Perhaps Poincaré was reflecting how two opposing schools of philosophical thought had disagreed on wherever the primary source of human knowledge was experience (the empiricists) or pure reasoning (the rationalists), but elsewhere in the same text Poincairé (1902/1913/2015) dismisses the idea that the laws of physics can be obtained by simple reflection on human intuitions. Such intuitions can lead us astray.
If he is being consistent then, surely "the contrary hypothesis is [only] singularly repugnant to the mind" because "the commonest experience confirms…the principle of relative motion". That is, suggestions that are clearly contrary to our common experience – such as, perhaps, the earth is moving? – are readily rejected as being nonsensical and ridiculous.
If that is so, then Poincaré was not really offering two independent lines of argument as his second reason was dependent upon his first.
This put me in mind of some comments of Kryten, a character in the sci-fi series 'Red Drawf',
{responding to a crew suggestion "Why don't we drop the defensive shields?"}
"A superlative suggestion, sir, with just two minor flaws.
One, we don't have any defensive shields, and
two, we don't have any defensive shields.
Now I realise that, technically speaking, that's only one flaw but I thought it was such a big one it was worth mentioning twice."
Kryten (mechanoid assigned to the mining spaceship Red Dwarf)
or alternatively,
{responding to the crew suggestion "I got it! We laser our way through [the 53 doors from here to the science deck]!"}
Ah, an excellent plan, sir, with only two minor drawbacks.
One, we don't have a power source for the lasers; and
two, we don't have any lasers.
Kryten
French physicist Poincaré'Red Dwarf' character, Kryten
The principle of relative motion
What Poincairé meant by 'the principle of relative motion' was that
"The motion of any system must obey the same laws, whether it be referred to fixed axes, or to moveable axes carried along in a rectilinear and uniform motion."
the principle of relative motion
In other words, imagine a train passing a station at 10 ms-1, in which a naughty physics student throws a pencil eraser of mass m with a force of F at another passenger sitting in front on him; while a model physics student observes this from the stationary station [sic] platform.
The student on the train would consider the eraser to be at rest before being thrown, and can explore its motion by taking u=0 ms-1 and applying some laws summarised by
F=ma,
v=u+at,
v2=u2+2as,
s=ut +1/2at2…
From the frame or reference of someone in the the station it is the train that moves, (Image by StockSnap from Pixabay) but……From the frame of reference of the train (or tram), it seems to be the rest of the world that is moving past (Image by Pasi Mämmelä from Pixabay)
The student on the platform would observe the eraser to initially be moving at 10 ms-1, but could calculate what would happen using the same set of equations, but taking u=10 ms-1
Any values of v calculated would be consistent across the two frames (when allowing for the 10 ms-1 discrepancy) and other values calculated (s, t) would be the same.
This reflects the relativity principle of Galileo which suggests that there is no absolute way of determining whether a body is moving at constant velocity or stationary: rather what appears to be the case depends on one's frame of reference.
We might think that obviously it is the platform which is really stationary, as our intuition is that the earth under our feet is stationary ground. Surely we could tell if the ground moves?
We can directly feel acceleration, and we can sometimes feel the resistance to motion (the air on our face if we cycle, even at a constant velocity), but the idea that we can directly tell whether or not we are moving is an alternative conception.
For centuries the idea of a moving earth was largely considered ridiculous as experience clearly indicated otherwise. But if someone was kidnapped whilst asleep (please note, this would be illegal and is not being encouraged) and awoke in a carriage that had been set up to look like a hotel bedroom, on a train moving with constant velocity, they would not feel they were in motion. Indeed anyone who as travelled on a train at night when nothing is visible outside the carriage might well have experienced the impression that the train is stationary whilst it moves at a steady rate.
Science has shown us that there are good reasons to think that the earth is spinning, and orbiting the sun, as part of the solar system which moves through the galaxy, so who is to say what is really stationary? We cannot tell (and the question may be meaningless).
Who is to say what is moving – we can only make relative judgements? (Image by Drajt from Pixabay)
Source cited:
Poincaré, H. (1902/1913/2015). Science and Hypothesis (G. B. Halstead, Trans.). In The Foundations of Science. Cambridge University Press. {I give three dates because Poincaré published his book in French in 1902, and it was later published in an English translation in 1913, but I have a 2015 edition.}
"why the brain can't multitask is still very much a topic of considerable debate"
Prof. Paul Dux
Is it true that brains cannot multitask? I think mine can. (Image by Gerd Altmann from Pixabay)
The podcast was an episode of the ABC radio programme All in the Mind (not to be confused with the BBC radio programme All in the Mind, of course) entitled 'Misadventures in multitasking'
"All in the Mind is an exploration of the mental: the mind, brain and behaviour — everything from addiction to artificial intelligence." An ABC radio programme and podcast.
