As part of the primary scientific literature, it publishes articles written by specialist scientists in a technical language intended to be understood by other specialists. Dense scientific terminology is not used to deliberately exclude general readers (as sometimes suggested), but is necessary for scientists to make a convincing case for new knowledge claims that seem persuasive to other specialists. This requires being precise, using unambiguous technical language."The thingamajig kind of, er, attaches to the erm, floppy bit, sort of" would not do the job.
Science News however is news media – it publishes journalism (indeed, 'since 1921' the site reports – although that's the publication and not its website of course.) While science journalism is not essential to the internal processes of science (which rely on researchers engaging with each other's work though scholarly critique and dialogue) it is very important for the public's engagement with science, and for the accountability of researchers to the wider community.
Science journalists have a job similar to science teachers – to communicate abstract ideas in a way that makes sense to their audience. So, they need to interpret research and explain it in ways that non-specialists can understand.
The news article told me
"Like a shaggy dog in springtime, some black holes have to shed… Unlike dogs with their varied fur coats, isolated black holes are mostly identical. They are characterized by only their mass, spin and electric charge. According to a rule known as the no-hair theorem, any other distinguishing characteristics, or "hair," are quickly cast off. That includes magnetic fields."
Conover, 2013
Here there is clearly the use of an analogy – as a black hole is not the kind of thing that has actual hair. This would seem to be an example of a journalist creating an analogy (just as a science teacher would) to help 'make the unfamiliar familiar' to her readers:
just as
dogs with lots of hair need to shed some ready for the warmer weather (a reference to a familiar everyday situation)
so, too, do
black holes (no so familiar to most people) need to lose their hair…
Surely a better analogy would be along the lines that just as dogs with lots of hair need to shed some ready for the warmer weather, so to do black holes need to lose their magnetic fields…
An analogy is used to show a novel conceptual structure (here, relating to magnetic fields around black holes) maps onto a more familiar, or more readily appreciated, one (here, that a shaggy dog will shed some of its fur). A teaching analogy may not reflect a deep parallel between two systems, as its function may be just to introduce an abstract principle.
Conover did not invent the 'hair' reference for her ScienceNews piece – rather she built her analogy on a term used by the scientists themselves. Indeed, the title of the cited research journal article was "Magnetic Hair and Reconnection in Black Hole Magnetospheres", and it was a study exploring the consequences of the "no-hair theorem" – as the authors explained in their abstract:
"The no-hair theorem of general relativity states that isolated black holes are characterized [completely described] by three parameters: mass, spin, and charge."
Bransgrove, Ripperda & Philippov, 2021
However, some black holes "are born with magnetic fields" or may "acquire magnetic flux later in life", in which case the fields will vary between black holes (giving an additional parameter for distinguishing them). The theory suggests that these black holes should somehow lose any such field: that is, "The fate of the magnetic flux (hair) on the event horizon should be in accordance with the no-hair theorem of general relativity" (Bransgrove, Ripperda & Philippov, 2021: 1). There would have to be a mechanism by which this occurs (as energy will be conserved, even when dealing with black holes).
So, the study was designed to explore whether such black holes would indeed lose their 'hair'. Despite the use of this accessible comparison (magnetic flux as 'hair'), the text of the paper is pretty heavy going for someone not familiar with that area of science:
"stationary, asymptotically flat BH spacetimes…multipole component l of a magnetic field…self-regulated plasma…electron-positron discharges…nonzero stress-energy tensor…instability…plasmoids…reconnection layer…relativistic velocities…highly magnetized collisionless plasma…Lundquist number regime…Kerr-schild coordinates…dimensionless BH spin…ergosphere volume…spatial hypersurfaces…[…and so it continues]"
(Bransgrove, Ripperda & Philippov, 2021: 1).
"Come on Harry, you know full well that 'the characteristic minimum plasma density required to support the rotating magnetosphere is the Goldreich-Julian number density' [Bransgrove, Ripperda & Philippov, 2021: 2], so hand me that hyperspanner." Image from Star Trek: Voyager (Paramount Pictures)
Spoiler alert
I do not think I will spoil anything by revealing that Bransgrove and colleague conclude from their work that "the no-hair theorem holds": that there is a 'balding process' – the magnetic field decays ("all components of the stress-energy tensor decay exponentially in time"). If any one reading this is wondering how they did this work, given that most laboratory stores do not keep black holes in stock to issue to researchers on request, it is worth noting the study was based on a computer simulation.
That may seem to be rather underwhelming as the researchers are just reporting what happens in a computer model, but a lot of cutting-edge science is done that way. Moreover, their simulations produced predictions of how the collapsing magnetic fields of real black holes might actually be detected in terms of the kinds of radiation that should be produced.
As the news item explained matters:
Magnetic reconnection in balding black holes could spew X-rays that astronomers could detect. So scientists may one day glimpse a black hole losing its hair.
Conover, 2013
So, we have hairy black holes that go through a balding process when they lose their hair – which can be tested in principle because they will be spewing radiation.
Balding is to hair, as…
Here we have an example of an analogy for a scientific concept. Analogies compare one phenomenon or concept to another which is considered to have some structural similarity (as in the figure above). When used in teaching and science communication such analogies offer one way to make the unfamiliar familiar, by showing how the unfamiliar system maps in some sense onto a more familiar one.
hair = magnetic field
balding = shedding the magnetic field
Black holes are expected to be, or at least to become, 'hairless' – so without having magnetic fields detectable from outside the event horizon (the 'surface' connecting points beyond which everything, even light, is unable to 'escape' the gravitational field and leave the black hole). If black holes are formed with, or acquire, such magnetic fields, then there is expected to be a 'balding' process. This study explored how this might work in certain types of (simulated) black holes – as magnetic field lines (that initially cross the event horizon) break apart and reconnect. (Note that in this description the magnetic field lines – imaginary lines invented by Michael Faraday as a mental tool to think about and visualise magnetic fields – are treated as though they are real objects!)
Some such comparisons are deliberately intended to help scientists explain their ideas to the public – but scientists also use such tactics to communicate to each other (sometimes in frivolous or humorous ways) and in these cases such expressions may do useful work as short-hand expressions.
So, in this context hair denotes anything that can be detected and measured from outside a black hole apart form its mass, spin, and charge (see, it is much easier to say 'hair')- such as magnetic flux density if there is a magnetic field emerging from the black hole.
A dead metaphor?
In the research paper, Bransgrove, Ripperda and Philippov do not use the 'hair' comparison as an analogy to explain ideas about black holes. Rather they take the already well-established no-hair theorem as given background to their study ("The original no-hair conjecture states that…"), and simply explain their work in relation to it ("The fate of the magnetic flux (hair) on the event horizon should be in accordance with the no-hair theorem of general relativity.")
