Category: science communication

Making molecular mechanisms familiar

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.

Read about making the unfamiliar familiar

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 Principles did 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' – a maelstrom 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.

Read about science metaphors

Nature and nurture

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.

Read about personification in science

"All proteins begin life…"

Anthropomorphism: living metaphors

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").

Read about types of pseudo-explanation

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".

Read about examples of similes in science

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 of molecular 'sorting office'…"
    • endosomes and lysomes "form a kind of intracellular digestive system and 'breaker's yard'."
    • "Proteins can act as gatekeepers of the cell…"
    • "Proteins can…act as chemical controllers"
    • proteins "can act as defensive weapons…"
    • "The proteins which perform these feats are not gates, but 'pumps'..."
    • "Proteins could be described as the 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 like a 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.

Read about examples of analogies in science

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
fairgroundcell
people at a fairgroundmolecules in the cytosol
you at the fairgrounda specific enzyme in the cytosol
people entering the fairground that know you personallymolecules of a type that binds to the specific enzyme
chance of you meeting someone you knowrate 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 car unlocks 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 conceptanalogue
"…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:
Notes:

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.

Read about Science learning doctors

4 This is the crux of the so called 'constructivist' perspective on teaching science – a perspective discussed in depth elsewhere on the site.

Read about constructivism

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)].

* For example, read 'A tangible user interface for teaching fairy tales about chemical bonding'

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.

Read more about common misconceptions of ionic bonding

6 As the author of a paper called ' Mediating mental models of metals: acknowledging the priority of the learner's prior learning', I must confess to being somewhat partial to some decent alliteration.

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.

Read more about science and religion

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.

Read about being a learning doctor

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.

Creeping bronzes

Evidence of journalistic creep in 'surprising' Benin bronzes claim

Keith S. Taber

How certain can we be about the origin of metals used in historic artefacts? (Image by Monika from Pixabay)

Science offers reliable knowledge of the natural world – but not absolutely certain knowledge. Conclusions from scientific studies follow from the results, but no research can offer absolutely certain conclusions as there are always provisos.

Read about critical reading of research

Scientists tend to know this, something emphasised for example by Albert Einstein (1940), who described scientific theories (used to interpret research results) as "hypothetical, never completely final, always subject to question and doubt".

When scientists talk to one another within some research programme they may used a shared linguistic code where they can omit the various conditionals ('likely', 'it seems', 'according to our best estimates', 'assuming the underlying theory', 'within experimental error', and the rest) as these are understood, and so may be left unspoken, thus increasing economy of language.

When scientists explain their work to a wider public such conditionals may also be left out to keep the account simple, but really should be mentioned. A particular trope that annoyed me when I was younger was the high frequency of links in science documentaries that told me "this could only mean…" (Taber, 2007) when honest science is always framed more along the lines "this would seem to mean…", "this could possibly mean…", "this suggested the possibility"…

Read about scientific certainty in the media

Journalistic creep

By journalistic creep I mean the tendency for some journalists who act as intermediates between research scientists and the public to keep the story simple by omitting important provisos. Science teachers will appreciate this, as they often have to decide which details can be included in a presentation without loosing or confusing the audience. A useful mantra may be:

Simplification may be necessary – but oversimplification can be misleading

A slightly different type of journalist creep occurs within stories themselves, Sometimes the banner headline and the introduction to a piece report definitive, certain scientific results – but reading on (for those that do!) reveals nuances not acknowledged at the start. Teachers will again appreciate this tactic: offer the overview with the main point, before going back to fill in the more subtle aspects. But then, teachers have (somewhat) more control over whether the audience engages with the full account.

I am not intending to criticise journalists in general here, as scientists themselves have a tendency to do something similar when it comes to finding titles for papers that will attract attention by perhaps suggesting something more certain (or, sometimes, poetic or even controversial) than can be supported by the full report.

An example of a Benin Bronze (a brass artefact from what is now Nigeria) in the British [sic] Museum

(British Museum, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons)

Where did the Benin bronzes metal come from?

The title of a recent article in the RSC's magazine for teachers, Education in Chemistry, proclaimed a "Surprise origin for Benin bronzes".1 The article started with the claim:

"Geochemists have confirmed that most of the Benin bronzes – sculptured heads, plaques and figurines made by the Edo people in West Africa between the 16th and 19th centuries – are made from brass that originated thousands of miles away in the German Rhineland."

So, this was something that scientists had apparently confirmed as being the case.

Reading on, one finds that

  • it has been "long suspected that metal used for the artworks was melted-down manillas that the Portuguese brought to West Africa"
  • scientists "analysed 67 manillas known to have been used in early Portuguese trade. The manillas were recovered from five shipwrecks in the Atlantic and three land sites in Europe and Africa"
  • they "found strong similarities between the manillas studied and the metal used in more than 700 Benin bronzes with previously published chemical compositions"
  • and "the chemical composition of the copper in the manillas matched copper ores mined in northern Europe"
  • and "suggests that modern-day Germany, specifically the German Rhineland, was the main source of the metal".

So, there is a chain of argument here which seems quite persuasive, but to move from this to it being "confirmed that most of the Benin bronzes…are made from brass that originated …in the German Rhineland" seems an example of journalistic creep.

The reference to "the chemical composition of the copper [sic] in the manillas" is unclear, as according to the original research paper the sample of manilla analysed were:

"chemically different from each other. Although most manillas analysed here …are brasses or leaded brasses, sometimes with small amounts of tin, a few specimens are leaded copper with little or no zinc."

Skowronek, et al., 2023

The key data presented in the paper concerned the ratios of different lead isotopes (205Pb:204Pb; 206Pb:204Pb; 207Pb:204Pb; 208Pb:204Pb {see the reproduced figure below}) in

  • ore from different European locations (according to published sources)
  • sampled Benin bronze (as reported from earlier research), and
  • sampled recovered manillas

and the ratios of different elements (Ni:AS; Sb:As; Bi:As) in previously sampled Benin bronzes and sampled manillas.

The tendency to consider a chain of argument where each link seems reasonably persuasive as supporting fairly certain conclusions is logically flawed (it is like concluding from knowledge that one's chance of dying on any particular day is very low, that one must be immortal) but seems reflected in something I have noticed with some research students: that often their overall confidence in the conclusions of a research paper they have scrutinised is higher than their confidence in some of the distinct component parts of that study.

An example of a student's evaluation of a research study

This is like being told by a mechanic that your cycle brakes have a 20% of failing in the next year; the tyres 30%; the chain 20%; and the frame 10%; and concluding from this that there is only about a 20% chance of having any kind of failure in that time!

A definite identification?

The peer reviewed research paper which reports the study discussed in the Education in Chemistry article informs readers that

"In the current study, documentary sources and geochemical analyses are used to demonstrate that the source of the early Portuguese "tacoais" manillas and, ultimately, the Benin Bronzes was the German Rhineland."

"…this study definitively identifies the Rhineland as the principal source of manillas at the opening of the Portuguese trade…"

Skowronek, et al.,2023

which sounds pretty definitive, but interestingly the study did not rely on chemical analysis alone, but also 'documentary' evidence. In effect, historical evidence provided another link in the argument, by suggesting the range of possible sources of the alloy that should be considered in any chemical comparisons. This assumes there were no mining and smelting operations providing metal for the trade with Africa which have not been well-documented by historians. That seems a reasonable assumption, but adds another proviso to the conclusions.

The researchers reported that

Pre-18th century manillas share strong isotopic similarities with Benin's famous artworks. Trace elements such as antimony, arsenic, nickel and bismuth are not as similar as the lead isotope data…. The greater data derivation suggests that manillas were added to older brass or bronze scrap pieces to produce the Benin works, an idea proposed earlier.

and acknowledges that

Millions of these artifacts were sent to West Africa where they likely provided the major, virtually the only, source of brass for West African casters between the 15th and the 18th centuries, including serving as the principal metal source of the Benin Bronzes. However, the difference in trace elemental patterns between manillas and Benin Bronzes does not allow postulating that they have been the only source.

The figure below is taken from the research report.

Part of Figure 2 from the open access paper (© 2023 Skowronek et al. – distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The chart shows results from sampled examples of Benin bronzes (blue circles); compared with the values of the same isotope ratios from different copper ore site (squares) and manillas sampled from different archaeological sties (triangles).

The researchers feel that the pattern of clustering of results (in this, and other similar comparisons between lead isotope ratios) from the Benin bronzes, compared with those from the sampled manillas, and the ore sites, allows them to identify the source of metal re-purposed by the Edo craftspeople to make the bronzes.

It is certainly the case that the blue circles (which refer to the artworks) and the green squares (which refer to copper ore samples from Rhineland) do seem to generally cluster in a similar region of the graph – and that some of the samples taken from the manillas also seem to fit this pattern.

I can see why this might strongly suggest the Rhineland (certainly more so than Wales) as the source of the copper believed to be used in manillas which were traded in Africa and are thought to have been later melted down as part of the composition of alloy used to make the Benin bronzes.

Whether that makes for either

  • definitive identification of the Rhineland as the principal source of manillas (Skowronek paper), or
  • confirmation that most of the Benin bronze are made from brass that originated thousands of miles away in the German Rhineland (EiC)

seems somewhat less certain. Just as scientific claims should be.

A conclusion for science education

It is both human nature, and often good journalistic or pedagogic practice to begin with a clear, uncomplicated statement of what is to be communicated. But we also know that what is heard or read first may be better retained in memory than what follows. It also seems that people in general tend to apply the wrong kind of calculus when there are multiple source of doubt – being more likely to estimate overall doubt as being the mean or modal level of the several discrete sources of doubt, rather than something that accumulates step-on-step.

It seems there is a major issue here for science education in training young people in critically questioning claims, looking for the relevant provisos, and understanding how to integrate levels of doubt (or, similarly, risk) that are distributed over a sequence of phases in a process.

All research conclusions (in any empirical study in any discipline) rely on a network of assumptions and interpretations, any one of which could be a weak link in the chain of logic. This is my take on some of the most critical links and assumptions in the Benin bronzes study. One could easily further complicate this scheme (for example, I have ignored the assumptions about the validity of the techniques and calibration of the instrumentation used to find the isotopic composition of metal samples).

Work cited:
Note:

1 It is not clear to me what the surprise was – but perhaps this is meant to suggest the claim may be surprising to readers of the article. The study discussed was premised on the assumption that the Benin Bronzes were made from metal largely re-purposed from manillas traded from Europe, which had originally been cast in one of the known areas in Europe with metal working traditions. The researchers included the Rhineland as one of the potential regional sites they were considering. So, it was surely a surprise only in a similar sense to rolling a die and it landing on 4, rather than say 2 or 5, would be a surprise.

But then, would you be just as likely to read an article entitled "Benin bronzes found to have anticipated origin"?

Explaining Y T cells stop working

Communicating oncology research

Keith S. Taber

…to the best of my knowledge, there is absolutely no reason to suspect that Prof. Theodorescu falsified his academic credentials…

The following text is an extract from a podcast item reporting recently published research into bladder cancer:

"The Y-negative cells cause an immune evasive environment in the tumour, and that, if you will, paralyses, the T cells, and exhausts them, makes them tired and ineffective, and this prevents the Y-negative tumour from being rejected, therefore allowing it to grow much better."

"Exhausted T cells have lost their ability to kill cancer cells, and have lots of proteins on their surface known as checkpoints, which put the brakes on immune responses.

But this exhausting environment made by the tumours could actually be their undoing"

"What they also did, inadvertently I'm sure, is made themselves a lot more vulnerable to one of the most useful and prevalent therapeutics in cancer today, which is immune checkpoint inhibitors."

"Immune checkpoint inhibitors are a class of drugs that block those checkpoint proteins that sit on the surface of T cells, effectively taking the brakes off immune responses, causing T cells to become more aggressive."

Dan Theodorescu & Nick Petrić Howe speaking on the Nature Podcast

Prof. Dan Theodorescu MD, PhD, is the Director of the Samuel Oschin Comprehensive Cancer Institute at Cedars-Sinai, Professor of Surgery, Pathology and Laboratory Medicine; and corresponding author on the paper (Abdel-Hafiz et al., 2023) published in Nature, and discussed in the podcast.

Nick Petrić Howe, Senior Multimedia Editor at Nature Research, was the journalist presenting the item on the podcast.

Communicating science

Scientific research is communicated to other specialist scientists through research reports which reflect a particular genre of writing, and are written with specialist researchers in the same field as the main target readership. Such reports are usually of a quite technical nature, and (appropriately) assume that readers will have a high level of prior understanding of concepts in the field and the technical language used. Such tropes as simile and analogy certainly can sometimes feature, but generally figurative language is kept to a minimum.

Communication to a wider audience of people with a general interest in science needs to adopt a different register. As I have noted on this site before, this is quite challenging as a general public audience is likely to be very diverse in terms of its level of knowledge and understanding of background to any scientific research. Perhaps that is why as a former teacher (and so a science communicator that could make reasonably informed assumptions about the background of my audience in any particular lesson) I find the language of this type of science dissemination fascinating.

Read about science in public discourse and the media

The gist

The study discussed in the podcast reported on a line of research exploring the genomics of bladder cancer, and in particular how tumours that develop from cells that have deficiencies in the Y chromosome seem to have particular characteristics.

Put simply, tumours of this kind were likely to be inherently more damaging to the patient, although also likely to be more responsive to an existing class of medicines. (At this stage the work has largely relied on in vitro studies and 'animal models' (mice) so the implications for actual human cancer patients are reasonable, but speculative.)

The language used

The short extract of the dialogue I have transcribed above seems quite 'dense' in interesting language when de-constructed:

Y-negative cells – a new technical term?

The extract starts with reference to Y-negative cells. Earlier in the item it had been explained that some cells have no Y chromosome, or an incomplete Y chromosome. (For someone to understand this information, they would need to have some background knowledge relating to what chromosomes are, and why they are important in cells. 1 ) The term Y-negative cell therefore, given that context, refers to a cell which lacks the usual Y chromosome. 2 If such a cell turns cancerous it will give rise to a tumour which is Y-negative (as all the tumour cells are formed from the division of that cancerous cell). The published report notes "Loss of the Y chromosome (LOY) is observed in multiple cancer types, including 10-40% of bladder cancers" (Abdel-Hafiz et al., 2023), an observation which motivates the area of research.

An immune evasive environment?

The word 'evasion' appears in the title of the paper. To evade something means to avoid it, which might suggest a sense of deliberation. Immune evasion is a recognised issue, as in cancers "interactions between the immune system and the tumour occur through complex events that usually eventually climax either in successful tumour eradication or immune evasion by the tumour" (Vinay et al., 2015): that is, either the immune system destroys the cancer, or the cancer is able to grow due to some mechanism(s) that prevent the immune system killing the tumour cells. The 'immune evasive environment' then refers to the environment of the tumour's cells in a context where aspects of the normal immune mechanisms are inoperative or restricted.

Paralysed, exhausted and tired T cells

T cells are one of the classes of cell that make up the immune system, and the item was suggesting that with 'LOY' the T cells are unable to function in the way they normally do when interacting with cancer cells that have an intact Y chromosome. ('LOY' is the acronym for a process, viz., "loss of the Y chromosome", but once defined can be used in a way that reifies LOY as if it refers to an object. 3 In "…with 'LOY'…", I am treating LOY as a medically diagnosable condition.)

Are the T cells paralysed? That normally means not able to move, which is not the case here. So 'paralysed' seems to be used as a metaphor, a way of 'making the unfamiliar familiar' for a non specialist audience. A large part of the task of a science teacher is to make the unfamiliar [become] familiar to learners.

Read about making the unfamiliar familiar

Actually, I would better class this specific use as a simile rather than a metaphor:

"The Y-negative cells cause an immune evasive environment in the tumour, and that, if you will, paralyses, the T cells"

A simile in poetic language normally refers to something being 'like' or 'as' something else, as when the star Betelgeuse was said to be "like an imbalanced washing machine tub" or a laser was described as being used as a "kind of spark plug". Here, Prof. Theodorescu marks the term 'paralyses' with 'if you will' in a similar way to how when selection theory has been said to be "like a Tibetan prayer-wheel…" the word 'like' marks that this is noting a similarity, not an identity (selection theory is not suggested to be a prayer-wheel, but rather to be in some way like one).

Read examples of similes used in discussing science

The T cells were said to be as if paralysed, but they were also exhausted and tired. Yet, again, 'exhausted' does not seem to be meant literally. The T cell has not used up its supply of something (energy, or anything else), so this is another metaphor. 'Tired' can be seen as synonymous to exhausted, except usually 'tired' refers to a subjective experience. The T cells are not sentient and presumably do not feel tired – so, this is another metaphor; indeed an anthropomorphic metaphor, as it refers to the cells as though they have subjective experience like a person.

Read examples of metaphors used in discussing science

Hey, you immune cells – are you feeling tired? How about taking a break, and doing some stretching exercises and a little yoga?

Images from Pixabay

Anthropomorphism is a common trope in science discourse, especially in biological contexts. It can sometimes help communication of abstract material to present scientific phenomena in a narrative that relates to human subjective experience – perhaps referring to disease 'evading' the immune system – but consequently often gets adopted into in students' pseudo-explanations (e.g., the reaction happened because the atom wanted another electron, the gas expands because the molecules wanted more space). 4

Read about types of pseudo-explanations

Read examples of anthropomorphism in science discourse

Yet the term 'exhausted' also appears in the published research report ("Ylow bladder cancers contained a higher proportion of exhausted and progenitor exhausted CD8+ T cells..."). So, this is a term that is being adopted into the terminology of the research field. A paper from 2019 set out to define what this means: "'T cell exhaustion' is a broad term that has been used to describe the response of T cells to chronic antigen stimulation, first in the setting of chronic viral infection but more recently in response to tumours" (Blank, et al., 2019). Another study notes that

"It is now clear that T cells are not necessarily physically deleted under conditions of antigen persistence but can instead become functionally inept and incapable of elaborating the usual array of effector activities typically associated with robust, protective, effector and memory T-cell populations."

Yi, Cox, & Zajac, 2010

It is not unusual for terms that seem to be initially used metaphorically, to become adopted in a scientific field as technical terms (such as the 'birth' and 'death' of stars in astronomy). Indeed, inept seem to me a term that is normally applied to people who have agency and can learn skills, but lack skill in an area where the are active. The field of oncology seems to have adopted the notion of ineptitude, to label some T cells as 'inept'.

Unlike in human hereditary, where we would not assume a child can directly inherit a lack of skill in some area of activity from its parents (there is no gene for playing chess, or spraying cars, or heart surgery, or balancing account books), at the cellular level it is possible to have "inept T-cell lineages" (Fredholm et al, 2018). If one is going to anthropomorphise cells, then perhaps 'inept' is an unfair descriptor for structural changes that modify functionality, and can be passed on to 'daughter' cells: should these cells be considered to have a disability rather than be inept? For that matter, an exhausted T-cell seems to have more in common with a metamorphosed caterpillar than an exhausted marathon runner.

Rejection – a dead metaphor?

'Rejection' is a technical terms used in medical science for when the immune system 'attacks' something that it 'identifies' as not self: be that a tumour or a transplanted tissue. Note that here terms such as 'attacks' and 'identifies' are really also anthropomorphic metaphors to label complex processes and mechanisms that we gloss in human terms.

What actually happens is in effect some chemistry – there is nothing deliberate about what the cancer cells or the immune cells are doing. Tumours that grow quickly are described as 'aggressive' ("…causing T cells to become more aggressive") another term that might be understood as an anthropomorphic metaphor, as aggression normally refers to an attitude adopted. The tumour cells are just cells that grow and divide: they have no attitude nor intentions, and do not deliberately harm their host or even deliberately divide to grow the cancer.

When the term 'rejection' was first suggested for use in these contexts it will have been a metaphor itself, a word transplanted [sic] from one context where it was widely used to another novel context. However, the 'transplant took' (rather than being 'rejected'!) and came to be accepted as having a new biological meaning. Such a term is sometimes called a dead metaphor (or a clichéd metaphor) as it has lost its metaphorical status, and become a technical term. Tumours are now literally rejected. And T cells do now become exhausted (and inept). And tumours can now be aggressive.

Within the specialist field, such words now have nuanced technical meanings, related to, but subtly different from, their source words' usage in general language. Experts know that – but lay people may not always realise. Strictly, the words aggressive in 'an aggressive drunk' and 'an aggressive tumour' are homonyms.

Seated checkpoints: quo vardis, friend or foe?

