Tag: gravity

The passing of stars

Birth, death, and afterlife in the universe

Keith S. Taber

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

One of the themes I keep coming back to here is the challenge of communicating abstract scientific ideas. Presenting science in formal technical language will fail to engage most general audiences, and will not support developing understanding if the listener/reader cannot make good sense of the presentation. But, if we oversimplify, or rely on figures of speech (such as metaphors) in place of formal treatments of concepts, then – even if the audience does engage and make sense of the presentation – audience members will be left with a deficient account.

Does that matter? Well, often a level of understanding that provides some insight into the science is far better than the impression that science is so far detached from everyday experience that it is not for most people.

And the context matters.

Public engagement with science versus science education

In the case of a scientist asked to give a public talk, or being interviewed for news media, there seems a sensible compromise. If people come away from the presentation thinking they have heard about something interesting, that seems in some way relevant to them, and that they understood the scientist's key messages, then this is a win – even if it is only a shift to an over-simplified account, or an understanding in terms of a loose analogy. (Perhaps some people will want to learn more – but, even if not, surely this meets some useful success criterion?)

In this regard science teachers have a more difficult job to do. 1 The teacher is not usually considered successful just because the learners think they have understood teaching, but rather only when the learners can demonstrate that what they have learnt matches a specified account set out as target knowledge in the curriculum. This certainly does not mean a teacher cannot (or should not) use simplification and figures of speech and so forth – this is often essential – but rather that such such moves can usually only be seen as starting points in moving learners onto temporary 'stepping stones' towards creditable knowledge that will eventually lead to test responses that will be marked correct.

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"

The Death of Stars

With this in mind, I was fascinated by an episode of the BBC's radio show, 'In Our Time' which took as its theme the death of stars. Clearly, this falls in the category of scientists presenting to a general public audience, not formal teaching, and that needs to be borne in mind as I discuss (and perhaps even gently 'deconstruct') some aspects of the presentation from the perspective of a science educator.

The show was broadcast some months ago, but I made a note to revisit it because I felt it was so rich in material for discussion, and I've just re-listened. I thought this was a fascinating programme, and I think it is well worth a listen, as the programme description suggests:

"Melvyn Bragg and guests discuss the abrupt transformation of stars after shining brightly for millions or billions of years, once they lack the fuel to counter the force of gravity. Those like our own star, the Sun, become red giants, expanding outwards and consuming nearby planets, only to collapse into dense white dwarves. The massive stars, up to fifty times the mass of the Sun, burst into supernovas, visible from Earth in daytime, and become incredibly dense neutron stars or black holes. In these moments of collapse, the intense heat and pressure can create all the known elements to form gases and dust which may eventually combine to form new stars, new planets and, as on Earth, new life."

https://www.bbc.co.uk/sounds/play/m0018128

I was especially impressed by the Astronomer Royal, Professor Martin Rees (and not just because he is a Cambridge colleague) who at several points emphasised that what was being presented was current understanding, based on our present theories, with the implication that this was open to being revisited in the light (sic) of new evidence. This made a refreshing contrast to the common tendency in some popular science programmes to present science as 'proven' and so 'certain' knowledge. That tendency is an easy simplification that distorts both the nature and excitement of science.

Read about scientific certainty in the media

Presenter Melvyn Bragg's other guests were Carolin Crawford (Emeritus Member of the Institute of Astronomy, and Emeritus Fellow of Emmanuel College, University of Cambridge) and Mark Sullivan (Professor of Astrophysics at the University of Southampton).

Public science communication as making the unfamiliar familiar

Science communicators, whether professional journalists or scientists popularising their work, face similar challenges to science teachers in getting across often complex and abstract ideas; and, like them, need to make the unfamiliar familiar. Science teachers are taught about how they need to connect new material with the learners' prior knowledge and experiences if it is to make sense to the students. But successful broadcasters and popularisers also know they need to do this, using such tactics as simplification, modelling, metaphor and simile, analogy, teleology, anthropomorphism and narrative.

There were quite a few examples of the speakers seeking to make abstract ideas accessible to listeners in such ways in this programme. However, perhaps the most common trope was one set up by the episode title, and one which could very easily slip under radar (so to speak). In this piece I examine the seemingly ubiquitous metaphor (if, indeed, it is to be considered a metaphor!) of stars being alive; in a sequel I discuss some of the wide range of other figures of speech adopted in this one science programme.

