Particle intuitions may not match scientific models
Keith S. Taber
Sophia was a participant in the Understanding Science Project. I first talked to her when she was in Y7, soon after she began her secondary school course.
One of the first topics she studied in her science was 'solids, liquids and gases', where she had learnt,
that solids are really hard and they stay together more, and then liquids are close together but they move around, and gases are really free and they just go anywhere
She had studied a little about the topic in her last year of primary school (Y6), but now she was being told
about the particles…the things that make – the actual thing, make them a solid, and make them a gas and make them a liquid
Particle theory, or basic kinetic theory, is one of the most fundamental theories of modern science. In particular, much of what is taught in school chemistry is explained in terms of theories involving how the observed macroscopic properties emerge from the characteristics and interactions of conjectured sub-microscopic particles that themselves often have quite unfamiliar properties. This makes the subject very abstract, challenging, and tricky to teach (Taber, 2013a).
Particle theory is often introduced in terms of the states of matter. Strictly there are more than three states of matter (plasma and Bose-Einstein condensates are important in some areas of science) but the familiar ones, and the most important in everyday phenomena, are solid, liquid and gas.
The scientific account is, in simple terms, that
different substances are made up of different types of particle
the different states of matter of a single substance have the same particles arranged differently
These are very powerful ideas, even if there are many complications. For example,
the terms solid, liquid and gas only strictly apply to pure samples of a single substance, not mixtures (so not, for example, to bronze, or honey, or, milk, or ketchup, or even {if one is being very pedantic} air or sea water. And cats (please note, BBC) are completely inadmissible. )
common salt is an example of a pure substance, that none-the-less is considered to be made up of more than one type of particle
This reflects a common type of challenge in teaching science – the full scientific account is complex and nuanced, and not suitable for presenting in an introductory account; so we need to teach a simplified version that introduced the key ideas, and then only once this is mastered by learners are they ready to develop a more sophisticated understanding.
Yet, there is a danger that students will learn the simplified models as truths supported by the authority of science – and then later have difficulty shifting their thinking on. This is not only counter-productive, but can be frustrating and de-motivating for learners who find hard-earned knowledge is not as sound as they assumed.
One response to this is to teach science form very early in a way that is explicit about how science builds models of the natural world: models that are often simplifications which are useful but need to be refined and developed to become powerful enough to expand the range of contexts and examples where they can be applied. That is, students should learn they are being taught models that are often partial or imperfect, but that is just a reflection of how science works, developing more sophisticated understanding over time (Taber, 2017).
Sophia confirmed that the iron clamp stand near where she was sitting would have particles in it, as would a lump of ice.
Are they the same particles in the ice as the iron?
Yeah, because they are a solid, but they can change.
Ah, how can they change?
Cause if, erm, they melted they would be a liquid so they would have different particles in.
Right, so the iron is a solid,
Uh hm.
So that's got one type of particle?
Yeah.
And ice is also a solid?
Yeah.
So that has the same sort of particles?
Yeah, but they can change.
The ones in the ice?
Mm,
To a learner just meeting particle theory for the first time, it may seem just as feasible that the same type of particle is found in one state as in one substance.
In the scientific model, we explain that different substances contain different types of particles, whereas different states of the same substance contain different arrangements of the same particles: but this may not be intuitively obvious to learners.1 It seemed Sophia was thinking that the same particles would be in different liquids, but a change of state led to different particles. This may seem a more forced model to a teacher, but then the teacher is already very familiar with the scientific account, and also has an understanding of the nature of those particles (molecules, ions, atoms – with internal structure and charges that interact with each other within and between the particles) – which are just vague, recently imagined, entities to the novice.
Sophia seemed to misunderstood or misremembered the model she had been taught, but to a novice learner these 'particles' have no more immediate referent than an elf or an ogre and would be considerably more tenuous than a will-o'-the-wisp.
Sophia seemed to have an alternative conception, that all solids have one type of particle, and all liquids another. If I had stopped probing at that point I might have considered this to be her thinking on the matter. However, when one spends time talking to students it soon becomes clear that often they have ideas that are not fully formed, or that may be hybrids of different models under consideration, and that often as they talk they can talk themselves into a position.
So, if I melted the ice – that changes the particles in the solid?
Well they are still the same particles but they are just changing the way they act…
Oh.
How do they change?
A particle in a liquid [sic, solid] is all crammed together and don't move around, but in a liquid they can move around a little but they are still close and, can, you can pour a liquid, where you can't a solid, because they can move in.
Okay, so if I have got my ice, that's a solid, and there are particles in the ice, and they behave in a certain way, and if the ice melts, the particles behave differently?
Yeah.
Do you know why they behave differently in the liquid?
No. {giggles} So, they can, erm
• • • • • • • • • • • • [A pause of approximately 12 s]
They've more room cause it's all spread out more1, whereas it would be in a clump
The literature on learners conceptions often suggests that students have this or that conception, or (when survey questions are used) that this percentage thinks this, and that percentage thinks that (Taber, 2013b). That this is likely to be a simplification seems obvious is we consider what thinking is – whatever thought may be, is it a dynamic process, something that moves along. Our thinking is, in part, resourced by accessing what we have represented in memory, but it is not something fixed – rather something that shifts, and that often becomes more sophisticated and nuanced as we explore a focus in greater depth.
I think Sophia did seem to have an intuition that there were different types of particles in different states of matter, and that therefore a change of state meant the particles themselves changed in some way. As I probed her, she seemed to shift to a more canonical account where change of state involved a change in the arrangement or organisation of particles rather than their identity.
This may have simply been her gradually bringing to mind what she had been taught – remembering what the teacher had said. It is also possible that the logic of the phenomenon of a solid becoming a liquid impressed on her that they must be the same particles. I suspect there was a little of both.
When interviewing students for research we inevitably change their thinking and understanding to some extent (hopefully, mostly in a beneficial way!) (If only teachers had time to engage each of their students in this way about each new topic they might both better understand their students' thinking, and help reinforce what has been taught.)
Did Sophia 'have a misconception'? 1 What did she 'really think'? That, surely, is to oversimplify.
She presented with an alternative conception, that under gentle questioning she seemed to talk /think herself out of. The extent to which her shift in position reflected further recall (so, correcting her response) or 'thinking through' (so, developing her understanding) cannot be known. Likely there was a little of both. What memory research does suggest is that being asked to engage in and think about this material will have modified and reinforced her memories of the material for the future.
Johnson, P. M. (2012). Introducing Particle Theory. In K. S. Taber (Ed.), Teaching Secondary Chemistry (Second ed., pp. 49-73). Association for Science Education/John Murray.
1 Actually, the particles in a liquid are not substantially spread further apart than in a solid. (Indeed, when ice melts the water molecules move closer together on average.) Understanding melting requires an appreciation of the attractions between particles, and how heating provides more energy for the particles. This idea of increased separation on melting is therefore something of an alternative conception, if one that is sometimes encouraged by the diagrams in school textbooks.
Teaching an introductory particle theory based on the arrangement of particles in different states, without reference to the attractions between particles is problematic as it offers no rational basis for why condensed states exists, and why energy is needed to disrupt them – something highlighted in the work of Philip Johnson (2012).
It may be difficult to know what counts as an alternative conception in some topics – and sometimes research does not make it any clearer
Keith S. Taber
If a reader actually thought the researchers themselves held these alternative conceptions then one could have little confidence in their ability to distinguish between the scientific and alternative conceptions of others
I recently published an article here where I talked in some detail about some aspects of a study (Tarhan, Ayyıldız, Ogunc & Sesen, 2013) published in the journal Research in Science and Technological Education. Despite having a somewhat dodgy title 1, this is a well respected journal published by a serious publisher (Routledge/Taylor & Francis). I read the paper because I was interested in the pedagogy being discussed (jigsaw learning), but what promoted me to then write about it was the experimental design: setting up a comparison between a well-tested active learning approach and lecture-based teaching. A teacher experienced in active learning techniques taught a control group of twelve year old pupils through a 'traditional' teaching approach (giving the children notes, setting them questions…) as a comparison condition for a teaching approach based on engaging group-work.
The topic being studied by the sixth grade, elementary school, students was physical and chemical changes.
I did not discuss the outcomes of the study in that post as my focus there was on the study as possibly being an example of rhetorical research (i.e., a demonstration set up to produce a particular outcome, rather than an open-ended experiment to genuinely test a hypothesis), and I was concerned that the control conditions involved deliberately providing sub-optimal, indeed sub-standard, teaching to the learners assigned to the comparison condition.
The researchers actually tested the outcome of their experiment in two ways (as well as asking students in the experimental condition about their perceptions of the lessons), a post-test taken by all students, and "ten-minute semi-structured individual interviews" with a sample of students from each condition.
Analysis of the post-test allowed the researchers to identify the presence of students' alternative conceptions ('misconceptions'2) related to chemical and physical change, and the identified conceptions are reported in the study. Interviewees were purposively selected,
"Ten-minute semi-structured individual interviews were carried out with seven students from the experimental group and 10 students from the control group to identify students' understanding of physical and chemical changes by acquiring more information about students' unclear responses to [the post-test]. Students were selected from those who gave incorrect, partially correct and no answers to the items in the test. During the interviews, researchers asked the students to explain the reasons for their answers to the items."
Tarhan et al., 2013, p.188
I was interested to read about the alternative conceptions they had found for several reasons:
I have done research into student thinking, and have written a lot about alternative conceptions, so the general topic interests me;
More specifically, it is interesting to compare what researchers find in different educational contexts, as this gives some insight into the origins and developments of such conceptions;
In this post I am going to question whether the author's claims in their research report about some of the alternative conceptions they reported finding are convincing. First, however, I should explain the second point here.
Cultural variations in alternative conceptions
Some alternative conceptions seem fairly universal, being identified in populations all around the world. These may primarily be responses to common experiences of the natural world. An obvious example relates to Newton's first law (the law of inertia): we learn from very early experience, before we even have language to talk about our experiences, that objects that we push, throw, kick, toss, pull… soon come to a stop. They do not move off in a straight line and continue indefinitely at a constant speed.
Of course, that experience is not actually contrary to Newton's first law (as various forces are acting on the objects concerned), but it presents a consistent pattern (objects initially move off, but soon slow and stop) that becomes part of out intuitions about the world and so makes learning the scientific law seem counter-intuitive, and so more difficult to accept and apply when taught in school.
By contrast, no one has ever tested Newton's first law directly by seeing what happens under the ideal conditions under which it would apply (see 'Poincaré, inertia, and a common misconception').
Other alternative conceptions may be less universal: some may be, partially at least, due to an aspect of local cultural context (e.g. folk knowledge, local traditions), the language of instruction, the curriculum or teaching scheme, or even a particular teacher's personal way of presenting material.
So, to the extent that there are some experiences that are universal for all humans, due to commonalities in the environment (e.g., to date at least, all members of the species have been born into an environment with a virtually constant gravitational field and a nitrogen-rich atmosphere of about 1 atmosphere pressure {i.e., c.105 Pa} and about 21% oxygen content), there is a tendency for people everywhere (on earth) to develop the same alternative conceptions.
And, conversely, to the extent that people in different institutional, social, and cultural contexts have contrasting experiences, we would expect some variations in the levels of incidence of some alternative conceptions across populations.
"Some common ideas elicited from children are spread, at least in part, through informal learning in everyday "life-world" contexts. Through such processes youngsters are inducted into the beliefs of their culture. Ideas that are common in a culture will not usually contradict everyday experience, but clearly beliefs may develop and be disseminated without matching formal scientific knowledge. …
Where life-world beliefs are relevant to school science – perhaps contradicting scientific principles, perhaps apparently offering an explanation of some science taught in school; perhaps appearing to provide familiar examples of taught principles – then it is quite possible, indeed likely, that such prior beliefs will interfere with the learning of school science. …
Different common beliefs will be found among different cultural groups, and therefore it is likely that the same scientific concepts will be interpreted differently among different cultural groups as they will be interpreted through different existing conceptual frameworks."
"This suggests that studies from different contexts (e.g., different countries, different cultures, different languages of instruction, and different curriculum organisations) should be encouraged for what they can tell us about the relative importance of educational variables in encouraging, avoiding, overcoming, or redirecting various types of ideas students are known to develop."
Language of instruction may sometimes be important. Words that supposedly are translated from one language to another may actually have different nuances and associations. (In English, it is clearly an alternative conception to think the chemical elements still exist in a compound, but the meaning of the French élément chemie seems to include the 'essence' of an element that does continue into compound.)
Research in different educational contexts can in principle help unravel some of this: in principle as it does need the various researchers to detail aspects of the teaching contexts and cultural contexts from which they report as well as the student's ideas (Taber, 2012a).
Chemical and physical change
Teaching about chemical and physical change is a traditional topic in school science and chemistry courses. It is one of those dichotomies that is understandably introduced in simple terms, and so, offers a simplification that may need to be 'unlearnt' later:
[a change is] chemical change or physical change
[an element is] metal or non-metal
[a chemical bond is] ionic bonding or covalent bonding
There are some common distinctions often made to support this discrimination into two types of change:
However, a little thought suggests that such criteria are not especially useful in supporting the school student making observations, and indeed some of these criteria simply do not stand up to close examination. 2
"the distinction between chemical and physical changes is a rather messy one, with no clear criteria to help students understand the difference"
So, I was especially interested to know what Tarhan and colleagues had found.
Methodological 'small print'
In reading any study, a consideration of the findings has to be tempered by an understanding of how the data were collected and analysed. Writing-up research reports for journals can be especially challenging as referees and editors may well criticise missing details they feel should be reported, yet often journals impose word-limits on articles.
Currently (2023) this particular journal tells potential authors that "A typical paper for this journal should be between 7000 and 8000 words" which is a little more generous than some other journals. However, Tarhan and colleagues do not fully report all aspects of their study. This may in part be because they need quite a lot of space to describe the experimental teaching scheme (six different jigsaw learning activities).
Whatever the reason:
the authors do not provide a copy of the post-test which elicited the responses that were the basis of the identified alternative conceptions; and
nor do they explain how the analysis to identify conceptions was undertaken – to show how student responses were classified;
similarly, there are no quotations from the interview dialogue to illustrate how the researchers interpreted student comments .
Data analysis is the process of researchers interpreting data so they become evidence for their findings, and generally research journals expect the process to be detailed – but here the reader is simply told,
"Students' understanding of physical and chemical changes was identified according to the post-test and the individual interviews after the process."
Although the term 'misconception' is used 32 times in the paper (not counting instances in the reference list), the term is not explained in the text, presumably because it is assumed that all those working in science education know (and agree) what it means. This is not at all unusual. I once wrote about another study
"[The] qualities of misconceptions are largely assumed by the author and are implicit in what is written…It could be argued that research reports of this type suggest the reported studies may themselves be under-theorised, as rather well-defined technical procedures are used to investigate foci that are themselves only vaguely characterised, and so the technical procedures are themselves largely operationalised without explicit rationale."
Unfortunately, in Tarhan and colleagues' study there are less well-defied technical procedures in relation to how data was analysed to identify 'misconceptions', so leaving the reader with limited grounds for confidence that what are reported are worthy of being described as student conceptions – and are not just errors or guesses made on the test. Our thinking is private, and never available directly to others, and, so, can only be interpreted from the presentations we make to representour conceptions in a public (shared) space. Sometimes we mis-speak, or we mis-write (so that then our words do not accurately represent our thoughts). Sometimes our intended meanings may be misinterpreted (Taber, 2013).
Perhaps the researchers felt that this process of identifying conceptions from students' texts and utterances was unproblematic – perhaps the assignments seemed so obvious to the researchers that they did not need to exemplify and justify their analytical method. This is unfortunate. There might also be another factor here.
Lost and found in translation?
The study was carried out in Turkey. The paper is in English, and this includes the reported alternative conceptions. The study was carried out "in a public elementary school" (not an international school, for example). Although English is often taught as a foreign language in Turkish schools, the language of instruction, not unreasonably, is Turkish.
So, it seems either
the data was collected in (what, for the children, would have been) 'L2' – a second language, or
a study carried out (questions asked; answers given) in Turkish has been reported in English, translating where necessary from one language to another.
This issue is not discussed at all in the paper – there is no mention of either the Turkish or English language, nor of anything being translated.
Yet the authors are not oblivious to the significance of language issues in learning. They report how one variant of Jigsaw teaching had "been designed specifically to increase interaction among students of differing language proficiencies in bilingual classrooms" (p.186) and how the research literature reports that sometimes children's ideas reflect "the incorrect use of terms in everyday language" (p.198). However, they did not feel it was necessary to report either that
data had been collected from elementary school children in a second language, or
data had been translated for the purposes of reporting in an English language journal
It seems reasonable to assume they would have appreciated the importance of mentioning option 1, and so it seems much more likely (although readers of the study should not have to guess) the reporting in English involved translation. Yet translation is never a simple algorithmic process, but rather always a matter of interpretation (another stage in analysis), so it would be better if authors always acknowledged this – and offered some basis for readers to consider the translations made were of high quality (Taber, 2018).
It is a general principle that the research community should adopt, surely, that whenever material reported in a research paper has been translated from another language (a) this is reported and (b) evidence of the accuracy and reliability of the translation is offered (Taber, 2018).
I make this point here, as some of the alternative conceptions reported by the authors are a little mystifying, and this may(?) be because their wording has been 'degraded' (and obscured) by imperfect translation.
An alternative conception of combustion?
For example, here are two of the learning objectives from one of the learning activities:
"The students were expected to be able to:
…comment on whether the wood has similar intensive properties before and after combustion
…indicate the combustion reactions in examples of several physical and chemical changes"
Tarhan et al., 2013, p.193
The wording of the first of these examples seems to imply that when wood is burnt, the product is still…wood. That is nonsense, but possibly this is simply a mistranslation of something that made perfect sense in Turkish. (The problem is that a reader can only speculate on whether this is the case, and research reports should be precise and explicit.)
The second learning objective quoted here implies that some combustion reactions are physical changes (or, at least, combustion reactions are components of some physical changes).
