing from the cytosol, so there is no target structure for the metabolite to bind to:
…and the binding could not occur if the protein was not present…
Then, even if a student has the expected prior learning, they will only interpret new information in terms of it if they realise its relevance. Teachers may assume it is obvious what prior leaning is being relied upon to make sense of new teaching, but sometimes this prior learning is not triggered as pertinent and so 'brought to mind' by the learner. (Or, to be fair to the teacher, they may have even deliberately reminded students of the relevant prior learning just before introducing the new material, but without the learner realising this was meant to be linked in any way!)
So, this is as if the two molecules are both present in a cell's cytosol, but they never come close enough to interact and bind:
…and binding could not occur if the metabolite molecule did not come into contact with the protein…
Now students often have alternative conceptions ('misconceptions') of science topics. So, even if they do know about the topic that the new teaching is expected to develop for them, if they have a different understanding of the topic, then – although they may interpret the new information in terms of their existing understanding of the topic – they will likely understand the new teaching in a distorted way so it fits with their alternative take on the topic.
I thought that, in my analogy, an alternative conception was like a protein that was 'mis-structured' (as may happen if there are genetic mutations). If a mutation only subtly changes the shape of the binding site on the protein it is possible that the complex may form, but with a different, more strained, conformation. So, the new complex structure will not match the usual canonical structure.
…and a mutation may change the conformation of the binding site so that the metabolite does not bind as effectively * …
It was at that point that I realised there was another possibility here. I will return to that in a moment.
My fourth class of system bug, or learning impediment, involved a learner understanding teaching in terms of some material which (from the teacher's perspective) was unrelated. These creative links are sometimes made, and can be misleading (e.g., sleeping is like putting a battery on change, so it gives us energy).
So, this was like our metabolite colliding with a completely different protein, but one to which it could bind, before it reached our target protein. There is a fit, but within the 'wrong' overall structure – teaching is (subjectively) understood, but in a completely idiosyncratic and non-canonical way:
…intended binding may not occur if the metabolite first comes into contact with another molecule with which it can bind to form a different complex…
It was when I was drawing out my mutated protein, such that binding was strained to distort the complex (like a student interpreting teaching through an alternative understanding of the right topic, so the meaning of teaching gets distorted) that I realised a mutation could also lead to the protein lacking a viable binding site at all.
In this case the protein is present, but there was no way to bind the metabolite with it to form a complex. The learner has prior learning of the topic, but it is not possible to link the new information presented in teaching with it, as it would simply not fit with the learners' alternative understanding of the topic (as when for many years it was assumed by chemists that no noble gas compounds could be made because the inert gases had inherently stable electronic configurations which could not be disrupted by chemical processes).
So here the 'cause' of the lack of complex formation (a mutated protein / an alternative conceptual framework) could lead to two different outcomes – new information being distorted to fit in the alternative structure (like a protein with a slightly altered binding site) or new information not being linked with the prior topic learning at all (akin to a mutation meaning a protein had no viable binding site for forming a complex with the metabolite).
…* and I realised that a mutated protein may have no functioning binding site (rather than just a slightly distorted one) which leads to a different outcome.
So, consideration of my analogy brought home to me that the presence of an alternative conception may have different impacts depending on the extent of the differences between the students' thinking and the canonical scientific account.
Two types of 'mutated' prior learning?
What might these two possibilities, these different extents of mutated conceptions, mean in practice?
Consider a learner who is taught that 'plants do not need to be given food as they can manufacture their own food by photosynthesis'. If the learner has a notion of plants that includes fungi such as mushrooms and toadstools then the new information can 'bind' to the existing conceptual structure, but the learning will be 'strained' in the sense that the intended meaning is distorted (because the learner now thinks mushrooms and toadstool photosynthesise). This was the kind of example I had had in mind as a grounded learning impediment caused by a prior alternative conception.
By contrast, a deficiency learning impediment had reflected the absence of prerequisite learning needed to make sense of teaching (such as teaching that the bonds in methane are formed by the overlap of sp3 hybrid orbitals with the hydrogen 1s atomic orbitals to a student who had not previously been introduced to atomic orbitals).
However, the absence of prerequisite knowledge need not be due to having missed prior teaching, but could instead be having formed alternative conceptions so that the topic is represented in the learner's conceptual structure, but in a distorted ('mutated') version.
Consider the example of a teacher explaining properties of substances in terms of quanticle (nanoscopic particle) models. The teacher may explain that ionic salts tend to have high melting temperatures because the solids comprise of a lattice of strongly bonded ions which therefore takes a good deal of energy to disrupt.
A very common alternative conception of ionic bonding is based on the (false) idea that ionic bonds are formed by electron transfer from a metal atom to a non-metal atom. Often when a student acquires this alternative conception they understand the ionic solid to be composed of small units held together by ionic bonds (e.g., Na+-Cl–), but held to each other by weaker forces. For a student holding this alternative conceptual framework ionic bonds are not easily disrupted by heating an ionic solid, but the weaker forces between the bonded units will easily be disrupted so that melting will occur. The student assumes the small units (such as NaCl ion pairs) are like molecules (or actually are molecules) that continue to exist in the liquid phase when a solid like ice melts.
This learner had existing prior learning of the ionic bonding concept, but because this was not canonical, but involved alternative conceptions, the new information did not fit with the prior learning (it could not 'bind' with the 'mutated' conceptual structure) so the intended learning did not occur – a kind of deficiency learning impediment.
So, a deficiency learning impediment is due to a lack of existing conceptual learning that the new information can bind to – but this may be either because there is no prior learning on the topic, or because alternative conceptions of aspects of the topic mean the conceptual structure has the wrong 'conformation' to be perceived as relating to the new information presented in teaching.
It is just a model
The model of kinds of learning impediments is just that – a model of conceptual learning. It is one that I found helpful in my own work, especially when researching student thinking. I hope it may offer some insights to others, including teachers. Any value it has is in informing our thinking about learning and the teaching that can promote it. The analogy discussed above is just a(nother) kind of model of that model – a teaching analogy to introduce an abstract idea
Here, I wanted to just share how I found my own use of the analogy as a teaching aid helped develop my own thinking about the target domain of student learning. Analogies are just models, but like all models they can be useful thinking tools as long as we remember that they only somewhat resemble, and are not the same as, the targets they are compared with.
A reflection on the pedagogy in Andrew Scott's 'Vital Principles'
Keith S. Taber
Andrew Scott's introduction to the chemistry of the cell is populated by a diverse cast of characters, including ballot machines, beads; blind engineers and blind-folded art-seekers; builders and breaker's yards; cars, freight vehicles and boats; Christmas shoppers, dancers; gatecrashers (despite gatekeepers) and their hosts; invaders, jack-in-the-boxes, legal summonses, light bulbs, mixing bowls, maelstroms, music tapes, office blocks; oceans, seas, rivers, streams, floods and pools; skeletons and their bones, split personalities, springs; sorting offices and postal systems; turnstiles, the water cycle, water wheels, ropes, pulleys and pumps; work benches and work stations; and weeding and seaweed forests.