Whereas an analogy uses an explicit comparison (this is like that because…), a comparison that is not explained is best seen as a metaphor. A metaphor has 'hidden meaning'. Unlike in an analogy, the meaning is only implied.
"The no-hair theorem of general relativity states that isolated black holes are characterized by three parameters: mass, spin, and charge";
"The original no-hair conjecture states that all stationary, asymptotically flat BH [black hole] spacetimes should be completely described by the mass, angular momentum, and electric charge"
Bransgrove and colleagues do not need to explain why they use the term 'hair' in their research report as in their community it has become an accepted expression where researchers already know what it is intended to mean. We might consider it a dead metaphor, an expression which was originally used to imply meaning through some kind of comparison, but which through habitual use has taken on literal meaning.
Science has lots of these dead metaphors – terms like electrical charge and electron spin have with repeated use over time earned their meanings without now needing recourse to their origins as metaphors. This can cause confusion as, for example, a learner may develop alternative conceptions about electron spin if they do not appreciate its origin as a metaphor, and assumes an electron spins in the same sense as as spinning top or the earth in space. Then there is an associative learning impediment as the learner assumes an electron is spinning on its axis because of the learner's (perfectly reasonable) associations for the word 'spin'.
The journalist or 'science writer' (such as Emily Conover), however, is writing for a non-specialist readership, so does need to explain the 'hair' reference. So, I would characterise the same use of the terms hair/no-hair and balding as comprising a science analogy in the news item, but a dead metaphor in the context of the research paper. The meaning of language, after all, is in the mind of the reader.
Is the work of cognition like the work of a palaeontologist? (Image by Brenda Geisse from Pixabay)
I like the reflexive nature of this account – of someone reconstructing an analogy
abouthow cognition reconstructs coherent wholes from partial, fragmented data
froma partial, fragmented memory representation.
I was reading something about memory function that piqued my interest in an analogy:
"Neisser, using an analogy initially developed by Hebb (1949) to characterize [sic] perception, likened the rememberer to a paleontologist who attempts to reconstruct a dinosaur from fragmentary remains: 'out of a few stored bone chips, we remember a dinosaur'…"
Schacter, 1995, p.10
I was interested enough to look up the original use of this analogy (as I report below).
This links to three things that have separately interested me:
the nature of memory
the constructivist account of learning and cognition
using analogies in teaching and comunicating science
The nature of our memories
I have long been interested in what memory is and how it works – and its role in academic learning (Taber, 2003). In part this perhaps derives from the limits of my own memory – I have been reasonably successful academically, but have never felt I had a good memory (and I seem to get more 'absent minded' all the time). This interest grew as it became clearer to me that our memory experiences seem to be quite different – my late wife Philippa would automatically and effortlessly remember things in a way that that seemed to me to be a kind of superpower. (She was once genuinely surprised that I could not picture what a family member had been wearing on arriving at a family event years before, whereas I thought I was doing pretty well to even remember I had been there.) Now that neurodiversity is widely recognised, it seems less surprising that we do not all experience memory in the same way.
A lot of people, however, understand memory in terms of a kind of folk-model (that is, a popular everyday account which does not match current scientific understanding) – along the lines that we put information into a memory store, where – unless it gets lost and we forget – we can later access it and so remember what it was that we committed to memory. Despite the ubiquity of that notion, research suggests that is not really how memory functions. We might say that this is a common alternative conception of how memory works.
Schacter was referring back to a tradition that began a century ago when Bartlett carried out a series of studies on memory. Bartlett (1932/1995) would, for example, expose people to a story that was unfamiliar to his study participants, and then later ask them to retell as much of the story as they could remember. As might be expected, some people remembered more details than others.
What perhaps was less predictable at the time was the extent to which people included in their retelling details that had not been part of the original story at all. These people were not deliberately embellishing or knowingly guessing, but reporting, as best they could, what their memory suggested had been part of the original story.
People who habitually exhibit this 'confabulation' to an pathological degree (perhaps remembering totally fantastic things that clearly could not be true) are recognised as having some kind of problem, but it transpires this is just an extreme of something that is normal behavior. Remembering is not the 'pulling something out of storage' that we may experience it as – as actually what we remember is more like a best guess based on insufficient data (but a guess made preconsciously, so it appears in our conscious minds as definitive) than a pristine copy of an original experience. Memory is often more a matter of constructing an account from the materials at hand than simply reading it out from something stored.
Thus the analogy. Here is some wider context for the quote presented above:
"The publication of Neisser's (1967) important monograph on cognitive psychology rekindled interest in Bartlett's ideas about schemas and reconstructive memory. According to Neisser, remembering the past is not a simple matter of reawakening a dormant engram or memory trace; past events are constructed by using preexisting knowledge and [schemata] to piece together whatever fragmentary remains of the initial episode are available in memory. Neisser, using an analogy initially developed by Hebb (1949) to characterize [sic] perception, likened the rememberer to a paleontologist who attempts to reconstruct a dinosaur from fragmentary remains: 'out of a few stored bone chips, we remember a dinosaur' (1967, p.285). In this view, all memories are constructions because they include general knowledge that was not part of a specific event, but is necessary to reconstruct it. The fundamentally constructive nature of memory in turn makes it susceptible to various kinds of distortions and inaccuracies. Not surprisingly, Neisser embraced Bartlett's observations and ideas about the nature of memory."
Schacter, 1995, p.10
These ideas will not seem strange to those who have studied science education, a field which has been strongly influenced by a 'constructivist' perspective on learning. Drawing on learning science research, the constructivist perspective focuses on how each learner has to build up their own knowledge incrementally: it is not possible for a teacher to take some complex technical knowledge and simply transfer it (or copy it) to a learner's mind wholesale.
Excavating the analogy: what did Hebb actually say?
Hebb is remembered for his work on understanding the brain in terms of neural structures – neurons connected into assemblies through synapses. His book 'The Organization of Behavior' has been described as "one of the most influential books in Psychology and Neuroscience" (Brown, 2020: 1).
The analogy referred to by Schacter was used by Hebb in describing perception. He discussed studies using a tachistoscope, an instrument for displaying images for very brief periods. This could be used to show an image to a person with an exposure insufficient for them to take in all the details,
"…the pattern is perceived, first, as a familiar one, and then with something missing or something added. The something, also, is familiar; so the total perception is a mélange of the habitual.