Combustion reactions are a class of chemical reactions. 'Chemical reaction' is synonymous with 'chemical change'. So, there are (if you will excuse the double negative) no examples of combustion reactions that are not chemical reactions and which would be said to occur in physical changes. So, this is mystifying, as it is not at all clear what the children were actually being taught unless one assumes the researchers themselves have very serious misconceptions about the chemistry they are teaching.
If a reader actually thought that the researchers themselves held these alternative conceptions
the product of combustion of wood is still wood
some combustion reactions are (or occur as part of) physical changes
then one could have little confidence in their ability to distinguish between the scientific and alternative conceptions of others. (A reader might also ask how come the journal referees and editor did not ask for corrections here before publication – I certainly wondered about this).
There are other statements the authors make in describing the teaching which are not entirely clear (e.g., "give the order of the changes in matter during combustion reactions", p.194), and this suggests a degree of scepticism is needed in not simply accepting the reported alternative conceptions at face value. This does not negate their interest, but does undermine the paper's authority somewhat.
One of the misconceptions reported in the study is that some students thought that "there is a flame in all combustion reaction". This led me to reflect on whether I could think of any combustion reactions that did not involve a flame – and I must confess none readily came to mind. Perhaps I also have this alternative conception – but it seems a harsh judgement on elementary school learners unless they had actually been taught about combustion reactions without flames (if, indeed, there are such things).
The study reported that some 12 year olds held the 'misconception' that "there is a flame in all combustion reaction[s]".
[Image by Susanne Jutzeler, Schweiz, from Pixabay]
Failing to control variables?
Another objective was for students to "comprehend that temperature has an effect on chemical reaction rate by considering the decay of fruit at room temperature, and the change in color [colour] from green to yellow of fallen leaves in autumn" (p.193). As presented, this is somewhat obscure.
Presumably it is not meant to be a comparison between:
the rate of decay of fruit at room temperature
and
the rate of change in colour of fallen leaves in autumn
Explaining that temperature has an effect on chemical reaction rate?
Clearly, even if the change of colour of leaves takes place at a different temperature to room temperature, one cannot compare between totally different processes at different temperatures and draw any conclusions about how "temperature has an effect on chemical reaction rate" . (Presumably, 'control of variables' is taught in the Turkish science curriculum.)
So, one assumes these are two different examples…
But that does not help matters too much. The "decay of fruit at room temperature" (nor, indeed, any other process studied at a single temperature) cannot offer any indication of how "temperature has an effect on chemical reaction rate". The change of colours in leaves of deciduous trees (that usually begins before they fall) is triggered by environmental conditions such as change in day length and temperature. This is part of a very complex system involving a range of pigments, whilst water content of the leaf decreases (once the supply of water through the tree's vascular system is cut off), and it is not clear how much detail these twelve year olds were taught…but it is certainly not a simple matter of a reaction changing rate according to temperature.
Evaluating conceptions
Tarhan and colleagues report their identified alternative conceptions ('misconceptions') under a series of headings. These are reported in their table 4 (p.195). A reader certainly finds some of the entries in this table easy to interpret: they clearly seem to reflect ideas contrary to the canonical science one would expect to be reflected in the curriculum and teaching. Other statements are less obviously evidence of alternative conceptions as they do not immediately seem necessarily at odds with scientific accounts (e.g., associating combustion reactions with flames).
Other reported misconceptions are harder to evaluate. School science is in effect a set of models and representations of scientific accounts that often simplify the actual current state of scientific knowledge. Unless we know exactly what has been taught it is not entirely clear if students' ideas are credit-worthy or erroneous in the specific context of their curriculum.
Moreover, as the paper does not report the data and its analysis, but simply the outcome of the analysis, readers do not know on what basis judgements have been made to assign learners as having one of the listed misconceptions.
Changes of state are chemical changes
A few students from the lecture-based teaching condition were identified as 'having' the misconception that 'changes of state are chemical changes'. This seems a pretty serious error at the end of a teaching sequence on chemical and physical changes.
However, this raises a common issue in terms of reports of alternative conceptions – what exactly does it mean to say that a student has a conception that 'changes of state are chemical changes'? A conception is a feature of someone's thinking – but that encompasses a vast range of potential possibilities from a fleeting notion that is soon forgotten ('I wonder if s orbitals are so-called because they are spherical?') to an on-going commitment to an extensive framework of ideas that a life is lived by (Buddhism, Roman Catholicism, Liberalism, Hedonism, Marxism…).
A person's conceptions can vary along a range of characteristics (Figure from Taber, 2014)
The statement that 'Changes of state are chemical changes' is unlikely to be the basis of anyone's personal creed. It could simply be a confusion of terms. Perhaps a student had a decent understanding of the essential distinction between chemical and physical changes but got the terms mixed up (or was thinking that 'changes of state' meant 'chemical reaction'). That is certainty a serious error that needs correcting, but in terms of understanding of the science, would seem to be less worrying than a deeper conceptual problem.
In their commentary, the authors note of these children:
"They thought that if ice was heated up water formed, and if water was heated steam formed, so new matter was formed and chemical changes occurred".
Tarhan et al., 2013, p.197
It is not clear if this was an explanation the learners gave for thinking "changes of state are chemical changes", or whether "changes of state are chemical changes" was the researchers' gloss on children commenting that "if ice was heated up water formed, and if water was heated steam formed, so new matter was formed and chemical changes occurred".
That a range of students are said to have precisely the same train of thought leads a reader (or, at least, certainly one with experience of undertaking research of this kind) to ask if these are open-ended responses produced by the children, or the selection by the children of one of a number of options offered by the researchers (as pointed out above, the data analysis is not discussed in detail in the paper). That makes a difference in how much weight we might give to the prevalence of the response (putting a tick by the most likely looking option requires less commitment to, and appreciation of, an idea than setting it out yourself in your own personally composed text), illustrating why it is important that research journals should require researchers to give full accounts of their instrumentation and analysis.
Because density of matter changes during changes of state, its identity also changes, and so it is a chemical change
Thirteen of the children (all in the lecture-based teaching condition) were considered to have the conception "Because density of matter changes during changes of state, its identity also changes, and so it is a chemical change". This is clearly a much more specific conception (than 'changes of state are chemical changes') which can be analysed into three components:
a change of state is a chemical change, AND
we know this because such changes involve a change in identity, AND
we know that because a change of state leads to a change in density
Terhan and colleagues claim this conception was "first determined in this study" (p.195).
The specificity is intriguing here – if so many students explicitly and individually built this argument for themselves then this is an especially interesting finding. Unfortunately, the paper does not give enough detail of the methodology for a reader to know if this was the case. Again, if students were just agreeing with an argument offered as an option on the assessment instrument then it is of note, but less significant (as in such cases students might agree with the statement simply because one component resonated – or they may even be guessing rather than leaving an item unanswered). Again this does not completely negate the finding, but it leaves its status very unclear.
Taken together these first two claimed results seem inconsistent – as at least 13 students seem to think "Changes of state are chemical changes". That is, all those who thought that "Because density of matter changes during changes of state, its identity also changes, and so it is a chemical change" would seem to have thought that "Changes of state are chemical changes" (see the Venn diagram below). Yet, we are also told that only five students held the less specific and seemingly subsuming conception "changes of state are chemical changes".
If 13 students think that changes of state are chemical changes because a change of density implies a change of identity; what does it mean that only 5 students think that changes of state are chemical changes?
This looks like an error, but perhaps is just a lack of sufficient detail to make the findings clear. Alternatively, perhaps this indicates some failure in translating material accurately into English.
The changes in the pure matters are physical changes
Six children in the lecture-based teaching condition and one in the jigsaw learning condition were reported as holding the conception that "The changes in the pure matters are physical changes". The authors do not explain what they mean here by "pure matters" (sic, presumably 'matter'?). The only place this term is used in the paper is in relation to this conception (p.195, p.197).
The only other reference to 'pure' was in one of the learning objectives for the teaching:
explain the changes of state of water depending on temperature and pressure; give various examples for other pure substances (p.191)
If "pure matter" means a pure sample of a substance, then changes in pure substances are all physical – by definition a chemical changes leads to a different substance/different substances. That would explain why this conception was "first determined [as a misconception] in this study", p.195, as it is not actually a misconception)". So, it does not seem clear precisely why the researchers feel these children have got something wrong here. Again, perhaps this is a failure of translation rather than a failure in the original study?
Changes in shape?
Tarhan and colleagues report two conceptions under the subheading of 'changes in shape'. They seem to be thinking here more of grain size than shape as such. (Another translation issue?) One reported misconception is that if cube sugar is granulated, sugar particles become small [smaller?].
Is it really a misconception to think that "If cube sugar is granulated, sugar particles become small"?
(Image by Bruno /Germany from Pixabay)
Tarhan and colleagues reported that two children in the experimental condition, and 13 in the control condition thought that "If cube sugar is granulated, sugar particles become small". Sugar cubes are made of granules of sugar weakly joined together – they can easily be crumbled into the separate grains. The grains are clearly smaller than the cubes. So, what is important here is what is meant/understood* by the children by the term 'particles'.
(* If this phrasing was produced by the children, then we want to know what they meant by it. If, however, the children were agreeing with a phrase presented to them by researchers, then we wish to know how they understood it.)
If this means quanticle level particles, molecules, then it is clearly an alternative conception – each grain contain vast numbers of molecules, and the molecules are unchanged by the breaking up the cubes. If, however, particles here refers to the cube and grains**, then it is a fair reflection of what happens: one quite large particle of sugar is broken up into many much smaller particles. The ambiguity of the (English) word 'particles' in such contexts is well recognised.
(** That is, if the children used the word 'particles' – did they mean the cubes/grains as particles of sugar? If however the phrasing was produced by the researchers and presented to the children, and if the researchers meant 'particles' to mean 'molecules'; did the children appreciate that intention, or did they understand'particles' to refer to the cubes and grains?)
However, as no detail is given on the actual data collected (e.g., is this the children's own words; was this based on an open response?), and how it was analysed (and, as I suspect this all occurred in Turkish) the reader has no way to check on this interpretation of the data.
What kind of change is dissolving?
Tarhan and colleagues report a number of 'misconceptions' under the heading of 'molecular solubility'. Two of these are:
"The solvation processes are always chemical changes"
"The solvation processes are always physical changes"
This reflects a problem of teaching about physical and chemical changes. Dissolving is normally seen as a physical change: there is no new chemical substance formed and dissolving is usually fairly readily reversed. However, as bonds are broken and formed it also has some resemblance to chemical change.2
In dissolving common salt in water, strong ionic bonds are disrupted and the ions are strongly solvated. Yet the usual convention is still to consider this a physical change – the original substance, the salt, can be readily recovered by evaporation of the solvent. A solution is considered a kind of mixture. In any case, as Tarhan and colleagues refer to 'molecular' solubility (strictly solubility refers to substances, not molecules, but still) they were, presumably, only dealing with examples of the dissolving of substances with discrete molecules.
Taking together these two conceptions, it seems that Tarhan and colleagues think that dissolving is sometimes a physical change, and sometimes a chemical change. Presumably they have some criterion or criteria to distinguish those examples of dissolving they consider physical changes from those they consider chemical changes. A reader can only speculate how a learner observing some solute dissolve in a solvent is expected to distinguish these cases. The researchers do not explain what was taught to the students, so it is difficult to appreciate quite what the students supposedly got wrong here.
Sugar is invisible in the water, because new matter is formed
The idea that learners think that new matter is formed on dissolving would indeed be an alternative conception. The canonical view is that new matter is only formed in very high energy processes – such as in the big bang. In both chemical and physical processes studied in the school laboratory there may be transformations of matter, but no new matter.
This seems a rather extreme 'misconception' for the learners to hold. However, a reader might wonder if the students actually suggested that a new substance was formed, and this has been mistranslated. (The Turkish word 'madde' seems to mean either matter or substance.) If these students thought that a new type of substance was formed then this would be an alternative conception (and it would be interesting to know why this led to sugar being invisible – unless they were simply arguing that different appearance implied different substance).
While sugar is dissolving in the water, water damages the structure of sugar and sugar splits off
Whether this is a genuine alternative conception or just imprecise use of language is not clear. It seems reasonable to suggest that while sugar is dissolving in the water, the process breaks up the structure of solid sugar and sugar molecules split off – so some more detail would be useful here. Again, if there has been translation from Turkish this may have lost some of the nuance of the original phrasing through translation into English.
The phrasing reflects an alternative conception that in chemical reactions one reactant is an active agent (here the water doing the damaging) and the other the patient, that is passive and acted upon (here the sugar being damaged) – rather than seeing the reaction as an interaction between two species (Taber & García Franco, 2010) – but there is no suggestion in their paper that this is the issue Tarhan and colleagues are highlighting here.
When sugar dissolves in water, it reacts with water and disappears from sight
If the children thought that dissolving was a chemical reaction then this is an alternative conception – the sugar does indeed disappear from sight, but there has been no reaction.
Again, we might ask if this was actually a misunderstanding (misconception), or imprecise use of language. The sugar does 'react' with the water in the everyday sense of 'reaction'. But this is not a chemical reaction, so this terminology should be avoided in this context.
Even in science, 'reaction' means something different in chemistry and physics: in the sense of Newtonian physics, during dissolving, when a water molecule attracts a sugar molecule {'action')'} there will be an equal and oppositely directed reaction as the sugar molecule attracts the water molecule. This is Newton's third law, which applies to quanticles as much as to planets. If a water molecule and a sugar molecule collide, the force applied by the sugar molecule on the water molecule is equal to the force applied by the water molecule on the sugar molecule.
a use of the everyday term 'reaction' in a context where this should be avoided as it can be misunderstood
These are somewhat different problems for a teacher to address.
Molecules split off in physical changes and atoms split off in chemical changes
Ten of the children are said to have demonstrated the 'misconception' that molecules split off in physical changes and atoms split off in chemical changes. The authors claim that this misconception has not been reported in previous studies. But is this really a misconception? It may be a simplistic, and imprecise, statement – but I think when I was teaching youngsters of this age I would have been happy to find they have this notion – which at least seems to reflect an ability to imagine and visualise processes at the molecular level.
In dissolving or melting/boiling of simple molecular substances, molecules do indeed 'split off' in a sense, and in at least some chemical changes we can posit mechanisms that, in simple terms at least, involve atoms 'splitting off' from molecules.
So, again, this is another example of how this study is tantalising, without being very informative. The reader is not clear in what sense this is viewed as wrong, or how the conception was detected. (Again, for ten different students to specifically think that 'molecules split off in physical changes and atoms split off in chemical changes' makes one wonder if they volunteered this, or have simply agreed with the statement when having it presented to them).
The researchers do not detail their data collection and analysis instruments and protocols in sufficient detail for a readers to appreciate what they mean by their results. In particular, what it means to have a misconception – e.g., to give a definitive statement in an interview, or just to select some response on a test as the answer that looked most promising at the time. Clearly we give much more weight to a notion that a learner presents in their own words as an explanation for some phenomenon, than the selection of one option from a menu of statements presented to them that comes with no indication of their confidence in the selection made.
Of particular concern: either the children were asked questions in a second language that they may not have been sufficiently fluent in to fully understand questions or compose clear responses; or none of the misconceptions reported are presented in their original form and they have all been translated by someone (unspecified) of uncertain ability as a translator. (A suitably qualified translator would need to have high competence in both languages and a strong familiarity with the subject matter being translated.)
In the circumstances, Tarhan and colleagues' reported misconceptions are little more than intriguing. In science, the outcome of a study is only informative in the context of understanding exactly how the data were obtained, and how they have been processed. Without that, readers are asked to take a researcher's conclusions on faith, rather than be persuaded of them by a logical chain of argument.
p.s. For anyone who did not know, but wondered: s orbitals are not so-called because they are spherical: the designation derives from a label ('sharp') that was applied to some lines in atomic spectra.
1 To my reading, the publication title 'Research in Science and Technological Education' seems to suggest the journal has two distinct and somewhat disconnected foci, that is:
Research in ( Science ) and ( Technological Education )
And it would be better (that is, most consistently) titled as
Research in Science and Technology Education
{Research in ( Science and Technology ) Education}
or
Research in Scientific and Technological Education
{Research in ( Scientific and Technological ) Education}
but, hey, I know I am pedantic.
2 The table (Table 1.2 in the source) was followed by the following text:
"The first criterion listed is the most fundamental and is generally clear cut as long as the substances present before and after the change are known. If a new substance has been produced, it will almost certainly have different melting and boiling temperatures than the original substance.
The other [criteria] are much more dubious. Some chemical changes involve a great deal of energy being released, such as the example of burning magnesium in air, or even require a considerable energy input, such as the example of the electrolysis of water. However, other reactions may not obviously involve large energy transfers, for example when the enthalpy and entropy changes more or less cancel each other out…. The rusting of iron is a chemical reaction, but usually occurs so slowly that it is not apparent whether the process involves much energy transfer ….
Generally speaking, physical changes are more readily reversible than chemical changes. However, again this is not a very definitive criterion. The idea that chemical reactions tend to either 'go' or not is a useful approximation, but there are many examples of reactions that can be readily reversed…. In principle, all reactions involve equilibria of forward and reverse reactions, and can be reversed by changing the conditions sufficiently. When hydrogen and oxygen are exploded, it takes a pedant to claim that there is also a process of water molecules being converted into oxygen and hydrogen molecules as the reaction proceeds, which means the reaction will continue for ever. Technically such a claim may be true, but for all practical purposes the explosion reflects a reaction that very quickly goes to completion.