The argument against multitasking
Now mutlitasking is doing several things at once – such as perhaps having a phone conversation whilst reading an unrelated email. Some aspects of the modern world seem to encourage this – such as being queued on the telephone (as when I was kept on hold for over an hour waiting to get an appointment at my doctor's surgery – I was not going to just sit by the phone in the hope I would eventually get to the top of the queue). Similarly 'notifications' that seek to distract us from what we are doing on the computer, as if anything that arrives is likely to be important enough for us to need immediate alerting, add little to the sum of human happiness.1
Now I have heard the argument against multitasking before. The key is attention. We may think we are doing several things at once, but instead of focusing on one activity, completing, it, then shifting to another, what multitaskers actually do is continuously interrupt their focus on one activity to refocus attention on the another. The working memory has limited capacity (this surely is what limits our ability to reflectively multitask?), and we can only actually focus on one activity at a time, so multitasking is a con – we may think we are being more productive but we are not.
Now, people do tire, and after, say 45 minutes at one task it may be more effective to break, do something unrelated, and come back to your work fresh. If you are writing, and you break, and take the washing out of the machine and hang it up to dry, and make a cup of tea, and then come back to your writing fifteen or twenty minutes later, this is likely to be ultimately more productive than just ploughing on. You have been busy, not just resting, but a very different kind of activity, and your mind (hopefully) is refreshed. If you have been at your desk for 90 minutes without a break, then go for a walk, or even a quick lie down.
That however, is very different from doing your writing, as you check your email inbox, and keep an eye on a social media feed, and shop online. You can only really do one of those things at a time and if you try to multitask you are likely to quickly tire, and make mistakes as you keep interrupting your flow of concentration. (So, if you have been doing your writing, and you feel the need to do something else, give yourself a definite period of time to completely change activity, and then return fully committed to the writing.)
Now, I find that line of argument very convincing and in keeping my with own experience. (Which is not to say I always follow my own advice, of course.) Yet, I still thought Prof. Dux was wrong. And, indeed, there is one sense in which I would like to think deliberate reflective multitasking is not counterproductive.
If your brain cannot multitask you'd perhaps better hope it focuses on breathing
The brain is complex…
This is a short extract from the programme,
Paul Dux: Why the brain can't multitask is still very much a topic of considerable debate because we have these billions of neurons, trillions of synaptic connections, so why can't we do two simple things at once?
Sana Qadar: This is Professor Paul Dux, he's a psychologist and neuroscientist at the University of Queensland. He takes us deeper into what's going on in the brain.
Paul Dux: A lot of people would say it's because we have these capacities for attention. The brain regions that are involved in things like attention are our lateral prefrontal cortex. You have these populations of neurons that respond to lots of different tasks and multiple demands. That of course on one hand could be quite beneficial because it means that we are able to learn things quickly and can generalise quickly, but maybe the cost of that is that if we are doing two things at once in close temporal proximity, they try to draw on the same populations of neurons, and as a result leads to interference. And so that's why we get multitasking costs.
Sana Qadar: Right, so that's why if you are doing dishes while chatting to a friend, a dish might end up in the fridge rather than the cupboard where it's supposed to go.
Paul Dux: That's right, exactly.
Paul Dux talking to Sana Qadar who introduces 'All in the mind'
Now I imagine that Prof. Dux is an expert, and he certainly seemed authoritative. Yet, I sensed a kind of concept-creep, that led to a category error, here.
A category error
A category error is where something is thought of or discussed as though a member of an inappropriate class or category. A common example might be gender and sex. At one time it was widely assumed that gender (feminine-masculine) was directly correlated to biological sex (female-male) so terms were interchangeable. It is common to see studies in the literature which have looked for 'sex differences' when it seems likely that the researchers have collected no data on biological sex.
Models that suggest that the 'particles' (molecules, ions, atom) in a solid are touching encourage category errors among learners: that such quanticles are like tiny marbles that have a definite surface and diameter. This leads to questions such as whether on expansion the particles get larger or just further apart. (Usually the student is expected to think that the particles get further apart, but it is logically more sensible to say they get larger. But neither answer is really satisfactory.)
If someone suggested that a mushroom must photosynthesise because that is how plants power their metabolism then they would have made a category error. (Yes, plants photosynthesise. However, a mushroom is not a plant but a fungus, and fungi are decomposers.)
The issue here, to my mind (so to speak) was the distinction between brain (a material object) and conscious mind (the locus of subjective experience). Whilst it is usually assumed that mind and brain are related (and that mind may arise, emerge from processes in the brain) they may be considered to relate to different levels of description. So, mind and brain are not just different terms for the same thing.