Scott, A. (1988). Vital Principles. The molecular mechanisms of life. Basil Blackwell.
The task of the popular science writer
This piece is not a formal review of, what is, now, hardly a recent title 1, but a reflection on an example of a science book aimed at – not a specific level of student, but – a more general audience. The author of a 'popular science book' has both a key advantage over the author of many science textbooks, and a challenge. The advantage is being able to define your own topic – deciding what you wish to cover and in how much detail. By contrast, a textbook author, certainly at a level related to formal national examination courses, has to 'cover' the specified material. 2
However the textbook author has the advantage of being able to rely on a fairly well defined model of the expected background of the readership. 3 Students taking 'A level' physics (for example) will be expected to have already covered a certain range of material at a known level through science teaching at school ('G.C.S.E. level') and to have also demonstrated a high level of competence against the school maths curriculum. This is important because human learning is incremental, and interpretive, and so iterative: we can only take in a certain amount of new material at any time, and we make sense of it in terms of our pool of existing interpretative resources (past learning and experiences, etc.) 4
The teacher or textbook author designs their presentation of material based on a mental model of the interpretive resources (e.g., prerequisite learning, familiar cultural referents that may be useful in making analogies or similes, etc.) available to, and likely to be activated in the mind of, the learner when engaging with the presentation.
So, the science teacher works with a model of the thinking of the students, so as to pitch material in manageable learning quanta, that should relate to the prior learning. The teacher's mental model can never be perfect, and consequently teaching-learning often fails (so the good teacher becomes a 'learning doctor' diagnosing where things have gone wrong). However, at least the teacher has a solid starting point, when teaching 11 year olds, or 15 year olds, or new undergraduates, or whatever.
The textbook author shares this, but the popular science author has a potential readership of all ages and nationalities and levels of background in the subject. Presumably the reader has some level of interest in the topic (always helpful to support engagement) but beyond that…
Now the role of the science communicator – be they research scientist with a general audience, teacher, lecturer, textbook author, journalist, documentary producer, or popular science author – is to make what is currently unfamiliar to the learner into something familiar. The teacher needs to make sure the learners both have the prerequisite background for new teaching and appreciate how the new material relates to and builds upon it. Even then, they will often rely on other techniques to make the unfamiliar familiar – such as offfering analogies and similes, anthropomorphism, narratives, models, and so forth.
As the popular science writer does not know about the background knowledge and understanding of her readers, and, indeed, this is likely to be extremely varied across the readership, she has to reply more on these pedagogic tactics. Or rather, a subset of these ways of making the unfamiliar familiar (as the teacher can use gestures, and computer animations, and physical models; and even get the class to role-play, say, electrons moving through a circuit, or proteins binding to enzymes). Thus, popular science books abound with analogies, similes, metaphors and the like – offering links between abstract scientific concepts, and what (the author anticipates) are phenomena or ideas familiar to readers from everyday life. In this regard, Andrew Scott does not disappoint.
Andrew Scott
Scott's website tells us he has a B.Sc. in biochemistry from Edinburgh, and a Ph.D. from Cambridge in chemistry, and that he has produced "science journalism published by academic publishers, newspapers, magazines and websites", and he is an "author of books translated into many languages". I have not read his other books (yet), but thought that Vital Principlesdid a good job of covering a great deal of complex material – basically biochemistry. It was fairly introductory (so I doubt much could be considered outdated) but nonetheless tackled a challenging and complex topic for someone coming to the book with limited background.
I had a few quibbles with some specific points made – mainly relating to the treatment of underpinning physics and chemistry 5 – but generally enjoyed the text and thinking about the various comparisons the author made in order to help make the unfamiliar familiar to his readership.
Metaphors for molecular mechanisms
Andrew Scott's introduction to the chemistry of the cell is populated by a diverse cast of characters, including ballot machines, beads; blind engineers and blind-folded art-seekers; builders and breaker's yards; cars, freight vehicles and boats; Christmas shoppers, dancers; gatecrashers (despite gatekeepers) and their hosts; invaders, jack-in-the-boxes, legal summonses, light bulbs, mixing bowls, maelstroms, music tapes, office blocks; oceans, seas, rivers, streams, floods and pools; skeletons and their bones, split personalities, springs; sorting offices and postal systems; turnstiles, the water cycle, water wheels, ropes, pulleys and pumps; work benches and work stations; and weeding and seaweed forests.
A wide range of metaphors are found in the book. Some are so ubiquitous in popular science discourse that it may be objected they are not really metaphors at all. So, do "… 'chloroplasts'…trap the energy of sunlight…"? This is a simplification of course (and Scott does go into some detail of the process), but does photosynthesis actually 'trap' the energy of sunlight? That is, is this just a simplification, or is it a figurative use of language? Scott is well aware that energy is not a concept it is easy to fully appreciate,
"Energy is really an idea invented by mankind, rather than some definite thing…
energy can be thought of as some sort of 'force resistance' or 'antiforce' able to counteract the pushes or pulls of the fundamental forces."
pp.25-26
But considerable ingenuity has been used in making the biochemistry of the cell familiar through metaphor:
lipids "have split personalities" (and they have 'heads' and 'tails' of course)
proteins can "float around within a sea of lipid"
proteins are "the molecular workers"
the inside of cells can be a "seething 'metabolite pool' – amaelstrom of molecules"; "a swirling sea of chemical activity…the seething sea of metabolism" (so, some appealing alliteration, as well, here 6);
the molecules of the cell cytosol are "dancing"
"...small compressed springs of ATP, can be used to jack up the chemistry of the cell…"
"…thermal motion turns much of the chemical microworld into a molecular mixing bowl."
"The membranes of living cells…form a boundary to all cells, and they cordon off specific regions within a cell into distinct organelles."
"Some of these gatecrashers within other cells would then have slowly evolved into the mitochondria and chloroplasts of present-day life..."
"the 'Ca2+ channels' to open up, this causes Ca2+ ions to flood into the cell …"
"the 'ribosomes' … are the chemical automatons…"
The figurative flavour of the author's language is established early in the book,
"In a feat of stunning self-regulating choreography, billions of atoms, molecules and ions become a part of the frantic dance we call life. Each revolution of our planet in its stellar spotlight raises a little bit of the dust of earth into the dance of life, while a little bit of the life crumbles back into dust."
p.1
Phew – there is quite a lot going on there. Life is a dance, moreover a frantic dance, of molecular level particles: but not some random dance (though it relies on molecular motion that is said to be a random dance, p.42), rather one that is choreographed, indeed, self-choreographed. Life has agency. It is a dance that is in some sense powered by the revolution of the earth (abound its axis? around its star?) which somehow involves the cycling of dust into, and back out, of life – dust to dust. The reference to a stellar spotlight seems at odds with the Sun as symmetrically radiating in all directions out into the cosmos – the earth moves through that radiation field, but could not escape it by changing orbit. Perhaps this image is meant to refer to how the daily rotation of the earth brings its surface into, and out of, illumination.