One technique that can be used to separate iodine from sand is to warm the mixture gently in an evaporating basin, over which is placed an upturned beaker or funnel. The iodine will sublime – turn to vapour – before recondensing on the cold glass, separated from the sand. The same technique may be used if ammonium chloride is mixed with the sand. In both cases the separation is achieved because sand (which has a high melting temperature) is mixed with another substance in the solid state that is readily changed into a vapour by warming, and then readily recovered as a solid sample when the vapour is in contact with a colder surface. There are then reversible changes involved in both cases:
solid iodine ➝ iodine vapour
ammonium chloride ➝ ammonia + hydrogen chloride
In the first case, the process involves only changes of state: evaporation and condensation – collectively called sublimation. However the second case involves one substance (a salt) changing to two other substances. To a student seeing these changes demonstrated, there would be little basis to infer one is (usually considered as) a chemical change, but not the other. …
The final criterion in Table 1.2 concerns whether bonds are broken and made during a change, and this can only be meaningful for students once they have learnt about particle models of the submicroscopic structure of matter… In a chemical change, there will be the breaking of bonds that hold together the reactants and the formation of new bonds in the products. However, we have to be careful here what we mean by 'bond' …
When ice melts and water boils, 'intermolecular' forces between molecules are disrupted and this includes the breaking of hydrogen 'bonds'. However, when people talk about bond breaking in the context of chemical and physical changes, they tend to mean strong chemical bonds such as covalent, ionic and metallic bonds…
Yet even this is not clear cut. When metals evaporate or are boiled, metallic bonds are broken, although the vapour is not normally considered a different substance. When elements such as carbon and phosphorus undergo phase changes relating to allotropy, there is breaking, and forming, of bonds, which might suggest these changes are chemical and that the different forms of the same elements should be considered different substances. …
A particularly tricky case occurs when we dissolve materials to form solutions, especially materials with ionic bonding…. Dissolving tends to involve small energy changes, and to be readily reversible, and is generally considered a physical change. However, to dissolve an ionic compound such as sodium chloride (table salt), the strong ionic bonds between the sodium and chloride ions have to be overcome (and new bonds must form between the ions and solvent molecules). This would seem to suggest that dissolving can be a chemical change according to the criterion of bond breaking and formation (Table 1.2)."
An ancient iron column: Did "a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stop… it from rustingany more"
What do you need to build a skyscraper?
I was listening to a podcast from the Royal Institution (where Humphrey Davy and Michael Faraday were based). I must confess I had downloaded the 'Recipe for a Skyscraper' episode some time ago but it had been passed over for other titles.
My mistake. In this talk "structural engineer Roma Agrawal delves into the history of the materials that enable immense construction and the developments that have made our structures what they are today. All while noting the accomplishments of key visionary engineers of the past". This proved to be an engaging and fascinating talk.
A 'mega badass engineer'
On her website, Roma Agrawal , "a structural engineer, author and broadcaster, with a physics degree" describes herself as a "mega badass engineer". She is not above being a little mischievous.
The crumbly ages
For example, she has her own take on what historians used to call the 'dark ages', 1
"So, oddly enough, once the Roman empire fell, the use of concrete basically ended for nearly a thousand years, so that we call it the dark ages, or the crumbly ages as I like to call it, because they went back to using slightly older [construction materials], you know, mud and brick and things like that."
Roma Agrawal talking at the Royal Institution
But while the Romans may have championed the use of concrete, the Indians were outperforming them in the production of high quality iron: "The Romans actually used to import Indian steel at the time and they never knew how to make it because that secret was closely guarded…"
Iron is too reactive to be found 'native' but has to be produced by roasting its ores (that contain compounds of iron) with materials that will reduce the iron compounds to iron, and produce, as a by-product, slag – a complex mixtures of substances. The iron produced will contain some slag mixed into the metal unless this is carefully removed. 2
The Delhi column
As an example of the Indian expertise, Roma Agrawal referred to an old iron column near Delhi which "had not rusted" despite having been erected 1500 years ago.3 The column had originally been a stand for a statue of Garuda, the divine winged creature/demigod who acted as the vehicle for Vishnu. Garuda seems to have flown, but the iron column remains.
The (not quite 4) 'rustless wonder' (Srinivasan & Ranganathan, 2013): the Qtub Iron Pillar
Lord Vishnu on his mount Garuda (wood carving). It is thought the iron pillar near Delhi once supported a statue of Garuda.
(Image by waradet from Pixabay)
Iron is the main constituent of alloys known as steels, and by mixing other elements (principally, but not only, carbon) with iron it is possible to create steels with various properties, including corrosion resistance. 2 But iron itself readily rusts. The rust formed when iron corrodes is permeable and crumbly, exposing the unreacted metal beneath, which in turn forms rust that again fails to protect the iron beneath it. So, over time, a piece of iron can simply 'rust away' as the reacted material will simply fall off, or be eroded by weather.
Yet this iron column, erected around the time of the final collapse of the Roman Empire, seems to have survived throughout 'the crumbly ages' and through to the present day. Although, it is not that it never started rusting 4, but rather,
"it did initially rust, but then because of the climate in Delhi, the phosphorus, a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stopped it from rusting any more…"
Roma Agrawal talking at the Royal Institution
Corrosion (as with tarnishing) is a generic term. Corrosion leads to structural damage to metal objects (whereas tarnishing is a surface effect).
Rusting is specific to iron as it refers to the material produced when iron corrodes – i.e., rust.
Unreactive phosphorus?: An alternative conception
Roma Agrawal's claim seems incredible to a chemist or science teacher because phsophorus is a very reactive element, and a very reactive element does not seem a good choice of material to protect iron from reacting! Even if the phosphorus did not itself react with the iron and so corrode it, it would soon react with air. In the laboratory, some forms of phosphorus can burst into flames spontaneously, suggesting it is very unlikely to remain intact very long exposed to the elements in India. Certainly not many centuries.
Sacrificial elements
Now, sometimes a more valuable metal is protected by connecting it physically to a more reactive but less valuable metal which preferentially corrodes. As the metals are in electrical contact, the one that loses electrons and releases cations more readily reacts first. The metal allowed to corrode is called a 'sacrificial' metal. For example, bars of sacrificial metal may be dangled from piers or oil rigs to protect the structural metal. The sacrificial metal will slowly 'dissolve' away into the sea 5 – but not that slowly that it would not need replacing for over a millennium. In any case, phosphorus is a non-metal, where the sacrificial element of the pair needs to be the more electropositive. So, there is no helpful explanation there.
Alumina – when tarnishing prevents corrosion
Aluminium is a more reactive metal than iron, yet does not readily undergo substantive corrosion. This is because the surface of an aluminium object readily reacts with oxygen from the air to form a layer of aluminium oxide (alumina). This then protects the aluminium because the alumina formed is a fairly inert substance (unlike the highly reactive phosphorus), and it forms an impermeable layer (preventing oxygen from the air reaching the metal beneath).
Any layer that were to form on iron protect it from rusting also needs to be impermeable and relatively inert. Unlike reactive phosphorus.
Phosphorus would not protect iron
Phosphorus is a fire hazard that burns to produce toxic fumes. In the laboratory, the direct reaction of iron and phosphorus usually requires heating to initiate reaction. Without active heating, the rate of reaction would be too low for a useful laboratory process. However, a very low rate of reaction would not prevent reaction over the centuries since the iron column was erected.
Even if phosphorus was able to form a layer that coated over the iron, using it as a means to prevent corrosion would be like fireproofing a wooden building by coating it with petroleum jelly (e.g., Vaseline). [A correspondent to the British Dental Journal (Brewer, 2017) warned of "the death of a bedbound patient who smoked following application of E45 cream…a paraffin-based product, the residue of which can act as an accelerant when ignited". Smoking kills. And even more rapidly if you smother yourself in flammable oil products prior to lighting up.]
So, it seems we have a mystery.
Or, Roma Agrawal simply got it wrong.
Or, perhaps, more likely, when Roma Agrawal refers to a 'layer of phosphorus' she is using the term loosely, and is actually referring to something else. That is, the protective layer may contain one or more phosphorus compounds, but not phosphorus – just as a layer of the unreactive aluminium compound alumina stops corrosion, although aluminium itself is reactive. Is this distinction just being pedantic? Not to a science educator.
An elementary misconception
The claim that a layer of phosphorus could protect iron from corrosion is therefore not credible to the scientifically literate, but might seem perfectly reasonable to a person with limited science background. One of the great challenges of learning chemistry is making sense of the set of ideas that:
the compound of an element is a completely different substance to the element itself
the properties of compounds are often quite different (sometimes contrastingly so) to those of the elements the compound was formed from
although the compound does not behave like the elements, and does not 'contain' the elements in any straightforward way, there is a sense in which something of the elements persists in (and so the element may be recovered from) the compound.
So, sodium is a reactive metal that burns in air, and chlorine is a green, toxic, choking gas; and both should be avoided unless taking very careful precautions; yet they react, very energetically, to give the relatively unreactive compound sodium chloride – which people readily use in cooking, and to season their food, and to dissolve in water to gargle with, or to soak tired feet. Chlorine would destroy the lining of your throat. Yet sodium chloride solution (despite its chlorine 'constituent') will help ease a sore throat! Still, the sodium chloride has the potential to be 'separated' into the elements with their dangerous properties intact.
Although the distinction between elements and compounds is a lot easier to understand once students learn about molecules and atoms (at least, if avoiding the alternative conception that compounds comprise of molecules and elements comprise of atoms!) this topic is fraught with complications and hang-overs from historical ideas about atoms (Taber, 2003).
If not a layer of phosphorus?
The chemist or science teacher hearing about a protective 'layer of phosphorus' preventing rusting will immediately thinks this is not viable…but a compound of phosphorus might well have the necessary properties. Indeed, generally, the more reactive the elements, the more stable the compounds they form when reacting.
It seems that the layer that formed on the iron column contains the phosphorus compoundiron hydrogen phosphate hydrate (FePO4·H3PO4·4H2O),
"Several theories have been postulated regarding corrosion resistance of the Delhi iron pillar. Some of those refer to the inherent nature of the construction material, such as the selection of pure iron, presence of slag particles and slag coatings, surface finishing using mechanical operation, phosphate film formation, or the Delhi's climate…
Earlier studies have delineated the formation of crystalline iron hydrogen phosphate hydrate (FePO4·H3PO4·4H2O), 𝛼-, 𝛾-, 𝛿-FeOOH and magnetite in the case of Delhi iron pillar"
Yet this critical, and somewhat counter-intuitive, distinction between elements qua elements and elements as in some sense 'components' (or 'ingredients') of compounds needs to be acquired. Novices have to learn this. A common alternative conception is to assume that the properties of elements are carried over into their compounds.
So, if students hear that
phosphorus is essential in our diet, and that
phosphorus is important for healthy bones and teeth,
they can draw the obvious and reasonable conclusion – that phosphorus must be a pretty innocuous substance as it is part of our bodies and we eat it quite safely in our food. Actually, we need compounds of phosphorus in our food to allow our metabolisms to build and repair tissues that contain phosphorus compounds – and anyone misguided enough to try to eat any actual (elemental) phosphorus risks a nasty burn.
In conclusion, as a science graduate, Roma Agrawal presumably appreciates the key distinction between (i) elements as substances and (ii) elements as chemically combined components of other substances, and, as a structural engineer knowledgeable about different material properties, is using 'layer of phosphorus' as a shorthand for a layer of material that includes one or more phosphorus compounds.
That is fine as long as those hearing her talk appreciate that. Another scientist would likely automatically hear 'phosphorus layer' as meaning 'phosphorus compound containing layer'. A science teacher, however, might suspect that the reference to how "a very thin layer of phosphorus formed, between the rust and the fresh metal and basically stopped it from rusting" is likely to be misunderstood, and indeed to mislead, some listening to the podcast.
Minding your Ps…
One of the sources referred to reported how:
"P is found present in slag whereas the presence of P in iron was not detected within the limit of the analytical techniques used in this study. On the basis of this result, we speculate application of lime and other basic compounds during the iron making process which would have led to the transfer P to slag."
P is the symbol for phosphorus, the element. However, someone with a sufficient scientific background appreciates from the context that references to
P found in slag
P in iron
transfer [of] P to slag
cannot refer to P as phosphorus the element, but rather some compound or compounds of phosphorus. As a reactive element, phosphorus is not found native and so would not be present (as an element) in the raw materials and, in any case, could certainly not survive (as an element) the high temperature conditions of the processes of iron smelting. Therefore the relevant 'context' for reinterpreting 'P' as not standing for the element itself would be any set of circumstances other than the special conditions where phosphorus can be safely stored without risk of reaction.
This is the prerequisite background knowledge that prevents an audience member misinterpreting what must be meant by a "thin layer of phosphorus [sic]" protecting an exposed iron column – as it cannot possibly refer to a thin layer of [actual, elemental] phosphorus.
Sources cited
Anantharaman, T. R. (1997). The iron pillar at Delhi. In S. Ranganathan (Ed.), Iron and Steel Heritage of India (pp. 1-28). Indian Institute of Metals and Tata Steel.
Brewer, E. Patient safety: Paraffin-based products. British Dental Journal223, 620 (2017). https://doi.org/10.1038/sj.bdj.2017.936
Dwivedi, D., Mata, J. P., Salvemini, F., Rowles, M. R., Becker, T., & Lepková, K. (2021). Uncovering the superior corrosion resistance of iron made via ancient Indian iron-making practice. Scientific Reports, 11(1), 4221. doi:10.1038/s41598-021-81918-w
Falk, S. (2020). The Light Ages. A Medieval journey of discovery. Allen Lane.
Srinivasan, S., & Ranganathan, S. (2013). Minerals and Metals Heritage of India. Bangalore: National Institute of Advanced Studies.
1 A simplistic view was that advancing civilisation underwent something of a relapse during the middle ages, until the gains of the classical age (the Greeks, the Romans) were rediscovered in the Enlightenment. Thus, the term 'dark ages' applied to the 'middle ages'.
There were no dark ages: as a matter of fact, they are all dark
with apologies to Pink Floyd
That is clearly a great simplification, and ignores many medieval achievements, as well as being a rather Eurocentric view. Some historians have been seeking to redress this impression: for example, Seb Falk (2020) has renamed this period 'the light ages'.
2 To suggest that steel deliberately contains impurities added to iron could give the impression that iron artefacts are made of purer materials than steel ones. This is misleading. Basic iron smelting produces iron that is impure (sometimes known as 'pig iron') and which can contain quite high levels of impurities. Pig iron typically has a high level of carbon – more than is usually used in steels.
Wrought iron is produced by physical working of pig iron which expels much of the slag content, giving purer iron. Wrought iron has long been widely used in structures, but still does not have a high level of purity.
Alloys are mixtures of different metals, or of metallic elements with other elements. 'Metal' here is ambiguous as it can refer to
an electropositive element (the usual meaning in chemistry) or
a material with certain properties (the usual meaning in engineering) – i.e., malleable, ductile, high electrical and thermal conductivities, lustre, sonorous.
Steels are metals in the 'materials' sense, but 'chemically' are mixtures of the metallic element iron with other elements.
As the properties of steels are sensitive to the levels of other elements, making steel requires using high quality iron that has been treated to remove most of the impurities. This is similar to doping a semiconductor such as silicon to produce electronic components. Very pure silicon is needed as a starting point, so that just the right amount of a specific dopant can be added.
The Indian iron manufacture of Roman times tended to produce iron with a significant phosphorus content.
3 The column was made of wrought iron,
"The forging of wrought iron seems to have reached its zenith in India in the first millennium AD. The earliest large forging is the famous iron pillar with a height of over 7 m and weight of about 6 tons at New Delhi ascribed to Chandragupta Vikramaditya 400- 450 CE… the absence of corrosion is linked to the composition, the high purity of the wrought iron and the phosphorus content and the distribution of slag."
Srinivasan & Ranganathan, 2013
4 The lack of rusting may have been exaggerated,
"The first impression in 1961 was that the portion of the Pillar below the earth was "superficially rusted". However, on detailed examination, the buried portion of the Pillar was found covered with thick crusts of rust and, in fact, copious rust scales could be collected, ranging in thickness from a few millimeters (mm) to no less than 15 mm in some portions. Further, the bulbous base of the Pillar was found riddled with numerous cavities and hollows caused by deep corrosion and mineralization of the iron.
Anantharaman, 1997
Even so, the survival of an iron column exposed to weathering for this length of time is still worthy of note.
5 I thought I should put 'dissolve' into 'scare quotes' here. Corrosion is a chemical change, whereas dissolving refers to what is generally considered a physical change. As the sacrificial metal reacts, it releases cations into solution in the sea, in much the same was as, say, dissolving salt releases sodium ions when common salt is added to water. The metal reacts and enters solution – dissolves, if you are comfortable with that word in this context.
"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 treecould 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 abstractconcepts) 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 abstractconcepts from those foundational concepts, and then we build even more abstractconcepts 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 analogywith 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.
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 newconcept 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 abstractconcepts, 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?
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."
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.
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,
and
seeking 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 like
not 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.
substance
formula
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."
Actually, as discussed before here, this is contrary to the scientific account. The equation presents an equivalencebetween 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.
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).
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).
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=mc2is 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.
The danger here is that for many students such narratives are not simply useful ways to get them thinking about the science concepts (weakanthropomorphism) but seem quite sufficient as the basis of explanations (stronganthropomorphism) – 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 nottrying 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 anthropomorphicmetaphor 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.
"…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!)
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 isgigantic, 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 metaphoricallymade 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:
Eddington, A. (1933/1987). The Expanding Universe. Cambridge: Cambridge University Press.
Lakoff, G., & Johnson, M. (1980). The metaphorical structure of the human conceptual system. Cognitive Science, 4(2), 195-208.
Ulmer, M., Grace, V., Hudson, H., & Schwartz, D. (1972). Upper Limits to the X-Ray Luminosities of Five Supernovae. The Astrophysical Journal, 173, 205.
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…
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.
"From one of the known ingredients of steam being a highly inflammable body, and the other that essential part of the air which supports combustion, it was imagined that [steam] would have the effect of increasing the fire …"
Producing iron requires high temperatures: adding H2O does not help (Image by zephylwer0 from Pixabay)
The challenge of chemical combination
School science teachers are likely aware of how chemistry poses some significant leaning challenges for learners. One of these is the nature of chemical compounds. That is, compounds of chemical elements.