The same is the case with 'checkpoints'. Referring to proteins on the immune cell surface that interact with proteins on tumour cells, the label 'checkpoints' will have been a metaphorical transplant of an existing term (as in border checkpoints, where it is checked that someone's papers are in order for entry to a country); but, now, this is accepted usage.

T cells are able to destroy other cells. However, they have proteins on their surfaces which can bind to proteins on other cells, and when these are bound the T cells do not destroy the other cells. (Do these proteins really "sit on the surface of T cells" – or is sitting an action only available to organisms with certain types of anatomic features – such as buttocks and jointed legs perhaps? So, this is another metaphor, but one that conveys meaning so readily that most listeners will not have noticed it. 6 )

So, immune cells have evolved because they 'protect' the organism from 'foreign' cells, and the checkpoints have evolved because they prevent the immune cells destroying cells from the same individual organism. 5 This works to the extent that the binding of the checkpoints is specific. Tumour cells (which are derived from the individual) can sometimes bind, and so the T cells may be ineffective in destroying them. Immune checkpoint inhibitors can interfere with the mechanism by which tumour cells act on the T cells as 'self' cells – something sometimes referred to as a checkpoint 'blockade' (yet another metaphor) – something represented in the following image:

Figure entitled "Immune checkpoint blockade for T-cell activation" (note the 'exhausted' T cells) (Fig. 2, from Darvin, et al., 2018. Open access under http://creativecommons.org/licenses/by/4.0/). [There is an interesting mix of iconic (cell shapes) and symbolic (e.g., lightning strikes?) signs in the figure.]

The extract of dialogue quoted above suggests that the checkpoints "put the brakes on immune responses". There are of course no actual brakes, so this is again metaphorical. However, we might consider 'putting the brakes' on as having become an English idiom, that is, the term is now widely understood as applying to any situation where a process is brought to a stop, regardless of whether or not there are actual brakes involved. A raise in bank interest rates might be said to be intended to put the brakes on inflation. (Indeed, as my O level economics teacher at North Romford Comp. habitually explained managing the economy in terms of driving a car – which of course we were all too young to legally have experienced – he may well have actually said this.)

Can tumours behave advertently?

At one point Prof. Theodorescu, suggested that "what [the tumours] also did, inadvertently I'm sure, is made themselves a lot more vulnerable to one of the most useful and prevalent therapeutics in cancer today". I am also sure that this effect was inadvertent. Otherwise, the tumour acted advertently, which would mean it behaved deliberately with this outcome in mind.

It clearly would not seem to be in a tumour's interest to make itself more susceptible to therapeutics, but then agents do sometimes behave in ways that seem irrational to others – for example, because of bravado. So, I do not rule out apparently self-destructive behaviour from being deliberate (as I drafted this piece, the news broadcast reports on an apparent coup attempt in Russia, suggesting that a few tens of thousands of men are looking to take over a nation of over 140 million that had been paying them to fight in the illegal invasion of Ukraine). Rather, my reason for being sure this not deliberate, is that I do not think that a tumour is the kind of entity that can behave advertently. 7

So, I do not disagree with Prof. Theodorescu, but I do think that stating that, in this case, the behaviour was inadvertent seems to imply that that a tumour can in some circumstances act deliberately (i.e., anthropomorphism, again). I am sure that was not the intention, but it seems, inadvertently I'm sure, to reflect the tactic of conspicuously stating someone is not guilty of some act as a means of starting a contrary rumour.

So, I would like to make it absolutely clear, without any sense of ambiguity, that, certainly to the very best of my knowledge, there is absolutely no reason to suspect that Prof. Theodorescu falsified his academic credentials using red crayons and recycled cereal packets.

Work cited:
Notes:

1 Any communication of science will inevitably have to assume some background. In teaching, we can use conceptual analysis to break down any topic and identify pre-requisite prior knowledge that will be needed before introducing new information. Science education builds up understanding slowly over many years, 'building on' what learners have already been taught. Anyone asked to give an account or explanation to a general audience has to make an informed judgement of where it is reasonable to start.

2 It might seem that the cells of females are 'Y-negative' as these do not usually contain Y chromosomes. However, from the context (the discussion of loss of, or incomplete, Y-chromosomes) the term is being used to refer to cells with no Y chromosomes that derived ultimately (by imperfect copying) from a cell which did have a Y chromosome. That is, this is a feature of tumours in men.

Although women do not (usually) have Y chromosomes, it is sometimes suggested that the man's Y chromosome can be considered an incomplete X chromosome, so in a sense all men might be considered as incomplete, imperfect women, as some readers might have long suspected.

3 This is not meant as some kind of criticism, but rather an observation on one of the affordances of language in use. It is very useful for the scientist to package up an idea (here, the loss of the Y chromosome from a cell's set of nuclear chromosomes) in a new term or acronym, which can then be put to work as a neologism, thus simplifying sentence structure. The reader then needs to decode this new term in various contexts. That is perfectly reasonable within the genre of research reports (as this only adds minimally to the interpretative load of a specialist reader who is likely to have strong enough background to have capacity to readily make sense of the new term in various contexts). So, in the published paper (Abdel-Hafiz, 2023), we find, inter alia,

  • "…LOY correlates with…"
  • "…naturally occurring LOY mutant bladder cancer cells…"
  • "In ageing men, LOY has been associated with many adverse health consequences."
  • "…cancer cells with LOY…"
  • "…mouse tumours with LOY…"
  • "…human bladder cancer specimens with LOY…"
  • "…LOY is present early in disease progression…"
  • "…the lack of Y chromosome gene expression in the MB49 sublines was due to LOY"
  • "…the important role of these two genes in conferring the LOY phenotype…"
  • "…patients with LOY had a reduced overall survival following surgery…"
  • "…tumours with LOY grew more aggressively…"
  • "…the mechanism of LOY-driven tumour evasion…"

There is even a case of LOY being taken as a sufficiently familiar to be compounded into a further acronym, 'MADLOY':

"we used TCGA DNA sequencing data and mosaic alteration detection for LOY (MADLOY) to detect LOY".

4 Unfortunately, thinking anthropomorphically about viruses, cells, molecules, etc., can become a habit of mind. Students may come to see such anthropomorphisms as having the status of genuine scientific explanations (that they can use in exams, for example). Therefore, care is needed with using anthropomorphism in science teaching (Taber & Watts, 1996).

Read about anthropomorphism and science learning

5 So, we might suggest that

  • 'checkpoints' is a recently deceased metaphor, with its new meaning only familiar in the technical language community of oncologists and cognate specialists, whereas
  • 'sits' is a long dead metaphor as its broader meaning is likely to be understood widely within the natural language community of English speakers.

6 My use of 'because' is not to be read in a teleological sense as

  • immune cells have evolved in order to protect the organism from 'foreign' cells
  • the checkpoints have evolved in order to prevent the immune cells destroying cells form the same individual organism

Rather in the sense of the reason something has evolved is because it has a property that offers an advantage, and so was selected for:

  • immune cells have evolved because they were selected for because they protect the organism from 'foreign' cells
  • the checkpoints have evolved because they were selected for because they prevent the immune cells destroying cells from the same individual organism

7 I am making an 'ontological judgement'. I might say I am doing ontology. In my teaching of graduate students I found some were wary of terms like ontology and epistemology, but actually I would argue that we all 'do ontology' every time we make a judgement about the kind of entity something is (and we do epistemology every time we make a judgement about the likely truth value of some claim).

If you judge that fairies are imaginary or that dinosaurs are extinct, I suggest that you are doing ontology. For that matter, if you judge that fairies and dinosaurs are alive and well, and live at the bottom of your garden, then you are also doing ontology – if perhaps not so well.

Read about ontology

Would you like some rare earths with that?

A chemically illiterate internet meme

Keith S. Taber

The challenge of popular science writing

I often enjoy reading popular accounts of science topics, but sometimes one comes across statements that are vague or dubious or confusing – or simply wrong. Some of this reflects a basic challenge that authors of popular science share with science teachers and other science communicators: scientific ideas are often complex, subtle and abstract. Doing them justice requires detailed text and technical terminology. Understanding them often depends upon already having a good grasp of underpinning concepts. That is fine in a formal report for other scientists, but is not of any value to a non-specialist audience.

So, the author has to simplify, and perhaps round off some of the irregular detail; and to find ways to engage readers by using language and examples that will make sense to them. That is, finding ways to 'make the unfamiliar familiar'.

Read about making the unfamiliar familiar in teaching

I am sure that often the passages in popular science books that I as a scientist 1 get grumpy about are well motivated, and, whilst strictly inaccurate, reflect a compromise between getting the science perfect and making it accessible and engaging for the wider readership. Sometimes, however, one does get the impression that the author has not fully grasped the science they are writing about.

"Lucy Jane Santos is the Executive Secretary of the British Society for the History of Science…"

Public engagement with radium

I very much enjoyed reading a book, 'Half lives', by the historian of science Lucy Jane Santos, about how in the decades after its discovery by Pierre and Marie Curie, radium was the subject of wide public interest and engagement. One of the intriguing observations about this newly discovered element was that it appeared to glow in the dark. We now know that actually the glow comes from nitrogen in the air, as radium is radioactive and emissions by radium 'excite' (into a higher energy state) nitrogen molecules, which then emit visible light as they return ('relax') to their 'ground' state. This production of light without heating (a phenomenon generally called luminescence), when it is due to exposure to radioactivity, is known as radioluminescence.

Today, many people are very wary of radioactivity – with good reason of course – but Santos describes how at one time radium was used (or at least claimed as an ingredient) in all kinds of patent medicines and spa treatments and cosmetics (and even golf balls). This was a fascinating (and sometimes shocking) story.

What substance(s) can you find in quinine?

I did find a few things to quibble over – although across a whole book it was, only, a few. However, one statement that immediately stood out as dodgy science was the claim that quinine contained phospor:

"Quinine contains phosphor, a substance that luminesces when exposed to certain wavelengths of light…"

Santos, 2020

This may seem an unremarkable statement to a lay person, but to a scientist this is nonsensical. Quinine is a chemical compound (of carbon, hydrogen, nitrogen and oxygen), that is – a single substance. A single substance cannot contain another substance – any more than say, a single year can contain other years. An impure sample of a substance will contain other substances (it is in effect a mixture of substances), but quinine itself is, by definition, just quinine.

Molecular structure of the chemical compound quinine (C20H24N2O2) – a pure sample of quinine would contain only (a great many copies of) this molecule.

Note – no phosphorus, and no rare earth metal atoms.

(Image source: Wikimedia)

Confusing terminology

The term 'phosphor' refers to a luminescent material – one that will glow after it has been exposed to radiation (often this will be ultraviolet) or otherwise excited. The term is usually applied to solid materials, such as those used to produce an image in television and monitor screens.

The term derives by reference to the element phosphorus which is a luminescent substance that was accordingly itself given a name meaning 'light-bearing'. The term phosphorescent was used to describe substances that continue to glow for a time after irradiation with electromagnet radiation ceases. But it is now known that phosphorus itself is not phosphorescent, but rather its glow is due to chemiluminescence – there is a chemical reaction between the element and oxygen in the air which leads to light being emitted.

The widely used term phosphor, then, reflects an outdated, historical, description of a property of phosphorus; and does not mean that phosphors contain, or are compounds of, phosphorus. There is clearly some scope for confusion of terms here. 2

termmeaning
luminescencethe emission of light by a cold object (in contrast to incandescence)
– chemiluminescencea form of luminescence due to a chemical reaction
– – bioluminescencea form of chemiluminescence that occurs in living organisms
– electroluminescencea form of luminescence produced by passing electrical current through some materials
– photoluminescencea form of luminescence due to irradiation by electromagnetic radiation, such as ultraviolet
– – fluorescence a type of photoluminescence that only occurs whilst the object is being excited (e.g., by exposure to ultraviolet)
– – phosphorescencea type of photoluminescence that continues for some time after the object has been being excited (e.g., by exposure to ultraviolet)
– radioluminescencea form of luminescence due to a material being exposed to ionising radiation (e.g., 𝛂 radiation)
– sonoluminescencea form of luminescence due to a material being exposed to sound
phosphora material that exhibits luminescence
phosphorusa chemical element that exhibits chemiluminescence (when exposed to air)
There is a range of terms relating to luminescence. Here are some of those terms.

Some central ideas about luminescence (represented on a concept map)
A traditional medicine

Quinine, a substance extracted from the bark of several species of Cinchona, has long been used for medicinal purposes (e.g., by the Quechua people of the Americas 3), as it is a mild antipyretic and analgesic. It is an example of a class of compounds produced by plants known as an alkaloids. Plant alkaloids are bitter, and it is thought their presence deters animals from eating the plant. We might say that Quechua pain medication is a bitter pill to swallow.

Modern science has often adopted and developed technologies that had long been part of the 'traditional ecological knowledge' of indigenous groups – such as making extracts from Cinchona bark to use as medicines.

Sadly, the original discovers and owners of such technologies have not always been properly recognised when such technologies have been acquired, transferred elsewhere, and reported. 3

(Image by GOKALP ISCAN from Pixabay)

Quinine is an ingredient of tonic water (and bitter lemon drink) added because of its bitter taste.

(Why deliberately make a drink bitter? Quinine has anti-malarial properties which made it a useful substance to add to drinks in parts of the world where malaria is endemic. People liked the effect!)

Quinine glows when exposed to ultraviolet light. It is luminescent. To be more specific, quinine is photoluminescent. (This is responsible for the notion that someone offered a gin and tonic at a disco should test it under the 'blacklights' to make sure they have not been given pure gin to drink. Although, I am slightly sceptical about whether the kind of people that drink 'G&T's go to the kind of dances that have ultraviolet lighting.)

"I do apologise, I think I might have just splashed a tiny droplet of my tonic water on you"

(Image by Victoria_Watercolor from Pixabay)

It is reasonable to describe quinine as a phosphor in the wider sense of the term – but it does not contain another phosphor substance, any more than, say, iron contains a metallic substance or sulphur contains a yellow substance or sucrose contains a sweet substance or copper a conducting substance. So, a more accurate formulation would have been

"Quinine [is a] phosphor, a substance that luminesces when exposed to certain wavelengths of light…"

or, perhaps better still, simply

"Quinine [is] a substance that luminesces when exposed to certain wavelengths of light…"

Ask the oracle

I was intrigued at why Lucy Jane Santos might have been confused about this, until I did a quick internet search. Then I found a range of sites that claimed that quinine contains phosphors – indeed, often, rare earths are specified.

The rare earths (another unfortunate historic choice of name, as it transpired that they are neither especially rare nor 'earths', i.e., oxides) are a group of metallic elements. They are not as well known as, say, iron, copper, zinc, aluminium or gold, but they have with a wide range of useful applications.

Scandium, the first of the 'rare earth' metals. Probably not what you want in your tonic water.

(Creative Commons Attribution 3.0 Unported License, sourced from https://images-of-elements.com/scandium.php)

If something is repeated enough, does it become true?

Clearly there are not rare earths in quinine. So, the following quotes (from sites accessed on 7th March 2023) proffer misinformation.

"If you want to get a bit more scientific about it…. quinine contains rare earth compounds called phosphors.  These are the substances which glow when they are hit with particular wavelengths of the EM spectrum, including UV light.  Phosphors absorb UV light and then emit it in their own colour, in this case glowing blue light."

https://www.iceandaslice.co.uk/blogs/news/why-does-your-gin-and-tonic-glow-blue-in-ultraviolet-light

This claim is odd, as the previous paragraph explained more canonically: "why does quinine absorb UV light (the invisible component of sunlight that produces sun tans and sunburns!)? It is due to the structure of the quinine molecule, which enables it to take in energy in the form of invisible UV light and immediately radiate some of that same energy in the form of visible blue light." Other compounds cannot be inside a molecule – so this more canonical explanation is not consistent with quinine containing other "substances" which were "rare earth compounds."

"Quinine contains rare earth compounds called phosphors. These substances glow when they are hit with particular wavelengths of the EM spectrum, including UV light. Phosphors absorb UV light and then emit it in their own color [sic, colour]. Thus, the black light's UV radiation is absorbed by the phosphors in the quinine, and then emitted again in the form of glowing blue light."

https://sciencing.com/quinine-fluorescent-5344077.html

The following extract appeared under the subheading "Why is quinine fluorescence?" That reflects a category error as quinine is a substance and fluorescence is a process (and fluorescent the property) – so, presumably this should have read why is quinine fluorescent?

Why Quinine Glows

Quinine contains rare earth compounds called phosphors. … Phosphors absorb UV light and then emit it in their own color [sic, colour]. Thus, the black light's UV radiation is absorbed by the phosphors in the quinine, and then emitted again in the form of glowing blue light.

https://allfamousbirthday.com/faqs/does-tonic-water-make-things-glow-in-the-dark/

"Want to know one more fun fact about quinine? It glows.
Rare Earth compounds called phosphors in quinine glow under certain circumstances."

https://www.mixlycocktailco.com/blogs/news/does-tonic-water-go-bad

Why Does Tonic Water Glow Under UV Rays?

Tonic water glows and [sic] will fluoresce under UV rays because of quinine in it. Quinine is one of the most important alkaloids found in the cinchona bark, among many others. It has some rare earth compounds known as phosphors that glow when they hit certain wavelengths of the UV light. Phosphors in the quinine absorb the UV light and then reflect it or emit it again in the form of glowing blue light.

https://www.sawanonlinebookstore.com/why-does-tonic-water-glow-under-uv-rays/

Making magic mud – or not

Perhaps the most bizarre example was a site, 'emaze' which offered to show me "How to create magic mud…in 17 easy steps"

Step 1 was

"wash your potatoes!!!!"

However, perhaps due to exclamation fatigue(!), this went in a different, if now familiar, direction with step 2:

"Quinine contains rare earth compounds called phosphors. These substances glow when they are hit with particular wavelengths of the EM spectrum, including UV light. Phosphors absorb UV light and then emit it in their own color [sic, colour]. Thus, the black light's UV radiation is absorbed by the phosphors in the quinine, and then emitted again in the form of glowing blue light"

https://app.emaze.com/@AORQCIII#/16

This text was then repeated as each of steps 3-14. (Sadly steps 15-17 seemed to have been missed or lost. Or, perhaps not so sadly if they were just further repeats.) The first screen suggests this presentation was "done by Dr. Meena & Maha" but if Dr. Meena & Maha really exist (if you do, I am sorry, the internet makes me very sceptical) and 'done this', it is not clear if they got bored with their task very quickly, or whether the server managed to corrupt a much more coherent presentation when it was uploaded to the site.

This 'emaze' presentation seems to want to emphasise how quinine contains rare earth compounds…

According to Google, the site 'Course Hero' suggested

"Phosphors, which are found in quinine, are rare earth compounds. These chemicals glow when they are struck with particular wavelengths of the EM spectrum, …"

https://www.coursehero.com › Chemistry › 44733249–I…

but unfortunately (or perhaps fortunately given that snippet), the rest of the text seemed to be behind a pay-wall. This did not offer a strong incitement to pay for material on the site.

Toys coated with phosphorus?

Another website I came across was for a shop which claimed to be selling glow-in-the-dark objects that were made with phosoporus that needed to be illuminated to initiate a glow: a claim which seems not only scientifically incorrect (as mentioned above, phosphorus is not photoluminescent – it glows when in contact with air as it oxidises), and so unlikely; but, otherwise, dangerous and, surely, illegal.

Read about unscientific luminous creations

Defining scientific terms – badly

During my search, I came across a website (grammarist.com) offering to explain the difference between the words phosphorous and phosphorus. It did not discuss rare earths, but informed readers that

"Phosphate: Noun that means an electrically charged particle.
Phosphorus: Also a noun that means a mineral found in phosphate."
…We've already established that phosphorus is the simple mineral found in the particle phosphate, but phosphor is something else altogether."

https://grammarist.com/spelling/phosphorous-phosphorus/

So, that's 'no', 'no', 'no', and…I think at least one more 'no'.

Phosphorus is a reactive element, and is not found in nature as a mineral. To a scientist, a mineral is a material found in nature – as a component of rocks. Unfortunately, in discussing diet, the term minerals is often associated with elements, such as, for example, phosphorus, iodine, potassium and iron that are necessary for good health. However, one would not eat the element iron, but rather some compound of it. (Foods naturally contain iron compounds). And trying to eat phosphorus, iodine or potassium (rather than compounds of them) would be very hazardous.