Mind might well arise from brain, but it is not the same kind of thing. So, perhaps the notion of 'tasks' applies to minds, not brains? (Figure from Taber, 2013)
So, it is one thing to claim that the mind can only be actively engaged in one task at a time, but that is not equivalent to suggesting this is true of the brain that gives rise to that mind.2
Prof. Dax seemed to be concerned with the brain:
"the brain…billions of neurons, trillions of synaptic connections… brain regions…lateral prefrontal cortex…populations of neurons"
Yet it seems completely unfounded to claim that human brains do not multitask as we surely know they do. Our brains are simultaneously processing information from our eyes, our ears, our skin, our muscles, etc. This is not some kind of serial process with the brain shifting from one focus to another, but is parallel processing, with different modules doing different things at the same time. Certainly, we cannot give conscious attention to all these inputs at once, so the brain is filtering and prioritising which signals are worth notifying to head office (so to speak). We are not aware of most of this activity – but then that is generally the case with our brains.
The brain controls the endocrine system. The brain stem has various functions, including regulating breathing and heart rate and balance. If the brain cannot multitask we had perhaps better hope it focuses on breathing, although even then I doubt we would survive for long based on that activity alone.
Like the proverbial iceberg, most of our brain activity takes place below the waterline, out of conscious awareness. This is not just the physiological regulation – but a lot of the cognitive processing. So, we consolidate memories and develop intuitions and have sudden insights because our brains are constantly (but preconsciously) processing new data in the light of structures constructed through past experience.
If you are reading, you may suddenly notice that the room has become cold, or that the doorbell is ringing. This is because although you were reading (courtesy of your brain), your brain was also monitoring various aspects of the environment to keep alert for a cue to change activity. You (as in a conscious person, a mind if you like) may not be able to do two things at once, so your reading is interrupted by the door bell, but only because your brain was processing sensory information in the background whilst it was also tracking the lines of text in your book, and interpreting the symbols on the page, and recalling relevant information to provide context (how that term was defined, what the author claimed she was going to demonstrate at the start of the chapter…). Your mind as the locus of your conscious experience cannot multi-task, certainly, and certainly "brain regions that are involved in…attention" are very relevant to that, but your brain itself is still a master of multitasking.
Me, mybrain, and I
So, if the brain can clearly multitask, can we say that the person cannot multitask?
That does not seem to work either. The person can thermoregulate, digest food, grow hair and nails, blink to moisten the eye etc., etc as they take an examination or watch a film. These are automatic functions. So, might we say that it is the body, not the person carrying out those physiological functions? (The body of the person, but not the person, that is.)
Yet, most people (i.e., persons) can hold a conversation as they walk along, and still manage to duck under an obstruction. The conversation requires our direct attention, but walking and swerving seem to be things which we can do on 'autopilot' even if not automatic like our heartbeat. But if there was a complex obstruction which required planning to get around, then the conversation would likely pause.
So, it is not the brain, the body, or even the person that cannot multitask, but more the focus of attention, the stream of consciousness, the conscious mind. Perhaps confusion slips in because these distinctions do not seem absolute as our [sic] sense of identify and embodiment can shift. I kick out (with my leg), but it is my leg which hurts, and perhaps my brain that is telling me it is hurting?
There is also one sense in which I regularly multitask. I listen to music a lot. This includes, usually, when I am reading. And, usually, when I am writing. I like to think I can listen to music and work. (But Prof. Dux may suggest this is just another example of how humans "are not actually good at knowing our own limitations".)
I like to think it usually helps. I also know this is not indiscriminate. If I am doing serious reading I do not play music with lyrics as that may distract me from my reading. But sometimes when I am writing I will listen to songs (and, unfortunately for anyone in earshot, may even find I am singing along). I also know that for some activities I need to have familiar music and not listen to something new if the music is to support rather than disturb my activity.
Perhaps I am kidding myself, and am actually shifting back and forth between
being distracted from my work by my music
and
focusing on my work and ignoring the music.
I know that certainly sometimes is the case, but my impression is that usually I am aware of the music at a level that does not interfere with my work, and sometimes the music both seems to screen out extraneous noise and even provides a sense of flow and rhythm to my thinking.
The human brain has two somewhat self-contained, but connected, hemispheres. (Image by Gerd Altmann from Pixabay)
I suspect this has something to do with brain lateralisation and how, in a sense, we all have two brains (as the hemispheres are to some extent autonomous). Perhaps one of my hemispheres is quietly (sic) enjoying my music whilst the other is studiously working. I even fancy that my less verbal hemisphere is being kept on side by being fed music and so does not get bored (and so perhaps instigate a distracting daydream) whilst it waits for the other me, its conjoined twin, to finish reading or writing.