It may seem obvious to learners that when we 'mix' two components with different properties we should get a mixture with a combination of the component properties. So far, so good. But of course, in chemical reactions we do not just mix different substances, but rather they chemically react. So, sodium will react with chlorine, which can be understood in terms of processes occurring at the nanoscopic scale where molecules of a gas interact with the metallic lattice of sodium cations and delocalised electrons.
Sodium and chlorine behaving badly
Although we can model this process, we cannot observe it directly, or even the starting structures at that scale. Understandably, students often struggle to relate the macroscopic and molecular:
As Sodium is a reactive meterial [sic] and chlorine is a acid. When Sodium is placed in Chlorine, Sodium react badly making a flame and maybe a noise. I think why this reaction happen is because as Sodium reactive metal meaning that it atomic configuration is unstable make the metal danger And as Chlorine is a dangerous acid. When sodium is placed in Chlorine, the sodium start dissolving in the acid due to all the particle rushing around quickly pushing together with Chlorine atom. Producing Sodium chloride.
So, for example, if we do burn sodium in chlorine we end up with sodium chloride which is a new substance that has its own properties – properties which are not simply some mixture of, or intermediate between, the properties of the substances we start with (the reactants).
Indeed, sodium is a dangerous material to handle: it will react vigorously with water (in a person's sweat for example!) and burns violently in air. Chlorine is so nasty that it has been used as a weapon of war (and since banned as an 'unacceptable' weapon, even in war). In the 'great' war ('great' only because of its scale) the way men died in agony from breathing chlorine was much reported, as well as the effects on those who survived the gas – being blinded for example.
"In all my dreams before my helpless sight,
He plunges at me, guttering, choking, drowning."
Wilfred Owen, Dulce et Decorum Est1
Sweet and honourable? 1 (Image by Bruce Mewett from Pixabay)
Sodium chloride certainly has its associated hazards – if eaten in excess it is a risk factor for high blood pressure for example – but is certainly not dangerous in anything like the same sense. Many people put sodium chloride on their chips (often along with ethanoic acid solution). No one would want sodium on their food, or to eat in a canteen with a chlorine atmosphere!
When is something both present and not present?
Why this is especially challenging is that the chemistry teacher tells the students that although, at one level, the new substance does not contain its precursors – there is no sodium (substance) or chlorine (substance) in the substance sodium chloride – yet it is a compound of these elements and in some some sense the elements remain 'in' the compound.
This links to that key theoretical framework in chemistry where we can explain macroscopic (bench scale) phenomena in terms of models of matter at the submicroscopic (indeed nanoscopic or even subnanoscopic) scale. The sense in which sodium chloride 'contains' sodium and chlorine is that it is comprised of a lattice of sodium ions and chloride ions – species which include the specific types of nuclei (those of charge +11 and +17 respectively) that define those elements.
So, when we ask whether the elements are in some sense 'in' the compound we have to think in terms of these abstract models at a tiny scale – there is no sodium substance or chlorine substance present, but there is something that is inherently identified with these two elements. In a sense, but a very abstract sense, the elements are still present. Or, perhaps, better, something intrinsic to those elements is still present.
"We are working here with two complementary meanings for the idea of element, one at the (macroscopic) level of phenomena we can demonstrate to students (substances, and their reactions); the other deriving from a theoretical model in terms of conjectured submicroscopic entities ('quanticles'…).
However, there is also a sense in which an element is considered to be present, in a virtual or potential sense, within its compounds. This use is more common among French-speaking chemists, and in the English-speaking world we normally consider it quite inappropriate to suggest that sodium is somehow present in sodium chloride, or hydrogen in water. Yet, of course, chemical formulae (NaCl, H2O, etc) tell us that the compounds somehow 'contain' the elements."
This is easy to understand for someone very familiar with molecular level models – but is understandably difficult for novice learners. Thus we can reasonably understand why there are common alternative conceptions along the lines of students thinking that, for example, a compound of a dangerous element (say chlorine) must also be dangerous. Yet we 'mix' and react a soft, reactive, metal and a choking green gas – and get hard white crystals that safely dissolve in water to give a solution we can use in cooking, or to soak our feet, or to gargle with.
An historical precedent
Because science teachers and chemists are so used to thinking in models at the molecular level, we can forget just how unfamiliar this perspective is to the novice, and so the challenge of acquiring the scientific ways of thinking that have become 'second nature' through extensive application.
I was therefore fascinated to see an example of this same alternative conception, assuming a compound will show the properties of its constituent elements, reported by the scientist Sir John Herschel (astronomer, chemist, mathematician, philosopher…), not in a school science context, but rather an industrial context.
"The smelting of iron requires the application of the most violent heat that can be raised, and is commonly performed in tall furnaces, urged by great iron bellows driven by steam-engines. Instead of employing this power to force air into the furnace through the intervention of bellows, it was, on one occasion, attempted to employ the steam itself in, apparently, a much less circuitous manner; viz. by directing the current of steam in a violent blast, from the boiler at once into the fire. From one of the known ingredients of steam being a highly inflammable body, and the other that essential part of the air which supports combustion, it was imagined that this would have the effect of increasing the fire to tenfold fury, whereas it simply blew it out; a result which a slight consideration of the laws of chemical combination, and the state in which the ingredient elements exist in steam, would have enabled any one to predict without a trial."
Herschel, J. F. W. (1830/1851/2017), §37 2
So, here, instead of dropping marks on a test, this misunderstanding of the chemistry leads to a well-intentioned industrialist trying to generate heat in a blast furnace by adding water to the fire. But this does remind us just how counter-intuitive some of the things taught in science are. It might also be a useful anecdote to share with students to help them appreciate that that their errors are by no means unusual, or necessarily a reflection on their ability.
Perhaps this might even be a useful teaching example that could be built up into a historical anecdote which students might readily recall and that will help them remember that compounds have new properties that may be quite different from their constituent elements. So, while a mixture of the flammable gas hydrogen and oxygen can be explosive, a combination (that is, a chemical combination – a compound), of hydrogen and oxygen will not 'feed' a fire but dampen it down. Just as well, really, as otherwise emergency fire and rescue services would need to find an alternative to the widely available, inexpensive, recyclable, non-toxic, agent they widely use in fighting fires.
Compounds and mixtures are not interchangeable (Image by David Mark from Pixabay)
Work cited:
Herschel, J. F. W. (1830/1851/2017). Preliminary Discourse on the Study of Natural Philosophy. Project Gutenberg EBook.
1 Wilfred Owen was famous for his war poetry written about the horrors of the trench fighting in the 'first world war'. Owen was killed a week before the war ended. 'Dulce Et Decorum Est' referred to a Latin phrase or motto (dulce et decorum est pro patria mori) that Owen labelled as 'the old lie', that it was sweet and honourable to die in the service of one's country.
2 For some reason, "…it was imagined that this would have the effect of increasing the fire to tenfold fury, whereas it simply blew it out…" puts me in mind of
"the mighty ships tore across the empty wastes of space and finally dived screaming on to…Earth – where due to a terrible miscalculation of scale the entire battle fleet was accidentally swallowed by a small dog."
Douglas Adams, The Hitchhiker's Guide to the Galaxy
The BBC radio programme 'In Our Time' today tackled the electron. As part of the exploration there was the introduction of the positron, and the notion of matter-antimatter annihilation. These are quite brave topics to introduce in a programme with a diverse general audience (last week Melvyn Bragg and his guests discussed Plato's Atlantis and next week the programme theme is the Knights Templar).
Prof. Victoria Martin of the School of Physics and Astronomy at the University of Edinburgh explained:
If we take a pair of matter and antimatter, so, since we are talking about the electron today, if we take an electron and the positron, and you put them together, they would annihilate.
And they would annihilate not into nothingness, because they both had mass, so they both had energy from E=mc2 that tells us if you have mass you have energy. So, they would annihilate into energy, but it would not just be any kind of energy: the particular kind of energy you get when you annihilate an electron and a positron is a photon, a particle of light. And it will have a very specific amount of energy. Its energy will be equal to the sum of the energy of electron and the positron that they had initially when they collided together.
"An electron and the positron, and you put them together, they would annihilate…they would annihilate into energy" – but this could be misleading.
Now, I am sure that is somewhat different from how Prof. Martin would treat this topic with university physics students – of course, science in the media has to be pitched at the largely non-specialist audience.
It struck me that this presentation had the potential to reinforce a common alternative conception ('misconception') that mass is converted into energy in certain processes. Although I am aware now that this is an alternative conception, I seem to recall that is pretty much what I had once understood from things I had read and heard.
It was only when I came to prepare to teach the topic that I realised that I had a misunderstanding. That, I think, is quite common for teachers – when we have to prepare a topic well enough to explain it to others, we may spot flaws in our own understanding (Taber, 2009)
So, for example, I had thought that in nuclear processes, such as in a fission reactor or fusion in stars, the mass defect (the apparent loss of mass as the resulting nuclear fragments have less mass than those present before the process) was due to that amount of massbeing converted to energy. This is sometimes said to explain why nuclear explosions are so much more violent than chemical explosions, as (given E=mc2): a tiny amount of mass can be changed into a great deal of energy.
Prof. Martin's explanation seemed to support this way of thinking: "they would annihilate into energy".
An alternative conception of particle annihilation: This scheme seems to be implied by Prof. Martin's comments
What is conserved?
It is sometimes suggested that, classically, mass and energy were considered to be separately conserved in processes, but since Einstein's theories of relativity have been adopted, now it is considered that mass can be considered as if a form of energy such that what is conserved is a kind of hybrid conglomerate. That is, energy is still considered conserved, but only when we account for mass that may have been inter-converted with energy. (Please note, this is not quite right – see below.)
So, according to this (mis)conception: in the case of an electron-positron annihilation, the mass of the two particles is converted to an equivalent energy – the mass of the electron and the mass of the positron disappear from the universe and an equivalent quantity of energy is created. Although energy is created, energy is still conserved if we allow for the mass that was converted into this new energy. Each time an electron and positron annihilate, their masses of about 2 ✕ 10-30 kg disappear from the universe and in its place something like 2 ✕ 10-13 J appears instead – but that's okay as we can consider 2 ✕ 10-30 kg as a potential form of energy worth 2 ✕ 10-13 J.
However, this is contrary to what Einstein (1917/2004) actually suggested.
Einstein did not suggest that matter could be changed to energy
Equivalence, not interconversion
What Einstein actually suggested was not that mass could be considered as if another kind/form of energy (alongside kinetic energy and gravitational potential, etc.) that needed to be taken into account in considering energy conservation, but rather that inertial mass can be considered as an (independent) measure of energy.
That is, we think energy is always conserved. And we think thatmass is always conserved. And in a sense they are two measures of the same thing. We might see these two statements as having redundancy:
In a isolated system we will always have the same total quantity of energy before and after any process.
In a isolated system we will always have the same total quantity of mass before and after any process.
As mass is always associated with energy, and so vice versa, either of these statements implies the other. 1
Two conceptions of the shift from a Newtonian to a relativistic view of the conservation of energy (move the slider to change the image)
No interconversion?
So, mass cannot be changed into energy, nor vice versa. The sense in which we can 'interconvert' is that we can always calculate the energy equivalence of a certain mass (E=mc2) or mass equivalence of some quantity of energy (m=E/c2).
So, the 'interconversion' is more like a change of units than a change of entity.
Although we might think of kinetic energy being converted to potential energy reflects a natural process (something changes), we know that changing joules to electron-volts is merely use of a different unit (nothing changes).
If we think of a simple pendulum under ideal conditions 2 it could oscillate for ever, with the total energy unchanged, but with the kinetic energy being converted to potential energy – which is then converted back to kinetic energy – and so on, ad infinitum. The total energy would be fixed although the amount of kinetic energy and the amount of potential energy would be constantly changing. We could calculate the energy in joules or some other unit such as eV or ergs (or calories or kWh or…). We could convert from one unit to another, but this would not change anything about the physical system. (So, this is less like converting pounds to dollars, and more like converting an amount reported in pounds {e.g., £24.83} into an amount reported in pence {e.g., 2483p}.)
Using this analogy, the electron and positron being converted to a photon is somewhat like kinetic energy changing to potential energy in a swinging pendulum (something changes), but it is not the case that mass is changed into energy. Rather we can do our calculations in terms of energy or mass and will get (effectively, given E=mc2) the same answer (just as we can add up a shopping list in pounds or pence, and get the same outcome given the conversion factor, 1.00£ = 100p).
So, where does the mass go?
If mass is conserved, then where does the mass defect – the amount by which the sum of masses of daughter particles is less than the mass of the parent particle(s) – in nuclear processes go? And, more pertinent to the present example, what happens to the mass of the electron and positron when they mutually annihilate?
To understand this, it might help to bear in mind that in principle these process are like any other natural processes – such as the swinging pendulum, or a weight being lifted with pulley, or methane being combusted in a Bunsen burner, or heating water in a kettle, or photosynthesis, or a braking cycle coming to a halt with the aid of friction.
In any natural process (we currently believe)
the total mass of the universe is unchanged…
but mass may be reconfigured
the total energy of the universe is unchanged…
but energy may be reconfigured; and
as mass and energy are associated, any reconfigurations of mass and energy are directly correlated.
So, in any change that involves energy transfers, there is an associated mass transfer (albeit usually one too small to notice or easily measure). We can, for example, calculate the (tiny) increase in mass due to water being heated in a kettle – and know just as the energy involved in heating the water came from somewhere else, there is an equivalent (tiny) decrease of mass somewhere else in the wider system (perhaps due to falling of water powering a hydroelectric power station). If we are boiling water to make a cup of tea, we may well be talking about a change in mass of the order of only 0.000 000 001 g according to my calculations for another posting.
The annihilation of the electron and positron is no different: there may be reconfigurations in the arrangement of mass and energy in the universe, but mass (and so energy) is conserved.
So, the question is, if the electron and positron, both massive particles (in the physics sense, that they have some mass) are annihilated, then where does their mass go if it is conserved? The answer is reflected in Prof. Martin's statement that "the particular kind of energy you get when you annihilate an electron and a positron is a photon, a particle of light". The mass is carried away by the photon.
The mass of a massless particle?
This may seem odd to those who have learnt that, unlike the electron and positron, the photon is massless. Strictly the photon has no rest mass, whereas the electron and positron do have rest mass – that is, they have inertial mass even when judged by an observer at rest in relation to them.
So, the photon only has 'no mass' when it is observed to be stationary – which nicely brings us back to Einstein who noted that electromagnetic radiation such as light could never appear to be at rest compared to the observer, as its very nature as a progressive electromagnetic wave would cease if one could travel alongside it at the same velocity. This led Einstein to conclude that the speed of light in any given medium was invariant (always the same for any observer), leading to his theory of special relativity.
So, a photon (despite having no 'rest' mass) not only carries energy, but also the associated mass.
Although we might think in terms of two particles being converted to a certain amount of energy as Prof. Martin suggests, this is slightly distorted thinking: the particles are converted to a different particle which now 'has' the mass from both, and so will also 'have' the energy associated with that amount of mass.
Mass is conserved during the electron-positron annihilation
A slight complication is that the electron and position are in relative motion when they annihilate, so there is some kinetic energy involved as well as the energy associated with their rest masses. But this does not change the logic of the general scheme. Just as there is an energy associated with the particles' rest masses, there is a mass component associated with their kinetic energy.
The total mass-energy equivalence before the annihilation has to include both the particle rest masses and their kinetic energy. The mass-energy equivalence afterwards (being conserved in any process) also reflects this. The energy of the photon (and the frequency of the radiation) reflects both the particle masses and their kinetic energies at the moment of the annihilation. The mass (being perfectly correlated with energy) carried away by the photon also reflects both the particle masses and their kinetic energies.
How could 'In Our Time' have improved the presentation?
It is easy to be critical of people doing their best to simplify complex topics. Any teacher knows that well-planned explanations can fail to get across key ideas as one is always reliant on what the audience already understands and thinks. Learners interpret what they hear and read in terms of their current 'interpretive resources' and habits of thinking.
A physicist or physics student hearing the episode would likely interpret Prof. Martin's statement within a canonical conceptual framework. However, someone holding the 'misconception' that mass is converted to energy in nuclear processes would likely interpret "they would annihilate into energy" as fitting, and reinforcing, that alternative conception.
I think a key issue here is a slippage that apparently refers to energy being formed in the annihilation, rather than radiation: (i.e., Prof. Martin could have said "they would annihilate into [radiation]"). When the positron and electron 'become' a photon, matter is changed to radiation – but it is not changed to energy, as matter has mass, and (as mass and energy have an equivalence) the energy is already there in the system.
Energy is reconfigured, but is not formed, in the annihilation process.
So, this whole essay is simply suggesting that a change of one word – from energy to radiation – could potentially avoid the formation of, or the reinforcing of, the alternative conception that mass is changed into energy in processes studied in particle physics. As experienced science teachers will know, sometimes such small shifts can make a good deal of difference to how we are interpreted and, so, what comes to be understood.
1 In what is often called a closed system there is no mass entering or leaving the system. However, energy can transfer to, or from, the system from its surroundings. Classically it might be assumed that the mass of a closed system is constant as the amount of matter is fixed, but Einstein realised that if there is a net energy influx to, or outflow from, the system, than some mass would also be transferred – even though no matter enters or leaves.
2 Perhaps in a uniform gravitational field, not subject to to any frictional forces, with an inextensible string supporting the bob, and in thermal equilibrium with its environment.
we are made of particles that have existed since the moment the universe began…those atoms travelled 14 billion years through time and space
The Big Bang Theory (but not quite the big bang theory).
What is the Big Bang Theory?
The big bang theory is a theory about the origin and evolution of the universe. Being a theory, it is conjectural, but it is the theory that is largely taken by scientists as our current best available account.
According to big bang theory, the entire universe started in a singularity, a state of infinite density and temperature, in which time space were created as well as matter. As the universe expanded it cooled to its present state – some, about, 13.8 billion years later.
