Tag: electron spin

The states of (don't) matter?

Which state of matter is fire?

Keith S. Taber

A trick question?

Education in Chemistry recently posed the question

From Education in Chemistry

What state of matter is fire?

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.)

Article from Education in Chemistry

A personal response – a trick question?

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 'ontological category 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.

Appreciating the key distinction between material (often not able to be simply assigned to a state of matter) and individual substances (where pure samples under particular conditions can be understood in terms of solid / liquid / gas / plasma) is central to chemistry, but even the people who wrote the English National Curriculum for science seem confused on this – it incorrectly describes chocolate, butter and cream as substances.

Sometimes this becomes ridiculous – as when a BBC website to help children learn science asked them to classify a range of objects as solid, liquid or gas. Including a cat! So, Farrell's question may be a trick question, but when some educators would perfectly seriously ask learners the same question about a cat, it is well worth teachers of chemistry pausing to think why the question does not apply to fire.

Relating this to student learning difficulties

That was my response at Education in Chemistry, but I was also aware that it related to a wider issue about the nature of students' alternative conceptions.

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:
Note:

1 The idea that heat was a substance, known as caloric, was for a long time a respectable scientific idea.

Fingerprinting an exoplanet

Life, death, and multiple Gaias

Keith S. Taber

NASA might be said to be engaged in looking for other Gaias beyond our Gaia, as Dr Milam explained to another Gaia.

This post is somewhat poignant as something I heard on a radio podcast reminded me how science has recently lost one of its great characters, as well as an example of that most rare thing in today's science – the independent scientist.

Inside Science episode "Deep Space and the Deep Sea – 40 years of the International Whaling Moratorium", presented, perhaps especially aptly, by Gaia Vince

I was listening to the BBC's Inside Science pod-cast episode 'Deep Space and the Deep Sea – 40 years of the International Whaling Moratorium' where the presenter – somewhat ironically, in view of the connection I was making, Gaia Vince – was talking to Dr Stefanie Milam of Nasa's Goddard Space Flight Centre about how the recently launched James Webb Space Telescope could help scientists look for signs of life on other planets.

From: https://jwst.nasa.gov/content/meetTheTeam/people/milam.html

Dr Milam explained that

"spectra…give us all the information that we really need to understand a given environment. And that's one of the amazing parts about the James Webb space telescope. So, what we have access to with the wavelengths that the James Webb space telescope actually operates at, is that we have the fingerprint pattern of given molecules, things like water, carbon monoxide, carbon dioxide, all these things that we find in our own atmosphere, and so by using the infrared wavelengths we can look for these key ingredients in atmospheres around other planets or even, actually, objects in our own solar system, and that tells us a little bit about what is going on as far as the dynamics of that planet, whether or not its has got geological activity, or maybe even something as crazy as biology."

Dr Stefanie Milam, interviewed for 'Inside Science'
"Webb has captured the first clear evidence of carbon dioxide (CO2) in the atmosphere of a planet outside of our solar system!" (Hot Gas Giant Exoplanet WASP-39 b Transit Light Curve, NIRSpec Bright Object Time-Series Spectroscopy.)
Image: NASA, ESA, CSA, and L. Hustak (STScI). Released under 2.0 Generic (CC BY 2.0) License – Some rights reserved by James Webb Space Telescope
Do molecules have fingerprints

Fingerprints have long been used in forensic work to identify criminals (and sometimes their victims) because our fingerprints are pretty unique. Even 'identical' twins do not have identical fingerprints (thought I suspect that fact rather undermines some crime fiction plots). But, to have fingerprints one surely has to have fingers. A palm print requires a palm, and a footprint, a foot. So, can molecules, not known for their manual dexterity, have fingerprints?

Well, it is not exactly by coincidence (as the James Webb space telescope has had a lot of media attention) that I very recently posted here, in the context of new observations of the early Universe, that

"Spectroscopic analysis allows us to compare the pattern of redshifted spectral lines due to the presence of elements absorbing or emitting radiation, with the position of those lines as they are found without any shift. Each element has its own pattern of lines – providing a metaphorical fingerprint.

from: A hundred percent conclusive science. Estimation and certainty in Maisie's galaxy

In chemistry, elements and compounds have unique patterns of energy transitions which can be identified through spectroscopy. So, we have 'metaphorical fingerprints'. To describe a spectrum as a chemical substance's (or entity's, such as an ion's) fingerprint is to use a metaphor. It is not actually a fingerprint – there are no fingers to leave prints – but this figure of speech gets across an idea though an implicit comparison with something already familiar. *1 That is, it is a way of making the unfamiliar familiar (which might be seen as a description of teaching!)