So, there is not a spotlight in any literal, sense (the reference to "the central high energy furnace", p.39, is perhaps a more accurate metaphor), but the 'stellar spotlight' is a metaphor that offers a sense of changing illumination.
Similarly, the choreographed dance is metaphorical. Obviously molecules do not dance (a deliberate form of expression), but this gives an impression of the molecular movement within living things. That movement is not choreographed in the sense of something designed by a creator. But something has led to the apparently chaotic movements of billions of molecules and ions, of different kinds, giving rise to highly organised complex entities (organisms) emerging from all this activity. Perhaps we should think of one of those overblown, heavily populated, dance sequences in Hollywood films of the mid 20th century (e.g., as lampooned in Mel Brook's Oscar winning 'The Directors')?
So, in Vital Principles, Scott seeks to make the abstract and complex ideas of science seem familiar through metaphors that can offer a feel for the basic ideas of biochemistry. The use of metaphor in science teaching and other forms of science communication is a well established technique.
Later in the book a reader will find that the metaphorical choreographer is natural selection, and natural selection is just the tautological selection of what can best reproduce itself in the environment in which it exists,
"…the brute and blind force of natural selection can be relied upon to weed out the harmful mutations and nurture the beneficial ones. We must always remember, however, that the criterion by which natural selection judges mutations as harmful or beneficial is simply the effect of the mutations on an organism's ability to pass its genetic information on to future generations."
p.182
So, natural selection is a force which is brute and blind (more metaphors) and is able to either weed out (yes, another metaphor) or nurture. That is an interesting choice of term given the popular (but misleadingly over-simplistic) contrast often made in everyday discourse between 'nature' (in the sense of genetics) and 'nurture' (in the sense of environmental conditions). Although natural selection is 'blind', it is said to be able to make judgements.
Form and function in biology
Here we enter one of the major issues in teaching about biology: at one level, that of a naturalistic explanation 7, there is no purpose in life: and anatomical structures, biochemical processes, even instinctive behaviours, have no purpose – they just are; and because they were components of complexes of features that were replicated, they have survived (and have 'survival value').
Yet, it seems so obvious that legs are for walking, eyes are for seeing, and the heart's function is to pump blood around the body. A purist would deny each of these (strictly these suggestions are teleological) and replace each simple statement with a formally worded paragraph completely excluding any reference to, or hint at, purpose.
So, although it seems quite natural to write
"…hormones… are released from one cell to influence the activity of other cells;
…neurotransmitters…are released from nerve cells to transmit a nerve impulse…"
pp.120-121
we might ask: is this misleading?
One could argue that in this area of science we are working with a model which is founded on the theory of natural selection and which posits the evolved features of anatomy, physiology, biochemistry,etc., that increase fitness are analogous to designed and purposeful features that support the project of the continuation of life.
Something that scientists are very quick to deny (that organisms have been designed with purposes in mind) is nevertheless the basis of a useful analogy (i.e., we can consider the organism as if a kind of designed system that has coordinated component parts that each have roles in maintaining the 'living' status of the overall system). We then get the economy of language where
hormones and neurotransmitters are released for 'this' purpose, to carry out 'that' function;
being selected (!) over
more abstract and complex descriptions of how certain patterns of activity are retained because they are indirectly selected for along with the wider system they are embedded in.
Do scientists sometimes forget they are working with a model or analogy here? I expect so. Do learners appreciate that the 'functions' of organs and molecules in the living thing are only figurative in this sense? Perhaps, sometimes, but – surely -more often, not; and this probably both contributes to, and is encouraged by, the known learning demand of appreciating the "blind [nature of the] force of natural selection".
Scott refers to proteins having a particular task (language which suggests purpose and perhaps design) whilst being clear he is only referring to the outcomes of physical interactions,
"A protein folds up into a conformation which is determined by its amino acid sequence, and which presents to the environment around it a chemical surface which allows the protein to perform its particular chemical task; and the folding and the performance of the task (and, indeed, the creation of the protein in the first place) all proceed automatically governed only by physical laws and forces of nature – particularly the electromagnetic force."
pp.54-55
In practice, biologists and medical scientists – and indeed the rest of us – find it much more convenient to understand organisms in terms of form and function. That is fine if you always keep in mind that natural selection only judges mutations metaphorically. Natural selection is not the kind of entity which can make a judgement, but it is a process that we can conceptualise as if it makes judgements.
This is a difficult balancing act:
"Nature is a blind but a supremely effective engineer. Through the agency of undirected mutation she continually adjusts the structure and the mechanisms of the living things on earth."
p.182
Nature is here treated as if a person: she is an engineer tinkering with her mechanisms. Personification of nature is a long-standing trope, once common among philosophers and not always eschewed by scientists in their writings (e.g., Nicolaus Copernicus, Henri Poincaré, Michael Faraday, even Albert Einstein have personified Nature) – and she is always female.
But usually a competent engineer tinkers according to a plan, or at least with a purpose in mind, whereas nature's tinkering is here described as 'undirected' – it is like she arbitrarily changes the size of a gear or modifies the steam pressure in a cylinder or changes the number of wheels on the locomotive, and then tinkers some more with those that stay on the tracks and manage to keep moving.
Personification (by referring to her, she, etc.) is not needed to imply entities have some human traits. Indeed, a very common pedagogic technique used when explaining science, anthropomorphism, is to use a kind of metaphorical language which treats inanimate objects or non-human beings as if they are people – as if they can feel, and think, and plan, and desire; and so forth.
"Once an enzyme had met and captured the required starting materials …"
"Some [non-protein metabolites] act as 'coenzymes', which becomes bound to enzymes and help them to perform their catalytic tasks."
"Cells, which had previously been aggressively independent individualists, discovered the advantages of communal life."
"…descendants of cells which took up residence within other cells and then became so dependent on their hosts, and also so useful to them, that neither hosts nor gatecrashers could afford to live apart."
So, for example, plants are living beings, but do not have a central nervous system and do not experience and reflect on life as people do: so, they do not wish for things,
"…the oxidation of sugars, is also performed by plants when they wish to convert some of their energy stores (largely held in the form of complex carbohydrates) back into ATP."
p.144
Again, such phrasing offers economy of language. Plants do not wish, but any technically correct statement would likely be more complicated and so, arguably, more difficult to appreciate.
Dead metaphors
A key issue in discussing metaphors is that in many cases different readers are likely to disagree over whether a term is indeed being used figuratively or literally. Language is fluid (metaphorically speaking), and a major way language grows is where the need for new terms (to denote newly invented artefacts or newly discovered phenomena) is satisfied by offering an existing term as a metaphor. Often, in time the metaphor becomes adopted as standard usage – so, no longer a metaphor. These examples are sometimes called dead metaphors (or clichéd metaphors). So, for example, at some point, many decades ago, astronomers started to talk of the 'life cycle' of stars which have a moment of 'birth' and eventual 'death'. These metaphors have become so established they are now treated as formal terms in the language of the discipline, regularly used in academic papers as well as more general discourse (see 'The passing of stars: Birth, death, and afterlife in the universe').