Our current best understanding of the Cosmos is that the entire Universe was formed in a 'big bang' (Image by Gerd Altmann from Pixabay)
The term 'big bang' was originally intended as a kind of mockery – a sarcastic description of the notion – but the term was adopted by scientists, and has indeed become widely used in general culture.
Which brings me to 'The Big Bang Theory', which is said to have been the longest ever running sitcom ('situation comedy') – having been in production for longer than even 'Friends'.
The Big Bang Theory: Not science fiction, but fictional science? (Five of these characters have PhDs in science: one 'only' has a master's degree in engineering.)
A situation comedy is set around a situation. The situation was that two Cal Tech physicists are sharing an apartment. Leonard (basically a nice guy, but not very successful with women) is flatmate to Sheldon, a synaesthete, and kind of savant (a device on which to lever much of the humour) – a genius with an encyclopaedic knowledge of most areas of science but a deficient 'theory of mind' such that he lacks
insight into others, and so also
empathy, and
the ability to tell when people are using humour or being sarcastic to him.
If most physicists were like Sheldon we could understand why the big bang theory is still called the big bang theory even though the term was intended to be facetious. The show writers claim that Sheldon was not deliberately written to be on the autistic spectrum, but he tends to take statements literally: when it is suggested that he is crazy, he responds that he knows he is not as his mother had him tested as a child.
Sheldon (at right, partially in shot) has been widely recognised by viewers as showing signs of high-functioning Autism or Aspergers syndrome. (Still from The Big Bang Theory)
These guys hang out with Raj (Rajesh), an astrophysicist and Cambridge graduate so shy he is unable to speak to women, or indeed in their presence (presumably not a problem inherited from his father who is is a successful gynaecologist in India), and an engineer, Howard, who to my viewing is just an obnoxious creep with no obvious redeeming qualities. (But then I've not seen the full run.) When Howard becomes a NASA astronaut, he is bullied by the other astronauts, and whilst bullying is never acceptable, it is difficult to be too judgemental in his case.
This group are scientists, and they are 'nerds'. They watch science fiction and superhero movies, buy comic books and action figures, play competitive board games and acquire all the latests technical gadgets. And, apart from Sheldon (who has a strong belief in following a principled rigorous regime of personal hygiene that makes close contact with other humans seem repulsive) they try, and largely fail, to attract women.
In case this does not seem sufficiently stereotypical, the situation is complete when a young woman moves into in the flat opposite Leonard and Sheldon: Penny is the 'hot' new neighbour, who comes across as a 'dumb blonde' (she wants to be an actress – she is actually a waitress whilst she works at that), something of a hedonist, and not having the slightest knowledge of, or interest in, science. Penny's plan in life is to become a movie star, and her back-up plan is to become a television star.
If Sheldon and his friends tend to rather fetishise science and see it as inherently superior to other ways of engaging in the world, then Penny seems to reflect the other side of 'the two cultures' of C. P. Snow's famous lecture/essay that described an arts-science divide in mid-twentieth century British public life. That is, not only an acknowledged ignorance of scientific matters, but an ignorance that is almost worn as a badge of honour. Penny, of course, actually has a good deal of knowledge about many areas of culture that our 'heroes' are ignorant of.
Initially, Penny is the only lead female character in the show. This creates considerable ambiguity in how we are expected to see the show's representations of scientists during the early series. Is the viewer meant to be sharing their world where women are objects of recreation and sport and a distraction from the important business of the scientific quest? Or, is the audience being asked to laugh at these supposedly highly intelligent men who actually have such limited horizons?
Sheldon: I am a physicist. I have a working knowledge of the entire universe and everything it contains.
Penny. Who's Radiohead?
[pause]
Sheldon: I have a working knowledge of important things in the universe.
Penny has no interest in science
So, the premise is: can the nerdy, asthmatic, short-sighted, physicist win over the pretty, fun-loving, girl-next-door who is clearly seen to be 'out of his league'.
Spoiler alert
Do not read on if you wish to watch the show and find out for yourself. 😉
A marriage made in the heavens?
I recently saw an episode in series n (where n is a large positive integer) where Leonard and Penny decided to go to Las Vagas and get married. Leonard said he had written his own marriage vows – and it was these that struck me as problematic. My complaint was nothing to do with love and commitment, but just about physics.
Cal Tech physicist Leonard Hofstadter (played by Johnny Galecki) wrote his own vows for marriage to Penny (Kaley Cuoco) in 'The Big Bang Theory'
A non-physical love?
I made a note of Leonard's line:
"Penny, we are made of particles that have existed since the moment the universe began. I like to think those atoms travelled 14 billion years through time and space to create us so that we could be together and make each other whole."
Leonard declares his love
Sweet. But wrong.
Perhaps Leonard had been confused by the series theme music, the 'History of Everything', by the band Barenaked Ladies. The song begins well enough:
"Our whole universe was in a hot dense state
Then nearly fourteen billion years ago, expansion started…"
Lyrics to History of Everything (The Big Bang Theory Theme)
but in the second verse we are told
"As every galaxy was formed in less time than it takes to sing this song.
A fraction of a second and the elements were made."
Lyrics to History of Everything (The Big Bang Theory Theme)
So, the theme song seems to suggest that once the big bang had occurred, "nearly fourteen billion years ago", the elements were formed in a matter of seconds, and the galaxies in a matter of minutes. Leonard goes further, and suggests the atoms that he and Penny are comprised of have existed since "the moment the universe began". This is all contrary to the best understanding of physicists.
Surely Leonard, who defended his PhD thesis on particle physics, would know more about the canonical theories about the formation of those particles? (If not, he could ask Raj who once applied for a position in stellar evolution.)
The "hot dense state" was so hot that no particles could have condensed out. Certainly, some particles began to appear very soon after the big bang, but for much of the early 'history of everything' the only atoms that could exist were of the elements hydrogen, helium and lithium – as only the nuclei of these atoms were formed in the early universe.
The formation of heavier elements – carbon, oxygen, silicon and all the rest – occurred in stars – stars that did not exist until considerable cooling from the hot dense state had occurred. (See for example, 'A hundred percent conclusive science. Estimation and certainty in Maisie's galaxy'.) Most of the matter comprising Leonard, Penny, and the rest of us, does not reflect the few elements formed in the immediate aftermath of the big bang, but heavier elements that were formed billions of years later in stars that went supernovae and ejected material into space. 1 As has often been noted, we are formed from stardust.
"…So don't forget the human trial, The cry of love, the spark of life, dance thru the fire
Stardust we are Close to divine Stardust we are See how we shine"
From the lyrics to 'Stardust we are' (The Flower Kings – written by Roine Stolt and Tomas Bodin)
Does it matter – it is only pretend
Of course The Big Bang Theory (unlike the big bang theory) is not conjecture, but fiction. So, does it matter if it gets the science wrong? The Big Bang Theory is not meant to be science fiction, but a fiction that uses science to anchor it into a situation that will allow viewers to suspend disbelief.
Leonard is a believable character, but Sheldon is an extreme outlier. Howard and Raj are caricatures, exaggerations, as indeed are Amy (neurobiologist) and Bernadette (microbiologist) the other core characters introduced later.
But the series creators and writers seem to have made a real effort at most points in the show to make the science background authentic. Dialogue, whiteboard contents, projects, laboratory settings and the like seem to have been constructed with great care so that the scientifically literate viewer is comfortable with the context of the show. This authentic professional context offers the credible framework within which the sometimes incredible events of the characters' lives and relationships do not seem immediately ridiculous.
In that context, Leonard getting something so wrong seems incongruent.
Then again, he is in love, so perhaps his vows are meant to tell the scientifically literate viewer that there is a greater truth than even science – that in matters of the heart, poetic truth trumps even physics?
A Marillion song tells us:
A wise man once wrote That love is only An ancient instinct For reproduction Natural selection A wise man once said That everything could be explained And it's all in the brain
But as the same song asks: "where is the wisdom in that?"
Source cited:
Snow, C. P. (1959/1998). The Rede Lecture, 1959: The two cultures. In The Two Cultures (pp. 1-51). Cambridge University Press.
Note:
1 I was tempted to write 'most of the atoms'. Certainly most of the mass of a person is made up of atoms 2 that were formed a long time after the big bang. However, in terms of numbers of atoms, there are more of the (lightest) hydrogen atoms than of any other element: we are about 70% water, and water comprises molecules of H2O. So, that is getting close to half the atoms in us before we consider all the hydrogen in the fats and proteins and so forth.
2 That, of course, assumes the particles we are made of are atoms. Actually, we are comprised chemically of molecules and ions and relatively very, very few free atoms (those that are there are accidentally there in the sense they are not functional). No discrete atoms exist within molecules. So, to talk of the hydrogen atoms in us is to abstract the atoms from molecules and ions.
Leonard confuses matters (and matter) by referring initially to particles (which could be nucleons, quarks?) but then equating these to atoms – even though atoms are unlikely to float around for nearly 14 billion years without interacting with radiation and other matter to get ionised, form molecules, that may then dissociate, etc.
For many people reading this, I am making a pedantic point. When we talk of the atoms in a person's body, we do not actually mean atomsper se, but component parts of molecules of compounds of the element indicated by the atomreferred to*. A water molecule does not contain two hydrogen atoms and an oxygen atom, but it does contain two hydrogen atomic nuclei, and the core of an oxygen atom (its nucleus, and inner electron 'shell') within an 'envelope' of electrons.
* So, it is easier to use the shorthand: 'two atoms of hydrogen and one of oxygen'.
The reason it is sometimes important to be pedantic is that learners often think of a molecule as just a number of atoms stuck together and not as a new unitary entity composed of the same set of collective components but in a new configuration that gives it different properties. (For example, learners sometimes think the electrons in a covalent bond are still 'owned' by different atoms.) There is an associated common alternative conception here: the assumption of initial atomicity, where students tend to think of chemical processes as being interactions between atoms, even though reacting substances are very, very rarely atomic in nature.
This referred to an article in a recent issue of the magazine (May 2022, and also available on line) which proposed the slightly more subtle question 'Is fire a solid, liquid, gas, plasma – or something else entirely?'
This was an interesting and fun article, and I wondered how other readers might have responded.
An invitation
No one had commented on the article on line, so I offered my own comment, reproduced below. Before reading this, I would strongly recommend visiting the web-page and reading the original article – and considering how you would respond. (Indeed, if you wish, you can offer your own response there as a comment on the article.)
Ian Farrell (2022) asks: "Is fire a solid, liquid, gas, plasma – or something else entirely?" I suggest this is something of a trick question. It is 'something else', even if not 'something else entirely'.
It is perhaps not 'something else entirely' because fire involves mixtures of substances, and those substances may be describable in terms of the states of matter.
However, it is 'something else', because the classification into different states of matter strictly applies to pure samples of substances. It does not strictly apply to many mixtures: for example, honey, is mostly ('solid') sugar dissolved in ('liquid') water, but is itself neither a solid nor a liquid. Ditto jams, ketchup and so forth. Glass is in practical everyday terms a solid, obviously, but, actually, it flows and very old windows are thicker near their bottom edges. (Because glass does not have a regular molecular level structure, it does not have a definite point at which it freezes/melts.) Many plastics and waxes are not actually single substances (polymers often contain molecules of various chain lengths), so, again, do not have sharp melting points that give a clear solid-liquid boundary.
Fire, however, is not just outside the classification scheme as it involves a mixture (or even because it involves variations in mixture composition and temperature at different points in the flame), but because it is not something material, but a process.
Therefore, asking if fire is a solid, liquid, gas, or plasma could be considered an 'ontologicalcategory error' as processes are not the type of entities that the classification can be validly applied to.
You may wish to object that fire is only possible because there is material present. Yes, that is true. But, consider these questions:
Is photosynthesis a solid, liquid, gas, plasma…?
Is distillation a solid, liquid, gas, plasma…?
is the Haber process a solid, liquid, gas, plasma…?
is chromatography a solid, liquid, gas, plasma…?
Is fermentation a solid, liquid, gas, plasma… ?
Is melting a solid, liquid, gas, plasma…?
In each case the question does not make sense, as – although each involves substances, and these may individually, at least at particular points in the process, be classified by state of matter- these are processes and not samples of material.
Farrell hints at this in offering readers the clue "once the fuel or oxygen is exhausted, fire ceases to exist. But that isn't the case for solids, liquids or gases". Indeed, no, because a sample of material is not a process, and a process is not a sample of material.
I am sure I am only making a point that many readers of Education in Chemistry spotted immediately, but, unfortunately, I suspect many lay people (including probably some primary teachers charged with teaching science) would not have spotted this.
Prof. Michelene Chi, a researcher at Arizona State University, has argued that a common factor in a wide range of student alternative conceptions relates to how they intuitively classify phenomena on 'ontological trees'.
"Ontological categories refer to the basic categories of realities or the kinds of existent in the world, such as concrete objects, events, and abstractions."
Chi, 2005, pp.163-164
We can think of all the things in the world as being classifiable on a series of branching trees. This is a very common idea in biology, where humans would appear in the animal kingdom, but more specifically among the Chordates, and more specifically still in the Mammalia class, and even more specifically still as Primates. Of course the animals branch could also be considered part of a living things tree. However, some children may think that animals and humans are inherently different types of living things – that they would be on different branches.
Some student alternative conceptions can certainly be understood in terms of getting typologies wrong. One example is how electron spin is often understood. For familiar objects, spin is a contingent property (the bicycle wheel may, or may not, be spinning – it depends…). Students commonly assume this applies to quanticles such as electrons, whereas electron spin is intrinsic – you cannot stop an electron 'spinning', as you could a cycle wheel, as spin is an inherent property of electrons. Just as you cannot take the charge away from an electron, nor can you remove its spin.
Two ways of classifying some electron properties (after Figures 8 and 9 in Taber, 2008). The top figure shows the scientific model; the bottom is a representation of a common student alternative conception.
Chi (2009) suggested three overarching (or overbranching?) distinct ontologial trees being entities, processes and mental states. These are fundamentally different types of category. The entities 'tree' encompasses a widely diverse range of things: furniture, cats, cathedrals, grains of salt, Rodin sculptures, iPads, tectonic plates, fossil shark teeth, Blue Peter badges, guitar picks, tooth picks, pick axes, large hadron colliders, galaxies, mitochondria….
Despite this diversity, all these entities are materials things, not be confused with, for example, a belief that burning is the release of phlogiston (a mental state) or the decolonisation of the curriculum (a process).
Chi suggested that often learners look to classify phenomena in science as types of material object, when they are actually processes. So, for example, children may consider heat is a substance that moves about, rather than consider heating as a process which leads to temperature changes. 1 Similarly 'electricity' may be seen as stuff, especailly when the term is undifferentiated by younger learners (being a blanket term relating to any electrical phenomenon). Chemical bonds are often thought of as material links, rather than processes that bind structures together. So, rather than covalent bonding being seen as an interaction between entities, it is seen as an entity (often as a 'shared pair of electrons').
Of course, science teachers (or at least the vast majority) do not make these errors. But any who do think that fire should be classifiable as one of the states of matter are making a similar, if less blatant, error of confusing matter and process. Chi's research suggests this is something we can easily tend to do, so it is not shameful – and Ian Farrell has done a useful service by highlighting this issue, and asking teachers to think about the matter…or rather, not the 'matter', but the process.
Work cited:
Chi, M. T. H. (2005). Commonsense Conceptions of Emergent Processes: Why Some Misconceptions Are Robust. Journal of the Learning Sciences, 14(2), 161-199. https://doi.org/10.1207/s15327809jls1402_1
Chi, M. T. (2009). Three types of conceptual change: Belief revision, mental model transformation, and categorical shift. In International handbook of research on conceptual change (pp. 89-110). Routledge.
Farrell, I. (2022). The burning question. Is fire a solid, liquid, gas, plasma – or something elkse entirely? Education in Chemistry, 59(3), 11.
Getting that sinking feeling on reading published studies
Keith S. Taber
this is like finding that, after a period of watering plant A, it is taller than plant B – when you did not think to check how tall the two plants were before you started watering plant A
Research on prelabs
I was looking for studies which explored the effectiveness of 'prelabs', activities which students are given before entering the laboratory to make sure they are prepared for practical work, and can therefore use their time effectively in the lab. There is much research suggesting that students often learn little from science practical work, in part because of cognitive overload – that is, learners can be so occupied with dealing with the apparatus and materials they have little capacity left to think about the purpose and significance of the work. 1
Okay, so is THIS the pipette? (Image by PublicDomainPictures from Pixabay)
Approaching a practical work session having already spent time engaging with its purpose and associated theories/models, and already having become familiar with the processes to be followed, should mean students enter the laboratory much better prepared to use their time efficiently, and much better informed to reflect on the wider theoretical context of the work.
I found a Swedish paper (Winberg & Berg, 2007) reporting a pair of studies that tested this idea by using a simulation as a prelab activity for undergraduates about to engage with an acid-base titration. The researchers tested this innovation by comparisons between students who completed the prelab before the titration, and those who did not.
The work used two basic measures:
types (sophistication) of questions asked by students during the lab. session
elicitation of knowledge in interviews after the laboratory activity
The authors found some differences (between those who had completed the prelab and those that had not) in the sophistication of the questions students asked, and in the quality of the knowledge elicited. They used inferential statistics to suggest at least some of the differences found were statistically significant. From my reading of the paper, these claims were not justified.
A peer reviewed journal (no, really, this time)
This is a paper in a well respected journal (not one of the predatory journals I have often discussed on this site). The Journal of Research in Science Teaching is published by Wiley (a major respected publisher of academic material) and is the official journal of NARST (which used to stand for the National Association for Research in Science Teaching – where 'national' referred to the USA 2). This is a journal that does take peer review very seriously.
The paper is well-written and well-structured. Winberg and Berg set out a conceptual framework for the research that includes a discussion of previous relevant studies. They adopt a theoretical framework based on the Perry's model of intellectual development (Taber, 2020). There is considerable detail of how data was collected and analysed. This account is well-argued. (But, you, dear reader, can surely sense a 'but' coming.)