Dead metaphors

But perhaps this has become a 'dead metaphor' so that now chemicals do have fingerprints? One of the main ways that language develops is by words changing their meanings over time as metaphors become so commonly used they case to be metaphorical.

For example, I understand the term electrical charge is a dead metaphor. When electrical charge was first being explored and was still unfamiliar, the term 'charge' was adopted by comparison with the charging of a canon or the charge of shot used in a shotgun. The shot charge refers to the weight of shot included in a cartridge. Today, most people would not know that, whilst being very familiar with the idea of electrical charge. But when the term electrical charge was first used most people knew about charging guns.

So, initially, electrical 'charge' was a metaphor to refer to the amount of 'electricity' – which made use of a familiar comparison. Now it is a dead metaphor, and 'electrical charge' is now considered a technical tern in its own right.

Another example might be electron spin: electrons do not spin in the familiar sense, but really do (now) have spin as the term has been extended to apply to quanticles with inherent angular momentum by analogy with more familiar macroscopic objects that have angular momentum when they are physically rotating. So, we might say that when the term was first used, it was a metaphor, but no longer. (That is, physicists have expanded the range of convenience of the term spin.)

Perhaps, similarly, fingerprint is now so commonly used to mean a unique identifier in a wide range of contexts, that it should no longer be considered a metaphor. I am not sure if that is so, yet, but perhaps it will be in, say, a century's time – and the term will be broadly used without people even noticing that many things have acquired fingerprints without having fingers. (A spectrum will then actually be a chemical substance's or entity's fingerprint.) After all, many words we now commonly use contain fossils of their origins without us noticing. That is, metaphorical fossils, of course. *2

James Lovelock, R.I.P.

The reason I found this news item somewhat poignant was that I was listening to it just a matter of weeks after the death (at age 103) of the scientist Jim Lovelock. *3 Lovelock invented the device which was able to demonstrate the ubiquity of chlorofluorocarbons (CFCs) in the atmosphere. These substances were very commonly used as refrigerants and aerosol propellants as they were very stable, and being un-reactive (so non-toxic) were considered safe.

But this very stability allowed them to remain in and spread through the atmosphere for a very long time until they were broken down in the stratosphere by ultraviolet radiation to give radicals that reacted with the ozone that is so protective of living organisms. Free radical reactions can occur as chain reactions as when a radical interacts with a molecule it leads to a new molecule, plus a new radical which can often take part in a further interaction with another molecule: so, each CFC molecule could lead to the destruction of many ozone molecules. CFCs have now been banned for most purposes to protect the ozone 'layer', and so us.

Life is chemistry out of balance

But another of Lovelock's achievements came when working for NASA to develop means to search for life elsewhere in the universe. As part of the Mariner missions, NASA wanted Lovelock to design apparatus that could be sent to other worlds and search for life (and I think he did help do that), but Lovelock pointed out that one could tell if a planet had life by a spectroscopic analysis.

Any alien species analysing light passing through earth's atmosphere would see its composition was far from chemical equilibrium due to the ongoing activity of its biota. (If life were to cease on earth today, the oxygen content of the atmosphere would very quickly fall from 21% to virtually none at all as oxygen reacts with rocks and other materials.) If the composition of an atmosphere seemed to be in chemical equilibrium, then it was unlikely there was life. However, if there were high concentrations of gases that should react together or with the surface, then something, likely life, must be actively maintaining that combination of gases in the atmosphere.

"Living systems maintain themselves in a state of relatively low entropy at the expense of their nonliving environments. We may assume that this general property is common to all life in the solar system. On this assumption, evidence of a large chemical free energy gradient between surface matter and the atmosphere in contact with it is evidence of life. Furthermore, any planetary biota which interacts with its atmosphere will drive that atmosphere to a state of disequilibrium which, if recognized, would also constitute direct evidence of life, provided the extent of the disequilibrium is significantly greater than abiological processes would permit. It is shown that the existence of life on Earth can be inferred from knowledge of the major and trace components of the atmosphere, even in the absence of any knowledge of the nature or extent of the dominant life forms. Knowledge of the composition of the Martian atmosphere may similarly reveal the presence of life there."

Dian R. Hitchcock and James E. Lovelock – from Lovelock's website (originally published in Icarus: International Journal of the Solar System in 1967)

The story was that NASA did not really want to be told they did not need to send missions with spacecraft to other words such as Mars to look for life, rather that they only had to point a telescope and analyse the spectrum of radiation. Ironically, perhaps, then, that is exactly what they are now doing with planets around other star systems where it is not feasible (not now, perhaps not ever) to send missions.