I may well be completely wrong about that.
Perhaps I am just as hopeless at multitasking with my propensity to attempt simultaneous scholarship and music appreciation as those people who think they can monitor social media whilst effectively studying.3 Perhaps it is just an excuse to listen to music when I should be working.
But even if that is so, I am confident my brain can multitask, even if I cannot.
Another email has arrived inviting me to talk at some medical conference on a specialism I cannot even pronounce?
A fiend of a friend of a friend has posted some update on social media that I can put into Google translate if I can be bothered?
Someone I do not recall seems to have a job anniversary?
Someone somewhere seems to have read something I once wrote (and I can find out who and where for a fee)?
Luckily I have been notified immediately as now I know this I will obviously no longer wish to complete the activity I was in the middle of.
2 One could argue that when a person is conscious (be that awake, or dreaming) one task the brain is carrying out is supporting that conscious experience. So, anything else a brain of a conscious person is doing must be an additional task. Perhaps, the problem is that minds carry out tasks (which suggests an awareness of purpose), but brains are just actively processing?
3 As a sporting analogy for the contrast I am implying here, there is a tradition in England of attending international cricket matches, and listening to the 'test match special' commentary (i.e., verbal) on the radio while watching (i.e. visual) the match. This seems to offer complementary enhancement of the experience. But I have also often seen paying spectators on televised football matches looking at their mobile phones rather than watching the match.
I was aware that research has suggested that children often do not appreciate how carbon obtained from the carbon dioxide in the air is a key source of matter for plants to build up tissue, so learners may assume that the mass increase during growth of a plant will be balanced by a mass reduction in the soil it is growing in.
"The extra [mass of a growing tree] comes from the things it eats and drinks from the ground. It's just like us eating and getting larger."
Response of 15 year old student in the National science survey carried out the Assessment of Performance Unit of the Department of Education and Science, as reported in Bell and Brook, 1984: 12.
During an interview in her first year of secondary education (Y7), Sophia reported that she had been studying plants in science, and that generally a plant was "a living thing, that takes up things from soil, to help it grow" (although some grew in ponds). Sophia was therefore asked a hypothetical question about weighing a pot of soil in which a seed was planted, with the intention of seeing if she thought that the gain in mas of the seed as it grew into a mature plant would be balanced by a loss of mass from the soil.
Sophia was asked about a pot of soil (mass 400g) in which was planted a seed (1g), and which was then watered (adding 49g of water).
A learner considers that the mass of pot, seed and water is collectively 450g, and assumes that as the mass of plant grows, the mass of soil decreases accordingly to conserve total mass at 450g.
A learner is aware that in photosynthesis carbon is 'captured' from carbon dioxide in the air, so the mass of the plant in the soil will exceed 450g once the plant grows.
Of course, a learner might also invoke other considerations – the evaporation of the water, or the acquisition of water due to condensation of water from cold air (e.g., dew); that soil is not inert, but contains micro-organisms that have their own metabolism, etc.
I first wanted to check that Sophia appreciated we had (400 + 1 + 49 =) 450g of material at the point the seed was first watered. That was indeed her initial thought, but she soon 'corrected' herself.
Any idea how much it would weigh now?
[Four] hundred and fifty, no, cause, no cause it will soak it up, wouldn't it, so just over four hundred (400).
So we had four hundred (400) grammes of soil plus pot, didn't we?
Uh hm.
…And we had one (1) gramme of erm, of plant seed. Just one little seed, one (1) gramme. And forty nine (49) grammes of water. But the water gets soaked up into the soil, does it? So when it's soaked up, you reckon it would be, what?
Erm, four hundred and twenty (420).
Sophia's best guess at the mass of the pot with soil (initially 400g) after planting a 1g seed and adding 49g of water was 420g, as the water gets soaked up.
So, Sophia suggests that although 49g of water has been added to a pot (with existing contents) of mass 401g , the new total mass will be less than 450g, as the water is soaking into the soil. Her logic seems to be that some of the water will have soaked into the soil, so it's mass is not registered by the balance.
If you poured the water in, quite quickly, not so quickly that it splashes everywhere, but quite quickly. Before it had a chance to soak up, if you could read what it said on the balance before it had a chance to soak up, do you think it would say four hundred and twenty (420) grammes straight away?
No, it would probably be just under, erm, four hundred and fifty (450).
And it would gradually drop down to about four twenty (420) say, would it?
Yeah.
Might be four hundred and fifteen? (415) Could be four hundred and twenty five (425)?
Yeah.
Not entirely sure,
No
but something like that?
Yeah.
It appears Sophia recognises that in principle there would be a potential mass of 450g when the water is added, but as it soaks up, less mass is registered.