Experimental research into experimental work?
The authors do not seem to explicitly describe their research as an experiment as such (as opposed to adopting some other kind of research strategy such as survey or case study), but the word 'experiment' and variations of it appear in the paper.
For one thing, the authors refer to students' practical work as being experiments,
"Laboratory exercises, especially in higher education contexts, often involve training in several different manipulative skills as well as a high information flow, such as from manuals, instructors, output from the experimental equipment, and so forth. If students do not have prior experiences that help them to sort out significant information or reduce the cognitive effort required to understand what is happening in the experiment, they tend to rely on working strategies that help them simply to cope with the situation; for example, focusing only on issues that are of immediate importance to obtain data for later analysis and reflective thought…"
Winberg & Berg, 2007
Now, some student practical work is experimental, where a student is actively looking to see what happens when they manipulate some variable to test a hypothesis. This type of practical work is sometimes labelled enquiry (or inquiry in US spelling). But a lot of school and university laboratory work, however, is undertaken to learn techniques, or (probably more often) to support the learning of taught theory – where it is usually important the learners know what is meant to happen before they begin the laboratory activity.
Winberg and Berg refer to the 'laboratory exercise' as 'the experiment' as though any laboratory work counts as an experiment. In Winberg and Berg's research, students were asked about their "own [titration] experiment", despite the prelab material involving a simulation of the titration process, in advance of which "the theoretical concepts, ideas, and procedures addressed in the simulation exercise had been treated mainly quantitatively during the preceding 1-week instructional sequence". So, the laboratory titration exercise does not seem to be an experiment in the scientific sense of the term.
School children commonly describe all practical work in the lab as 'doing experiments'. It cannot help students learn what an experiment really is when the word 'experiment' has two quite distinct meanings in the science classroom:
I would imagine Winberg and Berg were well aware of what an experiment is, although their casual use of language might suggest a lack of rigour in thinking with the term. They refer to having "both control and experiment groups" in their studies, and refer to "the experimentalchronology" of their research design. So, they certainly seem to think of their work as a kind of experiment.
Experimental design
In a true experiment, a sample is randomly drawn from a population of interest (say, first year undergraduate chemistry students; or, perhaps, first year undergraduate chemistry students attending Swedish Universities, or… 3) and assigned randomly to the conditions being compared. Providing a genuine form of random assignment is used, then inferential statistical tests can guide on whether any differences found between groups at the end of an experiment should be considered statistically significant. 4
"Statistics can only indicate how likely a measured result would occur by chance (as randomisation of units of analysis to different treatments can only make uneven group composition unlikely, not impossible)…Randomisation cannot ensure equivalence between groups (even if it makes any imbalance just as likely to advantage either condition)"
That is, if the are difference that the stats. tests suggests are very unlikely to happen by chance, then they are very unlikely to be due to an initial difference between the groups in the two conditions as long as the groups were the result of random assignment. But that is a very important proviso.
There are two aspects to this need for randomisation:
to be able to suggest any differences found reflect the effects of the intervention, then there should be random assignment to the two (or more) conditions
to be able to suggest the results reflect what would probably would be found in a wider population, the sample should be randomly selected from the population of interest 3
In education, it is not always possible to use random assignment, so true experiments are then not possible. However, so-called 'quasi-experiments' may be possible where differences between the outcomes in different conditions may be understood as informative, as long as there is good reason to believe that even without random assignment, the groups assigned to the different conditions are equivalent.
In this specific research, that would mean having good reason to believe that without the intervention (the prelab):
students in both groups would have asked overall equivalent (in terms of the analysis undertaken in this study) questions in the lab.;
students in both groups would have been judged as displaying overall equivalent subject knowledge.
Often in research where a true experiment is not possible some kind of pre-testing is used to make a case for equivalence between groups.
Two control groups that were out of control
In Winberg and Berg's research there were two studies where comparisons were made between 'experimental' and 'control' conditions
n=78: first-year students, following completion of their first chemistry course in 2001
n=97: students who had been interviewed by the researchers during the same course in the previous year
Study 2
n=21 (of 58 in cohort)
n=37 (of 58 in same cohort)
In the first study, a comparison was made between the cohort where the innovation was introduced and a cohort from the previous year. All other things being equal, it seems likely these two cohorts were fairly similar. But in education all thing are seldom equal, so there is no assurance they were similar enough to be considered equivalent.
In the second study
"Students were divided into treatment (n = 21) and control (n = 37) groups. Distribution of students between the treatment and control groups was not controlled by the researchers".
Winberg & Berg, 2007
So, some factor(s) external to the researchers divided the cohort into two groups – and the reader is told nothing about the basis for this, nor even if the two groups were assigned to the treatments randomly.5 The authors report that the cohort "comprised prospective molecular biologists (31%), biologists (51%), geologists (7%), and students who did not follow any specific program (11%)", and so it is possible the division into two uneven sized groups was based on timetabling constraints with students attending chemistry labs sessions according to their availability based on specialism. But that is just a guess. (It is usually better when the reader of a research report is not left to speculate about procedures and constraints.)
What is important for a reader to note is that in these studies:
the researchers were not able to assign learners to conditions randomly;
nor were the researchers able to offer any evidence of equivalence between groups (such as near identical pre-test scores);
so, the requirements for inferring significance from statistical tests were not met;
so, claims in the paper about finding statistically significant differences between conditions cannot therefore be justified given the research design;
and therefore the conclusions presented in the paper are strictly not valid.
If students are not randomly assigned to conditions, then any statistically unlikely difference found at the end of an experiment cannot be assumed to be likely to be due to intervention, rather than some systematic initial difference between the groups. (Figure adapted from Taber, 2019)
This is a shame, because this is in many ways an interesting paper, and much thought and care seems to have been taken about the collection and analysis of meaningful data. Yet, drawing conclusions from statistical tests comparing groups that might never have been similar in the first case is like finding that careful use of a vernier scale shows that after a period of watering plant A, plant A is taller than plant B – having been very careful to make sure plant A was watered regularly with carefully controlled volumes, while plant B was not watered at all – when you did not think to check how tall the two plants were before you started watering plant A.
In such a scenario we might be tempted to assume plant A has actually become taller because it had been watered; but that is just applying what we had conjectured should be the case, and we would be mistaking our expectations for experimental evidence.
Work cited:
Taber, K. S. (2013). Non-random thoughts about research. Chemistry Education Research and Practice, 14(4), 359-362. doi:10.1039/c3rp90009f
Winberg, T. M., & Berg, C. A. R. (2007). Students' cognitive focus during a chemistry laboratory exercise: Effects of a computer-simulated prelab. Journal of Research in Science Teaching, 44(8), 1108-1133. https://doi.org/https://doi.org/10.1002/tea.20217
Notes:
1 The part of the brain where we can consciously mentipulate ideas is called the working memory (WM). Research suggests that WM has a very limited capacity in the sense that people can only hold in mind a very small number of different things at once. (These 'things' however are somewhat subjective – a complex idea that is treated as a single 'thing' in the WM of an expert can overload a novice.) This limit to ~WM is considered to be one of the most substantial constraints on effective classroom learning. This is also, then, one of the key research findings informing the design of effective teaching.
2 The organisation has seemingly spotted that the USA is only one part of the world, and now describes itself as a global organisation for improving science education through research.
3 There is no reason why an experiment cannot be carried out on a very specific population, such as first year undergraduate chemistry students attending a specific Swedish University such a, say, Umea ̊ University. However, if researchers intend their study to have results generalisable beyond their specific research contexts (say, to first year undergraduate chemistry students attending any Swedish University) then it is important to have a representative sample of thatpopulation.
4 It might be assumed that scientists, and researchers know what is meant by random, and how to undertake random assignment. Sadly, the literature suggests that in practice the term 'randomly' is sometimes used in research reports to mean something like 'arbitrarily' (Taber, 2013), which fills short of being random.
One of the most fundamental ideas in physics, surely taught in every secondary school science curriculum around the world, is also the focus of one of the most common alternative conceptions documented in science education. Inertia. Much research in the latter part of the twentieth century has detailed how most people have great trouble with this very simple idea.
But that would likely not have surprised the nineteenth century French physicist (and mathematician and philosopher) Henri Poincaré in the least. Over a century ago he had this to say about the subject of Newton's first law, inertia,
"The principle of inertia. A body acted on by no force can only move uniformly in a straight line.
Is this a truth imposed a priori upon the mind? If it were so, how could the Greeks have failed to recognise it? How could they have believed that motion stops when the cause which gave birth to it ceases? Or again that every body if nothing prevents, will move in a circle, the noblest of motions?
If it is said that the velocity of a body can not change if there is no reason for it to change, could it not be maintained just as well that the position of this body can not change, or that the curvature of its trajectory can not change, if no external cause intervenes to modify them?
Is the principle of inertia, which is not an a priori truth, therefore an experimental fact? But has any one ever experimented on bodies withdrawn from the action of every force? and, if so, how was it known that these bodies were subjected to no force?"
Poincaré, 1902/1913/2015
There is quite a lot going on in that quote, so it is worth breaking it down.
The principle of inertia
"The principle of inertia. A body acted on by no force can only move uniformly in a straight line."
Poincaré, 1902/1913/2015
We might today choose to phrase this differently – at least in teaching. Perhaps along the lines that
a body remains at rest, or moving with uniform motion, unless it is acted upon by a net (overall) force
That's a pretty simple idea.
If you want something that is stationary to start moving, you need to apply a force to it. Otherwise it will remain stationary. And:
If you want something that is moving with constant velocity to slow down (decelerate), speed up (accelerate), or change direction, you need to apply a force to it. Otherwise it will carry on moving in the same direction at the same speed.
A simple idea, but one which most people struggle with!
It is worth noting that Poincaré's formulation seems simpler than the versions more commonly presented in school today. He does not make reference to a body at rest; and we might detect a potential ambiguity in what is meant by "can only move uniformly in a straight line".
Is the emphasis:
can only move uniformly in a straight line:
i.e., 〈 can only 〉 〈 move uniformly in a straight line 〉, or
can only move uniformly in a straight line:
i.e., 〈 can only move 〉 〈 uniformly in a straight line 〉
That is, must such a body "move uniformly in a straight line" or must such a body, if moving, "move uniformly in a straight line"? A body acted on by no force may be stationary.
Perhaps this is less ambiguous in the original French? But I suspect that, as a physicist, Poincairé did not, particularly, see the body at rest as being much of a special case.
To most people the distinction between something stationary and something moving is very salient (evolution has prepared us to notice movement). But to a physicist the more important distinction is between any body at constant velocity, and one accelerating* – and a body not moving has constant velocity (of 0 ms-1!)
*and for a physicist accelerating usually includes decelerating, as that is just acceleration with a negative vale, or indeed positive acceleration in a different direction. These 'simplifications' seem very neat – to the initiated (but perhaps not to novices!)
A historical scientific conception
Poincaré then asks:
Is this a truth imposed a priori upon the mind? If it were so, how could the Greeks have failed to recognise it? How could they have believed that motion stops when the cause which gave birth to it ceases?"
Poincaré, 1902/1913/2015
Poincairé asks a rhetorical question: "Is this a truth imposed a priori upon the mind?" Rhetorical, as he immediately suggests the answer. No, it cannot be.
In this way, it diverges from a rationalist approach to understanding the world based on reflection and reasoning that occurs without seeking empirical evidence.
An aside on simulations and perpetual change
Yet, even empirical science depends on some (a priori) metaphysical commitments that cannot themselves be demonstrated by scientific observation (e.g., Taber, 2013). As one example, the famous 'brain in a vat' scenario (that informed films such as The Matrix) asks how we could know that we really experience an external world rather than a very elaborate virtual reality fed directly into our central nervous system (assuming we have such a thing!) 1
Science only makes sense if we believe that the world we experience is an objective reality originating outside our own minds (Image by Gerd Altmann from Pixabay)
Despite this, scientists operate on the assumption this is a physical world (that we all experience), and one that has a certain degree of stability and consistency. 2 The natural scientist has to assume this is not a capricious universe if science (a search for the underlying order of the world) is to make sense!
It may seem this (that we live in is an objective physical world that has a certain degree of stability and consistency) is obviously the case, as our observations of the world find this stability. But not really: rather, we impose an assumption of an underlying stability, and interpret accordingly. The sun 'rises' every day. (We see stability.) But the amount of daylight changes each day. (We observe change, but assume, and look for, and posit, some underlying stability to explain this.)
Continental drift, new comets, evolution of new species and extinction of others, supernovae, the appearance of HIV and COVID, increasing IQ (disguised by periodically renormalising scoring), climate change, the expanding universe, plant growth, senile dementia, rotting fruit, printers running out of ink, lovers falling out of love, et cetera,…are all assumed to be (and subsequently found to be) explainable in terms of underlying stable and consistent features of the world!
But it would be possible to consider nothing stays the same, and seek to explain away any apparent examples of stability!
Parmenides thought change is impossible
Heraclitus though everything was in flux
An a priori?
So Poincaré was asking if the principle of is inertia was something that would appear to us as a given; is inertia something that seems a necessary and obvious feature of the world (which it probably does to most physicists – but that is after years of indoctrination into that perspective).
But, Poincaré was pointing out, we know that for centuries people did not think that objects not subject any force would continue to move with constant velocity.
There were (considered to be) certain natural motions, and these had a teleological aspect. So, heavy objects, that were considered mainly earth naturally fell down to their natural place on the ground. 3 Once there, mission accomplished (so to speak), they would stop moving. No further explanation was considered necessary.
Violent motions were (considered to be) different as they needed an active cause – such as a javelin moving through the air because someone had thrown it. Yet, clearly (it was believed), the athlete could only impart a finite motion to the javelin, which it would soon exhaust, so the javelin would (naturally) stop soon enough.
Today, such ideas are seen as alternative conceptions (misconceptions), but for hundreds of years these ideas were largely taken as self-evident and secure principles describing aspects of the world. The idea that the javelin might carry on moving for ever if it was 'left to its own devices' seemed absurd. (And to most people today who are not physicists or science teachers, it probably still does!)
An interesting question is if, and if so, to what extent, the people who become physicists and physics teachers start out with intuitions more aligned with the principles of physics than most of their classmates.
"Assuming that there is significant variation in the extent to which our intuitive physics matches what we are taught in school, I would expect that most physics teachers are among those to whom the subject seemed logical and made good sense when they were students. I have no evidence for this, but it just seems natural that these students would have enjoyed and continued with the subject.
If I am right about this intuition, then this may be another reason why physics is so hard for some of our students. Not only do they have to struggle with subject matter that seems counterintuitive, but the very people who are charged with helping them may be those who instinctively think most differently from the way in which they do."
Taber, 2004, p.124
Another historical scientific conception
And Poincaré went on:
"Or again that every body if nothing prevents, will move in a circle, the noblest of motions?"
Poincaré, 1902/1913/2015
It was also long thought that in the heavens bodies naturally moved spontaneously in circles – a circle being a perfect shape, and the heavens being a perfect place.
Orbital motion – once viewed to be natural (i.e., not requiring any further explanation) and circular in 'the heavens'. (Image by WikiImages from Pixabay: Body sizes and separations not to the same scale!)
It is common for people to feel that what seems natural does not need further explanation (Watts & Taber, 1996) – even though most of what we consider natural is likely just familiarity with common phenomena. We start noticing how the floor arrests the motion of falling objects very young in life, so by the time we have language to help reflect on this, we simply explain this as motion stopping because the floor was in the way! Similarly, reaction forces are not obvious when an object rests on another – a desk, a shelf, etc – as the object cannot fall 'because it is supported'.
Again, we (sic, wethe initiated) now think that without an acting centripetal force, an orbiting body would move off at a tangent – but that would have seemed pretty bizarre for much of European history.
The idea that bodies moved in circles (as the fixed stars seemed to do) was maintained despite extensive observational evidence collected over centuries that the planets appeared to do something quite different. Today Kepler's laws are taught in physics, including that the solar system's orbiting bodies move (almost) in ellipses. ('Almost', as they bodies perturb each other a little.)
But when Kepler tried to fit observations to theory by adopting Copernicus's 'heliocentric' model of the Earth and planets orbiting the Sun (Earth and other planets, we would say), he still struggled to make progress for a considerable time because of an unquestioned assumption that the planetary motions had to be circular, or some combination of multiple circles.
Learners' alternative conceptions
These historical ideas are of more than historical interest. Many people, research suggests most people, today share similar intuitions.
Objects will naturally come to a stop when they have used up their imparted motion without the need for any forces to act.
Something that falls to the floor does not need a force to act on it to stop it moving, as the ground is in its way.
Moons and planets continue in orbits because there is no overall force acting on them.
The vast majority of learners some to school science holding versions of such alternative conceptions.
The majority of learners also leave school holding versions of such alternative conceptions – even if some of them have mastered the ability to usually respond to physics test questions as if they accepted a different worldview.
The idea that objects soon stop moving once the applied force ceases to act may be contrary to physics, but it is not, of course, contrary to common experience – at least not contrary to common experience as most people perceive it.
Metaphysical principles
Poincaré recognised this.
"If it is said that the velocity of a body can not change if there is no reason for it to change [i.e. the principle of inertia],
could it not be maintained just as well that
the position of this body can not change, or
that the curvature of its trajectorycan not change,
if no external cause intervenes to modify them?"
Poincaré, 1902/1913/2015 (emphasis added)
After all, as Poincairé pointed out, there seems no reason, a priori, that is intuitively, to assume the world must work according to the principle of inertia (though some physicists and science teachers whom have been indoctrinated over many years may have come to think otherwise – of course after indoctrination is not a priori!), rather than assuming, say, that force must act for movement to occur and/or that force must act to change an orbit.
Science as an empirical enterprise
Science teachers might reply, that our initial intuitions are not the point, because myriad empirical tests have demonstrated the principle of inertia. But Poincairé suggested this was strictly not so,
"Is the principle of inertia, which is not an a priori truth, therefore an experimental fact? But has any one ever experimented on bodies withdrawn from the action of every force? and, if so, how was it known that these bodies were subjected to no force?"