Science: making the familiar, unfamiliar?

If when working as a teacher I saw a major part of my work as making the unfamiliar familiar to learners, in my research there was a sense in which I needed to make the familiar unfamiliar. Often, the researcher needs to focus afresh on the commonly 'taken-for-granted' and to start to enquire into it as if one does not already know about it. That is, one needs to problematise the common-place. (This reflects a process sometimes referred to as 'bracketing'.)

To give one obvious example. Why do some students do well in science tests and others less well? Obviously, because some learners are better science students than others! (Clearly in some sense this is true – but is it just a tautology? 2) But one clearly needs to dig into this truism in more detail to uncover any insights that would actually be useful in supporting students and improving teaching!

The same approach applies in science. We do not settle for tautologies such as fire burns because fire is the process of burning, or acids are corrosive because acids are the category of substances which corrode; nor what are in effect indirect disguised tautologies such as heavy objects fall because they are largely composed of the element earth, where earth is the element whose natural place is at the centre of the world. (If that seems a silly example, it was the widely accepted wisdom for many centuries. Of course, today, we do not recognise 'earth' as a chemical element.)

I mention this, because I would like to invite readers to share with me in making the familiar unfamiliar here – otherwise you could easily miss my point.

"so much in the Universe, and much of our understanding of it, depends on changes in stars as they die after millions or billions of stable years"

Tag line for 'the Death of Stars'

The lives of stars

The episode opens with

"Hello. Across the universe, stars have been dying for millions of years…

Melvyn Bragg introducing the episode

The programme was about the death of stars – which directly implies stars die, and, so, also suggests that – before dying – they live. And there were plenty of references in the programme to reinforce this notion. Carolin Crawford suggested,

"So, essentially, a star's life, it can exist as a star, for as long as it has enough fuel at the right temperature at the right density in the core of the star to stall the gravitational collapse. And it is when it runs out of its fuel at the core, that's when you reach the end of its lifetime and we start going through the death processes."

Prof. Carolin Crawford talking on 'In Our Time'

Not only only do stars have lives, but some have much longer lives than others,

"…more massive stars can … build quite heavy elements at their cores through their lifetimes. And … they actually have shorter lifetimes – it is counter-intuitive, but they have to chomp through their fuel supply so furiously that they exhaust it more rapidly. So, the mass of the star dictates what happens in the core, what you create in the core, and it also determines the lifetime of the star."

"The mass of the star…determines the lifetime of the star….
our sun…we reckon it is about halfway through its lifetime, so stars like the sun have lifetimes of 10 billions years or so…"


Prof. Carolin Crawford talking on 'In Our Time'

This was not some idiosyncratic way that Professor Crawford had of discussing stars, as Melvyn's other guests also used this language. Here are some examples I noted:

  • "this is a dead, dense star" (Martin Rees)
  • "the lifetime of a stable star, we can infer the … life cycles of stars" (Martin Rees)
  • "stars which lived and died before our solar system formed…stars which have more complicated lives" (Martin Rees)
  • "those old stars" (Martin Rees)
  • "earlier generations of massive stars which had lived and died …those long dead stars" (Martin Rees)
  • "it is an old dead star" (Mark Sullivan)
  • "our sun…lives by itself in space. But most stars in the universe don't live by themselves…" (Mark Sullivan)
  • "two stars orbiting each other…are probably born with different masses" (Mark Sullivan)
  • "when [stars] die" (Mark Sullivan)
  • "when [galaxies] were very young" (Martin Rees)
  • "stars that reach the end point of their lives" (Carolin Crawford )
  • "a star that's younger" (Martin Rees)

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

The processes that support a star's luminosity come to an end: but does the star therefore die?

(Cover art for the Royal Philharmonic Orchestra's recording of David Bedford's composition Star's End. Photographer: Monique Froese)

Are stars really alive?

Presumably, the use of such terms in this context must have originally been metaphorical. Life (and so death) has a complex but well-established and much-discussed meaning in science. Living organisms have certain necessary characteristics – nutrition, (inherent) movement, irritability/sensitivity, growth, reproduction, respiration, and excretion, or some variation on such a list. Stars do not meet this criterion. 3 Living organisms maintain a level of complex organisation by making use of energy stores that allow them to decrease entropy internally at the cost of entropy increase elsewhere.