Sophia recognises that mass is initially conserved, at least before the water soaks into the soil.
In other words Sophia in the context of water soaking into soil is not conserving mass.
This is a similar thought experiment to when students are asked about the mass registered during dissolving, where some learners suggest that as a solid dissolves the total mass of the beaker/flask plus its contents decreases, as if the mass of the dissolved material is not registered (Taber, 2002). In that case it has been mooted that ideas about buoyancy may be involved – at least when it is clear that the learners recognise the dissolved material is still present in the solution.
However, that would not explain why Sophia thinks the balance would not register the mass of water soaked into the soil in this case. Rather, it sees more a notion that 'out of sight' is out of mass. Sophia's understanding of what is happening to mass here would be considered an alternative conception or misconception, and is likely based on her intuition about the scenario (acting as a grounded learning impediment) rather than something she has been told.
Sources cited:
Bell, B., & Brook, A. (1984). Aspects of Secondary Students' Understanding of Plant Nutrition. Leeds: : Centre for Studies in Science and Mathematics Education, University of Leeds.
I was checking some proofs for something I had written today* [Taber, 2017], and was struck by an ironic parallel between one of the challenges for teaching about the scientific theory of evolution by natural selection and one of the arguments put forward by those who deny the theory. The issue concerns the value of having only part of an integrated system.
The challenge of evolutionary change
One of the arguments that has long been made about the feasibility of evolution is that if it occurs by many small random events, it could not lead to progressive increases in complexity – unless it was guided by some sense of design to drive the many small changes towards some substantive new feature of ability. So, for example, birds have adaptations such as feathers that allow them to fly, even though they are thought to have evolved from creatures that could not fly. The argument goes that for a land animal to evolve into a bird there need to be a great many coordinated changes. Feathers would not appear due to a single mutation, but rather must be the result of a long series of small changes. Moreover, simply growing features would not allow an animal to fly without other coordinated changes such as evolving very light bones and changes in anatomy to support the musculature needed to power the wings.
The same argument can be made about something like the mammalian eye, which can hardly be one random mutation away from an eyeless creature. The eye requires retinal cells, linked to the optic nerve, a lens, the iris, and so on. The eye is an impressive piece of equipment which is as likely to be the result of a handful of random events, as would be – say, a pocket watch found walking on the heath (to use a famous example). A person finding a watch would not assume its mechanism was the result of a chance accumulation of parts that had somehow fallen together. Rather, the precise mechanism surely implies a designer who planned the constructions of the overall object. In 'Intelligent Design' similar arguments are made at the biochemical level, about the complex systems of proteins which only function after they have independently come into existence and become coordinated into a 'machine' such as a flagellum.
The challenge of conceptual change
The parallel concerns the nature of conceptual changes between different conceptual frameworks. Paul Thagard (e.g., 1992) has looked at historical cases and argued that such shifts depend upon judgements of 'explanatory coherence'. For example, the phlogiston theory explained a good many phenomena in chemistry, but also had well-recognised problems.
The very different conceptual framework developed by Lavoisier [the Lavoisiers? **] (before he was introduced to Madame Guillotine) saw combustion as a chemical reaction with oxygen (rather than a release of phlogiston), and with the merits of hindsight clearly makes sense of chemistry much more systematically and thoroughly. It seems hard now to understand why all other contemporary chemists did not readily switch their conceptual frameworks immediately. Thagard's argument was that those who were very familiar with phlogiston theory and had spent many years working with it genuinely found it had more explanatory coherence than the new unfamiliar oxygen theory that they had had less opportunity to work with across a wide range of examples. So chemists who history suggests were reactionary in rejecting the progressive new theory were actually acting perfectly rationally in terms of their own understanding at the time. ***
Evolution is counter-intuitive
Evolution is not an obvious idea. Our experience of the world is of very distinct types of creatures that seldom offer intermediate uncertain individuals. (That may not be true for expert naturalists, but is the common experience.) Types give rise to more of their own: young children know that pups come from dogs and grow to be adult dogs that will have pups, and not kittens, of their own. The fossil record may offer clues, but the extant biological world that children grow up in only offers a single static frame from the on-going movie of evolving life-forms. [That is, everyday 'lifeworld' knowledge can act as substantial learning impediment – we think we already know how things are.]
Natural selection is an exceptionally powerful and insightful theory – but it is not easy to grasp. Those who have become so familiar with it may forget that – but even Darwin took many years to be convinced about his theory.