The subject's reports [make it] clear that the subject is not only responding to the diagram as a whole; he perceives its parts as separate entities, even though presentation is so brief. Errors are prominent, and such as to show that all the subject really perceives–and then only with rough accuracy–is the slope of a few lines and their direction and distance from one another"
Hebb, 1949: pp.46-47
That is, the cognitive system uses the 'clues' available from the incomplete visual data to build (in effect) a hypothesis of what was seen, based on correspondences between the data actually available and familiar images that match that limited data. What the person becomes consciously aware of 'seeing' is not actually a direct report from the visual field of the presented image, but a constructed image that is a kind of conjecture of what might have been seen – 'filling-in' missing data with what seems most likely based on past visual experiences.
Cognitive scientist Annette Karmiloff-Smith developed the concept of 'representational redescription' as a way of describing how initially tacit knowledge could eventually become explicit. She suggested that "intra-domain and inter-domain representational relations are the hallmark of a flexible and creative cognitive system" (Karmiloff-Smith,1996: 192). The gist was that the brain is able to re-represent its own internal representations in new forms with different affordances.
An loose analogy might be someone who takes a screenshot when displaying an image from the JPEG photo collection folder on the computer, opens the screenshot as a pdf file, and then adds some textual annotations before exporting the file to a new pdf. The representation of the original image is unchanged in the system, but a new representation has been made of it in a different form, which has then been modified and 'stored' (represented) in a different folder.
Hebb was describing how a representation of visual data at one level in the cognitive system has been represented elsewhere in the system (representational redescription?) at a level where it can be mentipulated by 'filling-in'.
Hebb then goes on to use the analogy:
"A drawing or a report of what is seen tachistoscopically is not unlike a paleontologist's reconstruction of early man from a tooth and a rib. There is a clear effect of earlier experience, filling in gaps in the actual perception, so that the end result is either something familiar or a combination of familiar things–a reconstruction on the basis of experience."
Hebb, 1949: p.47
Teaching analogies
Hebb was writing a book that can be considered as a textbook, so this can be seen as a teaching analogy, although such analogies are also used in communicating science in other contexts.
Teaching is about making the unfamiliar familiar, and one way we do that is by saying that 'this unfamiliar thing you need to learn about is a bit like this other thing that you already know about'. Of course, when teaching in this way we need to say in what way there is an analogy, and it may also be important to say in what ways the two things are not alike if we do not want people to map across irrelevant elements (i.e., to develop 'associative' learning impediments).
Hebb is saying that visual perception is often not simply the detection of a coherent and integral image, but is rather a construction produced by building upon the available data to construct a coherent and integral image. In extremis, a good deal may be made of very little scraps of input – akin to a scientist reconstructing a model of a full humanoid body based on a couple of bits of bone or tooth.
Hebb's analogy
There are examples where palaeontologists or anthropologists have indeed suggested such complete forms based on a few fossil fragments as data. This is only possible because of their past experiences of meeting many complete forms, and the parts of which they are made. (And of course, sometimes other scientists completely disagree about their reconstructions!)
An exscientific analogy?
Often in teaching science we use teaching analogies that compare an unfamiliar scientific concept to some familiar everyday phenomenon – perhaps a reaction profile is a bit like a roller-coaster track. Perhaps we could call these adscientific analogies as the meaning is transferred to the scientific concept from the everyday.
Sometimes, however, familiar scientific phenomena or ideas are used as the source – as here. Perhaps these could be called exscientific analogies as the meaning is taken from the science concept and applied elsewhere.
Developing the palaeontology analogy
So, Hebb had originally used the palaeontology analogy in the context of discussing perception. When I looked into how Neisser had used the comparison in his "important monograph on cognitive psychology" I found he had developed the analogy, returning to it at several points in his book.
Do we analyse what we attend to?
Neisser's first reference was also in relation to perception, rather than memory. Neisser argued that before we can attend to part of a scene there must already have been the operation of "preattentive mechanisms, which form segregated objects" from which we can select what to attend to. These processes might be referred to as analyses:
"…the detailed properties and features that we ordinarily see in an attended figure…arise…only because part of the input was selected for attention and certain operations then performed on it. Neither the object of analysis nor the nature of the analysis is inevitable, and both may vary in different observers and at different times."
Neisser, 1967, p.94
But Neisser was not sure this really was 'analysis', which he understood as drawing on another (what I labelled above) exscientific analogy:
"The very word 'analysis' may not be apt. It suggests an analogy with chemistry: a chemist 'analyses' unknown substances to find out what they 'really' are."
Neisser, 1967, p.94
Rather than refer to analysis, we could draw on Hebb's palaeontological analogy:
"More appropriate…is Hebb's (1949, p.47) comparison of the perceiver with a paleontologist, who carefully extracts a few fragments of what might be bones from a mass of irrelevant rubble and 'reconstructs' the dinosaur that will eventually stand in the Museum of Natural History. In this sense it is important to think of focal attention as a constructive, synthetic activity rather than as purely analytic. One does not simply examine the input and make a decision; one builds an appropriate visual object."
Neisser draws upon the analogy repeatedly in developing his account of perception:
"Such emotion-flooded experiences [as 'physiognomic' perception: 'Everyone has perceived such traits as suppressed anger in a face, gaiety in a movement, or peaceful harmony in a picture'] can be thought of as the result of particular kinds of construction. The same fragments of bone that lead one paleontologist to make an accurate model of an unspectacular creature might lead another, perhaps more anxious or more dramatic, to 'reconstruct' a nightmarish monster." (pp.96-97)
"To 'direct attention' to a figure is to attempt a more extensive synthesis of it. Of course, synthesis presupposes some prior analysis, as the paleontologist must have some fragments of bone before he can build his dinosaur…" (p.103)
"Recognition, whether of spelling patterns or words as wholes, must be mediated by relevant features, as meaningless in themselves as the bone chips of the paleontologist." (p.114)
"The process of figural synthesis does not depend only on the features extracted from the input, just as the dinosaur constructed by a paleontologist is not based only on the bone chips he has found. Equally important is the kind of perceptual object the perceiver is prepared to construct. The importance of set and context on the perception of words has been demonstrated in a great many experiments." (pp.115-116)
Neisser, 1967
And as with perception, so memory…
When Neisser discusses memory he uses a kind of double analogy – suggesting that memory is a bit like perception, which (as already established) is a bit like the work of the palaeontologist:
"Perception is constructive, but the input information often plays the largest single role in determining the constructive process. A very similar role, it seems to me, is played by the aggregate of information stored in long-term memory.
This is not to say that the stimuli themselves are copied and stored; far from it. The analogy being offered asserts only that the role which stored information plays in recall is like the role which stimulus information plays in perception….The model of the paleontologist, which was applied to perception and focal attention in Chapter 4, applies also to memory: out of a few stored bone chips, we remember a dinosaur….one does not recall objects or responses simply because traces of them exist in the mind, but after an elaborate process of reconstruction, (which usually makes use of relevant stored information).