So, when Scott writes of "how some micro-organism, say a virus, invades the body…"(p.109) it is very likely most readers will not notice 'invade' as being a metaphor, as this usage is widely used and so probably familiar. The (former?) metaphor is extended to describe selective immune components "binding to foreign invaders [that] can act as a very effective means of defence against disease." These terms are very widely used in discussing infections: though of course there are substantive differences, as well as similarities, with when a country defends itself against actual foreign invaders.
I suspect that considering the lipid bilayer to be "a stable sandwich of two layers of lipid molecules" (p.115) is for many, a dead metaphor. The reference to a DNA double-helix leading to"two daughter double-helices" reflects how atomic nuclei and cells are said to give rise to 'daughters' on fission: again terminology that has become standard in the field.
Sharing a psuedo-explanation for covalent bonding
One phrase that seems to have become a dead metaphor is the notion of electrons being 'shared' in molecules, which "…are formed when their constituent atoms come together to leave at least some of their electrons shared between them" (pp.28-29). Whilst this seems harmless as a description of the structure, it is also used as an explanation of the bonding:
"'hydrogen molecules and water molecules (and all other molecules) are held together by virtue of the fact that electrons are shared between the individual atoms involved, a similarity recognised by saying that in such cases the atoms are held together by 'covalent' bonds.
p.29
But we might ask: How does 'sharing' a pair of electrons explain the molecule being 'held together'? Perhaps a couple with a strained relationship might be held together by sharing a house; or two schools in a confederation by sharing a playing field; or two scuba divers might be held together if the breathing equipment of one had failed so that they only had one functioning oxygen cylinder shared between them?
In these examples, there is of course a sense of ownership involved. Atoms do not 'own' 'their' electrons: the only bonds are electromagnetic; not legal or moral. This may seem so obvious it does not deserve noting: but some learners do come to think that the electrons are owned by specific atoms, and therefore can be given, borrowed, stolen, and so forth, but should ultimately return to their 'own' atom! So, if we acknowledge that there is no ownership of electrons, then what does it even mean for atoms to 'share' them?
So, why would two atoms, each with an electron, become bound by pooling these resources? (Would sharing two houses keep our couple with a strained relationship together; or just offer them a ready way to separate?) The metaphor does not seem to help us understand, but the notion of a covalent bond as a shared electron pair is so well-established that the description commonly slips into an explanation without the explainer noticing it is only a pseudo-explanation (a statement that has the form of an explanation but does not explain anything, e.g., "a covalent bond holds two atoms together because they share a paired of electrons").
Elsewhere in the book Scott does explain (if still anthropomorphically) that viable reactions occur because:
"In the new configuration, in other words, the electromagnetic forces of attraction and repulsion between all the electrons and nuclei involved might be more fully satisfied, or less 'strained' than they were before the reaction took place."
p.36
How are metaphors interpreted?
The question that always comes to my mind when I see metaphorical language used in science communication, is how is this understood by the audience? Where I am reading about science that I basically understand reasonably well (and I was a science teacher for many years, so I suspect I cannot be seen a typical reader of such a book) I do reflect on the metaphors and what they are meant to convey. But that means I am often using the familiar science to think about the metaphor, whereas the purpose of the metaphor is to help someone who does not already know the science get a take on it. This leads me to two questions:
to what extent does the metaphor give the reader a sense of understanding the science?
to what extent does the metaphor support the reader in acquiring an understanding that matches the scientific account?
These are genuine questions about the (subjective and objective) effectiveness of such devices for making the science familiar. There is an interesting potential research programme there.
Shifting to similes
The difference between metaphors and similes is how they are phrased. Both make a comparison between what is being explained/discussed and something assumed to be more familiar. A metaphor describes the target notion as being the comparison (nature is an engineer), but the listener/reader is expected to realise this is meant figuratively, as a comparison. A simile makes the comparison explicit. The comparison is marked – often by the use of 'as' or 'like' as when physicist Max Planck suggested that the law of conservation of energy was "like a sacred commandment".
So, when Scott refers to how proteins "act as freight vehicles transporting various chemicals around the body", and "as chemical messages which are sent from one cell to another" (p.10), these are similes.
Springs are used as similes for the interactions between molecules or ions in solids or the bonds within molecules
"…even in solids the constituent molecules and atoms and ions are constantly jostling against one another and often vibrating internally like tiny sub-microscopic springs. All chemical bonds behave a bit like tiny springs, constantly being stretched and compressed as the chemicals they are part of are jostled about by the motion of the other chemicals all around them."
p.39
[Actually the bonds in molecules or crystals are behaving like springs because of the inherent energy of the molecule or lattice: the 'jostling' can transfer energy between molecules/ions and 'springs' so that the patterns of "being stretched and compressed" change, but it is always there. The average amount of 'jostling' depends on the temperature of the material. 5]
In the way the word is usually used in English, jostling is actually due to the deliberate actions of agents – pushing through a crowd for example, so strictly jostling here can be seen as an anthropomorphic metaphor, but the intended meanings seems very clear – so, I suspect many readers will not even have noticed this was another use of figurative language.
One way of marking phrases meant as similes is putting then in inverted commas, so-called scare-quotes, as in
"A rather simple chemical 'cap', for example, is added to the start of the RNA, while a long 'tail' consisting of many copies of the nucleotide A is added to its end…The most significant modifications to the precursor, however, involve the removal of specific portions from the interior [sic] of the RNA molecule, and the joining together of the remaining portions into mature mRNA… This 'splicing' process …"
p.79
Here we have something akin to a cap, and something akin to a tail. As noted above, a difficulty in labelling terms as metaphors or similes is that language is not static, but constantly changing. In science we often see terms borrowed metaphorically from everyday life to label a technical process as being somewhat like something familiar – only for the term to become adopted within the field as a technical term. The adopted terms become literal, with a related, but somewhat different – and usually more precise – meaning in scientific discourse. (This can be the basis of one class of learning impediments as students may not realise the familiar term has specials affordances or restrictions in its technical context.)
Here 'splicing' is marked as a simile – there is a process seen as somewhat similar to how, for example, radio programmes and musical recordings used to be edited by the cutting and resequencing strips of magnetic tape. Yet gene splicing is now widely accepted as a literal use of splicing, rather than being considered figurative. [I suspect a young person who was told about, for example, the Beatles experiments with tape splicing might guess the term is used because the process is like gene splicing!]
The following quote marks a number of similes by placing them within inverted commas:
"The interior of the cell is criss-crossed by a network of structural proteins which is known as the cytoskeleton. The long protein 'bones' of this skeleton are formed by the spontaneous aggregation of many individual globular protein molecules…
Cells use many strong chemical 'pillars' and 'beams' and 'glues' and 'cements', both inside them, to hold the internal structure of cells together, and outside of them, to hold different cells together; but the electromagnetic force is the fundamental 'glue' upon which they all depend."
pp.995-6
Again the phrasing here suggests something being deliberately undertaken towards some end by an active agent (teleology): the cell uses these construction materials for a purpose.