Understanding natural selection means coordinating a range of different ideas about inheritance, and fitness, and random mutations, and environmental change, and geographical separation of populations, and so forth. Put it all together and the conceptual system seems elegant – perhaps even simple, and perhaps with the advantage of hindsight even obvious. It is said that when Huxley read the Origin of Species his response was "How extremely stupid not to have thought of that!" That perhaps owes as much to the pedagogic and rhetorical qualities of Darwin's writing in his "one long argument". However, Huxley had not thought of it. Alfred Russel Wallace had independently arrived at much the same scheme and it may be no coincidence that Darwin and Wallace had both spent years immersing themselves in the natural history of several continents.
Evolution is counter-intuitive, and only makes sense once we can construct a coherent theoretical structure that coordinates a range of different components. Natural selection is something like a shed that will act as a perfectly stable building once we have put it together, but which it is very difficult to hold in place whilst still under construction. Good scaffolding may be needed.
Incremental change
The response to those arguments about design in evolution is that the many generations between the land animal and the bird, or the blind animal and the mammal, get benefits from the individual mutations that will collectively, ultimately lead to the wing or mammalian eye. So a simple eye is better than no eye, and even a simple light sensitive spot may give its owner some advantage. Wings that are good enough to glide are useful even if their owners cannot actually fly. Nature is not too proud to make use of available materials that may have previously had different functions (whether at the level of proteins or anatomical structures). So perhaps features started out as useful insulation, before they were made use of for a new function. From the human scale it is hard not to see purpose – but the movie of life has an enormous number of frames and, like some art house movies, the observer might have to watch for some time to see any substantive changes.
A pedagogical suggestion – incremental teaching?
So there is the irony. Scientists counter the arguments about design by showing how parts of (what will later be recognised as) an adaptation actually function as smaller or different advantageous adaptations in their own right. Learning about natural selection presents a situation where the theory is only likely to offer greater explanatory coherence than a student's intuitive ideas about the absolute nature of species after the edifice has been fully constructed and regularly applied to a range of examples.
Perhaps we might take the parallel further. It might be worth exploring if we can scaffold learning about natural selection by finding ways to show students that each component of the theory offers some individual conceptual advantages in thinking about aspects of the natural world. That might be an idea worth exploring.
(Note. 'Representing evolution in science education: The challenge of teaching about natural selection' is published in B. Akpan (Ed.), Science Education: A Global Perspective. The International Edition is due to be published by Springer at the end of June 2016.)
Notes:
* First published 30th April 2016 at http://people.ds.cam.ac.uk/kst24/
** "as Madame Lavoisier, Marie-Anne Pierrette Paulze, was his coworker as well as his wife, and it is not clear how much credit she deserves for 'his' ideas" (Taber, 2019: 90). Due to the times in which they works it was for a long time generally assumed that Mme Lavoisier 'assisted' Antoine Lavoisier in his work, but that he was 'the' scientist. The extent of her role and contribution was very likely under-estimated and there has been some of a re-evaluation. It is known that Paulze contributed original diagrams of scientific apparatus, translated original scientific works, and after Antoine was executed by the French State she did much to ensure his work would be disseminated. It will likely never be know how much she contributed to the conceptualisation of Lavoisier's theories.
*** It has also been argued (in the work of Hasok Chang, for example) both that when the chemical revolution is considered, little weight is usually given to the less successful aspects of Lavoisier's theory, and that phlogiston theory had much greater merits and coherence than is usually now suggested.
Sources cited:
Taber, K. S. (2017). Representing evolution in science education: The challenge of teaching about natural selection. In B. Akpan (Ed.), Science Education: A Global Perspective (pp. 71-96). Switzerland: Springer International Publishing
Plants mainly respire at night because they are photosynthesising during the day
Keith S. Taber
Image by Konevi from Pixabay
Mandy was a participant in the Understanding Science Project. When I spoke to her in Y10 (i.e. when she was c.14 year old) she told me that photosynthesis was one of the topics she was studying in science. So I asked her about photosynthesis. She suggested that "respiration produces energy, but photosynthesis produces glucose which produces energy". (See 'How plants get their food to grow and make energy'). She told me that she respired to get energy.
How do you get your energy then?
We respire.
Is that different then [from photosynthesis]?
Yeah.
So what's respire then, what do you do when you respire?
We use oxygen to, and glucose to release energy.
Do plants respire?
Yes.
So when do you respire, when you are going to go for a run or something, is that when you respire, when you need the energy?
No, you are respiring all the time.
… What about plants? Do they respire all the time?
They mainly do it at night.
Why's that?
'cause they're photosynthesising during the day, cause they need the light.
I was not clear why Mandy thought that plants should respire less when they were photosynthesising.
So why do you need to respire all the time?
'cause you're making energy and you need energy to do everything.
So are you respiring at the same rate all the time, do you think?
No.
So sometimes more than others?
Yeah.
So when might you need to respire more?