So, whilst a nutritional supplement might well contain some minerals in the composition, strictly they are there as compounds that will provide a source of biologically important elements, and they will be metabolised into other compounds of those elements. (Iron from iron compounds will, for example, be used in synthesising the haem incorporated into red blood cells.) Unfortunately, learners commonly have alternative conceptions ('misconceptions') about the difference between mixtures and compounds and assume a compound maintains the properties of its 'constituent' elements (Taber, 1996).

"Compound is one or more elements mixed together"

alternative conception elicited from an Advance level chemisty student

The grammarist.com entry helpfully warned us that phosphate was "not to be confused with phosphoric acid, a chemical compound found in detergents and fertilizers". I suspect it is only found in detergents and fertilisers when something has gone wrong with the production process (notwithstanding diluted phosphoric acid has been used directly as a fertiliser) 4. It is a corrosive and irritant substance that can cause bronchitis – although tiny amounts are added to some colas. [n.b., cocaine also once featured in some cola, but that is no longer allowed.]

  • An ion is an electrically charged particle
  • The phosphate ion is one example of a type of ion.
  • Phosphates (such as calcium phosphate) are substances that contain phosphate ions.

So, phosphates contain electrically charged particles (phosphate ions), but that does not make phosphate an electrically charged particle, just as

  • blue does not mean a large marine mammal
  • bank does not mean a day of celebration where people do not need to go to work
  • vice does not mean a senior executive officer
  • motor does not mean a two wheeled vehicle
  • compact does not mean a flat circular object
  • final does not mean a simple musical instrument played with the breath
  • free does not mean a meal taken around noon or soon after, and
  • meal does not mean a token that provides entry or service

Grammarist invited feedback: I sent it some, so hopefully by the time you read this, the entry will have been changed.

It was on the internet: it must be true

The internet is an immense and powerful tool giving access to the vast resources of the World Wide Web. Unfortunately, the downside of a shared, democratic, free to access, reservoir of human knowledge is that there is no quality control. There is a lot of really good material on the web: but there is also a lot of nonsense on the web.

One example I have referred to before is the statement:

"energy is conserved in chemical reactions so can therefore be neither created nor destroyed"

This has the form of a logical structure

X so therefore Y

which is equivalent to

Y because X:

"energy can be neither created nor destroyed because it is conserved in chemical reactions"

This is just nonsense. There is no logical reason why the conservation of energy in chemical reactions implies a general principle of energy conservation.

We can deduce the specific from the general (days have 24 hours, so Sunday has 24 hours) but not the general from the specific (January has 31 days, so months have 31 days).

Perhaps this is easily missed by people who already know that energy is always conserved.

A parallel structure might be:

"association football teams always consist of eleven players so therefore sports teams always consist of eleven players"

"sports teams always consist of eleven players because association football teams always consist of eleven players"

This is 'obviously' wrong because we know that rugby teams and netball teams and volleyball teams and water polo teams (for example) do not consist of eleven players.

Yet, if you search for "energy can be neither created nor destroyed because it is conserved in chemical reactions", you will find that this claim is included on the public websites of many schools (Taber, 2020). That is because, despite being wrong, it has authority – it is included in the English National Curriculum for Science (which I find shocking – we all make mistakes, but did nobody check the document before publication?) The English government department responsible was made aware of the error but does not think that it is a priority to make corrections to the curriculum.

Artificial (ignorant) intelligence

But what about quinine containing rare earth compounds? A notion that is structurally similar to claiming that

  • France contains South American countries, or
  • 'Great Expectations' contains Jane Austin novels, or
  • February contains Autumn months, or
  • Cauliflower contains citrus fruits, or
  • Beethoven's 5th Symphony contains Haydn concerti

(in other words, something obviously silly to someone who has a basic understanding of the domain – chemistry or geography or literature or the calender or botany/horticulture or music – because it suggest one basic unit contains other units of similar status).

How does this error appear so often? Quite likely, a lot of website now are populated with material collected and collated by machines from other websites. If so, it only takes one human being (or government department) to publish something incorrect, and in time it is likely to start appearing in various places on the web.

There is currently a lot of talk of how artificial intelligence (AI) is getting better at writing essays, and answering questions, and even drafting lectures for busy academics. AI seemingly has great potential where it is provided with high quality feedback. Perhaps, but where the AI is based on finding patterns in publicly available texts, and has no real ability to check sense, then I wonder if the www is only going to become more and more polluted with misinformation and nonsense.

I do not know where Lucy Jane Santos got the idea that there are other substances in the single substance quinine (akin to having other countries in France), but if she did a web-search and relied on what she read, then I am in no position to be critical. I use the web to find things out and check things all the time. I am likely to spot gross errors in fields where I already have a strong background…but outside of that? I do seek to evaluate the likely authority of sources – but that does not mean I could not be taken in by a site which looked professional and authoritative.

The web started with imperfect people (because we all are) posting all kinds of material – with all kinds of motivations. I expect most of it was well-meaning, and usually represented something the poster actually believed; and indeed much of it was valid. However, a 'bot' can search, copy, and paste far quicker than a person, and if the internet is increasingly authored by programs that are indiscriminately copying bits and pieces from elsewhere to collage new copy to attract readers to advertising, then one cannot help wonder if the proportion of web-pages that cannot be trusted will be incrementally coming to dominate the whole network.

I (a fallible, but natural intelligence) hope not, but I am not very optimistic.

Work cited:

Notes:

1 Although my own research has been in science education and not one of the natural sciences, I am pleased that the learned societies (e.g. the Institute of Physics, the Royal Society of Chemistry, etc.) and the UK's Science Council, recognise the work of science educators as professional contributions to science.

2 One internet site suggests:

Luminescence is caused by various things like electric current, chemical reactions, nuclear radiation, electromagnetic radiation, etc. But phosphorescence takes place after a sample is irradiated with light.

• Phosphorescence remains for sometime even after the lighting source is removed. But luminescence is not so.

https://www.differencebetween.com/difference-between-luminescence-and-vs-phosphorescence/

The second paragraph is nonsensical since phosphorescence is a type of luminescence. (It should be, "…fluorescence" that does not.) The first paragraph seems reasonable except that the 'but' seems misplaced. However 'in the light of' the second sentence (which sees phosphorescence and luminescence as contrary) it seems that the (contrasting) 'but' was intended, and whoever wrote this did not realise that light is a form of electromagnetic radiation.

Another, more technical, site suggests,

Luminescence is the emission of light by a substance as a result of a chemical reaction (chemiluminescence) or an enzymatic reaction (bioluminescence).

https://www.moleculardevices.com/technology/luminescence

Here again a contrast is set up:

  • chemiluminescence (due to a chemical reaction) versus
  • bioluminescence (due to an enzymatic reaction).

However, the keen-eyed will have spotted that "an enzymatic reaction" is simply a chemical reaction catalysed by an enzyme. So, bioluminescence is a subtype of chemiluminescence, not something distinct.

3 Some sources claim that the medicinal properties of cinchona bark were discovered by Jesuit missionaries that travelled to South America as part of European imperial expansion there.

Nataly Allasi Canales of the Natural History Museum of Denmark, University of Copenhagen is reported as explaining that actually,

"Quinine was already known to the Quechua, the Cañari and the Chimú indigenous peoples that inhabited modern-day Peru, Bolivia and Ecuador before the arrival of the Spanish…They were the ones that introduced the bark to Spanish Jesuits."

https://www.bbc.com/travel/article/20200527-the-tree-that-changed-the-world-map

Learning about the history of indigenous technologies can be complicated because:

  • often they are transmitted by an oral and practice culture (rather than written accounts);
  • traditional practices may be disrupted (or even suppressed) by colonisation by external invaders; and
  • European colonisers, naturalists and other travellers, often did not think their indigenous informants 'counted', and rather considered (or at least treated) what they were shown as their own discoveries.

4 This again seems to reflect the common alternative conception that confuses mixtures and compounds (Taber, 1996): phosphoric acid is used in reactions to produce fertilizers and detergents, but having reacted is no longer present. It is a starting material, but not an ingredient of the final product.

Just as we do not eat iron and phosphorus, we do not use washing powders that contain phosphoric acid, even if they have been prepared with it. (Increasingly, phosphates are being replaced in detergents because of their polluting effects on surface water such as rivers and lakes.)

5 This gives the impression to me that the Department of Education sees schooling as little more than a game where students perform and are tested on learning whatever is presented to them, rather than being about learning what is worth knowing. There is surely no value in learning a logically flawed claim. Any student who understands the ideas will appreciate this statement is incorrect, but perhaps the English Government prefers testing for recall of rote learning rather than looking for critical engagement?

Unscientific luminous creations

Q: Which form of phosphorus both glows and is non toxic?

Keith S. Taber

I have just sent of an email to a company claiming to be selling glow-in-the-dark products containing non-toxic phosphorus…

The site offers answers to a range of questions, but unfortunately gets a lot wrong

Dear Pete's Luminous Creations

I am writing to raise concern about misleading information on your website, specifically some of the claims made on the page:

(accessed today, 18th March 2023).

This page contains a number of scientifically incorrect statements, but I am most concerned about your misleading characterisation of phosphorus as a 'safe' material.

Scientific errors

Your site claims that

  • "phosphorus…has the ability to absorb and store surrounding light"
  • "the ability to absorb and store surrounding light…works similar to the natural process of photosynthesis"
  • "Phosphorus glow absorbs and stores surrounding light. When it is dark, the stored light is slowly released in the form of a glow"
  • "Glow in the Dark products contain phosphorus…it needs to be exposed to light before it can work"
  • "Radium glow produces light on its own through a chemical process."

All of these claims are mistaken.

1. Luminescent materials do not store light. Light cannot be stored, it is a form of electromagnetic radiation. (In LASERS light is contained within a cavity by reflecting it back and forth by mirrors, but phosphorus is not able to do anything like this.) When the radiation is absorbed by a photoluminescent material the radiation ceases to exist. Because the molecules of the absorbing material are excited into a higher energy state, new electromagnetic radiation (light) may later be emitted – but it is not light that has been stored. (The energy transferred to the luminescent material by the radiation may be considered as stored: but not the light).

2. The process of photosynthesis does not involve "the ability to absorb and store surrounding light" – absorb, yes, but the light is not stored – it ceases to exist once absorbed.

3. Materials which absorb energy from radiation, and then release it slowly ('glow') are called phosphorescent. This does not (only) occur 'when it is dark', but from immediately after irradiation. (The process occurs regardless of whether it is dark enough to observe.)

4. Phosphorus is not itself a phosphorescent material. The glow seen around white phosphorus is due to a chemical reaction with oxygen in the air. Not only does this not store any light, but, also, it does not need light to initiate.

5. Radium does NOT produce light through a chemical process. Radium is radioactive. It undergoes radioactive decay (due to a change in the atomic nucleus). This is NOT considered a chemical process.

Now I turn to what I consider a more serous problem with your site.

Potentially dangerous misinformation

The more serious matter concerns your claim that to be selling products containing 'non toxic' phosphorus:

  • "Glow in the Dark products contain phosphorus (a non toxic substance) which has the ability to absorb and store surrounding light…"
  • "Phosphorus is non toxic and safe for general use."
  • "Phosphorus is a natural mineral found in the human body. Phosphorus Glow in the dark products is perfectly safe for everyday use"
  • "Many get confused and associate all green glow products to be radioactive. This is not true. Phosphorus glow is non toxic and non radioactive."

You may wonder why I think this matters enough to contact you.

It is very misleading to suggest to people reading the site (which could include children who might well be interested in glow-in-the-dark toys) that phosphorus is harmless, and this is completely wrong.

Phosphorus is not found as a natural mineral, as it is much too reactive to be found native (that is, as phosphorus) on earth – although many minerals are compounds of phosphorus (and thus do NOT share its chemical properties), and so sources of the element for use in agriculture etc. The human body does contain compounds of phosphorus, notably in the bones, but again there is no phosphorus (the substance phosphorus) in the human body – if you introduced some it would very quickly react. Sources of phosphorus are important in the diet, but it would be very unwise to try to eat phosphorus itself.

Phosphorus can be obtained in different forms (this is called allotropy where the same element can have different molecular structures – like graphite and diamond both being pure forms – allotropes -of carbon). Some allotropes of phosphorus are not especially dangerous. However, the form which glows is white (or yellow) phosphorus, and this is a very hazardous material.

So, handling phosphorus is dangerous and needs special precautions. (If you really did use phosphorus in your products, I imagine you would know that?) Here is some information from authoritative websites

"Ingestion of elemental white or yellow phosphorus typically causes severe vomiting and diarrhea [diarrhoea], which are both described as "smoking," "luminescent," and having a garlic-like odor. Other signs and symptoms of severe poisoning might include dysrhythmias, coma, hypotension, and death. Contact with skin might cause severe burns within minutes to hours…"

US Centres for Disease Control

"White phosphorus is extremely toxic to humans, while other forms of phosphorus are much less toxic. Acute (short-term) oral exposure to high levels of white phosphorus in humans is characterised by three stages: the first stage consists of gastrointestinal effects; the second stage is symptom-free and lasts about two days; the third stage consists of a rapid decline in condition with gastrointestinal effects, plus severe effects on the kidneys, liver, cardiovascular system, and central nervous system (CNS). Inhalation exposure has resulted in respiratory tract irritation and coughing in humans. Chronic (long-term) exposure to white phosphorus in humans results in necrosis of the jaw, termed "phossy jaw."

US Environmental Protection Agency

Please feel free to check on this information for yourself.

However, I recommend you change the information on your website. In particular, please stop suggesting that phosphorus is a safe, non-toxic material, when the form of phosphorus which glows is highly toxic. I trust that now this has been brought to your attention, you will appreciate that it would be highly irresponsible for you to continue to advertise your products using misleading information about a hazardous substance.

Best wishes

Keith

Batteries – what are they good for?

Okay, 'energy storage' – but what else are they good for?

Keith S. Taber

I was struck by an item on the BBC Radio 4 news headlines at 09.00 this morning (27th Feb. 2023):

"The collapsed battery maker Britishvolt which went into administration last month has been bought by an Australian company.
The new owners will focus initially on batteries for energy storage rather than electric vehicles."

BBC Radio 4 news item

Now on reflection, this was an ambiguous statement. I heard it as

"The new owners will focus initially on batteries for

  • energy storage, rather than
  • electric vehicles."

Which immediately provoked in my mind the question what batteries might be used for in electric vehicles – if not 'energy storage'?

It is possible to charge up an electric car because it includes a battery
(Image by Sabine Kroschel from Pixabay)

Conceptions of energy

Now, this whole area is, metaphorically, a bit of a linguistic minefield as when people say batteries they do not usually distinguish between an individual cell and a battery (of cells). Traditional electrochemical cells we are familiar with have a specific and usually modest e.m.f. – 1.5V or 1.2 V for example. The old 6V and 9V batteries that used to be commonly sold for many purposes (before the switch to most appliances having internal batteries) would be batteries of cells connected in series to work together to provide (1.5V + 1.5V + 1.5V + 1.5V = ) 6V (or whatever). Car batteries were traditionally batteries of lead-acid cells connected together. If each cell has an e.m.f. of 2V, then a dozen connected in series (i.e., the battery) offers 24V.

Moreover, energy is a highly abstract idea, such that even physics teachers do not always agree on how to describe it – the model of energy coming in a number of flavours, 'forms', and processes involving transformations in the form of the energy (e.g., a filament lamp converts electrical energy into heat energy) that many of us learnt (and some of us taught) has come to be seen as misleading and unhelpful by some (it not all) educators. Oh, and if you think I made a mistake there and forget that a lamp produces light energy – not at all. In the 'forms of energy' typology, heat is energy transferred due to a difference in temperature – so that covers all the radiation being emitted by the hot filament.

No wonder, that energy is a common topic for student alternative conceptions, as energy permeates (so to speak) all areas of science, but is a highly abstract notion.

Read about conceptions of energy

An alternative hearing?

Yet, I realised that the statement I had heard was ambiguous and could be parsed differently. It perhaps meant

"The new owners will focus initially on

  • batteries for energy storage

rather than

  • electric vehicles."

That is, I was putting my imaginary brackets in the wrong place and perhaps the company had previously intended to build complete electric cars and not just the batteries? If so, the news was not

  • The new owners will focus initially on batteries (for energy storage rather than electric vehicles).

but rather that

  • The new owners will focus initially on (batteries for energy storage) rather than (electric vehicles).

If this was the intention, it might have been better to have assumed listeners would know that batteries were used for 'energy storage', and to have simplified the statement to

"The new owners will focus initially on batteries rather than electric vehicles."

Batteries for under-performing sports cars?

That made more sense, as surely the BBC's news journalists do not think electric batteries in cars are used for something other than 'energy storage'. So, I checked on the BBC news website, where I found

"The company intends to start by focusing on batteries for energy storage and hopes to have those products available by the end of 2025.

It then intends to produce batteries for high-performance sports cars."

https://www.bbc.co.uk/news/business-64754879

So, I did not misinterpret the news item. According to the BBC (and to be fair, they are probably just reporting, albeit uncritically, what they have been told) under its new owners Britishvolt will

  • first work on batteries that can be used for energy storage, and
  • then shift attention to batteries for sports cars.

My best guess is that "batteries for energy storage" is shorthand for large scale devices for long term storage (that could, for example, be charged by wind generators when it is windy, and then later fed into the National Grid at times of high power demand). The characteristics of these devices would surely be different in detail from batteries used in electric vehicles.

However, I am pretty sure that "batteries for high-performance sports cars" also need to provide 'energy storage' or else those cars are not going to offer the kind of performance Britishvolt and the car manufacturers they will supply are looking for. After all, besides 'energy storage', what else are batteries actually good for?

Another late night writing copy in the newsroom?
(Image by mohamed_hassan from Pixabay)

Balls to Nature

Making the unfamiliar familiar – with everyday spheres


Keith S. Taber

Even scientists reporting their work in top research journals are not above using comparisons with everyday analogues to explain their ideas.

An analogue for a molecular structure?

(Image by Eduardo Ponce de Leon from Pixabay)

One of the phrases I return to a good deal on these pages is 'making the unfamiliar familiar' because a large part of science teaching is indeed about introducing scientific concepts that are currently unfamiliar to learners (oxidising agents, the endoplasmic reticulum, moments of inertia…the list is extensive!), so they become familiar to learners.

So, teachers use analogies, metaphors, narratives, images, models, and so forth, to help link something new (and often abstract) to whatever 'interpretive resources' the teacher thinks the learners have available to make sense of what is still novel to them.

Read about key ideas for constructivist teaching

This process can certainly go wrong – learners can confuse what is meant as a kind of stepping stone towards a scientific concept (e.g., a teaching analogy, or a simplified model) for the concept itself. So, as just one example, dot and cross figures showing electron transfer between atoms that are sometimes employed to help introduce the idea of ionic bonding come to be confused with ionic bonding itself – so that learners come to wrongly assume electron transfer is a necessary part of ionic bond formation – or, worse, that ionic bonding is electron transfer (e.g., Taber, 1994).

The familiarisation devices used in teaching, then, could be seen as a kind of 'dumbing down' as they work with the familiar and concrete or easily visualised or represented, and fall short of the scientific account. Yet, this approach may be necessary to produce meaningful learning (rather than rote learning that is not understood, and is soon forgotten or becomes confused).

Scientists need to make the unfamiliar familiar

So, it is worth pointing out that scientists themselves, not just science teachers and journalists, often appreciate the need to introduce new ideas in terms their readers can imagine and make sense of. I have noted lots of examples from such contexts on this site. 1 Now this happens a lot in 'popular' science communication, when a scientist is writing for a general audience or being interviewed by a journalist.

Read about science in public discourse and the media

But it also happens when scientists are primarily addressing their peers in the scientific research community. One of my favourite examples is the liquid drop model of the nucleus.

The atomic nucleus is like a drop of liquid because…

Lise Meitner had been working with Otto Hahn and Fritz Strassmann in the Kaiser Wilhelm Gesellschaft in Berlin, Germany, where they were investigating properties of radioactive elements. It was known some heavy elements would decay through processes such as alpha decay, which leads to an element with an atomic number two less than the starting material. 2 Their laboratory results, however, suggested that bombarding uranium with neutrons would directly lead to elements much less massive than the uranium.