Poincaré, 1902/1913/2015
For example, if we accept the ideas of universal gravitation, than anywhere in the universe a body will be subject to gravitational attractions (that is, forces). A body could only be completely free of this by being in a universe of its own with no other gravitating bodies. Then we might think we could test, in principle at least, whether the body "acted on by no force can only move uniformly in a straight line".
Well, apart from a couple of small difficulties. There would be no observers in this universe to see, as we have excluded all other massive bodies. And if this was the only body there, it would be the only frame of reference available – a frame of reference in which it was always stationary. It would always be at the centre of, and indeed would be the extent of, its universe.
Poincaré and pedagogic awareness
Poincaré was certainly not denying the principle of inertia so fundamental to mechanics. But he was showing that he appreciated that a simple principle which seems (comes to seem?) so basic and obvious to the inducted physics expert:
is not the only possible basic principle on which a mechanics (in some other universe) could be based
is contrary to immediate experience (that is, to those who have not been indoctrinated to 'see' resistive forces sch as friction acting everywhere)
could never be entirely demonstrated in a pure form, but rather must be inferred from experimental tests of more complex situations where we will only deduce the principle of inertia if we assume a range of other principles (about the action of gravitational fields, air resistance, etc.)
Poincaré may have been seen as one of the great physicists of his time, but his own expertise certainly did not him appreciating the challenges facing the learner of physics, or indeed the teacher of physics.
Work cited:
Taber, K. S. (2004) Intuitive physics: but whose intuition are we talking about?, Physics Education, 39 (2), pp.123-124.
Watts, M. and Taber, K. S. (1996) An explanatory gestalt of essence: students' conceptions of the 'natural' in physical phenomena, International Journal of Science Education, 18 (8), pp.939-954.
Notes
1 With current human technology we cannot achieve this – even the best virtual worlds clearly do not yet come close to the real one! But that argument falls away if 'the real' world we experience is such a virtual reality created by very advanced technology, and what we think of as virtual worlds are low definition simulations being created within that! (After all, when people saw the first jumpy black-and-white movies, they then came out from the cinema into a colourful, smooth and high definition world.) If you have ever awaken from a dream, only to later realise you are still asleep, and had been dreaming of being asleep in the dream, then you may appreciate how such nesting of worlds could work.
Probably no one actually believes they are a brain in a vat, but how would we know. There is an argument that
1) the evolution of complex life is a very slow process that requires a complex ecosystem, but
2) once humans (or indeed non-humans) have the technology to create convincing virtual worlds this can be done very much more quickly, and with much less resource [i.e., than the evolution of the physical world which within which the programmers of the simulations themselves live]. So,
3) if we are living in a phase of the universe where such technology has been achieved, then we would expect there to be a great many more such virtual worlds than planets inhabited by life forms with the level of self-consciousness to think about whether they are in a simulation.4 So,
4) [if we are living in a phase of the universe where such technology has been achieved] we would be much more likely to be living in one of these worlds (a character in a very complex simulation) than an actual organic being. 5
2 That is, not a simulation where an adolescent programmer is going to suddenly increase gravity or add a new fundamental force just to make things more interesting.
3 Everything on earth was considered to be made up of different proportions of the four elements, which in terms of increasing rarity were earth, water, air and fire. The rocks of the earth were predominately the element earth – and objects that were mainly earth fell to their natural place. (Rarity in this context means the inverse of density, not scarcity.)
4 When I was a child (perhaps in part because I think I started Sunday School before I could start 'proper' school), I used to muse about God being able to create everything, and being omniscient – although I am pretty sure I did not use that term! It seemed to me (and, sensibly, I do not think I shared this at Sunday School) that if God knew everything and was infallible, then he did not need to actually create the world as a physical universe, but rather just think what would happen. For God, that would work just as well, as a perfect mind could imagine things exactly as they would be in exquisite detail and with absolute precision. So, I thought I might just be an aspect of the mind of God – so part of a simulation in effect. This was a comforting rather than worrying thought – surely there is no safer place to be than in the mind of God?
Sadly, I grew to be much less sure of God (the creation seems just as incredible – in the literal sense – either way), but still think that, for God, thinking it would be as good as (if not the same as) making it. I suspect some theologians would not entirely dismiss this.
If I am just a character in someone's simulation, I'd rather it was that of a supreme being than some alien adolescent likely to abandon my world at the first sign of romantic interest from a passing conspecific.
5 Unless we assume a dystopian Matrix like simulation, the technology has to be able to create characters (sub-routines?) with self-awareness – which goes some way beyond just a convincing simulation, as it also requires components complex enough to be convinced about their own existence, as well as the reality of the wider simulation!
Trustworthy research findings are conditional on getting a lot of things right
Keith S. Taber
A good many experimental educational research studies that compare treatments across two classes or two schools are subject to potentially conflating variables that invalidate study findings and make any consequent conclusions and recommendations untrustworthy.
One of the papers I came across reported identifying, and then using P-O-E to respond to, students' alternative conceptions. The authors reported that
The pre-test revealed a number of misconceptions held by learners in both groups: learners believed that salts 'disappear' when dissolved in water (37% of the responses in the 80% from the pre-test) and that salt 'melts' when dissolved in water (27% of the responses in the 80% from the pre-test).
Kibirige, Osodo & Tlala, 2014, p.302
The references to "in the 80%" did not seem to be explained anywhere. Perhaps only 80% of students responded to the open-ended questions included as part of the assessment instrument (discussed below), so the authors gave the incidence as a proportion of those responding? Ideally, research reports are explicit about such matters avoiding the need for readers to speculate.
"This study revealed that the use of POE strategy has a positive effect on learners' misconceptions about dissolved salts. As a result of this strategy, learners were able to overcome their initial misconceptions and improved on their performance….The implication of these results is that science educators, curriculum developers, and textbook writers should work together to include elements of POE in the curriculum as a model for conceptual change in teaching science in schools."
Kibirige, Osodo & Tlala, 2014, p.305
This seemed pretty positive. As P-O-E is an approach which is consistent with 'constructivist' thinking that recognises the importance of engaging with learners' existing thinking I am probably biased towards accepting such conclusions. I would expect techniques such as P-O-E, when applied carefully in suitable curriculum contexts, to be effective.
Yet I also have a background in teaching research methods and in acting as a journal editor and reviewer – so I am not going to trust the conclusion of a research study without having a look at the research design.
All research findings are subject to caveats and provisos: good practice in research writing is for the authors to discuss them – but often they are left unmentioned for readers to spot. (Read about drawing conclusions from studies)
Kibirige and colleagues describe their study as a quasi-experiment.
Experimental research into teaching approaches
If one wants to see if a teaching approach is effective, then it seems obvious that one needs to do an experiment. If we can experimentally compare different teaching approaches we can find out which are more effective.
An experiment allows us to make a fair comparison by 'control of variables'.
Identify a representative sample of an identified population
Randomly assign learners in the sample to either an experimental condition or a control condition
Set up two conditions that are alike in all relevant ways, apart from the independent variable of interest
After the treatments, apply a valid instrument to measure learning outcomes
Use inferential statistics to see if any difference in outcomes across the two conditions reaches statistical significance
If it does, conclude that
the effect is likely to due to the difference in treatments
and will apply, on average, to the population that has been sampled
Now, I expect anyone reading this who has worked in schools, and certainly anyone with experience in social research (such as research into teaching and learning), will immediately recognise that in practice it is very difficult to actually set up an experiment into teaching which fits this description.
Nearly always (if indeed not always!) experiments to test teaching approaches fall short of this ideal model to some extent. This does not mean such studies can not be useful – especially where there are many of them with compensatory strengths and weaknesses offering similar findings (Taber, 2019a)- but one needs to ask how closely published studies fit the ideal of a good experiment. Work in high quality journals is often expected to offer readers guidance on this, but readers should check for themselves to see if they find a study convincing.
So, how convincing do I find this study by Kibirige and colleagues?
The sample and the population
If one wishes a study to be informative about a population (say, chemistry teachers in the UK; or 11-12 year-olds in state schools in Western Australia; or pharmacy undergraduates in the EU; or whatever) then it is important to either include the full population in the study (which is usually only feasible when the population is a very limited one, such as graduate students in a single university department) or to ensure the sample is representative.
Kibirige and colleagues refer to their participants as a sample
"The sample consisted of 93 Grade 10 Physical Sciences learners from two neighbouring schools (coded as A and B) in a rural setting in Moutse West circuit in Limpopo Province, South Africa. The ages of the learners ranged from 16 to 20 years…The learners were purposively sampled."
Kibirige, Osodo & Tlala, 2014, p.302
Purposive sampling means selecting participants according to some specific criteria, rather than sampling a populationrandomly. It is not entirely clear precisely what the authors mean by this here – which characteristics they selected for. Also, there is no statement of the population being sampled – so the reader is left to guess what population the sample is a sample of. Perhaps "Grade 10 Physical Sciences" students – but, if so, universally, or in South Africa, or just within Limpopo Province, or indeed just the Moutse West circuit? Strictly the notion of a sample is meaningless without reference to the population being sampled.
"An experiment may, for example, be comparing outcomes between different learners, different classes, different year groups, or different schools…It is important at the outset of an experimental study to clarify what the unit of analysis is, and this should be explicit in research reports so that readers are aware what is being compared."
In a true experiment the 'units of analysis' (which in different studies may be learners, teachers, classes, schools, exam. papers, lessons, textbook chapters, etc.) are randomly assigned to conditions. Random assignment allows inferential statistics to be used to directly compare measures made in the different conditions to determine whether outcomes are statistically significant. Random assignment is a way of making systematic differences between groups unlikely (and so allows the use of inferential statistics to draw meaningful conclusions).
Random assignment is sometimes possible in educational research, but often researchers are only able to work with existing groupings.
Kibirige, Osodo & Tlala describe their approach as using a quasi-experimental design as they could not assign learners to groups, but only compare between learners in two schools. This is important, as means that the 'units of analysis' are not the individual learners, but the groups: in this study one group of students in one school (n=1) is being compared with another group of students in a different school (n=1).
The authors do not make it clear whether they assigned the schools to the two teaching conditions randomly – or whether some other criterion was used. For example, if they chose school A to be the experimental school because they knew the chemistry teacher in the school was highly skilled, always looking to improve her teaching, and open to new approaches; whereas the chemistry teacher in school B had a reputation for wishing to avoid doing more than was needed to be judged competent – that would immediately invalidate the study.
Compensating for not using random assignment
When it is not possible to randomly assign learners to treatments, researchers can (a) use statistics that take into account measurements on each group made before, as well as after, the treatments (that is, a pre-test – post-test design); (b) offer evidence to persuade readers that the groups are equivalent before the experiment. Kibirige, Osodo and Tlala seek to use both of these steps.
Do the groups start as equivalent?
Kibirige, Osodo and Tlala present evidence from the pre-test to suggest that the learners in the two groups are starting at about the same level. In practice, pre-tests seldom lead to identical outcomes for different groups. It is therefore common to use inferential statistics to test for whether there is a statistically significant difference between pre-test scores in the groups. That could be reasonable, if there was an agreed criterion for deciding just how close scores should be to be seen as equivalent. In practice, many researchers only check that the differences do not reach statistical significance at the level of probability <0.05: that it they look to see if there are strong differences, and, if not, declare this is (or implicitly treat this as) equivalence!
This is clearly an inadequate measure of equivalence as it will only filter out cases where there is a difference so large it is found to be very unlikely to be a chance effect.
If we want to make sure groups start as 'equivalent', we cannot simply look to exclude the most blatant differences. (Original image by mcmurryjulie from Pixabay)
We can see this in the Kibirige and colleagues' study where the researchers list mean scores and standard deviations for each question on the pre-test. They report that:
"The results (Table 1) reveal that there was no significant difference between the pre-test achievement scores of the CG [control group] and EG [experimental group] for questions (Appendix 2). The p value for these questions was greater than 0.05."
Kibirige, Osodo & Tlala, 2014, p.302
Now this paper is published "licensed under Creative Commons Attribution 3.0 License" which means I am free to copy from it here.
According to the results table, several of the items (1.2, 1.4, 2.6) did lead to statistically significantly different response patterns in the two groups.
Most of these questions (1.1-1.4; 2.1-2.8; discussed below) are objective questions, so although no marking scheme was included in the paper, it seems they were marked as correct or incorrect.
So, let's take as an example question 2.5 where readers are told that there was no statistically significant difference in the responses of the two groups. The mean score in the control group was 0.41, and in the experimental group was 0.27. Now, the paper reports that:
"Forty nine (49) learners (31 males and 18 females) were from school A and acted as the experimental group (EG) whereas the control group (CG) consisted of 44 learners (18 males and 26 females) from school B."
"The achievement of the EG and CG from pre-test results were not significantly different which suggest that the two groups had similar understanding of concepts" (p.305). Pre-test results for an item with no statistically significant difference between groups (offered as evidence of 'similar' levels of initial understanding in the two groups)
While, technically, there may have been no statistically significant difference here, I think inspection is sufficient to suggest this does not mean the two groups were initially equivalent in terms of performance on this item.
Data that is normally distributed falls on a 'bell-shaped' curve
(Image by mcmurryjulie from Pixabay)
Inspection of this graphic also highlights something else. Student's t-test (used by the authors to produce the results in their table 1), is a parametric test. That means it can only be used when the data fit certain criteria. The data sample should be randomly selected (not true here) and normally distributed. A normal distribution means data is distributed in a bell-shaped Gaussian curve (as in the image in the blue circle above).If Kibirige, Osodo & Tlala were applying the t-test to data distributed as in my graphic above (a binary distribution where answers were either right or wrong) then the test was invalid.
So, to summarise, the authors suggest there "was no significant difference between the pre-test achievement scores of the CG and EG for questions", although sometimes there was (according to their table); and they used the wrong test to check for this; and in any case lack of statistical significance is not a sufficient test for equivalence.
I should note that the journal does claim to use peer review to evaluate submissions to see if they are ready for publication!
Comparing learning gains between the two groups
At one level equivalence might not be so important, as the authors used an ANCOVA (Analysis of Covariance) test which tests for difference at post-test taking into account the pre-test. Yet this test also has assumptions that need to be tested for and met, but here seem to have just been assumed.
However, to return to an even more substantive point I made earlier, as the learners were not randomly assigned to the two different conditions /treatments, what should be compared are the two school-based groups (i.e., the unit of analysis should be the school group) but that (i.e., a sample of 1 class, rather than 40+ learners, in each condition) would not facilitate using inferential statistics to make a comparison. So, although the authors conclude
"that the achievement of the EG [taking n=49] after treatment (mean 34. 07 ± 15. 12 SD) was higher than the CG [taking n =44] (mean 20. 87 ± 12. 31 SD). These means were significantly different"
Kibirige, Osodo & Tlala, 2014, p.303
the statistics are testing the outcomes as if 49 units independently experienced one teaching approach and 44 independently experienced another. Now, I do not claim to be a statistics expert, and I am aware that most researchers only have a limited appreciation of how and why stats. tests work. For most readers, then, a more convincing argument may be made by focussing on the control of variables.
Controlling variables in educational experiments
The ability to control variables is a key feature of laboratory science, and is critical to experimental tests. Control of variables, even identification of relevant variables, is much more challenging outside of a laboratory in social contexts – such as schools.
In the case of Kibirige, Osodo & Tlala's study, we can set out the overall experimental design as follows
Anything other than teaching approach which might make a difference to student learning
Variables in Kibirige, Osodo & Tlala's study
The researchers set up the two teaching conditions, measure learning gains, and need to make sure any other factors which might have an effect on learning outcomes, so called confounding variables, are controlled so the same in both conditions.
Of course, we cannot be sure what might act as a confounding variable, so in practice we may miss something which we do not recognise is having an effect. Here are some possibilities based on my own (now dimly recalled) experience of teaching in school.
The room may make a difference. Some rooms are
spacious,
airy,
well illuminated,
well equipped,
away from noisy distractions
arranged so everyone can see the front, and the teacher can easily move around the room
Some rooms have
comfortable seating,
a well positioned board,
good acoustics
…
Others, not so.
The timetable might make a difference. Anyone who has ever taught the same class of students at different times in the week might (will?) have noticed that a Tuesday morning lesson and a Friday afternoon lesson are not always equally productive.
Class size may make a difference (here 49 versus 44).
Could gender composition make a difference? Perhaps it was just me, but I seem to recall that classes of mainly female adolescents had a different nature than classes of mainly male adolescents. (And perhaps the way I experienced those classes would have been different if I had been a female teacher?) Kibirige, Osodo and Tlala report the sex of the students, but assuming that can be taken as a proxy for gender, the gender ratios were somewhat different in the two classes.
The gender make up of the classes was quite different: might that influence learning?
School differences
A potentially major conflating variable is school. In this study the researchers report that the schools were "neighbouring" and that
Having been drawn from the same geographical set up, the learners were of the same socio-cultural practices.
Kibirige, Osodo & Tlala, 2014, p.302
That clearly makes more sense than choosing two schools from different places with different demographics. But anyone who has worked in schools will know that two neighbouring schools serving much the same community can still be very different. Different ethos, different norms, and often different levels of outcome. Schools A and B may be very similar (but the reader has no way to know), but when comparing between groups in different schools it is clear that school could be a key factor in group outcome.
The teacher effect
Similar points can be made about teachers – they are all different! Does ANY teacher really believe that one can swap one teacher for another without making a difference? Kibirige, Osodo and Tlala do not tell readers anything about the teachers, but as students were taught in their own schools the default assumption must be that they were taught by their assigned class teachers.
Teachers vary in terms of
skill,
experience,
confidence,
enthusiasm,
subject knowledge,
empathy levels,
insight into their students,
rapport with classes,
beliefs about teaching and learning,
teaching style,
disciplinary approach
expectations of students
…
The same teacher may perform at different levels with different classes (preferring to work with different grade levels, or simply getting on/not getting on with particular classes). Teachers may have uneven performance across topics. Teachers differentially engage with and excel in different teaching approaches. (Even if the same teacher had taught both groups we could not assume they were equally skilful in both teaching conditions.)