When you are doing exercise. Running around a lot.
So are there time when you do not need to respire as much?
Yeah.
So when might you not need to respire very much?
When you 're sleeping or just sitting watching tele [television].
…Do you have to respire at all during the night – you are not doing anything are you?
You need a little bit of energy.
What for?
Erm, I don't [indistinct], well I suppose it's just to keep everything, cause if you did not have energy then your heart would not beat, and you need it to keep breathing, and your heart pumping.
Mandy recognised the need for people to respire continuously, although she associated this with functioning at the organism level (breathing, blood circulation) and did not seem to be thinking about cellular level metabolism.
Why do plants need to respire? What do they use it, the energy for?
Erm, to grow, and to fix cells that are – broken.
Oh right, like repair damage?
Yeah.
So, do you think they are like us then, that they sort of sleep sometimes and don't need to respire as much, or?
Not as much, I don't know. I don't know.
Do you think a plant sleeps, a tree has a good sleep?
No.
So when do you think plants need to respire the most, or do you think they respire the same all the time?
They respire more at night, because – they do it then instead of in the day because they do photosynthesis during the day, but they still respire a little bit.
So is it difficult to try and do both at the same time?
Probably.
Or just maybe they are too busy photosynthesising to do much respiration?
Yeah, erm, I don't know.
Not sure?
No.
Mandy was not offering any specific reason why a plant should need to respire less at night (and did not seem to have previously thought about this), but simply seemed to assume that when the plant was photosynthesising a lot it would only respire "a little bit". This seemed to be an intuition rather than a considered proposition. It was almost as if she implicitly assumed that the plant would be fully occupied photosynthesising, and so would put respiration 'on the back burner'.
It seemed Mandy's understanding of the roles of photosynthesis and respiration at that point in her learning was limited by not fully seeing how energy was involved in the two processes (i.e., respiration produces energy, but photosynthesis produces glucose which produces energy), and because she was not considering the need for respiration to support ongoing basic cell functions.
Sophia was a participant in the Understanding Science Project. In Y7, Sophia had told me that if molten iron was heated "some of it would evaporate but not all of it, 'cause it's not like water and it's more heavy". She thought only "a little" of the iron would evaporate to give iron vapour: The rest "really just stays as a liquid". [See 'Iron is too heavy to completely evaporate'.]
Just over a year later (in Y8) Sophia had been studying "that different erm substances have different freezing and melting and boiling points, and some aren't like a liquid at room temperatures, some are a solid and some are a gas and things like that".
Give me an example of something else that's a solid at room temperature?
Iron.
Do you think iron would have a melting point?
Yeah.
Yeah, and if I, what would I get if I, if I heated iron to its melting point?
It would become a liquid.
And why would it do that?
Because it's got so hot that particles – they have spread out or something?
So what do you think would happen if I heated the iron liquid?
It would stay a liquid.
No matter how much I heated it?
It might, I don't know if it would become a vapour.
Can you get iron vapour?
No, I don't think so.
You don't think so?
No.
So it seems that Sophia had shifted from accepting that iron would partially evaporate (when learning about the particle model of the different states), to considering that iron (probably) can not become a vapour. The notion of iron as a gas is not something we can readily imagine, and apparently did not seem very feasible. In part this might be because we think of iron the material (a metal, which cannot exist in in the vapour phase) rather than as a substance that can take different material forms.
It seems Sophia's prior knowledge of iron the material was working against her learning about iron the substance, an examples of a grounded learning impediment where prior knowledge impedes new learning.
In Y7 Sophia had seemed to have a hybrid conception where having been taught a general model of the states of matter and changes of state, she accepted the counter-intuitive idea that iron could evaporate, but thought that (unlike in the case of water) it could not completely evaporate . This might have been a 'stepping stone' between not accepting iron could be in the gaseous state and fitting it within the general model that all substances will when progressively heated first melt and then evaporate (or boil) as long as they did not decompose first.
However, it seems that a year later Sophia was actually more resistant to the idea that iron could exist as vapour and so now she thought molten iron would remain liquid no matter how much it was heated. If anything, she had reverted to a more intuitive understanding. This is not that strange: it has been shown that apparent conceptual gains which are counter to strongly held intuitions that are brought about by teaching episodes that are not regularly reinforced can drop away as the time since teaching increases. Conceptual change does not always involve shifts towards the scientific accounts.
[Sophia was in lower secondary school when I talked to her about this: but I was also told by a much older student that the idea of iron turning into a gas sounds weird.]