What is the information – the bone chips – on which reconstruction is based? The only plausible possibility is that it consists of traces of prior processes of construction. There are no stored copies of finished mental events, like images or sentences, but only traces of earlier constructive activity."
Neisser, 1967, p.285
Fleshing-out the metaphor
Neisser then pushes the analogy one step further, by pointing out that the 'fleshed-out' model of a dinosaur in the museum may be constructed in part based on the fossil fragments of bones, but those fragments themselves do not form part of the construction (the model). The bones are used as referents in building the skeletal framework (literally, the skeleton) around which the model will be built, but the model is made from other materials (wood, steel, fibreglass, whatever) and the fossil fragments themselves will be displayed separately or perhaps filed away in a drawer in the museum archives. (As in the representational redescription model – the original representation is redescribed at another level of the system.)
"The present proposal is, therefore, that we store traces of earlier cognitive acts, not of the products of those acts. The traces are not simply 'revised' or 'reactivated' in recall; instead, the stored fragments are used as information to support a new construction. It is as if the bone fragments used by the paleontologist did not appear in the model he builds at all – as indeed they need not, if it to represent a fully fleshed-out skin-covered dinosaur. The bones can be thought of, somewhat loosely, as remnants of the structure which created and supported the original dinosaur, and thus as sources of information about how to reconstruct it."
Neisser, 1967, pp.285-286
Neisser's development of Hebb's analogy
The head palaeontologist?
A final reference to the analogy is used when Neisser addresses the question of the cognitive executive: the notion that somewhere in the cognitive system there is something akin to an overseer who direct operations:
"Who does the turning, the trying, and the erring" Is there a little man in the head, a homonculus, who acts the part of the paleontologist vis-à-vis the dinosaur? p.293
Neisser, 1967, p.293
The homonculus can be pictured as a small person sitting in the brain's control room, for example, viewing the images being projected from the visual input.
It is usually considered this is a flawed model (potentially lading to an infinite regress), a failure to take a systemic view of the cognitive system. It is the system which functions and leads to our conscious experience of perceiving, attending, making decisions, planning, remembering, and so forth. Whilst there are specialist components (modules) including for the coordination of the system, there is not a discrete controller overlaying the system as a whole who is doing the seeing, hearing, thinking, etcetera based on outputs from processing by the system.
Here the homonculus would like an authority that the palaeontologist turned to in order to decide how to build her model: raising the question of how does that expert know, and who would they, in turn, ask?
Why change Hebb's orignal analogy?
Altohugh Neisser refers to the analogy as being that used by Hebb, he modifies it. A tooth and rib become fragments of bone, and the early man becomes a dinosaur. Whether the shift from the reconstruction of an early hominid to the reconstruction of a terrible lizard was a deliberate one (for greater effect? because Neisser thought it would be more familiar to his readers?) or not I do not know. The phrasing suggests that Neisser thought he was applying Hebb's original comparison – so I suspect this is how he recalled the analogy.
Perhaps Neisser had regularly used the analogy in his teaching, in which case it may have become so familiar to him that he did not feel the need to check the original version. That is, perhaps he was correctly remembering how he had previously misremembered the original analogy. That is not fanciful, as memory researchers suggest this is something that is very common. Each time we access a memory the wider representational context becomes modified by engagement with it.
That is, if what is represented (in 'long-term memory'*) is indeed "traces of prior processes of construction…traces of earlier constructive activity" then each time a 'memory' is experienced, by being constructed based on what is represented ('in memory'*), new traces of that process of constructing the memory are left in the system.
It is possible over the years to be very convinced about the accuracy of a distorted memory that has been regularly reinforced. (The extent to which this may in part be the origin of many wars, feuds, and divorces might be a useful focus for research?)
So perhaps Neisser had represented in his long-term memory the analogy of a palaeontologist with a few fossil fragments, and when he sought to access the analogy, perhaps in a classroom presentation, the other elements were filled-in: the 'tooth and rib' became 'a few fragments of what might be bones' and the 'early man' become 'a dinosaur' – details that made sense of the analogy in terms familiar to Neisser.
The account of cognition that Hebb, Neisser and Schater were presenting would suggest that if this had been the case then for Neisser there would be no apparent distinction between the parts of Hebb's analogy that Neisser was remembering accurately, and the parts his preconscious mind had filled-in to construct a coherent analogy. I like the reflexive nature of this account – of someone reconstructing an analogy about how cognition reconstructs coherent wholes from partial, fragmented data – from a partial, fragmented memory representation.
Sources cited:
Bartlett, F. C. (1932/1995). Remembering: A study in experimental and social psychology Cambridge: Cambridge University Press.
Brown, R. E. (2020). Donald O. Hebb and the Organization of Behavior: 17 years in the writing. Molecular Brain, 13(1), 55. doi:10.1186/s13041-020-00567-8
Hebb, D. O. (1949). The Organisation of Behaviour. A neuropsychological theory. New York: John Wiley & Sons, Inc.
Karmiloff-Smith, A. (1996). Beyond Modularity: A developmental perspective on cognitive science. Cambridge, Massachusetts: MIT Press.
Neisser, U. (1967). Cognitive Psychology. New York: Appleton-Century-Crofts.
Schacter, D. L. (1995). Memory distortion: history and current status. In D. L. Schacter (Ed.), Memory Distortion. How minds, brains, and societies reconstruct the past (pp. 1-43). Cambridge, Massachusetts: Harvard University Press.
* terms like 'in memory' and 'in long-term memory' may bring to mind the folk-notion of memory as somewhere in the brain where things are stored away, whereas it is probably better to think of the brain as a somewhat plastic processing system which is constantly being modified by its own functioning. The memory we experience is simply the outcome of active processing** in part of the system that has previously been modified by earlier mental activity (** active processing which is in turn itself further modifying the system).
Bert was a participant in the Understanding Science Project. Bert was interviewed in Y10 and asked about the topics he had been studying, which included circulation in biology, static electricity in physics, and oxidation in chemistry. He had talked about protons, electrons and atoms in both chemistry (studying atomic structure) and physics (studying static electricity), and was asked if this could also link with biology:
Do you think there are any links with Biology?
Yeah, well there are lots of atoms in you. And we did about the nucleus which we've been doing about in Biology. I'm not sure if there's a link between it, but.
Ah, that's interesting, so
'cause we did about plant and animal cells in Biology, so it's got a nucleus….as I was saying about the blood cells and things. We were doing about the animal and plant cells and, you know, we were seeing what's the same between them and what's different.
So a connection between physics and chemistry on one hand, and biology on the other, was that cells also had a nucleus. This is a term used across these three sciences, but of course the concepts of atomic and cellular nuclei are quite distinct. Was that clear to Bert? What did he understand about cellular nuclei?
So what's the nucleus then?