Animals and decomposers (such as fungi) take in material that can be processed to support their metabolism and then the 'lower quality' products are eliminated. Photosynthetic organisms such as green plants have similar metabolic processes, but preface these by using the energy 'in' sunlight to first facilitate endothermic reactions that allow them to build up the material used later for their mortal imperative of working against the tendencies of entropy. Put simply, plants synthesise sugar (from carbon dioxide and water) that they can distribute to all their cells to support the rest of the metabolism (a complication that is a common source of alternative conceptions {misconceptions} to learners 4).

By contrast, generally speaking, during their 'lifetimes', stars only gain and lose marginal amounts of material (compared with a 70 kg human being that might well consume a tonne of food each year) – and do not have any quality control mechanism that would lead to them taking in what is more useful and expelling what is not.

As far as life on earth is concerned, virtually all of that complex organisation of living things depends upon the sun as a source of energy, and relies on the process by which the sun increases the universe's entropy by radiating energy from a relatively compact source into the diffuse vastness of space. 4 In other words, if anything, a star like our sun better reflects a dead being such as a felled tree or a zebra hunted down by a lion, providing a source of concentrated energy for other organisms feeding on its mortal remains!

Are the lives and deaths of stars simply pedagogical devices?

So, are stars really alive? Or is this just one example of the kind of rhetorical device I referred to above being adopted to help make the abstract unfamiliar becomes familiar? Is it the use of a familiar trope employed simply to aid in the communication of difficult ideas? Is this just a metaphor? That is,

  • Do stars actually die, or…
  • are they only figuratively alive and, so, only suffer (sic) a metaphorical death?

I do not think the examples I quote above represent a concerted targeted strategy by Professors Crawford, Rees and Sullivan to work with a common teaching metaphor for the sake of Melvyn and his listeners: but rather the actual language commonly used in the field. That is, the life cycles and lifetimes of stars have entered into the technical lexicon of the the science. If so, then stars do actually live and die, at least in terms of what those words now mean in the discipline of astronomy.

Gustav Strömberg referred to "the whole lifetime of a star" in a paper in the The Astrophysical Journal as long ago as 1927. He did not feel the need to explain the term so presumably it was already in use – or considered obvious. Kip Thorne published a paper in 1965 about 'Gravitational Collapse and the Death of a Star". In the first paragraph he pointed out that

"The time required for a star to consume its nuclear fuel is so long (many billions of years in most cases) that only a few stars die in our galaxy per century; and the evolution of a star from the end point of thermonuclear burning to its final dead state is so rapid that its death throes are observable for only a few years."

Thorne, 1965, p.1671

Again, the terminology die/death/dead is used without introduction or explanation.

He went on to refer to

  • deaths of stars
  • different types of death
  • final resting states

before shifting to what a layperson would recognise as a more specialist, technical, lexicon (zero point kinetic energy; Compton wavelength of an electron; neutron-rich nuclei; photodistintegration; gravitational potential energy; degenerate Fermi gas; lambda hyperons; the general relativity equation of hydrostatic equilibrium; etc.), before reiterating that he had been offering

"the story of the death of a star as predicted by a combination of nuclear theory, elementary particle theory, and general relativity"

Thorne, 1965, p.1678

So, this was a narrative, but one intended to be fit for a professional scientific audience. It seems the lives and deaths of stars have been part of the technical vocabulary of astronomers for a long time now.

When did scientists imbue stars with life?

Modern astronomy is quite distinct from astrology, but like other sciences astronomy developed from earlier traditions and at one time astronomy and astrology were not so discrete (an astronomical 'star' such as Johannes Kepler was happy to prepare horoscopes for paying customers) and mythological and religious aspects of thinking about the 'heavens' were not so well compartmentalised from what we would today consider as properly the realm of the scientific.

In Egyptian religion, Ra was both a creative force and identified with the sun. Mythology is full of origin stories explaining how the stars had been cast there after various misadventures on earth (the Greek myths but also in other traditions such as those of the indigenous North American and Australian peoples 5) and we still refer to examples such as the seven sisters and Orion with the sword hanging in his belt. The planets were associated with different gods – Venus (goddess of love), Mars (the god of war), Mercury (the messenger of the gods), and so on.6 It was traditional to refer to some heavenly bodies as gendered: Luna is she, Sol is he, Venus is she, and so on. This usage is sometimes found in scientific writing on astronomy.