There are various other similes offered – some marked with inverted commas, some with explicit references to being comparisons ('kind of', 'act as', 'sort of', etc.)
"…amino acids comprise the chemical 'alphabet' from which the story of protein-based life (i.e., all life on earth) is constructed"
"the endoplasmic reticulum is a kind ofmolecular 'sorting office'…"
endosomes and lysomes "form a kind of intracellular digestive system and 'breaker's yard'."
"Proteins can act asgatekeepers of the cell…"
"Proteins can…act as chemical controllers"
proteins "can act asdefensive weapons…"
"The proteins which perform these feats are not gates, but 'pumps'..."
"Proteins could be described asthe molecular workers which actually construct and maintain all cells…"
"…proteins are the molecular 'labourers' of life, while genes are the molecular 'manuals' which store the information needed to make new generations of protein labourers…"
"Membrane proteins often float around within a sea of lipid (although they can also be 'held at anchor' in the one spot if required)"
"A ribosome travels down its attached mRNA, a bit like a bead running down a thread (or sometimes likea thread being pulled through a bead)..."
"…the 'ribosomes' – molecular 'work-benches' composed of protein and RNA…"
Nucleic acids "act as genetic moulds"
"the high energy structure of ATP really is very similar to the high energy state of a compressed spring"
"Some vital non-protein metabolites act as a sort of 'energy currency'…"
Advancing to analogies
Metaphors and similes point out a comparison, without detailing the nature and limits of that comparison. A key feature of an analogy is there is a 'structural mapping': that is that two systems can be represented as having analogous structural features. In practice, the use of analogy goes beyond suggesting there is a comparison, to specifying, at least to some degree, how the analogy maps onto the target.
Scott employs a number of analogies for readers. He develops the static image of the cell skeleton (met above) with its 'bones', 'pillars' and 'beams' into a dynamic scenario:
"Structural proteins are often referred to as the molecular scaffolding of life, and the analogy is quite apt since so many structural proteins are long fibres or rods; but we think of scaffolding as a static, unchanging, framework. Imagine, however, a structure built of scaffolding in which some of the scaffolding rods were able to slide past one another and then hold the whole framework in new positions."
p.96
Many good metaphors/similes may be based upon comparisons of this type, but they do not become analogies until this is set out, rather than being left to the listener/reader to deduce. For this reason, analogies are better tools to use in teaching than similes as they do not rely on the learners inferring (guessing?) what the points of comparison are intended to be. 8
So, Scott offers the simile of molecules released as 'messengers', but then locates this in the analogy of the postal system, before using another analogy to specify the kind of message being communicated,
"Cells achieve such chemical communication in various ways, but the most vital way is by releasing chemical 'messenger' molecules (the biological equivalent of the postal system, if you like analogies), and many of these messengers are either proteins, or small fragments of proteins." … "A biological messenger molecular is more like a legal summons than a friendly note or some junk mail advertisement – it commands the target cell to react in a precise way to the arrival of the message."
pp.102-103
In the following analogy the mapping is very clear:
"One gene occupies one region of a chromosome containing many genes, much like one song occupies one region of a music tape containing many songs overall."
p.7
Song on music tape is to gene on chromosome
For an analogy to be explicit the mapping between target and analogue must be clear, as here, where Scott spells out how workstations on a production line map onto enzymes,
"The production line analogy is a very good one. The individual 'work stations' are the enzymes, and at these molecular work stations various chemical components are brought together and fashioned into some new component of product. The product of one enzyme can then pass down the line, to become the substrate of the next enzyme, and so on until the pathway is complete."
p.147
Some analogies offer a fairly basic mapping between relatively simple systems:
"If there is lots of A around in the cell, for example, then the rate at which A tends to meet up with enzyme EAB will obviously increase (just as an increase in the number of people you happen to know entering a fairground will increase the chances of you meeting up with someone you know)."
p.150
fairground
cell
people at a fairground
molecules in the cytosol
you at the fairground
a specific enzyme in the cytosol
people entering the fairground that know you personally
molecules of a type that binds to the specific enzyme
chance of you meeting someone you know
rate of collision between enzyme and the specific molecules it binds to
An analogy with a vote counting machine
Scott compares a nerve cell, the activity of each of which is influenced by a large number of 'input' signals, to a ballot counting machine,
"…most nerve cells receive inputs, in the form of neurotransmitters, from many different cells, so the 'decision' about whether or not the cell should fire depends on the net effect of all the different inputs, some of which will be excitatory, and some inhibitory, with the pattern of input perhaps varying all the time.
So any single nerve cells acts like an [sic] tiny automatic ballot machine, assessing the number of 'yes' and 'no' votes entering it at any one time and either firing or not firing depending on which type of vote predominates at any one time.
…Nerve cells receive electrochemical signals from other cells, and each signal represents a 'yes' or a 'no' vote in an election to determine whether the cell should fire."
pp.166-8
Turnstiles in Alewife station, image from Wikimedia Commons (GNU Free Documentation License)
Scott uses the image of a turnstile, a device that blocks entry unless triggered by a coin or ticket, and which automatically locks once a person has passed through, as a familiar analogue for an ion channel into a cell. The mapping is not spelt out in detail, but should be clear to anyone familiar with turnstiles of this kind,
"When it is sitting in a polarised membrane, this protein is in a conformational state in which it is unable to allow any ions to pass through the cell. When the membrane around it becomes depolarised, however, the protein undergoes a conformational change which causes it briefly to form a channel through which Na+ ions can pass. The channel only remains open for a short time, however, since the conformational upheaval [sic] of the protein continues until it adopts a new conformation in which the passage of Na+ ions is once again blocked. The overall effect of this conformational change is a bit like the operation of a turnstile – it moves from one conformation which prevents anything from passing, into a new conformation which also prevents anything from passing, but in the process of changing from one conformation to another there is a brief period during which a channel allowing passage through is opened up."
p.163
An analogy between a sodium ion channel in a membrane, and a turnstile of the kind sometimes used to give entry to a sporting ground or transport system.
Whether there is an absolute distinction between metaphors/similes and analogies in practice can be debated. So, for example, Scott goes beyond simply suggesting that the nanoscale of molecules is like a mixing bowl, but does not offer a simple mapping between systems,
"Thermal motion turns much of the chemical microworld into a 'molecular mixing bowl' … So the solution of the cytosol acts as an all pervading chemical sea in which many of the chemicals of life are mixed together by random thermal motion as if in a molecular mixing bowl."
p.40
We could see the ocean as a simile (marked by 'acts as an') and the mixing bowl as another (marked by the scare quotes, and then 'as if in a') – but there is a partial mapping with a macroscopic mixing bowl: we are told (i) what is mixed, and (ii) the agent that mixes at the molecular scale, but it is assumed that we already know these should map to (i) the ingredients of a dish being mixed by (ii) a cook.