Gaia and Gaia

But Lovelock became best known for his development and championing of the Gaia theory. According to Gaia (the theory, not the journalist), the development of life on earth has shaped the environment (and not just exploited pre-existing niches) and developed as a huge integrated and interacting system (the biota, but also the seas, the atmosphere, freshwater, the soil,…) such that large scale changes in one part of the system have knock-on effect elsewhere. *4

So, Gaia can be understood not as the whole earth as a planet, or just the biota as the collective life in terms of organisms, but rather as the dynamic system of life of earth and the environment it interacts with. In a sense (and it is important to see this is meant as an analogy, a thinking tool) Gaia is like some supra-organism. Just as snail has a shell that it has produced for its self, Gaia has shaped the biosphere where the biota lives. *4

The system has built in feedback cycles to protect it from perturbations (not by chance, or due to some mysterious power, but due to natural selection) but if it is subject to a large enough input it would shift to a new (and perhaps very different) equilibrium state. *5 This certainly happened when oxygen releasing organisms evolved: the earth today is inhospitable to the organisms that lived here before that event (some survived to leave descendants, but only in places away from the high oxygen concentrations, such as in lower lays of mud beneath the sea), and most organisms alive today would die very quickly in the previous conditions.

It would be nice to think that Gaia, the science journalist that is, was named after the Gaia theory – but Lovelock only started publishing about his Gaia hypothesis about the time that Gaia was born.*6 So, probably not. Gaia is a traditional girl's name, and was the name of the Greek goddess who personified the earth (which is why the name was adopted by Lovelock).

Still, it was poignant to hear a NASA scientist referring to the current value of a method first pointed out by Lovelock when advising NASA in the 1970s and informed by his early thinking about the Gaia hypothesis. NASA might be said to now be engaged in looking for other Gaias on worlds outside our own solar system, as Dr Milam explained to – another – Gaia here on earth.

Notes:

*1 It is an implicit comparison, because the listener/reader is left to appreciate that it is meant as a figure of speech: unlike in a simile ('a spectrum is like a fingerprint') where the comparison is made explicit .

*2 For some years I had a pager (common before mobile phones) – a small electronic device which could receive a text message, so that my wife could contact me in an emergency if I was out visiting schools by phoning a message to be conveyed by a radio signal. If I had been asked why it was called a pager, I would have assumed that each message of text was considered to comprise a 'page'.

However, a few weeks ago I watched an old 'screwball comedy' being shown on television: 'My favourite wife' (or 'My favorite [sic] wife' in US release).

(On the very day that Cary Grant remarries after having his first wife, long missing after being lost at sea, declared legally dead, wife number one reappears having been rescued from a desert island. That this is a very unlikely scenario was played upon when the film was remade in colour, as 'Move Over Darling', with Doris Day and James Garner. The returned first wife, pretending to be a nurse, asks the new wife if she is not afraid the original wife would reappear, as happened in that movie; eliciting the response: 'Movies. When do movies ever reflect real life?')

Some of the action takes place in the honeymoon hotel where groom has disappeared from the suite (these are wealthy people!) having been tracked down by his first wife. The new wife asks the hotel to page him – and this is how that worked with pre-electronic technology:

Paging Mr Arden: Still from 'My Favorite Wife'

*3 So, although I knew Lovelock had died (July 26th), he was still alive at the time of the original broadcast (July 14th). In part, my tardiness comes from the publicly funded BBC's decisions to no longer make available downloads of some of its programmes for iPods and similar devices immediately after broadcast. (This downgrading of the BBC's service to the public seems to be to persuade people to use its own streaming service.)

*4 The Gaia theory developed by Lovelock and Lyn Margulis includes ideas that were discussed by Vladimir Vernadsky almost a century ago. Although Vernadsky's work was well known in scientific circles in the Soviet Union, it did not become known to scientists in Western Europe till much later. Vernadsky used the term 'biosphere' to refer to those 'layers' of the earth (lower atmosphere to outer crust) where life existed.

*5 A perturbation such as as extensive deforestation perhaps, or certainly increasing the atmospheric concentrations of 'greenhouse' gases beyond a certain point.

*6 Described as a hypothesis originally, it has been extensibility developed and would seem to now qualify as a theory (a "consistent, comprehensive, coherent and extensively evidenced explanation of aspects of the natural world") today.