Read about examples of personification in scientific writing

Yet this type of poetic license seems unlikely to explain the language of the life cycles of stars, even if there are parallels between scientific and poetic or spiritual accounts,

Stars are celestial objects having their own life cycles. Stars are born, grow up, mature and eventually die. …The author employs inductive and deductive analysis of the verses of the Quran and the Hadith texts related with the life and death of stars. The results show that the life and death of the stars from Islamic and Modern astronomy has some similarities and differences.

Wahab, 2015

After all, the heavenly host of mythology comprised of immortals, if sometimes starting out as mortals subsequently given a kind of immorality by the Gods when being made into stars. Indeed the classical tradition supported by interpretation of Christian orthodoxy was that unlike the mundane things of earth, the heavens were not subject to change and decay – anything from the moon outwards was perfect and unchanging. (This notion was held onto by some long after it was established that comets with their varying paths were not atmospheric phenomena – indeed well into the twentieth century some young earth creationists were still insisting in the perfect, unchanging nature of the heavens. 7)

So, presumably, we need to look elsewhere to find how science adopted life cycles for stars.

A natural metaphor?

Earlier in this piece I asked readers to bear with me, and to join with me in making the familiar unfamiliar, to 'bracket' the familiar notion that we say starts are born, live and later die, and to problematise it. In one scientific sense stars cannot die – as they were never alive. Yet, I accept this seems a pretty natural metaphor to use. Or, at least, it seems a natural metaphor to those who are used to hearing and reading it. A science teacher may be familiar with the trope of 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 a candidate project for anyone looking for a topic for a student research assignment: how would people who have never previously been exposed to this metaphor respond to the kinds of references I've discussed above? I would genuinely like to know what 'naive' people would make of this 8 – would they just 'get' the references immediately (appreciate in what sense stars are born, live, and die); or, would it seem a bizarre way of talking about stars? Given how readily people accept and take up anthropomorphic references to molecules and viruses and electrons and so forth, I find the question intriguing.

Read about anthropomorphism in science

What makes a star alive or dead?

Even if for the disciplinary experts the language of living stars and their life cycles has become a 'dead metaphor 'and is now taken (i.e., taken for granted) as technical terminology – the novice learner, or lay member of the public listening to a radio show, still has to make sense of what it means to say a star is born, or is alive, or is nearing the end of its life, or is dead.

The critical feature discussed by Professors Crawford, Rees and Sullivan concerns an equilibrium that allow a star to exist in a balance between the gravitational attraction of its component matter and the pressure generated through its nuclear reactions.

A star forms when material comes together under its mutual gravitational attraction – and as the material becomes denser it gets hotter. Eventually a sufficient density and temperature is reached such that there is 'ignition' – not in the sense of chemical combustion, but self-sustaining nuclear processes occur, generating heat. This point of ignition is the 'birth' of the star.

Fusion processes continue as long as there is sufficient fissionable material, the 'fuel' that 'feeds' the nuclear 'furnace' (initially hydrogen, but depending on the mass of the star there can be a series of reactions with products from one stage undergoing further fusion to form even heavier elements). The life time of the star is the length of time that such processes continue.

Eventually there will not be sufficient 'fuel' to maintain the level of 'burning' that is needed to allow the ball of material to avoid ('resist') gravitational collapse. There are various specific scenarios, but this is the 'death' of the star. It may be a supernova offering very visible 'death throes'.

The core that is left after this collapse is a 'dead' star, even if it is hot enough to continue being detectable for some time (just as it takes time for the body of a homeothermic animal that dies to cool to the ambient temperature).

It seems then that there is a kind of analogy at work here.

Organisms are alive as long as they continue to metabolise sufficiently in order to maintain their organisation in the face of the entropic tendency towards disintegration and dispersal.Stars are alive as long as they exhibit sufficient fusion processes to maintain them as balls of material that have much greater volumes, and lower densities than the gravitational forces on their component particles would otherwise lead to.

It is clearly an imperfect analogy.

Organisms base metabolism on a through-put of material to process (and in a sense 'harvest' energy sources).Stars do acquire new materials and eject some, but this is largely incidental and it is essentially the mass of fissionable material that originally comes together to initiate fusion which is 'harvested' as the energy source.
Organisms may die if they cannot access external food sources, but some die of built-in senescence and others (those that reproduce by dividing) are effectively immortal.

We (humans) die because the amazing self-constructing and self-repairing abilities of our bodies are not perfect, and somatic cells cannot divide indefinitely to replace no longer viable cells.		Stars 'die' because they run out of their inherent 'fuel'.