In places, then, Scott seems to rely on his readers to map features of analogies themselves. For example, in the following (where "The chaos of a large department store on Christmas Eve, or during the January sales, is a reasonable analogy [for the cell, as] there is order and logic within a scene of frantic and often seemingly chaotic activity"), the general point about scale was well made, but (for this reader, at least) the precise mapping remained obscure,
"The frantic chaos of chemistry proceeds too fast and too remotely for us to follow it without great difficulty. We are in the position of airborne observers who see trainloads of shoppers flowing into the city on Christmas Eve morning, and trainloads of the same shoppers laden with purchases flowing back to the suburbs in the evening. From the air we can see the overall effect of suburban shoppers 'reacting' with the shops full of goods, but we remain unaware of the hidden random chaos which allows the reaction to proceed!
p.44
Perhaps other readers immediately see this, but I am not sure what the shoppers are: molecules? but then they are unchanged by reactions? As they flow together into and out of the city (cell?) they could be ions in a nerve cell, but then what are the purchases they carry away (and have they paid for them in energy)? What are the trains? (ion channels? ribosomes?) What are the shops (mitochondria)? Perhaps I am trying to over-interpret an image that is not meant to be specific – but elsewhere Scott seems to have designed his analogies carefully to have specific mappings.
A reference to "a cofactor called 'heme' which actually acts as the chemical vessel on which the oxygen is carried"seems, by itself to be a metaphor, but when read in the context of text that precedes it, seems part of a more developed analogy:
"The most obvious system of bulk transport in the human body is the blood, which flows through our arteries, capillaries and veins like a 'river of life', bringing chemical raw materials (oxygen, water and food) to every cell of the body, and taking waste products away. Within this bulk system, however, the actual job of transporting specific substances is sometimes performed by small 'freighters' such as individual blood cells and even individual protein molecules."
p.98
The precise form of transport acting as an analogue shifts when the discussion shifts from the transport process itself to what I might refer to as the loading and unloading of the 'freighter',
"So the binding of one oxygen molecule to one subunit of an empty [sic] haemoglobin complex greatly encourages the binding of oxygen to the other three available sites. This makes the multi-subunit haemoglobin complex a bit like a four-seater car in which the first person into the carunlocks the door for another three passengers. The crucial step in loading the car is getting the first person in, after which the first person helps all the others to climb aboard.
An opposite effect occurs when loaded haemoglobin reaches a tissue in need of oxygen: the loss of one oxygen molecule from one subunit causes a conformational change in the complex which allows the other three oxygen molecules to be off-loaded much more readily. A suitable analogy to this would be an unstable four-man boat, since, if one man jumps overboard, he may rock the boat sufficiently to make the other three fall out!"
pp.100-101
Why is a child like an office block?
Child is to zygote as office building is to light bulb? (Images from Pixabay)
Scott compares the development of the child from a single cell with a self-assembling office block,
"When a human egg cell begins to divide and create a newborn child it achieves an enlargement equivalent to a lightbulb giving rise to a massive office block 250 metres high; which then, over the next 15 years or so, stretches and widens to an astounding 1,000 metres in height and nearly 250 metres across. In the 'office block' that is you all the plumbing, heating, lighting, telecommunication and ventilation systems were assembled automatically and work together smoothly to sustain a bewildering diversity of very different 'suites' and 'offices'.
p.4
Scott later revisits his office analogy, though now the building is not the growing organism, but just a single cell (one of the 'offices' from the earlier analogy?),
"Cells are not stable and unchanging structures like office blocks. Instead, most parts of a cell are in a state of continual demolition and renewal, known as 'metabolic turnover'. Imagine an office block in which a large team of builders is constantly moving through, knocking down existing walls and using the bricks to build up new ones; ripping apart the furniture and then reassembling it into new forms; peeling off wallpaper, then using it as the raw material to produce new paper which is then put back up again; and all the time some new materials are arriving through the door, to assist in the continual rebuilding, while some of the older materials are constantly being discarded out of the windows. The living cells is in a very similar siltation, with teams of enzymes constantly ripping down the structure of the cell while other teams of enzymes build it up.
… Life in the office block imagined earlier might sometimes be a little difficult and chaotic, but at least when change was required it could be brought about quickly, since the necessary tradesmen and supplies would always be on hand; and any mistakes made during the building process could always quickly be put right. Metabolic turnover bestows similar advantages on the living cell."
pp.118-119
The reference to 'teams' of enzymes is another subtle anthropomorphic metaphor. Those in a team are conscious of team membership and coordinate their activities towards a common goal – or at least that is the ideal. Enzymes may seem to be working together, but that is a just a slant we put on processes. Presumably the two sets of teams of enzymes (a catabolic set and an anabolic set) map onto the large team of builders – albeit the enzymes seem to be organised into more specialised working teams than the builders.
Some of Scott's prose, then, combines different ways of making the science familiar, as when he tells the reader
"Water, in other words, is the solvent of life, meaning that it is the liquid which permeates into all the nooks and crannies of the cell and in which all the chemical reactions of life take place. There are various small regions of the cell from which water is excluded, especially within the interior of some large molecules; but the chemistry of life largely proceeds in an ocean of water. It is not a clear ocean – thousands of different types of chemical are dissolved in it, and it is criss-crossed by a dense tangle of giant molecules which form 'fibres' or 'cables' or 'scaffolding' throughout the cell. Swimming through the cell 'cytosol' (the internal 'fluid' of the cell) would be like struggling through a dense underwater forest of seaweed, or through a thick paste or jelly, rather than darting though clear ocean."
p.6
On the molecular level, the water inside of a cell is "an ocean" (a metaphor), which can access the "nooks and crannies of the cell" (a metaphor). The ocean is interrupted by "giant molecules which form 'fibres' or 'cables' or 'scaffolding'…" These terms seem to be used as similes, marked by the use of inverted commas, although Scott also uses this convention to introduce new terms – 'cytosol' is not a simile. Presumably 'fluid' (marked by inverted commas) is being used as a simile as the cytosol is not a pure liquid, but a complex solution.
[The quote implies that "It is not a clear ocean – [as/because] thousands of different types of chemical are dissolved in it", but dissolved solutes would not stop a solution being clear: the actual ocean is very salty, with many different types of ions dissolved in it, but can be clear. Lack of transparency would be due to material suspended, but not actually dissolved, in the water.]
If this is a metaphorical ocean, it is an ocean that would be difficult to swim in, as the tangle of giant molecules is analogous to "a dense underwater forest of seaweed" so it would be like swimming trough "a thick paste or jelly".