It's kind of like erm, the brain of the cell kind of. It's, it's what gets the cell to do everything, it's like, the core of the cell.
This response is interesting because, at one level, it suggests that Bert did not have a detailed and well-focussed 'off pat' answer. However, that may not be such a bad thing – definitions that are learnt 'off by heart' may only represent rote learning and may not be well understood. Indeed, it has been argued (in the work of Thomas Kuhn, for example) that in learning science a technical definition is often only really useful once the concept has been acquired: that is once the meaning of the word being defined has, to some degree, already been grasped.
At another level, Bert's answer could be seen as quite sophisticated. What could be taken as an ambiguous response, a difficulty in finding the words to represent his thinking, could also be seen as multifaceted:
essential: the nucleus is the brain of the cell
functional: the nucleus controls the cell (it's what gets the cell to do everything)
structural: the nucleus is the core of the cell
That is, Bert's response could be read, not as a series of alternative suggestions and self-corrections, but rather as a set of complementary images or 'faces' of a complex idea. That would fit with a notion of concepts as being nodes in conceptual networks where the meaning of a particular concept depends upon the way it is associated with others.
The suggestion that the brain reference is intended to be about the essential nature of the nucleus is of course a reading of the text that must be seen as a speculative interpretation. (It probably does not even make sense to ask if Bert intended it this way, as in conversation much of our dialogue does not await deliberation, but is spontaneous, relying largely on implicit cognition.) But, as a teacher, I can see this as a kind of pedagogic device along the lines: 'you ask we what the nucleus is, let me compare it with something you will be familiar with, in essence it is like the brain of the cell'.
This is clearly meant metaphorically ("kind of like erm, the brain of the cell kind of"): that is, it is assumed that the person hearing the metaphor can make the expected sense of the comparison. Metaphors have an essential (sic) role in teaching and in communication more generally, though like other such 'figures' of speech (simile, analogy, anthropomorphism, animism), may become habitually used in place of the deeper meaning they are meant to introduce (Taber & watts, 1996).
It's kind of like erm, the brain of the cell kind of. It's, it's what gets the cell to do everything, it's like, the core of the cell.
Okay. And why is there a connection with Chemistry or the Physics then?
Because erm, we were doing, we were doing in Chemistry about the nucleus has the – neutrons and the protons in the nucleus, then around it is a field of electrons.
…So why is that a connection then? Why is that a connection between the Biology and the Chemistry and the Physics?
Well it's just the nucleus comes under both of them.
Comes under both of them. So is it the same thing?
I wouldn't have thought so, but because when I think of electrons and neutrons I think of electricity, which I don't really think of in our, in our bodies but it could be perhaps. We haven't been told about that.
So there is ambiguity in Bert's report: the nucleus comes up in chemistry and physics in the context of atoms, and in biology in the context of cells. Although the term is the same, so there is at least that connection, Bert "wouldn't have thought" it was the same thing in these different contexts (after all, he would not expect there to be electricity in our bodies!) …but, then again, "it could be perhaps", as they had not been told otherwise. (A possible subtext here being: surely the teacher(s) would have pointed out this was something different if they were going to use the same word for two different things in science lessons?)
The use of the same word label, nucleus, for the rather differently natured nuclei in atoms and cells has potential to act as a linguistic learning impediment (a form of associative learning impediment) as one meaning will likely already be established when a learner meets the other use of the word. It perhaps makes matters worse that part of the meaning, the central component (the structural 'face' of the concept), is the same, than had the usage been clearly unrelated (as in 'bank' being a financial institution and the structure at the edge of a rvier such that the context of use make confusion unlikely). Not only that, but for Bert, these were components of similarly "really microscopic" entities (see 'The cell nucleus is "probably" bigger than an atomic nucleus').
From the perspective of the science teacher, there is little basis for confusing the nucleus of an atom with that of a cell: obviously a cell is a complex entity with a great many components, each of which has itself a complex supra-molecular structure – so clearly the atomic nucleus is on a scale many orders of magnitude smaller than a cell nucleus. However, the expert perspective is based on relating a lot of knowledge that the novice may not yet have, or at least, may not yet be coordinating. In Bert's case, he was only just starting to coordinate these ideas (see 'The cell nucleus is "probably" bigger than an atomic nucleus').
Jim was a participant in the Understanding Science Project. When I was talking to students on that project I would ask them what they were studying in science, rather than ask them about my own agenda of topics. However, I was interested in the extent to which they integrated and linked their science knowledge, so I would from time to time ask if topics they told me about were linked with other topics they had discussed with me. The following extract is taken from the fourth of a sequence of interviews during Jim's first year in secondary school (Y7 in the English school system).
And earlier in the year, you were doing about dissolving sugar. Do you remember that?
Erm, yeah.
Do you think that's got anything to do with the human body?
Erm, we eat sugar.
Mm. True.
Gives us energy…It powers us.
Ah. And why do we need power do you think?
So we can move.
This seemed a reasonable response, but I was intrigued to know if Jim was yet aware of metabolism and how the tissues require a supply of sugar even when there is no obvious activity.
Ah what if you were a lazy person, say you were a very lazy rich person? And you were able to lie in bed all day, watch telly, whatever you like, didn't have to move, didn't have to budge an eyelid, … you're rich, your servants do everything for you? Would you till need energy?
Yes.
Why?
I dunno, 'cause being in bed's tired, tiring.
Is it?
When I'm ill, I stay off for a day, I just feel tired, and like at the end of the day, even more tired than I do when I come to school some times.
Jim's argument failed to allow for the difference in initial conditions
Staying in bed all day and avoiding exercise could indeed make one feel tired, but there seemed something of a confound here (being ill) and I wondered if the reason he stayed in bed on these days might be a factor in feeling even more tired than usual.
So maybe when you are ill, you should come to school, and then you would feel better?
No.
No, it doesn't work like that?
No.
Okay, so why do you think we get tired, when we are just lying, doing absolutely nothing?
Because, it's using a lot of our energy, doing something.
Hm, so even when we are lying at home ill, not doing anything, somehow we are using energy doing something, are we?
Yes.
What might that be, what might we use energy for?
Thinking.
I thought this was a good response, as I was not sure all students of his age would realise that thinking involved energy – although my own conceptualisation was in terms of cellular metabolism, and how thinking depend on transmitting electrical signals along axons and across synapses. I suspected Jim might not have been thinking in such terms.
Do you think it uses energy to think?
(Pause, c.3s)
Probably.
Why do you think that?
Well cause, like, when you haven't got any energy, you can't think, like the same as TV, when it hasn't got any energy, it can't work. So it's a bit like our brains, when we have not got enough energy we feel really tired, and we just want to go to sleep, which can give us more energy, a bit like food.