Lise Meitner in the laboratory (with Otto Hahn) [Hahn and Meitner in Emil Fischer's Chemistry Institute in Berlin, 1909 – source: https://commons.wikimedia.org/wiki/File:Hahn_and_Meitner_in_1912.jpg]

By the time these results were available, Meitner had left Germany for her own safety. She would have been subject to persecution by the Nazis – quite likely she would have been removed from her scientific work, and then later sent to one of the concentration camps before being murdered as part of the genocide carried out against people the Nazis identified as Jews. 3

Hahn and Strassmann sent Meitner their findings – which did not make sense in terms of the nuclear processes known at the time. With her nephew, Otto Robert Frisch, Meitner decided the results provided evidence of a new phenomenon based on a previously unexpected mechanism of nuclear decay – fission. Nuclear fission was the splitting of a heavy nucleus into two smaller nuclei of roughly similar mass (where alpha decay produced a daughter nearly as heavy along with the very light helium nucleus).

Meitner and Frisch explained this by suggesting a new model or analogy for the nucleus:

"On account of their close packing and strong energy exchange, the particles in a heavy nucleus would be expected to move in a collective way which has some resemblance to the movement of a liquid drop. If the movement is made sufficiently violent by adding energy, such a drop may divide itself into two smaller drops."

Meitner & Frisch, 1939

This was published in the top scientific journal, Nature – but this was no barrier to the scientists using an everyday, familiar, analogy to explain their ideas.

An energetic liquid drop may fission
(Image by Gerhard Bögner from Pixabay)
Chemistry and the beautiful game?

A much later example appeared in the same journal when Kroto and colleagues published their paper about the newly reported allotrope of carbon (alongside graphite and diamond) with formula C60 by including a photograph in their article. A photograph of…an ordinary football!

They used the football to explain the suggested molecular geometry of C60, which they referred to as buckinsterfullerene,

"Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1."

Kroto, et al., 1985

A football (notice the panels are hexagons and pentagons 4). (Image by NoName_13 from Pixabay)

Kroto and colleagues submitted a photograph like this to be published as a figure in their scientific report of the discovery of the buckminsterfullerene allotrope of carbon

What could be more familiar to people than the kind of ball used in Association Football ('soccer')? (Even if this is not really a truncated icosahedron 4). Their figure 1 showed,

"A football (in the United States, a soccerball) on Texas grass. The C60 molecule featured in this letter is suggested to have the truncated icosahedral structure formed by replacing each vertex on the seams of such a ball by a carbon atom."

Kroto, et al., 1985

The scientists explained they had come across the suggested shape when searching for a viable molecular structure that fitted the formula (sixty carbon atoms and nothing else) and which would also satisfy the need for carbon to be tetravalent. They investigated the works of the designer/architect Richard Buckminster Fuller, famous for his geodesic domes.

A stamp commemorating the life and works of Richard Buckminster Fuller and representing geodesic domes.

Thus they provisionally called the new substance buckinsterfullerene, albeit they acknowledged this name might be something of a 'mouthful', so to speak,

"We are disturbed at the number of letters and syllables in the rather fanciful but highly appropriate name we have chosen in the title [of their paper] to refer to this C60 species. For such a unique and centrally important molecular structure, a more concise name would be useful. A number of alternatives come to mind (for example, ballene, spherene, soccerene, carbosoccer), but we prefer to let this issue of nomenclature be settled by consensus."

Kroto, et al., 1985

We now know that the term 'buckyballs' has become popular, but only as a shorthand for the mooted name: buckinsterfullerene. (Later other allotropic form of carbon based on closed shell structures were discovered – e.g., C70. The shorter term fullerenes refers to this group of allotropes: buckminsterfullerene is one of the fullerenes.)

I recall seeing a recording of an interview with Harry Kroto where he suggested that the identification of the structure with the shape of a football came during a transatlantic phone call. What I would love to know is whether Kroto and his co-authors were being somewhat mischievous when they decided to illustrate the idea by asking the world's most famous science journal to publish a figure that was not some abstract scientific representation, but just a photograph of a football. Whether or not they were expecting kick-back [sorry] from the journal's peer reviewers and editor, it did not act as an impediment to Curl, Kroto and Smalley being awarded the 1996 Nobel prize for chemistry "for their discovery of fullerenes" (https://www.nobelprize.org/prizes/chemistry/1996/summary/).

Work cited:
  • Kroto, H., Heath, J., O'Brien, S., Curl, R. F. & Smalley, R. E. (1985) C60: Buckminsterfullerene. Nature, 318, 162-163. https://doi.org/10.1038/318162a0
  • Meitner, L., Frisch, O.R. (1939) Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction. Nature, 143, 239-240. https://doi.org/10.1038/143239a0
  • Taber, K. S. (1994) Misunderstanding the ionic bond, Education in Chemistry, 31 (4), pp.100-103.

Notes:

1 There is a range of tactics that can be used to help communicate science. Generally, to the extent these make abstract ideas accessible, they are presentations that fall short of the scientific account – and so they are best seen as transitional devices to offer intermediate understandings that will be further developed.

I have included on the site a range of examples I have come across of some of the ways in which science is taught and communicated through analogies, metaphors and so forth. Anthropomorphism is when non-human objects are discussed as if having human feelings intentions and so forth.

Read about science analogies

Read about science metaphors

Read about science similes

Read about anthropomorphism in science discourse

Scientific certainty in the media

Personification in science

2 The radioactive decay of unstable but naturally occurring uranium and thorium takes place by a series of nuclear processes, each producing another radioactive species, till a final step produces an isotope which can be considered stable – 206Pb (from decay of 238U), 207Pb (from decay of 235U) or 208Pb (from decay of 232Th). By a pure coincidence of language (a homograph), in English, these radioactive decay cascades lead to lead (Pb).

3 That is not to say most of those murdered because they were Jewish would not have self-identified as such, but rather that the Third Reich had its own racist criteria (established by law in 1935) for deciding who should be considered a Jew based on unscientific notions of bloodlines – so, for example, being a committed and practising Christian was no protection if the Nazis decided you were from a Jewish family.

(Nazi thinking also drew on a very influential but dangerous medical analogy of the volk (people) as a body that allowed those not considered to belong to the body to be seen as akin to foreign microbes that could cause disease unless eliminated.)

4 Of course a football is not a truncated icosahedron – it is intended to be, as far as possible, spherical! The pentagons and hexagons are made of a flexible material, and within them is a 'bladder' (nowadays this is just a metaphor!) which is an elastic sphere that when inflated presses against the outer layers.

If a football was built using completely rigid panels, then it would be a truncated icosahedron. However, such a 'ball' would not roll very well, and would likely cause some nasty head injuries. Presumably the authors were well aware of this, and assumed their readers would see past the problem with this example and spontaneously think of some kind of idealised, if far from ideal, football.

How to avoid birds of prey

…by taking refuge in the neutral zone

Keith S. Taber

Fact is said to be stranger than (science) fiction

Regular viewers of Star Trek may be under the impression that it is dangerous to enter the neutral zone between the territories claimed by the United Federation of Planets and that of the Romulan Empire in case any incursion results in an attack by a Romulan Bird of Prey.

A bird of prey (with its prey?)
(Image by Thomas Marrone, used by permission – full-size version at the source site here)

However, back here on earth, it may be that entering the neutral zone is actually a way of avoiding an attack by a bird of prey

A bird of prey (with its prey). Run rabbit, run rabbit…into the neutral zone
(Image by Ralph from Pixabay)

At least, according to the biologist Jakob von Uexküll

"All the more remarkable is the observation that a neutral zone insinuates itself between the nest and the hunting ground of many raptors, a zone in which they seize no prey at all. Ornithologists must be correct in their assumption that this organisation of the environment was made by Nature in order to keep the raptors from seizing their own young. If, as they say, the nestling becomes a branchling and spends its days hopping from branch to branch near the parental nest, it would easily be in danger of being seized by mistake by its own parents. In this way, it can spend its days free of danger in the neutral zone of the protected area. The protected area is sought out by many songbirds as a nesting and incubation site where they can raise their young free of danger under the protection of the big predator."

Uexküll, 1934/2010

This is a very vivid presentation, but is phrased in a manner I thought deserved a little interrogation. It should, however, be pointed out that this extract is from the English edition of a book translated from the original German text (which itself was originally published almost a century ago).

A text with two authors?

Translation is a process of converting a text from one natural language to another, but every language is somewhat unique regarding its range of words and word meanings. That is, words that are often considered equivalent in different language may have somewhat different ranges of application in those languages, and different nuances. Sometimes there is no precise translation for a word, and a single word in one language may have several near-equivalents in another (Taber, 2018). Translation therefore involves interpretation and creative choices.

So, translation is a skilled art form, and not simply something that can be done well by algorithmically applying suggestions in a bilingual dictionary. A good translation of an academic text not only requires someone fluent in both languages, but also someone having a sufficient understanding of the topic to translate in the best way to convey the intended meaning rather than simply using the most directly equivalent words. A sequence of the most equivalent individual words may not give the best translation of a sentence, and indeed when translating idioms may lead to a translation with no obvious meaning in the target language. It is worth bearing in mind that any translated text has (in effect) two authors, and reflects choices made by the translator as well as the original author.

Read about the challenges of translation in research writing

I am certainly not suggesting there is anything wrong with the translation of Uexküll's text, but it should be born in mind I am commenting on the English language version of the text.

A neutral zone insinuates itself

No it does not.

The language here is surely metaphorical, as it implies a deliberate action by the neutral zone. This seems to anthropomorphise the zone as if it is a human-like actor.

Read about anthropomorphism

The zone is a space. Moreover, it is not a space that is in any way discontinuous with the other space surrounding it – it is a human conception of a region of space with imagined boundaries. The zone is not a sentient agent, so it can not insinuate itself.

Ornithologists must be correct

Science develops theoretical knowledge which is tested against empirical evidence, but is always (strictly) provisional in that it should be open to revisiting in the light of further evidence. Claims made in scientific discourse should therefore be suitable tentative. Perhaps

  • ornithologists seem to be correct in suggesting…, or
  • it seems likely that ornithologists were correct when they suggested…or even
  • at present our best understanding reflects the suggestions made by ornithologists that...

Yet a statement that ornithologists must be correct implies a level of certainty and absoluteness that seems inconsistent with a scientific claim.

Read about certainty in accounts of science

The environment was made by Nature in order to…

This phrasing seems to personify Nature as if 'she' is a person. Moreover, this (…in order to…) suggests a purpose in nature. This kind of teleological claim is often considered inappropriate in science as it suggests natural events occur according to some pre-existing plan rather than unfolding according to natural laws. 1 If we consider something happens to achieve a purpose we seem to not need to look for a mechanism in terms of (for example) forces (or entropy or natural selection or…).

Read about personification of nature

Read about teleology in science

Being seized by mistake

We can understand that it would decrease the biological fitness of a raptor to indiscriminately treat its own offspring as potential food. There are situations when animals do eat their young, but clearly any species that's members committed considerable resources to raising a small number of young (e.g., nest building, egg incubation) but were also regular consumers of those young would be at a disadvantage when it came to its long-term survival.

So, in terms of what increases a species' fitness, avoiding eating your own children would help. If seeking a good 'strategy' to have descendants, then, eating offspring would be a 'mistake'. But the scientific account is not that species, or individual members of a species, seek to deliberately adopt a strategy to have generations of descendants: rather behaviour that tends to lead to descendants is self-selecting.

Just because humans can reflect upon 'our children's children's, children', we cannot assume that other species even have the vaguest notions of descendants. (And the state of the world – pollution, deforestation, habitat destruction, nuclear arsenals, soil degradation, unsustainable use of resources, etcetera – strongly suggests that even humans who can conceptualise and potentially care about their descendants have real trouble making that the basis for rational action.)

Even members of the very rare species capable of conceptualising a future for their offspring struggle to develop strategies taking the well-being of future generations into account.
(Image: cover art for 'To our children's children's children' {The Moody Blues}).

Natural selection is sometimes seen as merely a tautology as it seems to be a theory that explains the flourishing of some species (and not others) in terms that they have the qualities to flourish! But this is to examine the wrong level of explanation. Natural selection explains in general terms why it is that in a particular environment competing species will tend to survive and leave offspring to different extents. (Then within that general framework, specific arguments have to be made about why particular features or behaviours contribute to differential fitness in that ecological context.)

Particular evolved behaviours may be labelled as 'strategies' by analogy with human strategies, but this is purely a metaphor: the animal is following instincts, or sometimes learned behaviours, but is not generally following a consciously considered plan intended to lead to some desired outcome in the longer term.

But a reader is likely to read about a nestling being "in danger of being seized by mistake by its own parents" as the birds themselves making a mistake – which implies they have a deliberate plan to catch food, while excluding their own offspring from the food category, and so intended to avoid treating their offspring as prey. That is, it is implied that birds of prey are looking to avoid eating their own, but get it wrong.

Yet, surely, birds are behaving instinctively, and not conceptualising their hunting as a means of acquiring nutrition, where they should discriminate between admissible prey and young relatives. Again this seems to be anthropomorphism as it treats non-human animals as if their have mental experiences and thought processes akin to humans: "I did not mean to eat my child, I just failed to recognise her, and so made a mistake".

The protected area is sought out

Similarly, the songbirds also behave instinctively. They surely do not 'seek out' the 'protected' area around the nest of a bird of prey. There must be a sense in which they 'learn' (over many generations, perhaps) that they need not fear the raptors when they are near their own nests but it seems unlikely a songbird conceptualises any of this in a way that allows them to deliberately (that is, with deliberation) seek out the neutral zone.

In terms of natural selection, a songbird that has no fear of raptors and so does not seek to avoid or hide or flee from them would likely be at a disadvantage, and so tend to leave less offspring. Similarly, a songbird that usually avoided birds of prey, but nested in the neutral zone, would have a fitness advantage if other predators (small cats say) kept clear of the area. The bird would not have to think "hey, I know raptors are generally a hazard, but I'll be okay here as I'm close enough to be in the zone where they do not hunt", as long as the behaviour was heritable (and there was initially variation in the extent to which individuals behaved that way) – as natural selection would automatically lead to it becoming common behaviour.

(In principle, the bird could be responding to some cue in the environment that was a reliable but indirect indicator they were near a raptor nesting site. For example, perhaps building a nest very close to a location where there is a regular depositing of small bones on the ground gives an advantage, so this behaviour increases fitness and so is 'selected'.)

Under the protection of the big predator

Why are the songbirds under the protection of the raptors? Perhaps because other potential predators do not come into the neutral zone as they are vulnerable when approaching this area, even if they would be safe once inside. Again, if this is so, it surely does not reflect a conscious conceptualisation of the neutral zone.

For example, a cat that preys on small birds would experience a different 'umwelt' from the bird. A small songbird with a nest where it has young experiences the surrounding space differently to a cat (already a larger animal so experiencing the world at a different scale) that ranges over a substantial territory. Perhaps the songbird perceives the neutral zone as a distinct space, whereas to the cat it is simply an undistinguished part of a wider area where the raptors are regularly seen.

Or, perhaps, for the smaller predator, the area around the neutral zone offers too little cover to risk venturing into the zone. (Again, this does not mean a conscious thinking process along the lines "I'd be safe once I was over there, but I'm not sure I'd make it there as I could easily be seen moving between here and there", but could just be an inherited tendency to keep under cover.)

The birds of prey themselves will not take the songbirds, so the smaller birds are protected from them in the zone, but if this is simply an evolved mechanism that prevents accidental 'infanticide' this can hardly be considered as other birds being under the protection of the birds of prey. Perhaps the birds of prey do scare away other predators – but, if so, this is in no sense a desired outcome of a deliberate policy adopted by the birds of prey because they want to protect their more vulnerable neighbours.

One could understand how the birds of prey might hypothetically have evolved behaviour of not preying on smaller birds (which might include their own offspring) near their nest, but would still attack smaller predators that might threaten their own chicks. In that scenario 2, the birds of prey might have indeed protected nearby songbirds from potential predators (even if only incidentally), but this does not apply if, as Uexküll suggests, "they seize no prey at all" in the neutral zone.

Again the, 'under the protection of the big predator' seems to anthropomorphise the situation and treat the birds of prey as if they are acting deliberately to protect songbirds, and so this phrasing needs to be understood metaphorically.

Does language matter?

Uexküll's phrasing offers an engaging narrative which aids in the communication of the idea of the neutral zone to his readers. (He is skilled in making the unfamiliar familiar.) It is easier to understand an abstract idea if it seems to reflect a clear purpose or it can be understood in terms of human ways of thinking and acting, for example:

  • it is important to keep your children safe
  • it is good to look out for your neighbours

But we know that science learners readily tend to accept explanations that are teleological and/or anthropomorphic, and that sometimes (at least) this acts as an impediment to learning the scientific accounts based on natural principles and mechanisms.

Therefore it is useful for science teachers in particular to be alert to such language so they can at least check that learners are seeing beyond the metaphor and not mistaking a good story for a scientific account.

Work cited:
Notes:

1 Many people, including some scientists, do believe the world is unfolding according to a pre-ordained plan or scheme. This would normally be considered a matter of religious faith or at least a metaphysical commitment.

The usual stance taken in science ('methodological naturalism'), however, is that scientific explanations must be based on scientific principles, concepts, laws, theories, etcetera, and must not call upon any supernatural causes or explanations. This need not exclude a religious faith in some creator with a plan for the world, as long as the creator is seen to have set up the world to unfold through natural laws and mechanisms. That is, faith-based and scientific accounts and explanations may be considered to work at different levels and to be complementary.

Read more about the relationship between science and religion

2 That this does not seem to be the case might reflect how a flying bird perceives prey – if it has simply evolved to swoop upon and take any object in a certain size range {that we might explain as small enough to be taken, but not so small as not to repay the effort} that matches a certain class of movement pattern {that we might interpret as moving under its own direction and so being animate} then the option of avoiding smaller birds but taking other prey would not be available.

After all, studies show parent birds will try and feed the most simple representations of a hatchling's open beak – suggesting they do not perceive the difference between their own children and crude models of an open bird mouth.

The general form of a chick's open mouth (as shown by these hatchlings) is enough to trigger feeding behaviour in adult birds.
(Image by Tania Van den Berghen from Pixabay )

Uexküll himself reported that,

"…a very young wild duck was brought to me; it followed me every step. I had the impression that it was my boots that attracted it so, since it also ran occasionally after a black dachshund. I concluded from this that a black moving object was sufficient to replace the image of its mother…"

Uexküll, 1934/2010

(A year later, Lorentz would publish his classic work on imprinting which reported detailed studies of the same phenomenon.)

The book that EVERY physics student reads

Certainty as the Nemesis of science

Keith S. Taber

My library is in desperate need of some sorting and tidying, but I have a tendency, when entering in there and picking up a book I've not looked at for while, to dip into it rather than get organising.

So it was that I found myself re-reading the Introduction to Richard Muller's (1988) book 'Nemesis: The Death Star'. I presumably do not need to describe the book as it is so widely read (😉 see below) 1, but the Introduction was by Muller's colleague and former research supervisor Luis Alverez – a Nobel Prize winning physicist. He died the same year that Nemesis was published, so this was probably one of his last pieces of writing about science.

A claim that cannot be taken at face vlaue

In the introduction, Alverez suggests that,

"I am convinced that every student of physics will read and reread Nemesis several times, learning important lessons on each occasion, as well as having a wonderful time."

Alverez, 1988, p.xi

Now I struggle with this kind of claim.

Richard Muller's book 'Nemesis The Death Star' – has this been read and reread by every student of physics since 1988?

I have admitted here before to being rather pedantic, and although it's never been diagnosed as being on the autism spectrum, I recognise I do share some of the common traits – including a tendency to focus on literal meanings. (Perhaps that explains my regular exploration of scientific metaphors and the like on this site).

Clearly, Alverez thinks very highly of Muller, and the work reported is related to some of his own research, so there might be some quite understandable personal bias here. I am also prepared to be charitable, and read 'every student of physics' to only refer to those majoring in physics at university level rather than anyone taking a physics course.

Even so, I find this an extraordinary thing to write.

Now, I was recently asked to write something about a book I had been sent in manuscript and was quite happy to suggest that the book (on a critical but generally under-examined theme) should be required reading for all future science educators. But that is surely different: the kind of difference to be drawn between the claims:

  • all good citizens should pay their due taxes
  • all citizens do pay their due taxes

Alverez was not only suggesting that he thought all physics students would benefit from the book, but was apparently making a prediction, moreover a 'confident' prediction, that all future physics students would read the book (at least twice!) and enjoy it. The likelihood of that must have surely seemed infinitesimally small!