The water cycle of life
Perhaps the pièce de résistance in terms of an analogy adopted in the book was the use of a comparison between metabolism and the water cycle,
"I have drawn an analogy between the creation of living things containing many high energy chemicals (i.e. those in which the electromagnetic force is resisted much more than it could be), and the raising water vapour from the sea into the sky. We can continue with this analogy as we look deeper into the energetics of the living cell."
pp.126-127
Scott does indeed develop the analogy, as can be seen from the quotations parsed into the table below:
target concept
analogue
"…thermodynamic law determines that the energy of the sun must disperse out to the earth and raise the energy level of the things that are found there.
The raw materials of life are some of the things that are found there, and the energy from the sun raises these raw materials up into the higher energy levels associated with organised life,
just as
it raises water up into the sky and deposits some of it in tidy little mountain pools."
⧟
"…I have drawn an analogy between
the creation of living things containing many high energy chemicals…
and
the raising water vapour from the sea into the sky."
⧟
"The raising of water to the skies is not an isolated and irreversible event, but part of a cycle in which the water eventually loses the energy gained from the sun and returns to the earth as rain, only to absorb some more energy and be lifted up once more, and so on…
Similarly, of course,
the creation of a living being such as yourself is not an isolated and irreversible event, but is part of a cycle of life and death, of growth and decay…"
⧟
"If we look inside the chemical mechanisms of the living cell we find that they can harness the energy available in the environment, most of which ultimately comes from the sun,
in a manner similar to
the [person] who has built a water wheel, a pump, a reservoir and many secondary wheels used to power many different tasks…."
⧟
"In living things
the roles of
the water-wheels and pumps
are played by
various systems of proteins and membranes,
whilst
the the most common immediate energy reservoir is a chemical known as 'adenosine triphosphate' (ATP). ATP is the cell's
equivalent of
water stored in a high level reservoir or a tank
because
it takes an energy input to make it, while energy is given out when it breaks apart into ADP and phosphate."
⧟
"The considerable resistance to the electromagnetic force embodied in the structure of ATP imposes a strain on the ATP molecule.
It is like
the compressed spring of a jack-in-the-box just waiting to be released;
and when it is released in some appropriate chemical reaction, then the energy level of the molecule falls as it splits up into ADP and phosphate.
Just as the force of water falling from a high gravitational energy level to a lower one can be harnessed to make various energy-requiring processes proceed,
so
the force of an ATP molecule falling from a high chemical energy level to a lower one can be harnessed to make a wide variety of energy-requiring chemical reactions proceed…"
⧟
"The ATP manufacturing enzyme
is closely analogous to
a water-wheel,
for
as the hydrogen ions are allowed to flow back through the enzyme,
just as
water flows over a water-wheel,
so
the ensuing chemical reactions 'lift up' the precursors of ATP into their high energy ATP state."
⧟
"The principle of such energy coupling
can be understood by the simple analogy of
the water flowing downhill over a water-wheel, and thus serving to turn the wheel and, for example, raise some weight from the ground using a pulley."
⧟
"These proteins are the molecular machines
which take the place of
the water-wheels and ropes and pulleys which can couple the falling of water down a mountainside to the lifting of some weight beside the stream"
An extended analogy between two systems
Whether this should be seen as one extended analogy, or more strictly as several, somewhat distinct but related, comparisons is moot, as becomes clear when trying to map out the different features. My best attempt involved some duplication and ambiguity. (Hint to all designers of teaching analogies – map them out as parallel concept maps to help you visualise and keep track of the points being made.)
An analogy (or set of analogies) between biological/biochemical and physical systems
Visualisation – mental simulation
Teaching analogies usually link to what is expected to be (for the members of the audience) a familiar situation, experience, or phenomenon. Readers will be familiar with an office block, or swimming in water.
However, it is also possible for the science communicator to set up an analogy based on a scenario which is unlikely to be familiar, but which can be readily imagined by the reader.
"To appreciate the power of random motion to bring about seemingly purposeful change, imagine a room full of blindfolded people all instructed to walk about at random 'bouncing' off the walls and one another. Imagine also that they have been told to stop moving only when they bump into a small picture hanging from a wall. Finally, suppose that all the pictures are hung in a second room, linked to the room full of people by a narrow open doorway…"
p.40
Few if any readers will have been familiar with this scenario, but the components – groups of people in rooms, blindfolding, adjoining rooms, pictures hung on walls – are all familiar and there is nothing inherently problematic about the scenario even it does not seem very likely. So, here the reader has to build up the analogy from a number of familiar but distinct images.
So, we might consider this a kind of 'gedankenexperiment' or thought experiment – the reader is prompted to consider what would happen if…(and then to transfer what would happen to the target system at the molecular scale). Perhaps some readers immediately 'see' (intuit) what happens in this situation, but otherwise they can 'run' a mental simulation to find out – a technique scientists themselves have used (if probably not regarding blindfolded people in picture galleries).
Analogies only reflect some aspects of the target being compared. The features that map unproblematically are known as the positive analogy, but there is usually a negative analogy as well: features that do not match, and so which would be misleading if carried across. Realistically, the negative analogy will usually have more content than the positive analogy, although much of the negative analogy will be so obviously irrelevant that it is unlikely to confuse anyone.
So, for example, in the analogy the blindfolded people will be wearing clothes, may exchange apologies (or curses) on bumping into each other, and will likely end up bruised – and human nature being what it is, some may cheat by sneaking a look past the edge of the blindfold – but no reader is likely to think these are features that transfer across to the target! Perhaps, however, a reader might wonder if the molecules, like the blindfolded people, are drawing on a source of energy to keep up the activity, and would tire eventually?
There are some other potentially more problematic aspects of the negative analogy. In the thought experiment, the people have been given instructions about what to do, and when to stop, and are acting deliberately. These features do not transfer across, but a reader might not realise this, and could therefore understand the analogy anthropomorphically. It is in situations like this where the teacher can seek feedback on how the analogy is being interpreted (that is, use informal formative assessment), but an author of a book loses control once the manuscript is completed.
Molecular mechanisms made familiar?
There is nothing unusual in Scott's use of metaphor, simile and analogy in seeking to help readers understand abstract scientific ideas. This is an approach common to a good deal of science communication, within and beyond formal teaching. Vital Principles offers many examples, but such devices are common in books seeking to explain science.
I did raise two questions about these techniques above. How do we know if these comparisons are effective in communicating the science? To find out, we would need to talk to readers and question them about their interpretations of the text.
In formal science teaching the focus of such research would likely be the extent to which the presentation supported a learner in acquiring a canonical understanding of the science.
However, as I suggested above, if such research concerned popular science books, we might ask whether the purpose of such books is to teach science or satisfy reader interest. Thus, above, I distinguished an objective and a subjective aspect. If a reader selected a book purely for interest, and is satisfied by what they have read – it made sense to them, and satisfied their curiosity – then does it matter if they may have not understood canonically?
When I read such texts, I wonder about both how a general readership responds to the comparisons offered by authors to make the unfamiliar familiar, and what sense the readers come away with of the science. I guess to some extent popular science authors at least get some level of feedback on the former question – if readers come back for their other titles, then they must be doing something right.