So Jim here offered an argument about cause and effect- when you haven't got any energy, you can't think. This would certainly be literally true (without any source of energy, no biological functioning would continue, including thinking) although of course Jim had clearly never experienced that absolute situation (as he was still alive to be interviewed), and was presumably referring to experiences of feeling mentally tired and not being able to concentrate.
He offered an analogy, that we are like televisions, in that we do not work without energy. The TV needs to be connected to an electrical supply, and the body needs food (such as sugar, as Jim had suggested) and oxygen. But Jim also used a simile – that sleep was like food. Sleep, like food, according to Jim could give us energy.
So sleeping can give us energy?
Yeah.
How does that work?
Er, it's like putting a battery onto charge, probably, you go to sleep, and then you don't have to do anything, for a little while, and you, then you wake up and you feel – less tired.
Okay so, you think you might need energy to think, because if you have not got any energy, you are very tired, you can't think very well, but somehow if you have a sleep, that might somehow bring the energy back?
Yeah.
So where does that energy come from?
(Pause c.2s)
Erm – dunno.
So here Jim used another analogy, sleeping was like charging a battery. When putting a battery on change, we connect it to a charger, but Jim did not suggest how sleep recharged us, except in that we could rest. When sleeping "you don't have to do anything, for a little while", which might explain a pause in depletion of energy supplies, but would not explain how energy levels were built up again.
[A potentially useful comparison here might have been a television, or a lap top used to watch programmes, with an internal battery, where the there is a buffer between the external supply, and the immediate source for functioning.]
This was an interesting response. At one level it was a deficient answer, as energy is conserved, and Jim's suggestion seemed to require energy to be created or to appear from some unspecified source.
Jim's responses here offered a number of interesting comparisons:
sleep is a bit like food in providing energy
not having energy and not being able to think is like a TV which cannot work without energy
sleeping is like putting a battery on charge
Both science, and science teaching/communication draw a good deal on similes, metaphors and analogies, but they tend to function as interim tools (sources of creative ideas that scientists can then further explore; or means to help someone get a {metaphorical!} foothold on an idea that needs to later be more formally understood).
The idea that sleeping works like recharging a battery could act as an associative learning impediment as there is a flaw in the analogy: putting a battery on charge connects it to an external power source; sleep is incredibility important for various (energy requiring) processes that maintain physical and mental health, and helps us feel rested, but does not in itself source energy. Someone who thought that sleeping works like recharging a battery will not need to wonder how the body accesses energy during sleep as they they seem to have an explanation. (They have access to a pseudo-explanation: sleep restores our energy levels because it is like recharging a battery.)
Jim's discourse reflects what has been called 'the natural attitude' or the 'lifeworld', the way we understand common experiences and talk about them in everyday life. It is common folk knowledge that resting gives you energy (indeed, both exercise and rest are commonly said to give people energy!)
In 'the lifeworld', we run out of energy, we recharge our batteries by resting, and sleep gives us energy. Probably even many science teachers use such expressions when off duty. Each of these notions is strictly incorrect from the scientific perspective. A belief that sleep gives you energy would be an alternative conception, and one that could act as a grounded learning impediment, getting in the way of learning the scientific account.
Yet they each also offer a potential entry point to understanding the scientific accounts. In one respect, Jim has useful 'resources' that can be built on to learn about metabolism, as long as the habitual use of technically incorrect, but common everyday, ways of talking do not act as learning impediments by making it difficult to appreciate how the science teacher is using similar language to express a somewhat different set of ideas.
Physicists see electromagnetism as one of the fundamental forces in the universe, and physics often includes a topic or module on 'electricity and magnetism'. Magnetism can be considered an electrodynamic effect (i.e., due to the movement of charges), but this will not be obvious to students.
Sophia was a participant in the Understanding Science Project. I spoke to here in Y7 (of the English school system) when she told me about the things she had been learning in the topic of electricity. I asked her,
Anything else you've done on electricity?
The er, I don't know what, it's not that much to do with electricity but, yesterday or the day (before) we done magnets.
Oh right. So that's a new topic, is it, not to do with electricity, or?
Well, I think we're still doing electricity. I don't know if it was just something – so we know what might, er, so we know what, what electricity will flow through, and maybe it's something to do with – 'cause magnets like stick to other things, they might be – I'm not sure, I think we might just have had a break from it, I don't know, but.
So, Sophia came up with some suggestions for why magnets might be featured in the electricity topic, but she was not very convinced about this rationale, and considered it was quite possible that the teacher was just interspersing other material to give a 'break' from the main topic. So, instead, they "done magnets".
It is interesting that one of Sophia's suggestions was "what electricity will flow through". The constructivist theory of learning ( read about constructivism here) suggests that meaningful learning involves learners making sense of what they are taught by linking it to their existing ideas and wealth of past experiences. This is a creative process, and sometimes students make unhelpful associations, that can act as learning impediments. Although ceramic magnets are increasingly common, iron, a good conductor, and its alloys, are still used for bar and horseshoe magnets that children will often be familiar with – so this association has potential to be built on constructively.
Of course electricity and magnetism were at one time considered quite distinct phenomena by scientists – and James Clerk Maxwell is rightly remembered for his synthesising theoretical work showing that electricity, magnetism and light could all be understood as manifestations of a single underlying 'phenomenon' of electromagnetism. (Indeed it seems stretching then notion of phenomena to refer to electromagnetism as a single phenomenon, as no one would intuitively perceive its manifestations as being observations of the same phenomenon!) We can hardly expect students to appreciate why electricity and magnetism might be considered a unitary physics topic in school science.
To the science teacher, magnetism is an electrical effect, and electromagnetism is one of the fundamental forces in nature. The unification of electricity, magnetism, and electromagnetic radiation is seen as a major integrative step forwards in science–but our students are not going to see the connections without some help.
When I asked her to tell me what she learnt about magnets she told me that the north pole and the south poles go together because one of them is coming out and one is going in.
Sandra was a participant in the Understanding Science Project. When I interviewed Sandra about her science lessons in Y7 she told me "I've done changing state, burning, and we're doing electricity at the moment". She talked about burning as being a chemical change, and when asked for another example told me dissolving was a chemical change, as when salt was dissolved it was not possible to turn it back to give salt grains of the same size. She talk me that is the water was boiled off from salt solution "you'd have the same [amount of salt], but there would just be more particles, but they'd be smaller".
As Sandra had referred to had referred to the salt 'particles' being smaller,(as as she had told me she had been studying 'changing state') I wondered if she had bee taught about the particle model of matter
So the salt's got particles. The salt comes as particles, does it? Yeah. Do other things come as particles? Everything has particles in it. Everything has particles? Yeah. But with salt, you can get larger particles, or smaller particles? Well, most things. Like it will have like thousands and thousands of particles inside it. So these are other types of particles, are they? Mm.