Had this been part of the cover blurb, I might have suspected the publisher had taken liberties with the text (which should not surprise me as publishers now seem to regularly issue contracts asking authors for the right to change their scholarly text in any way that suits them). I had wondered if that had happened, for example, when I read on the cover of a book on evolution the author's claim that today everyone accepts Darwin's theory.2 But Alverez was not writing an endorsement, but a part of the book itself. (This was not even a Foreword – but the actual Introduction to the book.)

I can only understand Alverez's claim if I understand it as a piece of rhetoric, indeed hyperbole – surely the author could not possibly really think that henceforth every physics student was going to read and reread this book about one specialised programme of research (and which was very unlikely to be directly relevant to the assignments and examinations that would given them course credit) no mater how interesting it might be? Surely, rather, he was just communicating via rhetoric that the book was so worthy of attention that in his view it would justify such a broad readership.

What's wrong with rhetoric?

I see this as an issue worth raising because (a) the statement is a knowledge claim and (b) the claim was made by a scientist in the context of part of a book reporting scientific work.

Yet it is in the nature of scientific knowledge that it is theoretical, and, strictly, provisional (always open to be revisited in the light of new evidence or ways of interpreting evidence) – and therefore scientific knowledge claims should reflect this, and not be absolute.

Read about the nature of scientific knowledge

This is one way that some accounts of science that appear in the news and other media distort the nature of science (and usually the original reports of that science as presented in research journals) by suggesting scientists have made discoveries that definitively prove some idea or other and reflect certain, absolute, knowledge

Read about scientific certainty in the media

Alverez's claim is absolute: all physics students WILL read and re-read this book.

I am not suggesting that there is no place for rhetoric in science. Scientific claims are presented in formal research reports which are organised to make an argument for the claims being presented. They are rhetorical.

Read about rhetoric in science writing

But, even if scientific claims are structured rhetorically in order to make a case, they still need to be measured, and honest, and – if they are to be considered scientific – suitably provisional.

This was perhaps [sic] exemplified when Crick and Watson, reporting what was arguably [sic] one of the most important scientific discoveries of the twentieth, if not all, centuries, pointed out that

"It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."

Watson & Crick, 1953

They did not suggest that

"our model of D.N.A. structure definitely provides the mechanism by which genetic material IS copied and is without doubt the basis of heredity".

Counterfactual: what Crick and Watson did not publish in Nature

So, rhetoric is important in science – scientists need the ability to present a best case for the argument being made so that other scientists can readily appreciate the logic of, and strength of, some new claim. However, hyperbole involves making such extreme exaggerations that they are not expected to be taken literally, and surely has no place in scientific writing. When a scientist make an absolutist claim (e.g., "every student of physics will read and reread Nemesis several times [and have a] wonderful time") other scientists know this cannot be seen as an authentic scientific claim, and so are likely to simply disregard it as something which cannot be interpreted sensibly within the context of scientific discourse.

Sources cited
  • Alvarez, L. W. (1988). Introduction. In Nemesis: The Death Star. The story of a scientific revolution (pp. xi-xiii). Guild Publishing.
  • Watson, J. D., & Crick, F. H. C. (1953). Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid. Nature, 171(4356), 737-738.
  • Muller, R. (1988). Nemesis: The Death Star. The story of a scientific revolution. Guild Publishing.
  • Eldredge, N. (1995). Reinventing Darwin: The great evolutionary debate. Weidenfeld and Nicolson.

Note:

1 Just in case anyone has not read the book, it describes a theory that the earth is subject to regular mass extinction events due to the effect of a planet (Nemesis) with such a large and eccentric orbit that it only comes near the sun once every 26 million years. The publisher tells readers that

"…the Nemesis hypothesis has established itself as the only viable scientific theory to explain a bewildering variety of phenomena in fields ranging from geology to astronomy to palaeontology…"

but then the editor responsible for this claim has presumably NOT won a physics Nobel prize.

(Image by Bela Geletneky from Pixabay)

2 The back cover of 'Reinventing Darwin' (Eldredge, 1995) tells potential readers that,

"No one doubts that Darwin's theory of Evolution by Natural Selection is correct."

No matter how much one recognises natural selection and Neodarwinism as the consensus view, the present paradigm, in the scientific community, it is difficult to believe that any person on earth who has taken any interest in the matter is not aware that there are large numbers of people (albeit, only a small proportion of practising scientists) who not only 'doubt' Darwin was correct but, in many cases, are strongly committed to the idea that he was completely wrong!

A molecular Newton's cradle?

A chain reaction with no return

Keith S. Taber

Have chemist's created an atomic scale Newton's cradle?

(Image by Michelle from Pixabay)

Mimicking a Newton's cradle

I was interested to read in an issue of Chemistry World that

"Scientists in Canada have succeeded in setting off a chain of reactions in which fluorine atoms are passed between molecules tethered to a copper surface. The sequence can be repeated in alternating directions, mimicking the to-and-fro motions of a Newton's cradle."

Blow, 2022

The Chemistry World report explained that

"The team of researchers…affixed fluorocarbons to a [copper] surface by chemisorption, constructing chains of CF3 molecules terminated by a CF2 molecule – up to four molecules in total….

The researchers applied an electron impulse to the foremost CF3 molecule, causing it to spit out a fluorine atom along the chain. The second CF3 absorbed this atom, but finding itself unstable, ejected its leading fluorine towards the third molecule. This in turn passed on a fluorine of its own, which was taken up by the taken up by the CF2 molecule in fourth position."

Blow, 2022

There is some interesting language here – a molecule "spits out" (a metaphor?) an atom, and another "finds itself" (a hint of anthropomorphism?) unstable.

Molecular billiards?
Can a line of molecules 'tethered' onto a metal surface behave like a Newton's cradle?

Generating reverse swing

The figure below was drawn to represent the work as described, showing that "another electron impulse could be used to set… off…a reverse swing".

A representation of the scheme described in Chemistry World. The different colours used for the fluorine 'atoms' 1 are purely schematic to give a clear indication of the changes – the colours have no physical significance as all the fluorine atoms are equivalent. 2 The molecules are shown here as if atoms were simply stuck to each other in molecules (rather than having become one larger multi-nuclear structure) for the same reason. 1 In science we select from different possible models and representations for particular purposes.3

That reference to "another electron impulse" being needed is significant,

"What was more, each CF3 had been flipped in the process, so the Newton's cradle as a whole was a mirror image of how it had begun, giving the potential for a reverse swing. Unlike a desk Newton's cradle, it did not swing back on its own accord, but another electron impulse could be used to set it off."

Blow, 2022
"…the Newton's cradle as a whole was a mirror image of how it had begun"

Mirroring a Newton's cradle

Chemistry World is the monthly magazine of the Royal Society of Chemistry (a learned society and professional body for chemists, primarily active in the UK and Eire) sent to all its members. So, Chemistry World is part of the so-called secondary literature that reports, summarises, and comments on the research reports published in the journals that are considered to comprise the primary academic literature. The primary literature is written by the researchers involved in the individual studies reported. Secondary literature is often written by specialist journalists or textbook authors.

The original report of the work (Leung, Timm & Polanyi, 2021) was published in the research journal Chemical Communications. That paper describes how:

"Hot [sic] F-atoms travelling along the line in six successive 'to-and-fro' cycles paralleled the rocking of a macroscopic Newton's cradle."

Leung, Timm & Polanyi, 2021, p.12647
A simple representation of a Newton's cradle (that is, "a macroscopic Newton's cradle")

These authors explain that

"…energised F can move to- and-fro. This occurs in six successive linear excursions, under the influence of electron-induced molecular dissociation at alternate ends of the line…. The result is a rocking motion of atomic F which mirrors, at the molecular scale, the classic to-and-fro rocking of a macroscopic Newton's cradle. Whereas a classic Newton's cradle is excited only once, the molecular analogue [4] here is subjected to opposing impulses at successive 'rocks' of the cradle.

The observed multiple knock-on of F-atoms travelling to-and-fro along a 1D row of adsorbates [molecules bound to a substrate] is shown…to be comparable with the synchronous motion of a Newton's cradle."

Leung, Timm & Polanyi, 2021, p.12647-50
Making molecules rock?

'Rocking' refers to a particular kind of motion. In a macroscopic context, there are familiar example of rocking as when a baby is cradled in the arms and gently 'rocked' back and forth.

A rocking chair is designed to enable a rocking motion where the person in the chair moves back and forth through space.

The molecular system described by Leung and colleagues is described as "mirror[ing], at the molecular scale…to-and-fro rocking"

[Image by OpenClipart-Vectors from Pixabay]

The researchers are suggesting that, in some sense, the changes in their molecular scale system are equivalent to "the synchronous motion of a Newton's cradle".

Titles and texts in scientific writing

One feature of interest here is a difference between the way work is described in the article titles and the main texts.

Chemistry society professional journalAcademic research journal
Title"…molecular Newton's cradle""…an atomic-scale Newton's cradle"
TextThe effect was "mimicking … a Newton's cradle."The effect
"paralleled…
mirrors…
[is] comparable with"
Newton's cradle
Bold titles: nuanced details

Titles need to capture the reader's attention (and in science today the amount of published material is vastly more than only one person could read) so there is a tendency to be bold. Both these articles have titles suggesting that they are reporting a nanoscopic Newton's cradle. The reader enticed to explore further then discovers that there are caveats. What is being claimed is not a Newton's cradle at minuscule scale but something which though not actually a Newton's cradle, does have some similarity to (mimics, parallels, mirrors) one.

This is important as "the molecular analogue" is only analogous in some respects.

The analogy

There is an analogy, but the analogy can only be drawn so far. In the analogy, the suspended balls of the Newton's cradle are seen as analogous to the 'chemisorbed' molecules lined up on the surface of a copper base.

Analogies are used in teaching and in science communication to help 'make the unfamiliar familiar', to show someone that something they do not (yet) know about is actually, in some sense at least, a bit like something they are already familiar with. In an analogy, there is a mapping between some aspect(s) of the structure of the target ideas and the structure of the familiar phenomenon or idea being offered as an analogue. Such teaching analogies can be useful to the extent that someone is indeed highly familiar with the 'analogue' (and more so than with the target knowledge being communicated); that there is a helpful mapping across between the analogue and the target; and that comparison is clearly explained (making clear which features of the analogue are relevant, and how).

Analogies only map some features from analogue to target. If there was a perfect transfer from one system to the other, then this would not be an analogy at all, but an identity! So, in a sense there are no perfect analogies as that would be an oxymoron. Understanding an analogy as intended therefore means appreciating which features of the analogue do map across to the target, and which do not. Therefore in using analogies in teaching (or communicating science) it is important to be explicit about which features of the analogue map across (the 'positive' analogy) and which do not, including features which it would be misleading to seek to map across – the so called 'negative analogy.' For example, when students think of an atom as a tiny solar system, they may assume that atom, like the solar system, is held together by gravitational force (Taber, 2013).

It probably seems obvious to most science teachers that, if comparing the atom with a solar system, the role that gravity has in binding the solar system maps across to the electrical attraction between a positive nucleus and negative electrons; but when a sample of 14-18 year-olds were asked about atoms and solar systems, a greater number of them suggested the force binding the atom was gravitational than suggested it was electrical (Taber, 2013)!

Perhaps the most significant 'negative analogy' in the research discussed here was pointed out in both the research paper and the subsequent Chemistry World report, and relates to the lack of inherent oscillation in the molecular level system. The nanoscopic system is like a Newton's cradle that only has one swing, so the owner has to reset it each half cycle.

  • "Unlike a desk Newton's cradle, it did not swing back on its own accord, but another electron impulse could be used to set it off."
  • "Whereas a classic Newton's cradle is excited only once, the molecular analogue here is subjected to opposing impulses at successive 'rocks' of the cradle"

That is quite a major difference when using the Newton's cradle for an analogy.

Image by Peggy und Marco Lachmann-Anke from Pixabay
Image by Peggy und Marco Lachmann-Anke from Pixabay

Who wants a Newton's cradle as an executive toy if it needs to be manually reset after each swing?

The positive and negative analogies

We can consider that the Newton's cradle is a little like a simple pendulum that swings back and forth, with the complication that instead of a single bob swinging back and forth, the two terminal spheres share the motion between them due to the momentum acquired by one terminal sphere being transferred thorough the intermediate spheres to the other terminal sphere.

In understanding the analogy it is useful to separately consider these two features of a Newton's cradle

  • a) the transfer of momentum through the sequence
  • b) moving a mass through a gravitational field

If we then think of the Newton's cradle as a 'pendulum with complications' it seems that the molecular system described by Leung and colleagues fails to share a critical feature of a pendulum.

A chain reaction – the positive analogy

The two systems map well in so far as that they comprise a series of similar units (spheres, molecules) that are carefully aligned, and constrained from moving out of alignment, and that there is a mechanism that allows a kind of chain reaction.

In the molecular scenario, the excitation of a terminal molecule causes a fluorine atom to become unbound from the molecule and to carry enough momentum to collide with and excite a second molecule, binding to it, whilst causing the release of one of the molecule's original fluorine atoms which is similarly ejected with sufficient momentum to collide with the next molecule…

This 'chain reaction' 5 is somewhat similar to how, in a Newton's cradle, the momentum of a swinging sphere is transferred to the next, and then to the next, and then the next, until finally all the momentum is transferred to the terminal sphere. (This is an idealised cradle, in any real cradle the transfer will not be 100% perfect.) This happens because the spheres are made from materials which collide 'elastically'.6

The positive analogy: The notion of an atomic level Newton's cradle makes use of a similarity between two systems (at very different scales) where features of one system map onto analogous features of the other.

The negative analogy

Given that positive mapping, a key difference here is the way the components of the system (suspended spheres or chemisorbed molecules) are 'tethered'.

Chemisorbed molecules

The molecules are attached to the copper surface by chemical bonding, which is essentially an electromagnetic interaction. A sufficient input of energy could certainly break these bonds, but the the impulse being applied parallel to the metal surface is not sufficient to release the molecules from the substrate. It is enough to eject a fluorine atom from a molecule where carbon is already bound to the surface and three other fluorines atoms (carbon is tetravalent, but it is is bonded to the copper as well as the fluorines) – but the final molecule is an adsorbed CF2 molecule, which 'captures' the fluorine and becomes an absorbed CF3 molecule.

Now, energy is always conserved in all interactions, and momentum is also always conserved. If the kinetic energy of the 'captured' fluorine atom does not lead to bond breaking it must end up somewhere else. The momentum from the 'captured' atom must also be transferred somewhere.

Here, it may be useful to think of chemical bonds as having a similarity to springs – in the limited sense that they can be set vibrating. If we imagine a large structure made up of spheres connected by springs, we can see that if we apply a force to one of the spheres, and the force is not enough to break the spring, the sphere will start to oscillate, and move any spheres connected to it (which will move spheres attached to them…). We can imagine the energy from the initial impulse, and transferred through the chain of molecules, is dissipated though the copper lattice, and adds to its internal energy. 7

The fluorocarbon molecules are bound to the surface by chemical bonding. If the energy of impact is insufficient to cause bond breaking, it will be dissipated.

Working against gravity

In a simple pendulum, work is done on a raised sphere by the gravitational field, which accelerates the bob when it is released, so that it is moving at maximum speed when it reaches the lowest point. So, as it is moving, it has momentum, and its inertia means it continues to swing past the equilibrium position which is the 'attractor' for the system. In a Newton's cradle the swinging sphere cannot continue when it collides with the next sphere, but as its momentum is transferred through the train of spheres the other terminal sphere swings off, vicariously continuing the motion.

In an ideal pendulum with no energy losses the bob rises to its original altitude (but on the other side of the support) by which time it has no momentum left (as gravitational force has acted downwards on it to reduce its momentum) – but gravitational potential energy has again built up in the system to its original level. So, the bob falls under gravity again, but, being constrained by the wire, does not fall vertically, rather it swings back along the same arc.

It again passes the equilibrium position and returns to the point where it started, and the process is repeated. In an ideal pendulum this periodic oscillation would continue for ever. In a real pendulum there are energy losses, but even so, a suitable bob can swing back an forth for some time, as the amplitude slowly reduces and the bob will eventually stop at the attractor, when the bob is vertical.

In a (real) Newton's cradle, one ball is raised, so increasing the gravitational potential energy of the system (which is the configuration of the cradle, with its spheres, plus the earth). When it is released, gravity acts to cause the ball to fall. It cannot fall vertically as it is tethered by a steel (or similar) wire which is barely extendible, so the net force acting causes the ball to swing though an arc, colliding with the next ball.

The Newton's cradle design allows the balls to change their 'height' in relation to a vertical gravitational field direction – in effect storing energy in a higher gravitational field configuration that can do work to continue the oscillation. The molecular analogue 4 does not include an equivalent mechanism that can lead to simultaneous oscillation.
(Image by 3D Animation Production Company from Pixabay)
Two types of force interactions

The steel spheres, however, are actually subject to two different kinds of force. They are, like the molecules, also tethered by the electromagnetic force (they are attached to steel wires which are effectively of fixed length due to the bonding in the metal 8), but, in addition, subject to the gravitational field of the earth. 9 The gravitational field is relevant because a sphere is supported by a wire that is fixed to a rigid support (the cradle) at one end, but free to swing at the end attached to the sphere.

The Newton's cradle operates in what is in effect a uniform gravitational field (neither the radial nature or variation with altitude of the earth's field are relevant on the scale of the cradle) – and the field direction is parallel to the plane in which the balls hang. So, the gravitational potential of the system changes as a sphere swings higher in the field.

In a Newton's cradle, a tethered sphere's kinetic energy allows it to rise in a gravitational field, before swinging back gaining speed (and regaining kinetic energy)

The design of the system is such that a horizontal impulse on a sphere leads to it swinging upwards – and gravity then acts to accelerate it towards a new collision. 10 This collision, indirectly, gives a horizontal impulse to the sphere at the other end of the 'train' where again the nature of the support means the sphere swings upward – being constrained by both the wire maintaining its distance from the point of suspension at the rigid support of the frame, and its weight acting downwards.

The negative analogy concerns the means of constraining the system components

The two systems then both have a horizontal impulse being transferred successively along a 'train' of units. Leung and colleagues' achievement of this at the molecular scale is impressive.

However, the means of 'tethering' in the two systems is different in two significant ways. The spheres in the Newton's cradle are suspended from a rigid frame by inextensible wires that are free to swing. Moreover, the cradle is positioned in a field with a field direction perpendicular to the direction of the impulse. This combination allows horizontal motion to be converted to vertical motion reversibly.

The molecular system comprises molecules bound to a metal substrate. The chemisorbtion is less like attaching the molecules with long wires that are free to swing, and more like attaching them with short, stiff springs. Moreover, at the scale of the system, the substrate is less like a rigid frame, and more like a highly sprung mattress. So, even though kinetic energy from the 'captured' fluorine atom can be transferred to the bond, this can then be dissipated thorough the lattice.

The negative analogy: the two systems fail to map across in a critical way such that in a Newton's cradle one initial impulse can lead to an extended oscillation, but in the molecular system the initiating energy is dissipated rather than stored to reverse the chemical chain reaction.

The molecular system does not enable the terminal molecule to do work in some form that can be recovered to reverse the initial process. By contrast, a key feature of a Newton's cradle is that the spheres are constrained ('tethered') in a way that allows them to move against the gravitational field – they cannot move further away from, nor nearer to, their point of support, yet they can swing up and down and change their distance from the earth. Mimicking that kind of set-up in a molecular level system would indeed be an impressive piece of nano-engineering!

Work cited:
  • Blow, M. (2022). Molecular Newton's cradle challenges theory of transition states. Chemistry World, 19(1), 38.
  • Leung, L., Timm, M. J., & Polanyi, J. C. (2021). Reversible 1D chain-reaction gives rise to an atomic-scale Newton's cradle. Chemical Communications, 57(94), 12647-12650. doi:10.1039/D1CC05378G
  • Taber, K. S. (2013). Upper Secondary Students' Understanding of the Basic Physical Interactions in Analogous Atomic and Solar Systems. Research in Science Education, 43(4), 1377-1406. doi:10.1007/s11165-012-9312-3 (The author's manuscript version may be downloaded here.)
Notes

1 Strictly they are no distinct atoms once several atoms have been bound together into a molecule, but chemists tend to talk in a shorthand as if the atoms still existed in the molecules.

2 Whilst I expect this is obvious to people who might choose to read this posting, I think it is worth always being explicit about such matters as students may develop alternative conception at odds with scientific accounts.