Teacher variable is likely to be a major difference between groups.
Meta-effects
Another conflating factor is the very fact of the research itself. Students may welcome a different approach because it is novel and a change from the usual diet (or alternatively they may be nervous about things being done differently) – but such 'novelty' effects would disappear once the new way of doing things became established as normal. In which case, it would be an effect of the research itself and not of what is being researched.
Perhaps even more powerful are expectancy effects. If researchers expect an innovation to improve matters, then these expectations get communicated to those involved in the research and can themselves have an affect. Expectancy effects are so well demonstrated that in medical research double-blind protocols are used so that neither patients nor health professionals they directly engage with in the study know who is getting which treatment.
School effect Teacher effect Class size Gender composition of teaching groups Relative novelty of the two teaching approaches …
Variables in Kibirige, Osodo & Tlala's study
Now, of course, these problems are not unique to this particular study. The only way to respond to teacher and school effects of this kind is to do large scale studies, and randomly assign a large enough number of schools and teachers to the different conditions so that it becomes very unlikely there will be systematic differences between treatment groups.
A good many experimental educational research studies that compare treatments across two classes or two schools are subject to potentially conflating variables that invalidate study findings and make any consequent conclusions and recommendations untrustworthy (Taber, 2019a). Strangely, often this does not seem to preclude publication in research journals. 1
Advice on controls in scientific investigations:
I can probably do no better than to share some advice given to both researchers, and readers of research papers, in an immunology textbook from 1910:
"I cannot impress upon you strongly enough never to operate without the necessary controls. You will thus protect yourself against grave errors and faulty diagnoses, to which even the most competent investigator may be liable if he [or she] fails to carry out adequate controls. This applies above all when you perform independent scientific investigations or seek to assess them. Work done without the controls necessary to eliminate all possible errors, even unlikely ones, permits no scientific conclusions.
I have made it a rule, and would advise you to do the same, to look at the controls listed before you read any new scientific papers… If the controls are inadequate, the value of the work will be very poor, irrespective of its substance, because none of the data, although they may be correct, are necessarily so."
It seems clear that in this study there is no strict 'control' of variables, and the 'control' group is better considered just a comparison group. The authors tell us that:
"the control group (CG) taught using traditional methods…
the CG used the traditional lecture method"
Kibirige, Osodo & Tlala, 2014, pp.300, 302
This is not further explained, but if this really was teaching by 'lecturing' then that is not a suitable approach for teaching school age learners.
This raises two issues.
There is a lot of evidence that a range of active learning approaches (discussion work, laboratory work, various kinds of group work) engages and motivates students more than whole lessons spent listening to a teacher. Therefore any approach which basically involves a mixture of students doing things, discussing things, engaging with manipulatives and resources as well as listening to a teacher, tends to be superior to just being lectured. Good science teaching normally involves lessons sequenced into a series of connected episodes involving different types of student activity (Taber, 2019b). Teacher presentations of the target scientific account are very important, but tend to be effective when embedded in a dialogic approach that allows students to explore their own thinking and takes into account their starting points.
So, comparing P-O-E with lectures (if they really were lectures) may not tell researchers much about P-O-E specifically, as a teaching approach. A better test would compare P-O-E with some other approach known to be engaging.
"Many published studies argue that the innovation being tested has the potential to be more effective than current standard teaching practice, and seek to demonstrate this by comparing an innovative treatment with existing practice that is not seen as especially effective. This seems logical where the likely effectiveness of the innovation being tested is genuinely uncertain, and the 'standard' provision is the only available comparison. However, often these studies are carried out in contexts where the advantages of a range of innovative approaches have already been well demonstrated, in which case it would be more informative to test the innovation that is the focus of the study against some other approach already shown to be effective."
The second issue is more ethical than methodological. Sometimes in published studies (and I am not claiming I know this happened here, as the paper says so little about the comparison condition) researchers seem to deliberately set up a comparison condition they have good reason to expect is not effective: such as asking a teacher to lecture and not include practical work or discussion work or use of digital learning technologies and so forth. Potentially the researchers are asking the teacher of the 'control' group to teach less effectively than normally to bias the experiment towards their preferred outcome (Taber, 2019a).
This is not only a failure to do good science, but also an abuse of those learners being deliberately subjected to poor teaching. Perhaps in this study the class in School B was habitually taught by being lectured at, so the comparison condition was just what would have occurred in the absence of the research, but this is always a worry when studies report comparison conditions that seem to deliberately disadvantage students. (This paper does not seem to report anything about obtaining voluntary informed consent from participants, nor indeed about how access to the schools was negotiated. )
"In most educational research experiments of the type discussed in this article, potential harm is likely to be limited to subjecting students (and teachers) to conditions where teaching may be less effective, and perhaps demotivating…It can also potentially occur in control conditions if students are subjected to teaching inputs of low effectiveness when better alternatives were available. This may be judged only a modest level of harm, but – given that the whole purpose of experiments to test teaching innovations is to facilitate improvements in teaching effectiveness – this possibility should be taken seriously."
Even leaving aside all the concerns expressed above, the results of a study of this kind depends upon valid measurements. Assessment items must test what they claim to test, and their analysis should be subject to quality control (and preferably blind to which condition a script being analysed derives form). Kibirige, Osodo and Tlala append the test they used in the study (Appendix 2, pp.309-310), which is very helpful in allowing readers to judge at least its face validity. Unfortunately, they do not include a mark/analysis scheme to show what they considered responses worthy of credit.
"The [Achievement Test] consisted of three questions. Question one consisted of five statements which learners had to classify as either true or false. Question two consisted of nine [sic, actually eight] multiple questions which were used as a diagnostic tool in the design of the teaching and learning materials in addressing misconceptions based on prior knowledge. Question three had two open-ended questions to reveal learners' views on how salts dissolve in water (Appendix 1 [sic, 2])."
Kibirige, Osodo & Tlala, 2014, p.302
"Question one consisted of five statements which learners had to classify as either true or false."
Question 1 is fairly straightforward.
1.2: Strictly all salts do dissolve in water to some extent. I expect that students were taught that some salts are insoluble. Often in teaching we start with simple dichotomous models (metal-non metal; ionic-covalent; soluble-insoluble; reversible – irreversible) and then develop these to more continuous accounts that recognise difference of degree. It is possible here then that a student who had learnt that all salts are soluble to some extent might have been disadvantaged by giving the 'wrong' ('True') response…
…although[sic] , actually, there is perhaps no excuse for answering 'True' ('All salts can dissolve in water') here as a later question begins "3.2. Some salts does [sic] not dissolve in water. In your own view what happens when a salt do [sic] not dissolve in water".
Despite the test actually telling students the answer to this item, it seems only 55% of the experimental group, and 23% of the control group obtained the correct answer on the post test – precisely the same proportions as on the pre-test!
1.4: Seems to be 'False' as the ions exist in the salt and are not formed when it goes into solution. However, I am not sure if that nuance of wording is intended in the question.
Question 2 gets more interesting.
"Question two consisted of nine multiple questions" (seven shown here)
I immediately got stuck on question 2.2 which asked which formula (singular, not 'formula/formulae', note) represented a salt. Surely, they are all salts?
I had the same problem on 2.4 which seemed to offer three salts that could be formed by reacting acid with base. Were students allowed to give multiple responses? Did they have to give all the correct options to score?
Again, 2.5 offered three salts which could all be made by direct reaction of 'some substances'. (As a student I might have answered A assuming the teacher meant to ask about direct combination of the elements?)
At least in 2.6 there only seemed to be two correct responses to choose between.
Any student unsure of the correct answer in 2.7 might have taken guidance from the charges as shown in the equation given in question 2.8 (although indicated as 2.9).
How I wished they had provided the mark scheme.
The final question in this section asked students to select one of three diagrams to show what happens when a 'mixture' of H2O and NaCl in a closed container 'react'. (In chemistry, we do not usually consider salt dissolving as a reaction.)
Diagram B seemed to show ion pairs in solution (but why the different form of representation?) Option C did not look convincing as the chloride ions had altogether vanished from the scene and sodium seemed to have formed multiple bonds with oxygen and hydrogens.
So, by a process of elimination, the answer is surely A.
But components seem to be labelled Na and Cl (not as ions).
And the image does not seem to represent a solution as there is much too much space between the species present.
And in salt solution there are many water molecules between solvated ions – missing here.
And the figure seems to show two water molecules have broken up, not to give hydrogen and hydroxide ions, but lone oxygen (atoms, ions?)
And why is the chlorine shown to be so much larger in solution than it was in the salt? (If this is meant to be an atom, it should be smaller than the ion, not larger. The real mystery is why the chloride ions are shown so much smaller than smaller sodium ions before salvation occurs when chloride ions have about double the radii of sodium ions.)
So diagram A is incredible, but still not quite as crazy an option as B and C.
This is all despite
"For face validity, three Physical Sciences experts (two Physical Sciences educators and one researcher) examined the instruments with specific reference to Mpofu's (2006) criteria: suitability of the language used to the targeted group; structure and clarity of the questions; and checked if the content was relevant to what would be measured. For reliability, the instruments were piloted over a period of two weeks. Grade 10 learners of a school which was not part of the sample was used. Any questions that were not clear were changed to reduce ambiguity."
Kibirige, Osodo & Tlala, 2014, p.302
One wonders what the less clear, more ambiguous, versions of the test items were.
Reducing 'misconceptions'
The final question was (or, perhaps better, questions were) open-ended.
I assume (again, it would be good for authors of research reports to make such things explicit) these were the questions that led to claims about the identified alternative conceptions at pre-test.
"The pre-test revealed a number of misconceptions held by learners in both groups: learners believed that salts 'disappear' when dissolved in water (37% of the responses in the 80% from the pre-test) and that salt 'melts' when dissolved in water (27% of the responses in the 80% from the pre-test)."
Kibirige, Osodo & Tlala, 2014, p.302
As the first two (sets of) questions only admit objective scoring, it seems that this data can only have come from responses to Q3. This means that the authors cannot be sure how students are using terms. 'Melt' is often used in an everyday, metaphorical, sense of 'melting away'. This use of language should be addressed, but it may not be a conceptual error
As the first two (sets of) questions only admit objective scoring, it seems that this data can only have come from responses to Q3. This means that the authors cannot be sure how students are using terms. 'Melt' is often used in an everyday, metaphorical, sense of 'melting away'. This use of language should be addressed, but it may not (for at least some of these learners) be a conceptual error as much as poor use of terminology. .
To say that salts disappear when they dissolve does not seem to me a misconception: they do. To disappear means to no longer be visible, and that's a fair description of the phenomenon of salt dissolving. The authors may assume that if learners use the term 'disappear' they mean the salt is no longer present, but literally they are only claiming it is not directly visible.
Unfortunately, the authors tell us nothing about how they analysed the data collected form their test, so the reader has no basis for knowing how they interpreted student responded to arrive at their findings. The authors do tell us, however, that:
"the intervention had a positive effect on the understanding of concepts dealing with dissolving of salts. This improved achievement was due to the impact of POE strategy which reduced learners' misconceptions regarding dissolving of salts"
Kibirige, Osodo & Tlala, 2014, p.305
Yet, oddly, they offer no specific basis for this claim – no figures to show the level at which "learners believed that salts 'disappear' when dissolved in water …and that salt 'melts' when dissolved in water" in either group at the post-test.
Control of variables in educational contexts is often almost impossible.
Studies that compare different teaching approaches using two different classes each taught by a different teacher (and perhaps not even in the same school) can never be considered fair comparisons able to offer generalisable conclusions about the relative merits of the approaches. Such 'experiments' have no value as research studies. 1
Such 'experiments' are like comparing the solubility of two salts by (a) dropping a solid lump of 10g of one salt into some cold water, and (b) stirring a finely powdered 35g sample of the other salt into hot propanol; and watching to see which seems to dissolve better.
Only large scale studies that encompass a wide range of different teachers/schools/classrooms in each condition are likely to produce results that are generalisable.
The use of inferential statistical tests is only worthwhile when the conditions for those statistical tests are met. Sometimes tests are said to be robust to modest deviations from such acquirements as normality. But applying tests to data that do not come close to fitting the conditions of the test is pointless.
Any research is only as trustworthy as the validity of its measurements. If one does not trust the measuring instrument or the analysis of measurement data then one cannot trust the findings and conclusions.
The results of a research study depend on an extended chain of argumentation, where any broken link invalidates the whole chain. (From 'Critical reading of research')
So, although the website for the Mediterranean Journal of Social Science claims "All articles submitted …undergo to a rigorous double blindedpeer review process", I think the peer reviewers for this article were either very generous, very ignorant, or simply very lazy. That may seem harsh, but peer review is meant to help authors improve submissions till they are worthy of appearing in the literature, and here peer review has failed, and the authors (and readers of the journal) have been let down by the reviewers and the editor who ultimately decided this study was publishable in this form.
If I asked a graduate student (or indeed an undergraduate student) to evaluate this paper, I would expect to see a response something along these sorts of lines:
I still think P-O-E is a very valuable part of the science teacher's repertoire – but this paper can not contribute anything to support to that view.
Work cited:
Kibirige, I., Osodo, J., & Tlala, K. M. (2014). The effect of predict-observe-explain strategy on learners' misconceptions about dissolved salts. Mediterranean Journal of Social Sciences, 5(4), 300-310.
1 A lot of these invalid experiments get submitted to research journals, scrutinised by editors and journal referees, and then get published without any acknowledgement of how they fall short of meeting the conditions for a valid experiment. (See, for example, examples discussed in Taber 2019a.) It is as if the mystique of experiment is so great that even studies with invalid conclusions are considered worth publishingas long as the authors did an experiment.
Perhaps Poincaré was reflecting how two opposing schools of philosophical thought had disagreed on wherever the primary source of human knowledge was experience (the empiricists) or pure reasoning (the rationalists), but elsewhere in the same text Poincairé (1902/1913/2015) dismisses the idea that the laws of physics can be obtained by simple reflection on human intuitions. Such intuitions can lead us astray.
If he is being consistent then, surely "the contrary hypothesis is [only] singularly repugnant to the mind" because "the commonest experience confirms…the principle of relative motion". That is, suggestions that are clearly contrary to our common experience – such as, perhaps, the earth is moving? – are readily rejected as being nonsensical and ridiculous.
If that is so, then Poincaré was not really offering two independent lines of argument as his second reason was dependent upon his first.
This put me in mind of some comments of Kryten, a character in the sci-fi series 'Red Drawf',
{responding to a crew suggestion "Why don't we drop the defensive shields?"}
"A superlative suggestion, sir, with just two minor flaws.
One, we don't have any defensive shields, and
two, we don't have any defensive shields.
Now I realise that, technically speaking, that's only one flaw but I thought it was such a big one it was worth mentioning twice."
Kryten (mechanoid assigned to the mining spaceship Red Dwarf)
or alternatively,
{responding to the crew suggestion "I got it! We laser our way through [the 53 doors from here to the science deck]!"}
Ah, an excellent plan, sir, with only two minor drawbacks.
One, we don't have a power source for the lasers; and
two, we don't have any lasers.
Kryten
French physicist Poincaré'Red Dwarf' character, Kryten
The principle of relative motion
What Poincairé meant by 'the principle of relative motion' was that
"The motion of any system must obey the same laws, whether it be referred to fixed axes, or to moveable axes carried along in a rectilinear and uniform motion."
the principle of relative motion
In other words, imagine a train passing a station at 10 ms-1, in which a naughty physics student throws a pencil eraser of mass m with a force of F at another passenger sitting in front on him; while a model physics student observes this from the stationary station [sic] platform.
The student on the train would consider the eraser to be at rest before being thrown, and can explore its motion by taking u=0 ms-1 and applying some laws summarised by
F=ma,
v=u+at,
v2=u2+2as,
s=ut +1/2at2…
From the frame or reference of someone in the the station it is the train that moves, (Image by StockSnap from Pixabay) but……From the frame of reference of the train (or tram), it seems to be the rest of the world that is moving past (Image by Pasi Mämmelä from Pixabay)
The student on the platform would observe the eraser to initially be moving at 10 ms-1, but could calculate what would happen using the same set of equations, but taking u=10 ms-1
Any values of v calculated would be consistent across the two frames (when allowing for the 10 ms-1 discrepancy) and other values calculated (s, t) would be the same.
This reflects the relativity principle of Galileo which suggests that there is no absolute way of determining whether a body is moving at constant velocity or stationary: rather what appears to be the case depends on one's frame of reference.
We might think that obviously it is the platform which is really stationary, as our intuition is that the earth under our feet is stationary ground. Surely we could tell if the ground moves?
We can directly feel acceleration, and we can sometimes feel the resistance to motion (the air on our face if we cycle, even at a constant velocity), but the idea that we can directly tell whether or not we are moving is an alternative conception.
For centuries the idea of a moving earth was largely considered ridiculous as experience clearly indicated otherwise. But if someone was kidnapped whilst asleep (please note, this would be illegal and is not being encouraged) and awoke in a carriage that had been set up to look like a hotel bedroom, on a train moving with constant velocity, they would not feel they were in motion. Indeed anyone who as travelled on a train at night when nothing is visible outside the carriage might well have experienced the impression that the train is stationary whilst it moves at a steady rate.
Science has shown us that there are good reasons to think that the earth is spinning, and orbiting the sun, as part of the solar system which moves through the galaxy, so who is to say what is really stationary? We cannot tell (and the question may be meaningless).
Who is to say what is moving – we can only make relative judgements? (Image by Drajt from Pixabay)
Source cited:
Poincaré, H. (1902/1913/2015). Science and Hypothesis (G. B. Halstead, Trans.). In The Foundations of Science. Cambridge University Press. {I give three dates because Poincaré published his book in French in 1902, and it was later published in an English translation in 1913, but I have a 2015 edition.}