So although Sandra had referred to the smaller salt grains as being "smaller particles", it seemed he was aware that 'particles' could also refer to something other than the visible grains. Everything had particles in. Although salt particles (grains?) could be different sizes, it (any salt grain?) would have a great number ("like thousands and thousands") of particles (not grains – quanticles perhaps) inside it. So it seemed Sandra was aware of the possible ambiguity here, that there were small 'particles' of some materials, but all materials (or, at least, "most things") were made up of a great many 'particles' that were very much smaller.
So if you look at the salt, you can see there's tiny little grains? Yeah. But that's not particles then? Well it sort of is, but you've got more particles inside that.
"It sort of is" could be taken to mean that the grains are 'a kind of particle' in a sense, but clearly not the type of particles that were inside everything. She seemed to appreciate that these were two different types of particle. However, Sandra was not entirely clear about that:
So there's two types are of particles, are there? I don't know. Particles within particles? Yeah. Something like that, is it? Yeah. But everything's got particles has it, even if you can't see them? Yeah. So if you dissolved your salt in water, would the water have particles? Ye:ah. 'cause I've seen water, and I've never seen any particles in the water. The part¬, you can't actually see particles. Why not? Because they're too small. Things can be too small to see? Yeah. Oh amazing. So what can you see when you look at water, then? 'cause you see something, don't you? You can see – what the particles make up. Ah, I see, but not the individual particles? No.
Sandra's understanding here seems quite strong – the particles that are inside everything (quanticles) were too small to be seen, and we could only see "what the particles make up". That is, she, to some extent at least, appreciated the emergence of new properties when very large numbers of particles that were individually too small to see were collected together.
Despite this, Sandra's learning was clearly not helped by the associations of the word 'particle'. Sandra may have been taught about submicroscopic particles outside of direct experience, but she already thought of small visible objects like salt grains as 'particles'. This seems to be quite common – science borrows a familiar term, particle, and uses it to label something unfamiliar.
We can see this as extending the usual everyday range of meaning of 'particle' to also include much smaller examples that cannot be perceived, or perhaps as a scientific metaphor – that quanticles are called particles because they are in some ways like the grains and specks that we usually think of as being very small particles. Either way, the choice of a term with an existing meaning to label something that is in some ways quite similar (small bits of matter) but in other ways very different ('particles' without definite sizes/volumes or actual edges/surfaces) can confuse students. It can act as an associative learning impediment if students transfer the properties of familiar particles to the submicroscopic entities of 'particle' theory.
Amy was a participant in the Understanding Science Project. When I had talked to Amy when she was in Y10 she had referred to things being bonded: "where one thing is joined on to another thing, and it can be chemically bonded" and how "in a compound, where two or more elements are joined together, that's an example of chemical bonding".
The following year, in Y11, when she was studying fats she talked about "how they're made up and like with all the double bonds and single bonds" where a double bond was "where there are kind of like two bonds between erm carbon atoms instead of like one" and a bond was "how two atoms are joined together". Later in Y11, Amy told be that she did not know how to explain chemical bonding, but "in lessons like we've always been shown these kind of – things – where you kind of, you've got the atom, and then you've got the little, grey stick things which are meant to be the bonds, and you can just – fit them together."
As Amy had told me "everything is made up of atoms", I provocatively asked her if the chemical bond was made of atoms. Amy had "absolutely no idea" but she "suppose(d) it would have to be, wouldn't it".
Not only is this an alternative conception, but to a chemist, or science teacher, the idea that chemical bonds are themselves made up of atoms seems incongruous and offers a potential for infinite regress (are those atoms in the bonds, themselves bonded? If so, are those bonds also made of atoms?)
This alternative conception could be considered a kind of associative learning impediment – that is where a learner makes an unintended link and so applies an idea outside of its range of application. All material is considered to be made of atoms – or at least quanticles comprising one of more nuclei bound to electrons (i.e., ions, molecules). Even this is not an absolute: the material formed immediately after the big bang was not of this form, and nor is the matter in a neutron star, but the material we usually engage with is considered to be made of atom-like units (i.e., ions, molecules).
But to suggest that Amy has made an inappropriate association seems a little unfair. Had Amy thought "all matter was made of atoms" and then suggested that chemical bonding was made of atoms this would be inappropriate as chemical bonding is not material but a process – electrical interactions between quanticles. Yet it is hard to see how one can over-extend the range of 'everything', as in "everything is made up of atoms".
There is an inherent problem with the motto everything is made up of atoms. It is probably something that teachers commonly say, and think is entirely clear – that it is obvious what its scope is – but from the perspective of a student there is not the wealth of background knowledge to appreciate the implied limits on 'everything'.
Learners will readily pick up teaching mottos such as "everything is made of atoms" and take them quite literally: if everything is made of atoms then bonds must be made of atoms. So although she was wrong, I think Amy was just applying something she had learnt.
Bert was a participant in the Understanding Science Project. During one interview he reported that he had just completed a topic of alkanes and alkenes in his chemistry classes. He explained that a carbon atom has "to have four bonds", so if a carbon atom had "only got one two carbons on one side and one hydrogen then it'll make a double bond, to have four bonds". So I asked him what he understood a bond to be:
I: …what's a bond?
B: A bond is erm, it just, it's something to hold, hold two atoms together.
I: So what might you use to hold two atoms together?
B: Erm, So they can be kept, so that they're not too, I think it's just to make, so it can make big lines so it can erm, oh, so they, so not every, so because solids they have erm, I guess a lot of bonds, to keep it all, all together, I'm guessing. And erm like gas has a lot less bonds because it's a lot more free.
I: That makes sense [Bert], I'm just wondering what you would use to bond two atoms together. … I'm just wondering what kind of thing you use to bond two atoms together.
B: Erm • • I'm not sure. I guess, I guess they were just, when er, they're made with it I guess.
I: Yeah. Do you think it's made of adhesive? … is it made of a glue do you think?
B: No, I don't think so. I think it was like, I don't know, it could have been like evolution, like.
I: Ah.
B: Yeah, the atoms evolved so that they could hold on to each other.
I: Oh I love that. • • • The atoms evolved so that they could hold on to each other?
B: I guess so. That's how the world was made.
In this interview segment Bert seems not to have considered the nature of the bonds between atoms, but just to have accepted what he has learnt about valency. When asked about the nature of the bond he could offer no mechanism for bonding, but instead suggested that chemical bonds had evolved as "that's how the world was made". Here Bert is drawing upon a general explanation considered to be universal in the domain of living things, but applying his learning from biology to explain a physical phenomena.