In the present case, I would be wary of a learner thinking along the lines "of course the atom will go back to its own molecule"

Students will commonly transfer the concepts of 'ownership' and 'belonging' from human social affairs to the molecular level models used in science. Students often give inappropriate status to the history of molecular processes (as if species like electrons recall and care about their pasts). One example was a student who suggested to me that in homolytic bond breaking each atom would get its own electron back – meaning the electrons in the covalent bond would return to their 'own' atoms.

I have also been told that in double decomposition (precipitation) reactions the 'extra' electron in an anion would go back to its own cation in the reagents, before the precipitation process can occur (that is, precipitation was not due to the mutual attraction between ions known to be present in the reaction mixture: they first had to become neutral atoms that could then from an ionic bond by electron transfer!) In ionic bonding it is common for learners to think that an ionic bond can only be formed between ions that have been formed by a (usually fictitious) electron transfer event.

Read about common alternative conceptions of ionic bonding

Read about a classroom resource to diagnose common alternative conceptions (misconceptions) of ionic bonding

Read about a classroom resource to support learning about the reaction mechanism in precipitation reactions

3 I have here represented the same molecules both as atoms linked by bonds (where I am focusing on the transfer of fluorine atoms) and in other diagrams as unitary spheres (where I am focusing on the transfer of energy/momentum). All models and representations used for atoms and molecules are limited and only able to reflect some features of what is being described.

4 A note on terminology. An analogy is used to make the unfamiliar familiar by offering a comparison with something assumed to already be familiar to an audience, in this case the molecular system is the intended target, and the (that is, a generic) Newton's cradle is the analogue. However, analogy – as a mapping between systems – is symmetrical so each system can be considered the analogue of the other.

5 In some way's Leung's system is more like a free radical reaction than a Newton's cradle. A free radical is an atom (or molecule) with an unpaired electron – such as an unbound fluorine atom!

In a free radical reaction a free radical binds to a molecule and in doing so causes another atom to be ejected from the molecule – as a free radical. That free radical can bind to another molecule, again causing it to generate a new free radical. In principle this process can continue indefinitely, although the free radical could also collide with another free radical instead of a molecule, which terminates the chain reaction.

6 The balls need to be (near enough) perfectly elastic for this to work so the total amount of kinetic energy remains constant. Momentum (mv) is always conserved in any collision between balls (or other objects).

If there were two balls, then the first (swinging) sphere would be brought to a stop by the second (stationary) sphere, to which its momentum would be transferred. So, the first ball would stop swinging, but the second would swing in its place. The only way mv and mv2 (and so kinetic energy) can be both conserved in collisions between balls of the same mass is if the combination of velocities does not change. That is, mathematically, the only solutions are where neither of the two balls' velocities change, or where they are swapped to the other permutation (here, the velocity of the moving ball becomes zero, but the stationary ball moves off with the velocity that the ball that hit it had approached it with).

The first solution would require the swinging steel ball to pass straight through the stationary steel ball without disturbing it. Presumably, quantum mechanics would suggest that ('tunnelling') option has a non-zero (but tiny, tiny – I mean really tiny) probability. To date, in all known observations of Newton's cradles no one has reported seeing the swinging ball tunnel though the stationary ball. If you are hoping to observe that, then, as they say, please do not hold your breath!

With more balls momentum is transferred through the series: only the final ball is free to move off.

7 We can imagine that in an ideal system of a lattice of perfectly rigid spheres attached to perfect springs (i.e., with no hysteresis) and isolated from any other material (n.b., in Leung et al 's apparatus the copper would not have been isolated from other materials), the whole lattice might continue to oscillate indefinitely. In reality the orderliness will decay and the energy will have in effect warmed the metal.

8 Strictly, the wires will be longest when the spheres are directly beneath the points of support, as the weight of a sphere slightly extends the wire from its equilibrium length, and it will get slightly shorter the further the sphere swings away from the vertical position. In the vertical position, all the weight is balanced by a tension in the wire. As the ball swings away from the vertical position, the tension in the wire decreases (as only the component of weight acting along the wire needs to be balanced) and an increasing component of the weight acts to decelerate it. But the change in extension of the wire is not significant and is not noticeable to someone watching a Newton's cradle.

When the wire support is not vertical a component of the weight of the sphere acts to change the motion of the sphere

9 Molecules are also subject to gravity, but in condensed matter the effect is negligible compared with the very much stronger electromagnetic forces acting.

10 We might say that gravity decelerates the sphere as is swings upwards and then accelerates as it swings back down. This is true because that description includes a change of reference direction. A scientist might prefer to say that gravity applies a (virtually) constant downward acceleration during the swing. This point is worth making in teaching as a very common alternative conception is to see gravity only really taking effect at the top of the swing.

What the jet tried to do next…

Anthropomorphising surface tension

Keith S. Taber

it seems good training for a scientist to always read accounts of science with a critical filter primed to notice figurative language and to check that the communication can be understood in a non-metaphorical way

When water is poured from a bottle or other container the stream of liquid can take up complex shapes. In particular, it has long been noted how the stream can appear to have the shape of a chain or string of beads, with the flow seeming to be wider in some places that others.

A stream of poured water does not form a perfect cylinder – something that physics should be able to explain.

(Image by tookapic from Pixabay)

This is just the kind of thing that physicists think they should be able to explain…using physics. An article in Physics World (Jarman, 2022) reports some recent work on just this outstanding problem,

"If you pour water out of a bottle, the liquid stream will often adopt a chain-like structure….At the heart of the effect is the non-cylindrical profile of the jet as it emerges. To minimize surface tension, the jet tries to become a cylinder, but this motion overshoots and results in an oscillation in the profile shape."

Article in Physics World

What intrigued me here was the choice of phrasing: "To minimize surface tension, the jet tries to become a cylinder…". This language could be considered to reflect teleology, and even anthropomorphism.

Teleology?

Teleological explanations are those that explain something in terms of some kind of endpoint. Something happens in order to bring about some specific state of affairs. The sun shines to allow us to find our way. Plants produce oxygen so we can breathe. That is, there is seen to be purpose in nature, something that is characteristic of mythical and supernatural thinking. In science, teleological explanations are strictly considered a kind of pseudo-explanation – something that has the form of an explanation, but does not really explain anything. Sometimes we find apparently teleological explanations in science because they are being used as a kind of shorthand. For example, if we know that science suggests entropy always increases in processes, we might interpret a scientist's comment that something happens 'in order to increase entropy' to be a loose (or lazy) way of saying that some suggested mechanism or action is considered likely because it is consistent with the assumption that entropy will increase.

Read about pseudo-explanations

Read about teleology in science

Here it is suggested that the odd shape is formed in order "to" minimise surface tension. Scientists have observed that many phenomena (such as rain forming roundish drops) can be explained in terms that surface tension tends to be minimised (cf. entropy tends to increase, objects tend to roll down hills, people tend to get older). But the language here might suggest minimising surface tension is an end that nature seeks – that would be a teleological explanation.

Although perhaps this is not simple teleology, as it is not that the water forms into the shape it does to minimise surface tension, but something more nuanced is going on – the jet of water is actively trying, but not quite managing, to minimise surface tension.

anthropo… (to do with humans, as in anthropology)
…morphism (to do with form, as in morphology, amorphous)

…and anthropomorphism?

Anthropomorphic language refers to non-human entities as if they have human experiences, perceptions, and motivations. Both non-living things and non-human organisms may be subjects of anthropomorphism. Anthropomorphism may be used deliberately as a kind of metaphorical language that will help the audience appreciate what is being described because of its similarly to some familiar human experience. In science teaching, and in public communication of science, anthropomorphic language may often be used in this way, giving technical accounts the flavour of a persuasive narrative that people will readily engage with. Anthropomorphism may therefore be useful in 'making the unfamiliar familiar', but sometimes the metaphorical nature of the language may not be recognised, and the listener/reader may think that the anthropomorphic description is meant to be taken at face value. This 'strong anthropomorphism' may be a source of alternative conceptions ('misconceptions') of science.

Read about anthropomorphism

So, in our present case, we are told that "the "the jet tries to become a cylinder". This is anthropomorphic, as to try to do something means having a goal in mind and deliberately behaving in a way that it is believed, expected, or – at least – hoped, will lead to that goal. Human beings can try to achieve things. We can perceive our environment, have goals, conceptualise possibilities and means to reach them, and put in practice an intention.

Whether, and, if so, which, animals can try to do things rather than simply following evolved instincts is a debated issue.

  • Does a dog try to please its human companion by bringing the newspaper?
  • Does the dolphin try to earn a fish by jumping through a hoop? Perhaps.
  • Does the salmon try to get to a suitable spawning site ('ground', sic) by swimming upstream?
  • Does the spider try to make a symmetrical web?
  • Does the bee try to collect nectar by visiting flowers. Probably not.
  • Does she try to fertiliser those flowers with pollen to ensure there will be flowers for her to visit in future seasons? Almost certainly not!
Jets of water?

Do jets of water think that being cylindrical is desirable (perhaps because they recognise minimal surface tension as an inherent good?) , and so make efforts to bring this about? Clearly not. So, they do not try to do this. They do not try to do anything. They are not the kind of entities that can try.

So, this language is metaphorical. The reader is meant to read that "the jet tries to become a cylinder" to mean something other than "the jet tries to become a cylinder". Now, often figures of speech are used in science communication because the ideas being communicated are abstract and complex, and metaphorical language that describes the science in more familiar terms makes the text more accessible and increases engagement by the audience/readership.

A question here then, is what "the jet tries to become a cylinder" communicates that was more likely to be inaccessible to the reader. Physics World is the house magazine of the Institute of Physics, which means it is sent to all it members working across all areas of physics. So a broad readership, though largely a readership of physicists.

Tracing the stream back to the source

Another question that occurred to me was whether the reporter (Jarman) was simply reporting the original researchers' (Jordan, Ribe, Deblais and Bonn) ways of communicating their work. That report was in an academic journal, Physical Review Fluids, where formal, technical language would be expected. So, I looked up the paper, to see how the work was described there.

Under a heading of 'phenomenology', Jordan and colleagues explain

"Chain oscillations are most readily observed when the viscosities of the jet and the ambient fluid are low and the interface has a high surface tension. Water jets in air satisfy these criteria, and so it is no surprise that chain oscillations occur in many everyday situations. Deformation and vibration of a jet are capillary phenomena in which surface tension acts to reduce the jet's surface area. If the cross section is not circular, its highly curved portions are pulled inward and its weakly curved portions pushed outward relative to a circular section with the same area. But due to inertia the movement overshoots, with the result that the long and short axes of the section are interchanged. The shape of the section therefore evolves as it moves along the axis of the jet, producing a steady liquid chain when observed in the laboratory frame…"

Jordan, Ribe, Deblais & Bonn, 2022

"The shape of the section therefore evolves as it moves along the axis of the jet, producing a steady liquid chain when observed"

(Image by Kevin Phillips from Pixabay)

(This seemed to be a somewhat different meaning of 'phenomenology' to that sometimes used in science education or social science more generally. Phenomenology looks to explore how people directly experience and perceive the world. Jordan and colleagues include here a good deal of re-conceptualisation and interpretation of what is directly observed. 1 )

The effect Jordan and colleagues describe seems analogous to how a pendulum bob that is released and so accelerated (by gravity) towards the point directly beneath its support (where gravitational potential is minimised) acquires sufficient momentum to overshoot, and swing upwards, beginning an oscillatory motion. Something similar is seen in an ammeter where the needle often overshoots, and initially oscillates around the value of a steady current reading (unless the spring is 'critically damped'). The effect is also made use on in striking a tuning fork.

No need to try

There is no mention here of 'trying', so no clear anthropomorphism. So, this was a gloss added in the report in Physics World, perhaps because anthropomorphic narratives are especially engaging and readily accepted by audiences; perhaps because the reporter needed to rephrase so as not to borrow too much of the original text, or perhaps as part of preparing brief copy to an editorially assigned word length. Or, perhaps Sam Jarman was not even conscious of the anthropomorphism being used, as this seems such a natural way to communicate. 2

Surface tension acting up

Did the original authors avoid teleology? They do write about how "surface tension acts to reduce the jet's surface area?" This could be read as teleological – as there seems to be a purpose or goal in the 'action', even if it is not here presented as a premeditated action. Could any suggestions of such a purpose be avoided?

One response might be that, yes, a physicist might suggest the 'true' description is a mathematical formula (and there are plenty of formulae in Jordan et al's paper) and that a verbal description is necessarily the translation of an objective description into an inherently figurative medium (natural language).

And, of course, this is not some special case. We might read that gravity acts to pull something to the ground or air resistance acts to slow a projectile down and so forth. 'To' may just imply a cause of an outcome, not a purpose.

I think a rewording along the lines "the action of the surface tension reduces the jet's surface area"conveys the same meaning, but is more of a neutral description of a process, avoiding any suggestion that there is a purpose involved.

Reading and interpreting

But does this matter? In teaching young people such as school children, there is evidence that some figurative language that is anthropomorphic or teleological may be understood in those terms, and student thinking may later reflect this. Part of science education is offering learners an insight into how science does seek to (oh, science personified: sorry, scientists seek to) describe in neutral terms and not to rely on nature having inherent goals, or comprising of the actions of sentient and deliberate agents.

The readership of Physics World is however a professional audience of members of the community of inducted physicists who are well aware that, actually, surface tension does not try to do anything; and that minimising surface tension is a common observed pattern, not something set out as a target for physical systems to aim for. These physicists are unlikely to be led astray by the engaging prose of Sam Jarman and will fully appreciate the intended meaning.

That said, there is an intimate bidirectional relationship between our thinking and our speech – our speech reflects our thought pattens, but our language also channels our thinking. So, it seems good training for a scientist to always read accounts of science with a critical filter primed to notice figurative language and to check that the communication can be understood in a non-metaphorical way. That includes checking that our understanding of what we have read is in keeping with scientific commitments to exclude explanations that are framed in terms of nature's end goals, or the deliberate agency of non-sentient 'actors'.

  • Jarman, S. (2022). Flowing liquid 'chains' are best described by Niels Bohr, not Lord Rayleigh. Physics World, 35(12).
  • Jordan, D. T. A., Ribe, N. M., Deblais, A., & Bonn, D. (2022). Chain oscillations in liquid jets. Physical Review Fluids, 7(10), 104001. doi:10.1103/PhysRevFluids.7.104001
Notes

1 However, none of us are able to be completely naive observers of the world. As William James long ago pointed out, the un-mediated sensory experience of a newborn is a chaos of noise and shapes and colours and so on. Even recognising another person or the presence of a table is an act of interpretation that we learn.

So, experts in a field do see things others do not. A field palaeontologist sees a fossil fragment where the rest of us see undifferentiated dirt and stones. The biochemist sees a steroid structure in a patterns of lines. The football pundit sees a 4-4-2 formation where the occasional viewers just sees people running around. The experienced poker player sees a 'tell' that others would not notice. The professional musician hears a passage in E minor, when most of us just hear a tune.

2 This kind of language reflects a way of thinking and talking often called 'the natural attitude'. Science can be seen in part as a deliberate move to look beyond the common-sense world of the natural attitude to problematise phenomena that might be readily taken as given.

We may get used to, and simply accept, that ice is cold, fire burns, the Lord/King makes decisions and owns the land (and people!), rivers flow, things fall down, the heretic must die, the sun moves across the sky, etc. – and probably most people did for much of human history – where the critical (scientific) attitude is to always ask 'why?'

The complicated social lives of stars

Stealing, escaping, and blowing-off in space

Keith S. Taber

"After a lecture on cosmology and the structure of the solar system, James [William James] was accosted by a little old lady.

'Your theory that the sun is the centre of the solar system, and the earth is a ball which rotates around it has a very convincing ring to it, Mr. James, but it's wrong. I've got a better theory,' said the little old lady.

'And what is that, madam?' inquired James politely.

'That we live on a crust of earth which is on the back of a giant turtle.'

Not wishing to demolish this absurd little theory by bringing to bear the masses of scientific evidence he had at his command, James decided to gently dissuade his opponent by making her see some of the inadequacies of her position.

'If your theory is correct, madam,' he asked, 'what does this turtle stand on?'

'You're a very clever man, Mr. James, and that's a very good question,' replied the little old lady, 'but I have an answer to it. And it's this: The first turtle stands on the back of a second, far larger, turtle, who stands directly under him.'

'But what does this second turtle stand on?' persisted James patiently.

To this, the little old lady crowed triumphantly,

'It's no use, Mr. James – it's turtles all the way down.'

Ross, 1967, iv
"The Hindoos [sic] held the earth to be hemispherical, and to be supported like a boat turned upside down upon the heads of four elephants, which stood on the back of an immense tortoise. It is usually said that the tortoise rested on nothing, but the Hindoos maintained that it floated on the surface of the universal ocean. The learned Hindoos, however, say that these animals were merely symbolical, the four elephants meaning the four directions of the compass, and the tortoise meaning eternity." (The Popular Science Monthly, March, 1877; image via Wikipedia)

It's metaphors all the way down

A well-known paper in the journal 'Cognitive Science' is entitled 'The metaphorical structure of the human conceptual system' (Lakoff & Johnson, 1980). What the authors meant by this was that metaphor, or perhaps better analogy, was at the basis of much of our thinking, and so our language.

This links to the so-called 'constructivist' perspective on development and learning, and is of great significance in both the historical development of science and in science teaching and learning. Consider some of the concepts met in a science course (electron, evolution, magnetic flux, hysteresis, oxidation state, isomerism…the list is enormous) in comparison to the kind of teaching about the world that parents engage in with young children:

  • That is a dog
  • That is a tree
  • That is round
  • This is hot
  • This is aunty
  • etc.

Pointing out the names of objects is not a perfect technique – just as scientific theories are always underdetermined by the available data (it is always possible to devise another scheme that fits the data, even if such a scheme may have to be forced and convoluted), so the 'this' that is being pointed out as a tree could refer to the corpse of trees, or the nearest branch, or a leaf, or this particular species of plant, or even be the proper name of this tree, etc. 1

Pointing requires the other person to successfully identify what is being pointed at
(Images by Joe {background} and OpenClipart-Vectors {figures} from Pixabay)

But, still, the 'this' in such a case is usually more salient than the 'this' when we teach:

  • This is an electron
  • This is reduction
  • This is periodicity
  • This is electronegativity
  • This is a food web
  • This is a ᴨ-bond
  • This is a neurotransmitter
  • etc.

Most often in science teaching we are not holding up a physical object or passing it around, but offering a 'this' which is at best a model (e.g., of a generalised plant cell or a human torso) or a complex linguistic structure (a definition in terms of other abstract concepts) or an abstract representation ('this', pointing to a slope of an a graph, is acceleration; 'this', pointing to an image with an arrangement of a few letters and lines, is a transition state…).

So, how do we bridge between the likes of dogs and trees on one hand and electrons and the strong nuclear force on the other (so to speak!)? The answer is we build using analogy and we talk about those constructions using a great deal of metaphor.2 That is, we compare directly, or indirectly, with what we can experience. This refers to relationships as well as objects. We can experience being on top of, beneath, inside, outside, next to, in front of, behind, near to, a long way from (a building, say – although hopefully not beneath in that case), and we assign metaphorical relationships in a similar way to refer to abstract scenarios. (A chloroplast may be found in a cell, but is sodium found in (or on) the periodic table? Yes, metaphorically. And potassium is found beneath it!)

In a wall, the bricks on the top layer are supported by the bricks in the layer beneath – but those are in turn supported by those beneath them.

In building, we have to start at the foundations, and build up level by level. The highest levels are indirectly supported by the foundations.

(Image by OpenClipart-Vectors from Pixabay)

In science, we initially form formal concepts based on direct experience of the world (including experience mediated by our interventions, i.e., experiments), and then we build more abstract concepts from those foundational concepts, and then we build even more abstract concepts by combining the abstract ones. In the early stages we refine 'common sense' or 'life-world' categories into formal concepts so we can more 'tightly' (and operationally, through standard procedures) define what count as referents for scientific terms (Taber, 2013). So, the everyday phenomenon of burning might be reconceptualised as combustion: a class of chemical reactions with oxygen.

This is not just substituting a technical term, but also a more rigid and theoretical (abstract) conceptualisation. So, in the 'life-world' we might admit the effects of too much sunshine or contact with a strong acid within the class of 'burning' by analogy with the effect of fire (it hurts and damages the skin); but the scientific categorisation is less concerned with direct perception, and more with explanation and mechanism. So, iron burning in chlorine (in the absence of any oxygen) is considered combustion, but an acid 'burn' is not.