I thought Scott showed a good deal of ingenuity and craft in setting out an account of a challenging and complex area of science – but I would love to know how his different readers interpreted some of his comparisons.
Work cited:
Scott, A. (1988). Vital Principles. The molecular mechanisms of life. Basil Blackwell.
1 I have picked up a good many 'popular science books' over the years, but quite a few of them got put on the shelves till I had time to engage with them in any depth. Other things usually got in the way – lesson/lecture preparation being the most demanding imperative for soaking up time over my 'working' life. Retirement has finally allowed me to start going through the shelves…
2 In the English context, perhaps elsewhere, the textbook is now also often expected to not only cover the right content, but follow the examination board's line on the level of treatment, even to the degree of what is acceptable phrasing. Indeed, there are now textbooks associated with the different exam board syllabuses for the 'same' qualification (e.g., A level Chemistry). This seems very unhealthy, and come the revolution…
3 The model I am referring to here is the mental model in the teacher's mind of the learner or reader – the background knowledge they have available, their existing level of understanding, the sophistication of their thinking, the range of everyday references they are familiar with which might be useful in making comparisons, their concentration span for dealing with new material or complex language …
If we think of teaching-learning as a system, many system failure (failures of students to understand teaching as intended) can be considered to be due to a mismatch – the teacher's mental model is inaccurate in ways that leads to non-optimal choices in presenting material (Taber, 2001 [Download article]).
This is the basis of the 'learning doctor' approach.
5 There was little in the book I really would have argued with. However, there were a few questionable statements:
"Yet this apparent miracle is completed thousands of times each day throughout the world [in humans], and similar miracles create all manner of simpler creatures, from elephants and birds and flies to bacteria and flowers and mighty oaks."
p.5
This statement seemed to reflect the long-lasting notion of nature as a 'great chain of being' with humans (in the middle of the chain, below a vast range of angelic forms, but) top of the natural world. Bacteria are simpler than humans, I would acknowledge; but I am less sure about flies; even less sure about birds; and question considering trees and other flowering plants, or elephants, as (biologically) simpler than us. This seems an anthropocentric (human-centred), rather than a scientific, take.
"…the periodic table… lists the 92 naturally occurring atoms (plus a few man-made ones) which are the basic raw materials of chemistry…"
p.19
There are clearly more than 92 naturally occurring atoms in the universe. I believe we think there are 90 naturally occurring elements. That is 90 "naturally occurring [kinds of, in the specific sense of proton number] atoms".
Similarly, "a 'compound' is any chemical [sic] composed of two or more atoms chemically bonded together" (pp.29-30) would imply that H2, C60, N2, O2, F2, P4, S8, Cl2, etc are all compounds (when these are elements, not compounds).
Another slightly questionable suggestion was that
"…electrons appear to surround the atomic nucleus, but in a way that allows them to dart to and fro in a seemingly chaotic manner within a particular region of space."
p.21
The notion of electrons darting back and forth does not really reflect the scientific model, but the orbital/quantum model of the atom is subtle and difficult to explain, and was not needed at the level of the description being presented.
A more obvious error was that
"…'heat' is just a measure of the kinetic energy with which particles of matter are moving…"
p.26
In physics, the temperature of a material is considered to reflect the average kinetic energy of the particles (e.g., molecules). But heat is a distinct concept from temperature. Heat is the energy transferred between samples of matter, due to a difference in temperature. So, when Scott writes
"We all know that heat energy moves inevitably from hot places to cold places, and that it will never spontaneously move in the opposite direction."
p.32
this could be seen as a tautology: like saying that imports always come into the county rather than leave – because of how imports are defined.
Although heat and temperature are related concepts, confusing or conflating them is a common alternative conception found among students. Confusing heat with temperature is like confusing a payment into your bank account with the account balance.
Moreover, Scott uses the wrong term when writes,
"[The molecules of?] Chemicals come into contact with one another because they are all constantly moving with the energy we call heat."
p.191
This internal energy that substances have due to the inherent motion of their particles is not heat – it is present even when there is a perfectly uniform temperature throughout a sample (and so no heating going on).
Scott tells readers that "Another name for … a voltage difference is a 'potential difference'…" (p.162) but the term voltage (not voltage difference) normally refers to a potential difference, p.d.. (So, the term voltage difference implies a difference between potential differences, not a difference in potential. If you had one battery with a p.d. across its terminals of 6.0V, and another with a p.d. across its terminals of 4.5V, you could say the 'voltage difference' between the batteries was 1.5V.)
A common alternative conception which Scott seems to share, or at least is happy to reinforce, is the 'fairy tale'* of how ionic bonding results from the transfer of an electron from a metal atom to a neutral non-metal atom,
"When sodium atoms react with chlorine atoms electrons are actually transferred from one atom to the other (see figure [which shows electron transfer from one atom to another]). One electron which is relatively loosely held by a sodium atom can move over to become attached to a chlorine atom."
p.30
This describes a chemically very unlikely scenario (neither sodium nor chlorine are found in the atomic state under normal conditions on earth), and if a sodium atom were to somehow collide with a chlorine atom, the process Scott describes would be thermodynamically non-viable – it requires too much energy to remove even the outermost 'relatively loosely held' electron from the neutral sodium atom. Perhaps this is why in the school laboratory NaCl tends to be prepared from solutions that already contain the sodium ions [NaOH(aq)] and the chloride ions [HCl(aq)].
It is hard to be too critical of Scott here, as this account is found in many chemistry text books (and I have even seen it expected in public examinations) although from a scientific point of view, it is a nonsense. That many learners come to think that ionic bonding is due to (or even, 'is') a process of electron transfer is surely a pedagogic learning impediment (Taber, 1994) – a false idea that is commonly taught in school chemistry.
7 Many scientists will believe there is a purpose underpinning the evolution of life on earth, and will see creation as the unfolding of a supernatural plan. (Some others will vehemently reject this. Others still will be agnostic.) However, natural science is concerned with providing natural explanations of the world in terms of natural mechanisms. Even if a scientist thinks things are the way they are because that is God's will, that would be inadmissible as a scientific argument, as it does not explain how things came about through natural processes.
8 Teaching, or for that matter writing a science book, is informed by the teacher's/author's mental model of how the reader/listener will make sense of the text (see above). How they actually make sense of the text depends on the interpretive resources they have available, and bring to mind, and it is common for learners/readers not to interpret texts in the way intended – often they either do not make sense of the information, or make a different sense to that intended. A teacher who is a 'learning doctor' can seek to diagnose and treat these 'teaching-learning system failures' when they inevitably occur, but teachers can avoid a good many potential problems by being as explicit as possible and not relying on learners to spontaneously make intended associations with prior learning or cultural referents.
As suggested above, authors have an even more challenging task as their readerships may have a diverse range of prior knowledge and other available interpretive resources (e.g., a popular television programme or pop star in one country may be unknown to readers from another); and the author cannot check they have been understood as intended, in the way a teacher usually can.