Stars die when the hydrogen that came together to form them has substantially been processed.

Read about analogy in science

One person's dead star is another person's living metaphor

So, do stars die? Yes, because astronomers (the experts on stars) say they do, and it seems they are not simply talking down to the rest of us. The birth and death of stars seems to be based on an analogy: an analogy which is implicit in some of the detailed discussion of star life cycles. However, through the habitual use of this analogy, terms such as the birth, lifetimes, and death of stars have been adopted into mainstream astronomical discourse as unmarked (taken-for-granted) language such that to the uninitiated they are experienced as metaphors.

And these perspectival metaphors 9 become extended to describe stars that are considered young, old, dying, long dead, and so forth. These terms are used so readily, and so often without a perceived need for qualification or explanation, that we might consider them 'dead' metaphors within astronomical discourse – terms of metaphorical origin but now so habitually used that they have come to be literal (stars are born, they do have lifetimes, they do die). Yet for the uninitiated they are still 'living' metaphors, in the sense that the non-expert needs to work out what it means when a star is said to live or die.

There is a well recognised distinction between live and dead metaphors. But here we have dead-to-the-specialists metaphors that would surely seem to be non-literal to the uninitiated. These terms are not explained by experts as they are taken by them as literal, but they cannot be understood literally by the novice, for whom they are still metaphors requiring interpretation. That is, they are perspectival metaphors – zombie words that may seem alive or dead (as figures of speech) according to audience, and so may be treated as dead in professional discourse, but may need to be made undead when used in communicating to the public.

Other aspects of the In Our Time discussion of 'The death of stars' are explored as The complicated social lives of stars: stealing, escaping, and blowing-off in space

Sources cited:
  • Strömberg, G. (1927). The Motions of Giant M Stars. The Astrophysical Journal, 65, 238.
  • Thorne, K. S. (1965). Gravitational Collapse and the Death of a Star. Science, 150(3704), 1671-1679. http://www.jstor.org.ezp.lib.cam.ac.uk/stable/1717408
  • Wahab, R. A. (2015). Life and death of stars: an analysis from Islamic and modern astronomy perspectives. International Proceedings of Economics Development and Research, 83, 89.

Notes

1 In this regard, but not in all regards. As I have suggested here before, the teacher usually has two advantages:

a) generally, a class has a limited spread in terms of the audience background: even a mixed ability class is usually from a single school year (grade level) whereas the public presentation may be addressing a mixed audience of all ages and levels of education.

b) usually a teacher knows the class, and so knows something about their starting points, and their interests

2 Some students do well in science tests and others less well.

If we say this is because

  • some learners are better science students than others
  • and settle for defining better science students as those who achieve good results in formal science tests (that is tests as currently administered, based on the present curriculum, taught in our usual way)

then we are simply 'explaining' the explicandum (i.e., some students do better on science tests that others) by a rephrasing of what is to be explained (some students are better science students: that is, they perform well in science tests!)

Read about tautology

3 Criterion (singular) as a living organism has to satisfy the entries in the list collectively. Each entry is of itself a necessary, but not sufficient, condition.

4 A simple misunderstanding is that animals respire but plants photosynthesise.

In a plant in a steady state, the rates of build-up and break down of sugars would be balanced. However, plants must photosynthesise more than they respire overall in order to to grow and ultimately to allow consumers to make use of them as food. (This needs to be seen at a system level – the plant is clearly not in any inherent sense photosynthesising to provide food for other organisms, but has evolved to be a suitable nutrition source as it transpires [no pun intended] that increases the fitness of plants within the wider ecosystem.)

A more subtle alternative conception is that plants photosynthesise during the day when they are illuminated by sunlight (fair enough) and then use the sugar produced to respire at night when the sun is not available as a source of energy. See, for example, 'Plants mainly respire at night because they are photosynthesising during the day'.

Actually cellular processes require continuous respiration (as even in the daytime sunlight cannot directly power cellular metabolism, only facilitate photosynthesis to produce the glucose that that can be oxidised in respiration).

Schematic reflection of the balance between how photosynthesis generates resources to allow respiration – typically a plant produces tissues that feed other organisms.
The area above the line represents energy from sunlight doing work in synthesising more complex substances. The area below the lines represents work done when the oxidation of those more complex substances provides the energy source for building and maintaining an organism's complex organisation of structure and processes (homoestasis).