This seems to be a creative association drawing upon prior learning, but the idea of evolution is being used outside is canonical range of application, leading to a potential associative learning impediment. Potentially, Bert's thinking about evolution as explaining how atoms can bond (a potential explanation about origins, though inappropriate if evolution is understood as natural selection) could stand in place of seeking a physical explanation for the nature of bonding.
Letting the dirt out: Creating an explanation for the soot from Bunsen flames in the absence of appreciation the nature of combustion
Keith S. Taber
Jim was a participant in the Understanding Science Project. Jim, a Y7 student, had been studying burning in science. He had been using Bunsen burners, and had been taught about the different flames (i.e., the safety flame, and the 'roaring' blue flame used for heating), and the use of the valve at the base of the burner to select the frame. Not yet appreciating the nature of burning, he was not aware that the soot obtained when interrupting the safety flame was due to incomplete combustion. Rather he had developed his own interpretation of why using the burner with the hole closed off led to a dirty flame:
What is burning, then?
It usually involves a flame. Erm which can either be yellow, orangey-yellow, or …like a, bluey colour, bluey-purple.
I: Oh, so is that significant, the colour of the flame, does that mean something?
J: Well, the yellow one has a lot of …if you touch it with glass or something, …will go black, but if you use the blue flame, it won't, so if you are heating something, you should use the blue flame.
I: Why do you think it goes black, if you use the orangey-yellow flame?
J: Because with the Bunsen burners, if you are twisting the knob, open, the dirt gets out, and you get the nice clear blue flame, but to get the orange flame, you have to have it closed, don't you, and then that doesn't let the dirt out, so it doesn't kind of, when it gets out of the top it doesn't have time.
I: So what happens if the hole is open?
J: You get, a blue flame.
I: Right, and what happens if the hole is closed?
J: Get a yellow flame.
I: And why does the hole make a difference?
J: I don't know, it probably lets the dirt out, or the air get into it or something.
I: So what dirt is this, that might be let out, do you think. Dirt from where?
J: Maybe the excess gas particles that have already been burnt or something. Don't know.
Presumably no one had told Jim that the hole was to let dirt out of the Bunsen so it did not get into the flame. However the hole was presumably letting something in or out (he later suggests, the hole might let air in – perhaps something the teacher had told the class but which had not been readily recalled?) and there was dirt in the flame when it was closed, which was not there when it was open. Jim interpreted his observations in terms of prior knowledge (of what holes do, and of dirt) to construct an explanatory scheme that made some sense of the effect of closing or opening the air hole. This would seem to have potential to be an associative learning impediment of the 'creative' type.
Amy (Y10) suggested that a circuit was "a thing containing wires and components which electricity can pass through…it has to contain a battery as well". She thought that electricity could pass through "most things".
For Amy "resistance is anything which kind of provides a barrier that, which the current has to pass through, slowing down the current in a circuit", and she thought about this in terms of the analogy with water in pipes: "we've been taught the water tank and pipe running round it… just imagine the water like flowing through a pipe, and obviously like, if the pipe becomes smaller at one point, erm, the water flow has to slow down, and that's meant to represent the resistance of something".
So for Amy, charge flow was impeded by physical barriers effectively blocking its way. She made the logical association with the density of a material, on the basis that a material with densely packed particles would have limited space for the charge to flow:
So electricity would "not very easily" pass through a wooden bench "because wood is quite a dense material and the particles in it are quite closely bonded".
In air, however, the particles were "not as dense as a solid". When asked if that meant that electricity can pass through air quite easily, Amy replied: "yeah, I think so".
Amy's connection between the density of particles and the ease with which charge could flow is a logical one, but unfortunately involves a misunderstanding of how charge flows through materials, i.e., from a canonical scientific perspective, thinking about the charge flowing through gaps between particles is unhelpful here. (So this can be considered an alternative conception.) This seems to be a creative associative learning impediment, where prior learning (here, the spacing of quanticles in different materials) is applied, but in a context beyond its range of application.
Tim was a participant in the Understanding Science project. When I talked to Tim during the first term of his 'A level' (college) course, he had been studying materials with one of his physics teachers. He referred to molecules in wood (suggesting the analogy that molecules are like a jigsaw)*, and referred to a molecule as "a bit of a particle",
I: So what's a molecule?
T: Erm it's like a bit of a particle, so, something that makes up something.
He then went on to refer to how malleability depended upon atoms "because it's just what they're made out of, it's different things to make it up, different atoms and stuff". His understanding of the relationship between atoms and molecules was probed:
Ah, so we've got atoms?
Yeah.
Not molecules?
(Pause, c.2s)
This is something different this time?
Yeah.
Oh, okay, tell me about atoms.
I think, I think atoms make up molecules, which make particles. Well there's them three things, but I'm not entirely sure what order they go in, and I think atoms are the smallest one.
So we've got, these three words are related, are they, atoms, molecules, particles?
Yeah.
You think there is a relationship there?
Yeah.
And, what, they are similar in some way, but not quite the same, or?
Erm, yeah I think it's like order of size.
You think atom's the smallest?
Yeah.
And bigger than an atom you might have?
A molecule. No a particle, then a molecule, I think.
Yeah, is that the same for everything do you think? Or, are some things molecules, and some things atoms, and some things particles?
(Pause, c.2s)
I think it's the same, I think it all goes – like that.
The term 'particle' is ambiguous in school science. Sometimes by particle we mean a very small, but still macroscopic objects, such as a salt grain or a dust speck. However, often, we are referring to the theoretical submicroscopic entities such as atoms, molecules, ions, neutrons etc, which are components of our theoretical models of the structure of matter. (These particles, behave in ways that are sometimes quite unlike familiar particle behaviour because of the extent to which quantum effects can dominate at their scale. The term 'quanticle' has been proposed as a collective term for these particles.) Students are expected to know which usage of 'particles' we might mean at any given time.
Tim assumes to have misunderstood how the term particle is used (as a collective term) when used to describe quantiles, and so has come to the understanding that at this level there are three different categories of quanticle based on relative size: the atoms (the smallest), and also molecules and particles which are larger than atoms, but which he is unsure how to relate.
The use of the everyday word particle to refer to theoretical submicroscopic entities by analogy with the more familiar everyday particles is very clear to scientists and science teachers, but can act as an associative learning impediment to learners who may think that quanticle particles are just like familiar particles, but perhaps quite a lot smaller. In Tim's case, however, it seems that a different 'learning bug' had occurred. Presumably he had commonly come across the use of the terms 'atom', 'molecule' and 'particle' in science lessons to describe the components of matter at the submicroscopic level, but had not realised that particle was being used as a generic term rather than describing something different to atoms and molecules.
During his years of school science Tim had constructed a different 'ontology' of the submicroscopic constituents of matter to that expected by his teachers.