Combustion without oxygen: A Royal Society of Chemistry video demonstrating the reactions of iron with the halogens.

This is what science has done over centuries, and is also what happens in science education. So, one important tool for the teacher is concept analysis, where we check which prerequisite concepts need to be part of a student's prior learning before we introduce some new concept that is built upon then (e.g., do not try to teach mass spectroscopy before teaching about atomic structure, and do not teach about atomic structure before introducing the notion of elements; do not try to teach about the photoelectric effect to someone who does not know a little about the structure of metals and the nature of electromagnetic radiation.)

This building up of abstract concepts, one on another, is reflected in the density of metaphor we find in our language. (That is a metaphorical 'building', metaphorically placed one upon another, with a metaphorical 'density' which is metaphorically 'inside' the language and which metaphorically 'reflects' the (metaphorical) building process! You can 'see' (a metaphor for understand) just how extensive (oops, another metaphorical reference to physical space) this is. Hopefully, the (metaphorical) 'point' is (metaphorically) 'made', and so I am going to stop now, before this gets silly. 3

A case study of using language in science communication: the death of stars

Rather, I am going to discuss some examples of the language used in a single science programme, a BBC radio programme/podcast in the long-running series 'In Our Time' that took as its theme 'The Death of Stars'. The programme was hosted by Melvyn Bragg, and The Lord Bragg's guests were Professors Carolin Crawford (University of Cambridge), the Astronomer Royal Martin Rees (University of Cambridge) and Mark Sullivan (University of Southampton). This was an really good listen (recommended to anyone with an interest in astronomy), so I have certainly not picked it out to be critical, but rather to analyse the nature of some of the language used from the perspective of how that language communicates technical ideas.

An episode of 'In Our Time' on 'The Death of Stars'
"The image above is of the supernova remnant Cassiopeia A, approximately 10,000 light years away, from a once massive star that died in a supernova explosion that was first seen from Earth in 1690"

A science teacher may be familiar with stars being born, living, and dying – but how might a young learner, new to astronomical ideas, make sense of what was meant?

The passing of stars: birth, death, and afterlife in the universe
The lives and deaths of stars

Now there is already a point of interest in the episode title. Are stars really the kind of entities that can die? Does this mean they are living beings prior to death?

There are a good many references in the talk of these three astronomers in the episode that suggests that, in astronomy at least, stars do indeed live and die. That is, this does not seem to be consciously used as a metaphor – even if the terminology may have initially been introduced that way a long time ago. The programme offered so much material on this theme, that I have separated it out for a post of its own:

"So, in the language of astronomy, stars are born, start young, live; sometimes living alone but sometimes not, sometimes have complicated lives; have lifetimes, reach the end of their lives, and die, so, becoming dead, eventually long dead; and indeed there are generations of stars with life-cycles."

The passing of stars: birth, death, and afterlife in the universe

In this post I am going to consider some of the other language used.

Making the unfamiliar familiar

Language is used in science communication to the public, as it is in teaching, to introduce abstract technical ideas in ways that a listener new to the subject can make reasonable sense of. The constructivist perspective on learning tells us that meaning is not automatically communicated from speaker (or author or teacher) to listener (or reader or student). Rather, a text (spoken or written, or even in some other form – a diagram, a graph, a dance!) has to be interpreted, and this relies on the interpretive resources available to the learner. 4 The learner has to relate the communication to something familiar, and the speaker can help by using ways to make the new idea seem like something already familiar.

Read about constructivism in education

This is why it it is so common in communicating science to simplify, to use analogies and similes, to gesture, to use anthropomorphism and other narrative devices. There was a good deal of this in the programme, and I expect I have missed some examples. I have divided my examples into

  • simplifications: where some details are omitted so not to overburden the listener;
  • anthropomorphism: where narratives are offered such that non human entities are treated as if sentient actors, with goals, that behave deliberately;
  • analogies where an explicit comparison is made to map a familiar concept onto the target concept being introduced; 5
  • similes and metaphors: that present the technical material as being similar to something familiar and everyday.

Simplification

Simplification means ignoring some of the details, and offering a gloss on things. The details may be important, but in order to get across some key idea it is introduced as a simplification. Progress in understanding would involve subsequently filling in some details to develop a more nuanced understanding later.

In teaching there are dangers in simplification, as if the simplified idea is readily latched onto (e.g., there are two types of chemical bonds: ionic and covalent) it may be difficult later to shift learners on in their thinking. This may mean that there is a subtle balance to be judged between

giving learners enough time to become comfortable with the novel idea as introduced in a simplified form,andseeking to develop it out into a more sophisticated account before it become dogma.

In a one-shot input, such as a public lecture or appearance in the media, the best a scientist may be able to do is to present an account which is simple enough to understand, but which offers a sense of the science.

Simplification: all elements/atoms are formed in stars

When introducing the 'In Our Time' episode, Lord Bragg suggested that

"…every element in our bodies, every planet, was made in one of those stars, either as they burned, or as they exploded".

Clearly Melvyn cannot be an expert on the very wide range of topics featured on 'In our time' but relies on briefing notes provided by his guests. Later, in the programme he asks Professor Rees (what would clearly be considered a leading question in a research context!) "Is the sun recycled from previous dead stars?"

"Yes it is because we believe that all pristine material in the universe was mainly just hydrogen and helium, and all the atoms we are made of were not there soon after the big bang. They were all made in stars which lived and died before our solar system formed. And this leads to the problem of trying to understand more massive stars which have more complicated lives and give rise to supernovae…

The cloud from which our solar system formed was already contaminated by the debris, from earlier generations of massive stars which had lived and died more than say five billion years ago so we're literally the ashes of those long dead stars or if you are less romantic we're the nuclear waste from the fuel that kept those old stars shining."

Prof. Martin Rees

There is a potential for confusion here.

"…all the atoms we are made of were not there soon after the big bang. They were all made in stars which lived and died before our solar system formed…"seems to be meant to convey something likenot all the atoms we are made of were there soon after the big bang.
[Some were, but the rest/others] were all made in stars which lived and died before our solar system formed…

A different interpretation (i.e., that all atoms/elements are formed in stars) might well be taken, given Lord Bragg's introductory comments.

Professor Rees referred to how "…the idea that the elements, the atoms we are made of, were all synthesised in stars…" first entered scientific discourse in 1946, due to Fred Hoyle, and to

"this remarkable discovery that we are literally made of the ashes of long dead stars"

Prof. Martin Rees

Before the first star formation, the only elements present in the universe were hydrogen and helium (and some lithium) and the others have been produced in subsequent high energy nuclear processes. Nuclear fusion releases energy when heavier nuclei are formed from fusing together lighter ones, up to iron (element 56).

Forming even heavier elements requires an input of energy from another source. It was once considered that exploding stars, supernovae, gave rise to the conditions for this, but recently other mechanisms have been considered: and Prof. Sullivan described one of these:"we think these combining neutron stars are the main sites where heavy elements like strontium or plutonium, perhaps even gold or silver, these kinds of elements are made in the universe in these neutron stars combining with each other".

A human body includes many different elements, though most of these in relatively small amounts. Well represented are oxygen, carbon, calcium, and nitrogen. These elements exist because of the processes that occur in stars. However, hydrogen is also found in 'organic' substances such as the carbohydrates, proteins, and fats found in the human body. Typically the molecules of these substances contain more hydrogen atoms than atoms of carbon or any other element.

substanceformula
glucose (sugar)C6H12O6
leucine (amino aid)C6H13NO2
leukotriene B4 (inflammatory mediator)C20H32O4
thymine (nucleobase)C5H6N2O2
adreneline (hormone)C9H13NO3
insulin (hormone)C257H383N65O77S6
cholesterol (lipid)C27H46O
cobalamin (vitamin B12)C63H88CoN14O14P
formulae of some compounds found in human bodies

The body is also said to be about 60% water, and water has a triatomic molecule: two hydrogen atoms to one of oxygen (H2O). That is, surely MOST of "the atoms we are made of" are hydrogen, which were present in the universe before any stars were 'born'.

So, it seems here we have a simplification ("every element in our bodies…was made in one of those stars, either as they burned, or as they exploded"; "atoms we are made of … were all made in stars") which is contradicted later in the programme. (In teaching, it is likely the teacher would feel the need to draw the learner's attention to how the more detailed information was actually developing an earlier simplification, and not leave a learner to work this out for themselves.)

Simplification: mass is changed into energy

Explaining nuclear fusion, Prof. Crawford suggested that

"Nuclear fusion is when you combine nuclei of elements to form heavier elements, and when you do this there is a loss of mass, which is converted to energy which provides the thermal pressure and that is what counteracts the gravity and stalls the gravitational collapse."

Prof. Carolin Crawford

This seems to reflect a common alternative conception ('misconception') that, in nuclear processes, mass is converted to energy. This is often linked to Albert Einstein's famous equation E = mc2.

Actually, as discussed before here, this is contrary to the scientific account. The equation presents an equivalence between mass and energy, but does not suggest they can be inter-converted. In nuclear fusion, the masses of the new nuclei are very slightly less than the masses of the nuclei which react to form them (the difference is known as the mass defect), but this is because this omits some details of the full description of the process. If the complete process is considered then there is no loss of mass, just a reconfiguration of where the mass can be located.

The formation of helium from hydrogen in a star

(Image source: Wikamedia Commons)

Although the 4He formed has slightly less mass than four 1H; the positrons, neutrinos and gamma rays produced all have associated (energy and) mass, so that overall there is conservation of mass.

This is a bit like cooking some rice, and finding that when the rice is cooked the contents of the saucepan had slightly less weight than when we started – as some of the water we began with has evaporated and is no longer registering on our balance. In a similar way, if we consider everything that is produced in the nuclear process, then the mass overall is conserved.

As E = mc2 can be understood to tell us that mass follows the energy (or vice versa) we should expect mass changes (albeit very, very small ones) whenever work is done: when we climb the stairs, or make a cup of tea, or run down a mobile 'phone 'battery' (usually a cell?) – but mass is always conserved when we consider everything involved in any process (such as how the 'phone very, very slightly warms -and so very marginally increases the mass of – the environment).

Read 'How much damage can eight neutrons do?'

Despite the scientific principles of conservation of energy and conservation of mass always applying when we make sure we consider everything involved in a process, I have mentioned on this site another example of an astrophysicist suggesting mass can be converted into energy: "an electron and the positron, and you put them together, they would annihilate…they would annihilate into energy" (on a different episode of 'In Our Time': come on Melvyn…we always conserve mass).

Read 'The missing mass of the electron'

Perhaps this is an alternative conception shared by some professional scientists, but I wonder if it sometimes seems preferably to tell the "mass into energy" narrative because it is simpler than having to explain the full details of a process – which is inevitably a more complex story and so will be more difficult for a novice to take in. After all, the "mass into energy" story is likely to seem to fit with a listener's interpretive resources, as E=mc2 is such a famous equation that it can be assumed that it will be familiar to most listeners, even if only a minority will have a deep appreciation of how the equivalence works.

Anthropomorphic narratives

In science learning, anthropomorphism is (to borrow a much used metaphor) a double edged sword that can cut both ways. Teachers often find that using narratives that present inanimate entities which are foci of science lessons as if they are sentient beings with social lives and motivations engages learners and triggers mental images that a student can readily remember. So, students may recall learning about what happens at a junction in a circuit in terms of a story about an electron that had to make a decision about which way to go – perhaps she took one branch while her friend tried another? They recall that covalent bonds are the 'sharing' of electrons between atoms, and indeed that atoms want, perhaps even need, to fill their electron shells, and if they manage this they will be happy.

Read about anthropomorphism

The danger here is that for many students such narratives are not simply useful ways to get them thinking about the science concepts (weak anthropomorphism) but seem quite sufficient as the basis of explanations (strong anthropomorphism) – and so it may become difficult to shift them towards more canonical accounts. They will then write in tests that chemical reactions occur because the atoms want full shells, or that only one electron can be removed from a sodium atom because it then has a full shell. (That is, a force applied to an electron in an electric field is seen as irrelevant compared with the atom's desires. These are genuine examples reflecting what students have said.)

However, there is no doubt that framing scientific accounts within narratives which have elements of human experience as social agent does seem to help make these ideas engaging and accessible. Some such anthropomorphism is explicit, such as when gas molecules (are said to) like to move further apart, and some is more subtle by applying terms which would normally be used in relation to human experiences (not being bothered; chomping; escaping…).

What gravity did next

Consider this statement:

"All stars have the problem of supporting themselves against gravitational collapse, whether that is a star like our sun which is burning hydrogen into helium, and thus providing lots of thermal pressure to stop collapse, or whether it is a white dwarf star, but it does not have any hydrogen to burn, because it is an old dead star, fading away, so it has another method to stop itself collapsing and that is called degeneracy pressure. So, although a white dwarf is very dense, gravity is still trying to pull that white dwarf to be even denser and even denser."

Prof. Mark Sullivan

There is an explicit anthropomorphism here: from the scientific perspective gravity is not trying to pull the white dwarf to be even denser. Gravity does not try to do anything. Gravity is not a conscious agent with goals that it 'tries' to achieve.

However, there is also a more subtle narrative thread at work – that a star has the problem of supporting itself, and it seems that when its first approach to solving this problem fails, it has a fallback method "to stop itself collapsing". But the star is just a complex system where various forces act and so processes occur. A star is not the kind of entity that can have a problem or enact strategies to achieve goals. Yet, this kind of language seems to naturally communicate abstract ideas though embedding them within an accessible narrative.

Star as moral agents

In the same way, a star is not the type of entity which can carry out immoral acts, but

"A star like our sun will never grow in mass, because it lives by itself in space. But most stars in the universe don't live by themselves, they live in what are called binary systems where you have two stars orbiting each other, rather than just the single star that we have as the sun. They are probably born with different masses, and so they evolve at different speeds and one will become a white dwarf. Now the physics is a bit complicated, but what can happen, is that that white dwarf can steal material from its companion star."

Prof. Mark Sullivan

The meaning here seems very clear, but again there are elements of using an anthropomorphic narrative. For one star to steal material from another star, that material would have to first belong to that other star, and its binary 'partner' would have to deliberately misappropriate that material knowing it belongs to its 'neighbour' (indeed, "companion").

Such a narrative breaks down on analysis. If we were to accept that the matter initially belongs to the first star (leaving aside for the moment what kind of entities can be considered to own property) then given that the material in a star got to be there through mutual gravitational attraction, the only obvious basis for ownership is that that matter has become gravitationally bound as part of that star.

If we have no other justification than that (as in the common aphorism, possession is nine points of the law), then when the material is transferred to another star because its gravitational field gives rise to a net force causing the matter to become gravitationally bound to a different star, then we should simply consider ownership to have changed. There is no theft in a context where ownership simply depends on pulling with the greater force. Despite this, we readily accept an analogy from our more familiar human social context and understand that (in a metaphorical sense) one star has stolen from another!

Actually, theft can only be carried out by moral agents – those who have capacity to intend to deprive others of their property

"A person [sic] is guilty of theft if he dishonestly appropriates property belonging to another with the intention of permanently depriving the other of it; and "thief" and "steal" shall be construed accordingly"

U.K. Theft Act 1968

Generally, these days (though this was not always so), even non-human animals are seldom considered capable of being responsible for such crimes. Admittedly, the news agency Reuters reported that as recently as 2008 "A Macedonian court convicted a bear of theft and damage for stealing honey from a beekeeper", but this seems to have been less a judgement on the ability of the bear (convicted it its absence) to engage in ethical deliberation, and more a pragmatic move that allowed the bee-keeper to be awarded criminal damages for his losses.

But, according to astronomers, stars are not only involved in the petty larceny of illicitly acquiring gas, but observations of exoplanets suggests some stars may even commit more daring, large-scale, heists,

"fairly small rocky planets two or three times the mass of the earth, in quite tight orbits around their star and you can speculate that they were once giant planets like Jupiter that have had the outer gassy layers blasted off and you are left with the rocky core, or maybe those planets were stolen from another star that got too close"

Prof. Carolin Crawford
A ménage à trois?

And there were other suggestions of anthropomorphism. It is not only stars that "don't live by themselves" in this universe,

"Nickel-56 [56Ni] is what's called an iron peak element, so it lives with iron and cobalt on the periodic table…"

Prof. Mark Sullivan

And, it is not only gravity which seems to have preferences:

"And like Mark has described with electrons not wanting to be squeezed, you have neutron degeneracy pressure. Neutrons don't like to be compressed, at some point they resist it."

Prof. Carolin Crawford

Neither electrons nor neutrons actually have any preferences: but this is an anthropomorphic metaphor that efficiently communicates a sense of the natural phenomena. 'Resist' originally had an active sense as in taking a stand, but today would not necessarily be understood that way. Wanting and liking (or not wanting and not liking), however, strictly only refer to entities that can have desires and preferences.

Navigating photons

Professor Rees explained why some imploding stars are not seen as very bright stars that fade over years, but rather observed through extremely intense bursts of high energy radiation that fade quickly,

"The energy in the form of ordinary photons, ordinary light, that's arisen in the centre of a supernova, diffuses out and takes weeks to escape, okay, but if the star is spinning, then it will be an oblate spheroid, it will have a minor axis along the spin axis, and so the easy way out is for the radiation not to diffuse through but to find the shortest escape route, which is along the spin axis, and I mention this because gamma ray bursts are … when a supernova occurs but because the original star was sort of flattened there is an easy escape route and all the energy escapes in jets along the spin axis and so instead of it diffusing out over a period of weeks, as it does in a supernova, it comes out in a few seconds."

Prof. Martin Rees

Again, the language used is suggestive. Radiation is not just emitted by the star, but 'escapes' (surely a metaphor?). The phrasing "an easy way out" implies something not being difficult. Inanimate entities like photons do not actually (literally) find anything difficult or easy. Moreover, the radiation might "find the shortest escape route": language that does not reflect a playing out of physical forces but an active search – only a being able to seek can find. Yet, again, the language supports an engaging narrative, 'softening' the rather technical story by subtly reflecting a human quest.

Professor Rees also referred to how,

"when those big stars face a crisis they blow off their outer layers"

Prof. Martin Rees

again using phrasing which seems to present the stars as deliberate actors – they actively "blow off" material when they "face a crisis". A crisis is (or at least was originally) a point where a decision needs to be made. A star does not reach the critical point where it reluctantly decides it needs to shed some material – but rather is subject to changing net forces as the rate of heat generation from nuclear processes starts to decrease.

A sense of anthropomorphic narrative also attaches to Professor Crawford's explanation of how more massive stars process material faster,

"…more massive stars … actually have shorter lifetimes …they have to chomp through their fuel supply so furiously that they exhaust it more rapidly

Prof. Carolin Crawford

'Chomping', a term for vigorous eating (biting, chewing, munching), is here a metaphor, as a star does not eat – as pointed out in the companion piece, nutrition is a characteristics feature of living things, but does not map across to stars even if they are described as being born, living, dying and so forth. To be furious is a human emotional response: stars may process their remaining hydrogen quickly, but there is no fury involved. Again, though, the narrative, perhaps inviting associated mental imagery, communicates a sense of the science.

Laid-back gas

Another example of anthropomorphism was

"…if you have a gas cloud that's been sitting out in space for billions of years and has not bothered to contract because it's been too hot or it's too sparse…"

Prof. Carolin Crawford

This is an interesting example, as Prof. Crawford explicitly explains here that the gas cloud has not contracted because of the low density of material (so weak gravitational forces acting on the particles) and/or the high temperature (so the gas comprises of energetic, so fast moving, particles), so the suggestion that the material cannot be bothered (implication: that the 'cloud' operates as a single entity, and is sentient if perhaps a little lazy) does not stand in place of a scientific explanation, but rather simply seems to be intended to 'soften' (so to speak) the technical nature of the language used.

Analogy

An analogy goes beyond a simile or metaphor because there is some kind of structural mapping to make it explicit in what way or ways the analogue is considered to be like the target concept. 5 (Such as when explaining mass defect in relation to the material lost from the saucepan when cooking rice!)