Some molten iron would evaporate but not all of it, 'cause it's not like water and it's more heavy
Keith S. Taber
Sophia was a participant in the Understanding Science Project. In her first interview near the start of Y7, Sophia told me that she had learnt "about the particles…all the things that make – the actual thing, make them a solid, and make them a gas and make them a liquid" (i.e. the states of matter). All solids had particles, including (as examples) ice and an iron clamp stand. There would be the same particles in the ice as the iron.
"because they are a solid, but they can change , 'cause if erm they melted they would be a liquid so they would have different particles in…Well they are still the same particles but they are just changing the way they act".
Sophia's suggestion that particles in ice and the iron were the same types of particles as both were solid seems to be 'carving nature' at the wrong joints – that is in this model the particles in ice and (solid) iron would be of one type, whilst those of water and liquid iron would be of another type (that is she had an alternative ontology). Sophia quickly corrected this, so it is not clear if this reflected some intuitive idea or was just 'a slip of tongue'.
According to Sophia the ice could be melted "with something that's hot, like a candle" but for the iron "you need more heat, 'cause it's more, it's a lot more stronger…because it's got more particles pushed together".
Sophia's explanation suggested a causal path (right-hand side) quite different from a canonical causal path (left-hand side)
Strictly the difference is more about the strength of the interactions between particles, than how many were pushed together – although strong bonding forces would tend (all other factors being equal) to lead to particles being bound more tightly and being closer. We might argue here that Sophia seemed to confuse cause and effect – that a higher density of particles was an effect of strong bonding, which would also mean more energy was needed to overcome that bonding. (However, we should also be aware that when students use 'because' (which formally implies causality) they sometimes mean little more than 'is associated with'.)
If the water obtained from melting ice was heated more "it will evaporate into the sky". However, if the molten iron was heated Sophia thought that "some of it would evaporate but not all of it, 'cause it's not like water and it's more heavy". She thought only "a little" of the iron would evaporate to give iron vapour:
"No, I think that water all of it goes, but other material, other liquids some of it will go, not all of it". The rest "if it's cold enough, it will go back into a solid, but if not it really just stays as a liquid".
Sophia's idea that no matter how much liquid iron was heated it would not completely evaporate so some would remain liquid, which seemed to be linked in her mind to its density, seems to be evidence of an alternative conception. Students may not expect that something as (apparently) inherently solid as iron could evaporate (everyday experience may act as a grounded learning impediment), and so may not readily accept that the basic model of the states of matter and changes of state (i.e., a heated liquid will evaporate or boil) can apply to something like iron. Sophia seemed to have formed a hybrid conception – applying the taught model, but with a modification reflecting the counter-intuitive notion that iron could become a vapour.
Conceptual change can be a slow progress, although hybrid conceptions may be 'stepping stones' towards more scientific understandings. However, when I spoke to Sophia in Y8 she did not seem to have progressed further. [See 'Liquid iron stays a liquid when heated'.]
Atoms within an element don't need to be bonded because they're all the same sort
Keith S. Taber
Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonly used in chemistry teaching. Annie was shown a representation of the close packing of 'atoms' in a metal (with the iron symbol, Fe, shown).
Okay, have a look at number 6…
• • • • • • (pause, c.6 s)
They are obviously iron atoms within an element.
Iron atoms within the element?
Yeah.
Okay. Can you say anything about the arrangement of the atoms?
They're all lined together. They're all close together.
They're closely together, yes, and they're all lined together, there's some sort of regular pattern there okay?
Yeah.
So you think that's in the element, that's a lump of iron, a sort of, a magnified view of a lump of iron.
Yes.
So Annie did recognise the image as representing particles ('atoms') in solid iron. The image showed the particles close together, and Annie was asked if they would hold together – the intention being to find out what, if anything, Annie knew about metallic bonding. Annie did think the atoms would be held together, but she did not suggest this was due to a bond or even a force (cf. "Sodium and chlorine don't actually overlap or anything and would probably get held together by just forces"*).
Do you think those atoms will hold together?
Yes.
Why do you think that is?
Because they're all the same sort.
Does that make them hold together?
Yeah.
So it seemed that Annie held an alternative conception that atoms of the same sort would hold together because they were of the same type. This interpretation was tested.
Yeah? Do you think there is any kind of bonds between the atoms?
• • • • • • • • • (pause, c.9s)
No, because they're all the same and they don't need to be bonded.
Right, okay so recapping…here we've got an example of something where the atoms are all the same, and that holds them together even though there's no chemical bonds.
Yeah.
So Annie held an alternative conception of atomic coherence – that atoms of the same type did not need bonding to hold them together, as being the same kind of atom was sufficient for them to hold together.
It is unlikely that Annie had been taught this idea, and it seems quite possible it is an intuitive idea that might be acting as an example of a 'grounded learning impediment': a notion based on general experience, and inappropriately applied in the context of atomic interactions.