A potential teaching analogy to avoid alternative conceptions about mass defect in nuclear processes

Read about science analogies

So, Prof. Rees suggests that scientists can test their theories about star 'life cycles' by observation, even though an individual star only moves through the process over billions of years, and uses an analogy to a more familiar everyday context:

"We can test our theories, not only because we understand the physics, but because we can look at lots of stars. It is rather like if you had never seen a tree before, and you wandered around in a forest for a day, you can infer the life cycles of trees, you'd see saplings and big trees, etcetera. And so even though our lifetime is minuscule compared to the lifetime of a stable star, we can infer the population and life cycles of stars observationally and the theory does corroborate that fairly well."

Prof. Martin Rees

This would seem to make the basis of a good teaching analogy that could be discussed with students and would likely link well with their own experiences.

The other explicit analogy introduced by Prof. Rees is one well-known to physics teachers (sometimes in an ice-skater variant),

"If a contracting cloud has even a tiny little bit of spin, if it is rotating a bit, then as it contracts, then just like the ballerina who pulls in her arms and spins faster, then the contracting cloud will start to spin faster…"

Prof. Martin Rees

Stellar similes

I take the difference between a simile and a metaphor as the presence of an explicit marker (such as '…as…',…like…') to tell the listener/reader that a comparison is being made – so 'the genome is the blueprint for the body' would be a metaphor, where 'the genome is like a blueprint for the body' would be a simile.

As if a black hole cuts itself off

So, when Professor Rees describes how a massive black hole forms, he uses simile (i.e., "…as if were…"),

"So, if a neutron star gets above that mass, then it will compress even further, and will become a black hole – it will go on contracting until it, as it were, cuts itself off from the rest of the universe, leaving a gravitational imprint frozen in the space that's left. It becomes a black hole that things can fall into but not come out."

Prof. Martin Rees

There is an element of anthropomorphic narrative (see above) again here, if we consider the choice of active, rather than passive, phrasing

  • …as it were, cuts itself off from the rest of the universe, compared with
  • …as it were, becomes cut off from the rest of the universe

This is presented as something the neutron star itself does ("it will compress…become a black hole – it will go on contracting until it, as it were, cuts itself off…") rather than a process occurring in/to the matter of which it is comprised.

As if galaxies drop over the horizon

Prof. Rees uses another simile, when talking of how the expansion of space means that in time most galaxies will disappear from view,

"All the more distant universe which astronomers like Mark [Sullivan] study, galaxies far away, they will all have expanded their distance from us and in effect disappeared over a sort of horizon and so we just wouldn't see them at all. They'd be too faint, rather like …an inside-out black hole as it were, but in this case they moved so far away that we can't see them any more …"

Prof. Martin Rees

The term horizon, originally referring to the extent of what is in sight as we look across the curved Earth, has become widely used in astronomical contexts where objects cease to be in sight (i.e., the event horizon of a black hole beyond which any light being emitted by an object will not be able to leave {'escape!'} the black hole because of the intense gravitation field), but here Prof. Rees clearly marks out for listeners ("…in effect…a sort of…") that he is making a comparison with the familiar notion of a horizon that we experience here on Earth.

There is another simile here, the reference to the expansion of space leading to an effect "rather like…an inside-out black hole as it were" – but perhaps that comparison would be less useful to a listener new to the topic as it uses a scientific idea rather than an everyday phenomenon as the analogue.

Through a glass onion darkly?

Another simile used by Professor Rees was a references to a "sort of onion skin structure". Now 'onion skin' sometimes refers to the hard, dry, outer material (the 'tunic') usually discarded when preparing the onion for a dish. To a science teacher, however, this is more likely to mean the thin layer of epithelial tissue that can be peeled from the scales inside the bulb. These scales, which are potentially the bases of leaves that can grow if the bulb is planted, are layered in the bulb.

The skin is useful in science lessons as it is a single layer of cells, that is suitable for students to dissect from the onion, and mount for microscopic examination – allowing them to observe the individual cells. There is something at least superficially analogous to this in stars. Observations of the Sun show that convection processes gives rise to structures referred to as convection 'cells'.

Convection 'cells' at the Sun's surface (Source: NASA)
Onion skin magnified showing individual epithelial cells (Source: Wikimedia commons)

Yet, when Professor Rees' simile is heard in context, it seems that this is not the focus of the comparison:

"…all the nuclear processes which would occur at different stages in the heavy stars…which have this sort of onion skin structure with the hotter inner layers"

Prof. Martin Rees

Very large stars that have processed much of their hydrogen into helium can be considered to have a layered structure where under different conditions a whole sequence of processes are occurring leading to the formation of successively heavier and heavier elements, and ultimately to a build-up of iron near the centre.

The onion model of the structure of a large star (original image by Taken from Pixabay)

When I heard the reference to the onion, this immediately suggested the layered nature of the onion bulb being like the structure of a star that was carrying out the sequence of processes where the products of one fusion reaction become the raw material for the next. Presumably, my familiarity with the layered model of a star led me to automatically make an association with onions which disregarded the reference to the skin. That is, I had existing 'interpretive resources' to understand why the onion reference was relevant, even though the explicit mention of the skin might make the comparison obscure to someone new to the science.

Metaphors – all the way back up?

Some metaphors can easily be spotted (if someone suggests mitochondria are the power stations of the cell, or a lion is King of the jungle), but if our conceptual systems, and our language, are built by layers of metaphor upon metaphor then actually most metaphors are dead metaphors.

That is, an original metaphor is a creative attempt to make a comparison with something familiar, but once the metaphor is widely taken up, and in time becomes common usage and so a part of standard language, it ceases to act as a metaphor and becomes a literal meaning.

This presumably is what has happened with the adoption of the idea that stars are born, live out their lives, and then die: originally it was a poetic use of language, but now among astronomers it reflects an expanded standard use of terms that were once more restricted (born, live, lifetime, die etc.).

"…Stars dived in blinding skies / Stars die / Blinding skies…"
Stars die, but only due to artistic license
(Artwork from 'Star's die' by Porcupine Tree, photographer: Chris Kissadjekian)
If you see a standard candle…

When Professor Sullivan refers to a "standard candle", this is now a widely used astronomical notion (in relation to how we estimate distances to distant stars and galaxies that are much too far away to triangulate from parallax as the earth changes its position in the solar system) – but at one time this was used as a figure of speech.

Some figures of speech are created in the moment, but never widely copied and adopted. The astronomical community adopted the 'standard candle' such that it is now an accepted term, even though most young people meeting astronomical ideas for the first time probably have very little direct experience of candles. What might once have seemed a blatantly obvious allusion may now need explaining to the novice.

When Sir Arthur Eddington (famous for collecting observations during an eclipse consistent with predictions from relativity theory about the gravitational 'bending' of starlight) gave a public lecture in 1932, he seems to have assumed that his audience would understand the analogy between an astronomer's 'standard candles' (Cepheid variables) and standard candles they might themselves use!

"If you see a standard candle anywhere and note how bright it appears to you, you can calculate how far off it is; in the same way an astronomer observes his [or her] 'standard candle' in the midst of a nebula, notes its apparent brightness or magnitude, and deduces the distance of the nebula"

Eddington, 1933/1987, pp.7-8

This ongoing development in language means that it may not always be entirely clear which terms are still engaged with as if metaphors and which have now become understood as literal. That is, in considering whether some phrase is a metaphor we can ask two questions:

  • did the author/speaker intend this as a comparison, or do they consider the term has direct literal meaning?
  • does the reader/listener understand the term to have a literal meaning, or is it experienced as some novel kind of comparison with another context which has to be related back to the focus?

In the latter case we might also think it is important to distinguish between cases where the audience member can decode the intention of the comparison 'automatically' as part of normal language processing – and cases where they would have to consciously deliberate on the meaning. (In the latter case, the interpretation is likely to disrupt the flow of reading, and when listening could perhaps even require the listener to disengage from the communication such that subsequent speech is missed.)

(Metaphorical?) hosts

So, when Prof. Crawford suggests that

"The supernovae, particularly, are of fundamental importance for the host galaxy…"

Prof. Carolin Crawford

her use of the term 'host' is surely metaphorical (at least for a listener – this term is widely used in the literature of academic astronomy 6). A host offers hospitality for a guest. That does not seem to obviously reflect the relationship between a supernova and the galaxy it is found in and is part of. It is not a guest: rather, in Prof. Sullivan's terms we might suggest that star has 'lived its entire life' in that galaxy – it is its galactic 'home'. Despite this comparison not standing up to much formal analysis, I suspect the metaphor can be automatically processed by anyone with strong familiarity with the concept of a host. Precise alignment may not be a strong criterion for effective metaphors.

Another meaning of host refers to a sacrificial victim (as in the host in the Christian Eucharist) which seems unlikely to be the derivation here, but perhaps fits rather well with Prof. Crawford's point. A supernova too close to earth could potentially destroy the biosphere – an unlikely but not impossible event.

(Metaphorical?) bubbles

Professor Crawford described some of the changes during a supernova,

"You have got your iron core, it collapses down under gravity in less than a second, that kind of leaves the outer layers of the star a little behind, they crash down, bounce on the surface of the core, and then there's a shockwave, that propels all this stellar debris, out into space. So, this is part of the supernova explosion we have been talking about, and it carves out a bubble within the interstellar medium."

Prof. Carolin Crawford

There are a number of places here where everyday terms are applied in an unfamiliar context such as 'core', 'bouncing', 'layers' and 'debris'. But the idea of carving a bubble certainly seems metaphorical, if only because a familiar bubble would have a physical surface, where surely, here, there is no strict interface between discrete regions of gases. But, again, the term offers an accessible image to communicate the process. (And anyone looking at the NASA image above of convection cells in the Sun might well feel that these can be perceived as if bubbles.)

(Metaphorical?) pepper

Similarly, the idea of heavy elements from exploding suns being added to the original hydrogen and helium in the interstellar medium as like adding pepper also offers a strong image,

"…this is the idea of enrichment, you start off with much more primordial hydrogen and helium gas that gets steadily peppered with all these heavy elements…"

Prof. Carolin Crawford

Perhaps 'peppered' is now a dead metaphor, as it is widely used in various contexts unrelated to flavouring food.

(Metaphorical?) imprints

When Professor Rees referred to a neutron star that has become a black hole leaving a "gravitational imprint frozen in the space that's left" this makes good sense as the black hole will not be visible, but its gravitational field will have effects well beyond its event horizon. Yet, one cannot actually make an imprint in space, one needs a suitable material substrate (snow, plater, mud…) to imprint into; and nor has anything been 'frozen' in a literal sense. Indeed, the gravitational field will change as the black hole acquires more material through gravitational capture (and in the very long term loses mass though evaporates Hawking radiation – which is said to cause the black hole to 'evaporate'). So, this is a kind of double metaphor.

(Metaphorical?) blasts and blows

I report above both the idea that rocky planet close to large stars might have derived from 'giant' planets "that have had the outer gassy layers blasted off" and how "big stars…blow off their outer layers". Can stars really blow, or is this based on a metaphor. Blasts usually imply explosions, sudden events, so perhaps these are metaphorical blasts? And it is not just larger stars that engage in blowing off,

"[The sun] will blow off its outer layers and become a red giant, expanding so it will engulf the inner planets, but then the core will settle down to what's called a white dwarf, this is a dead, dense star, about a million times denser than normal stuff…."

Prof. Martin Rees

Metaphors galore!

Perhaps those last examples are not especially convincing – but this reflects a point I made earlier. Language changes over time: it is (metaphorically-speaking) fluid. If language started from giving names to things we can directly point at, then anything we cannot directly point at needs to be labelled in terms of existing words. Most of the terms we use were metaphors at some point, but became literal as the language norms changed.

But society is not a completely homogeneous language community. The requirements of professional discourse in astronomy (or any other specialised field of human activity) drive language modifications in particular regards ahead of general language use. It is not just people in Britain and the United States who are divided by a common language – we all are to some extent. What has become literal meaning for for one person (perhaps a science teacher) may well only be a metaphor to another (a student, say).

After all, when I look up what it is to blow off, I find that the most common contemporary meaning relates to a failure to meet a social obligation or arrangement – I am pretty sure (from the context) that that is not what Professor Rees was suggesting ("…when those big stars face a crisis they [let down] their outer layers".) Once we start looking at texts closely, they seem to be 'loaded' with figures of speech. A planet is not materially constrained in space, yet we understand why an orbit might be considered 'tight'.

In the proceeding quote, the core of a star seems to need no explanation although it presumably derives by analogy with the core of an apple or similar fruit, which itself seems to derive metaphorically form an original meaning of the heart. Again, what is meant by engulf is clear enough although originally it referred to the context of water and the meaning has been metaphorically (or analogously) extended.

The terms red giant and white dwarf clearly derive from metaphor. (Sure, a red giant is gigantic, but then, on any normal scale of human experience, so is a white dwarf.) These terms might mystify someone meeting them for the first time so not already aware they are used to refer to classes of star. This might suggest the value of a completely objective language for discussing science where all terms are tightly (hm, too metaphorical…closely? rigidly? well-) defined, but that would be a project reminiscent of the logical positivist programme in early twentieth century that ultimately proved non-viable. We can only define words with more words, and there are limits to the precision possible with a usable, 'living', language.

Take the "discovery that we are literally made of the ashes of long dead stars". Perhaps, but the term ashes normally refers to the remains of burnt organic material, especially wood, so perhaps we are not literally, but only metaphorically made of the ashes of long dead stars. Just as when when Professor Sullivan noted,

"the white dwarf is made of carbon, it's made of oxygen, and the temperature and the pressure in the centre of that white dwarf star can become so extreme, that carbon detonation can occur in the centre of the white dwarf, and that is a runaway thermonuclear reaction – that carbon burns in astronomer speak into more massive elements…"

Prof. Mark Sullivan
Are we stardust, ashes or just waste?

Burning is usually seen in scientific terms as another word for combustion. So, the nuclear fusion, 'burning' "in astronomer speak" of its nuclear 'fuel' in a star represents an extension of the original meaning by analogy with combustion. 9 Material that is deliberately used to maintain a fire is fuel. A furnace is an artefact deliberately built to maintain a high temperature – the nuclear furnace in a star is not an artefact but a naturally occurring system (gravity holds the material in place), but is metaphorically a furnace. A runaway is a fugitive who has absconded – so to describe a thermonuclear reaction (which is not going anywhere in spatial terms) as 'runaway' adopts what was a metaphor. (Astronomers also use the term 'runaway' to label a class of star that seem to be moving especially fast compared with the interstellar medium – a somewhat more direct borrowing of the usual meaning of 'runaway'.)

To consider us to be made from 'nuclear waste' relies on seeing the star-as-nuclear-furnace as analogous to a nuclear pile in a power station. In nuclear power stations we deliberately process fissile material to allow us to generate electrical power: and material is produced as a by-product of this process (that is, it is a direct product of the natural nuclear processes, but a by-product of our purposeful scheme to generate electricity). To consider something waste means making a value judgement.

If the purpose of a star is to shine (a teleological claim) and the fusion of hydrogen is the means to achieve that end, then the material produced in that process which is no longer suitable as 'fuel' can be considered 'waste'. If the universe does not have any purpose(s) for stars then there is no more basis for seeing this material as waste than there is for seeing stars themselves as the waste products of a process that causes diffuse matter to come together into local clumps. That is, this is an anthropocentric perspective that values stars as of more value than either the primordial matter from which they formed, or the 'dead' matter they will evolve into when they no longer shine 'for us'. Nature may not have such favourites! If it has a purpose, then stars seem to only be intermediate steps towards its ultimate end.

What does support the turtle? Surely, it's metaphors all the way down.
(Source: Pintrest)

Sources cited:
Notes:

1 It may seem fanciful that we give a specific individual tree a proper name but should a child inherently appreciate that we commonly name individual hamsters (say, or ships, or roads), but not individual trees? 'Major Oak' is a particular named Oak tree in Sherwood Forest, so the idea is not ridiculous. (It is very large, but apparently the name derives from it being described by an author with the army rank of major. Of course, this term for a soldier leading others derives metaphorically from a Latin word meaning bigger, so…)

2 "So how do we bridge between dogs and trees on one hand and electrons and the strong nuclear force on the other (so to speak!)? The answer is we build using analogy and we talk about those constructions using a great deal of metaphor."

  • We understand what is meant by bridge here in relation to an actual bridge that physically links two places – such as locations on opposite sides of a river or railway line.
  • There is no actual building up of materials, but we understand how we can 'build' in the abstract by analogy.
  • These things are not actually at hand, but we make a metaphorical comparison in terms of distinguishing items held in 'opposite' hands. We understand what is meant by a great deal of something abstract by analogy with a great deal of something we can directly experience, e.g., sand, water, etcetera.

Justice personified, on the one hand weighing up the evidence and on the other imposing sanctions

(Image by Sang Hyun Cho from Pixabay)

We construct scientific concepts and models and theories by analogy with how we construct material buildings – we put down foundations then build up brick by brick so that the top of the structure is only very indirectly supported by the ground.

(Image by joffi from Pixabay)

3 A point is a hypothetical, infinitesimally small, location in space, which is not something a person could actually make. The 'point' of an argument is metaphorically like the point of a pencil or spear which is metaphorically an approximation to an actual point. Of course, we (adult members of the English language community) all know what is meant by the point of an argument – but people new to a language (such as young children) have to find this out, without someone holding up the point of an argument for them to learn to recognise.

4 In part, this means linguistic resources. Each individual person has a unique vocabulary, and even though sharing most words with others, often has somewhat unique ranges of application of those words. But it also refers to personal experiences that can be drawn upon (e.g., having cared for an ill relative, having owned a pet, having undertaken part-time work in a hospital pharmacy, having been taken to work by a parent…) and the cultural referents that are commonly discussed in discourse (cultural icons like the Mona Lisa or Beethoven's fifth symphony; familiarity with some popular television show or film; appreciating that Romeo and Juliet were tragic lovers, or that Gandhi is widely considered a moral role model, and so forth.)

"Penny, I'm a physicist. I have a working knowledge of the entire universe and everything it contains."

"Who's Radiohead?"

"I have a working knowledge of the important things in the universe."

Still from 'The Big Bang Theory' (Chuck Lorre Productions / Warner Bros. Television)

The interpretive resources are whatever mental resources are available to help make sense of communication.

5 I am using the term concept in an 'inclusive' sense (Taber, 2019), in that whenever a person can offer a discrimination about whether something is an example of some category, then they hold a concept (vague or detailed; simple or complex; canonical or alternative).

That is, if someone can (beyond straight guesswork) try to answer one of the questions "what is X? ", "is this an example of X?" or "can you suggests an example of X?", then they have a relevant concept – where X could be…

  • a beaker
  • a force
  • a bacterium
  • opaque
  • a transition metal
  • an isomer
  • distillation
  • neutralisation
  • a representation of the ideal gas law
  • and so forth

Read more about concepts

6 The earliest reference to 'host galaxies' I found in a quick search of the scientific literature was from 1972 in a paper which used the term 'host galaxy' 8 times, including,

"We estimated the distances [of observed supernovae]…by four different methods:

  • (1) Estimating the absolute luminosity of the host galaxy.
  • (2) Estimating the absolute luminosity of the supernova.
  • (3) Using the measured redshift of the host galaxy and assuming the Hubble constant H = 75 km (s Mpc)-1 …
  • (4) Identifying the host galaxy with a cluster of galaxies for which the distance from Earth had already been estimated.
Ulmer, Grace, Hudson & Schwartz, 1972, p.209

The term 'host galaxy' was not introduced or defined in the paper, suggesting that either it was already in common use as a scientific term (and so a dead metaphor within the astronomical community) in 1972 or Ulmer and colleagues assumed it was obvious enough not to need explanation.

7 It should be pointed out that 'In Our Time' is not presented as succession of mini-lectures, or as a tightly scripted programme, but as a conversation between Melvyn as his guests. Of course, there is some level of preparation by those involved, but in adopting a conversational style, avoiding the sense of prepared statements, it is inevitable that a guest's language will sometimes lack the precision of a drafted and much revised account.

8 A supernova may appear as a new star in the sky if it is so far away that the star was not previously detectable, or as a known star quick;y becoming very much brighter.

9 One should be careful in making such equivalences, as in that although we may equate burning with combustion, burning is an everyday ('life world') phenomenon, and combustion is a scientific concept: often our scientific concepts are more precisely defined than the related everyday terms. (Which is why melting has a broader meaning in everyday life {the sugar melts in the hot tea; the stranger melted away into the mist} than it does in science.) But although we might say, as suggested earlier in the text, we have been burned by exposure to the sun's ultraviolet rays, or by contact with a caustic substance, in those contexts we are unlikely to consider our skin as 'fuel' for the process.