5 Museum Victoria offers a pdf that can be downloaded and copied by teachers to teach about how "How the southern night sky is seen by the Boorong clan from north-west Victoria":

'Stories in the Stars – the night sky of the Boorong people' shows the constellations as recognised by this group, the names they were given, and the stories of the people and creatures represented.

(This is largely based on the nineteenth century reports made by William Edward Stanbridge of information given by Boorong informants – see 'Was the stellar burp really a sneeze?')

The illustration shown here is of 'Kulkunbulla' – a constellation that is considered in the U.K. to be only part of the constellation known here as Orion. (Constellations are not actual star groupings, but only what observers have perceived as stars seeming to be grouped together in the sky – the Boorong's mooting of constellations is no more right or wrong than that suggested in any other culture.)

6 The tradition was continued into modern times with the discovery of the planets that came to be named Neptune and Uranus after the Gods of the sea and sky respectively.

7 Creationism, per se, is simply the perspective or belief that the world (i.e., Universe) was created by some creator (God) and so creationism as such is not necessarily in conflict with scientific accounts. The theory of the big bang posits that time, space and matter had a beginning with an uncertain cause which could be seen as God (although some theorists such as Professor Roger Penrose develop theories which posit a sequence of universes that each give rise to the next and that could have infinite extent).

Read about science and religion

Young earth creationists, however, not only believe in a creator God (i.e., they are creationists), but one who created the World no more than about 10 thousand years ago (the earth is young!), rather than over 13 billion years ago. This is clearly highly inconsistent with a wide range of scientific findings and thinking. If the Young Earth Creationists are right, then either

  • a lot of very strongly evidenced science is very, very wrong
  • some natural laws (e.g. radioactive decay rates) that now seem fixed must have changed very substantially since the creation
  • the creator God went to a lot of trouble to set up the natural world to present a highly misleading account of its past history

8 I am not using the term naive here in a discourteous or demeaning way, but in a technical sense of someone who is meeting something for the first time.

9 That is, terms that will appear as metaphors from the perspective of the uninitiated, but now seem literal terms from the perspective of the specialist. We cannot simply say they are or are not metaphors, without asking 'for whom?'

NASA puts its hand in the oven

A tenuous analogy

Keith S. Taber

The Parker Solar Probe

I recently listened to NASA's Nicky Fox being interviewed about the Parker Solar Probe which (as the name suggests) is being used to investigate the Sun.

Screenshot from http://parkersolarprobe.jhuapl.edu (© 2019 The Johns Hopkins University Applied Physics Laboratory LLC. All rights reserved. Permission for use requested.)

There is a website for the project which, when I accessed it (28th December 2021), suggested the spacecraft was 109 279 068 km from the Sun's surface (which I must admit would have got a marginal comment on one of my own student's work along the lines "is the Sun's surface so distinctly positioned that this level of precision can be justified?") and travelling at 57 292 kph (kilometers per hour). This unrealistic precision derives from the details being based on "mission performance modeling [sic] and simulation and not real-time data…" Real-time data is not necessarily available to the project team itself – the kind of shielding needed to protect the spacecraft from such extreme conditions also creates a challenge in transmitting data back to earth.

But the serious point is that returning to the website at another time it is possible to see how the probe's speed and position have changed (as shown on 'the Mission' webpage – indeed by the time I took the 'screenshot' it had moved about 7000 km), as the spacecraft moves through a sequence of loops in space orbiting the Sun on a shifting elliptical path that takes it periodically very close (very close, in solar system terms, that is) to the sun. Like any orbiting body, the probe will be moving faster when closest to the sun and slowest when furthest from the sun. (The balance shifts between its kinetic and potential energy – as it works to move away against the sun's gravity when receding from it 1.)

Touching the Sun

Publicity still from the Danny Boyle film 'Sunshine'

Getting too close the Sun – with its high temperature, the 'solar wind' of charged particles emitted into space, occasional solar flares, and the high flux of radiation from across the electromagnetic spectrum – is very dangerous, making the design and engineering of any craft intended to investigate our local star up close very challenging. A key feature is a protective heat shield facing the Sun . This was the premise of the sci-fi film 'Sunshine' 2.

For the Parker probe

"the spacecraft and instruments will be protected from the Sun's heat by a …11.43 cm carbon-composite shield, which will need to withstand temperatures outside the spacecraft that reach nearly …1,377 degrees Celsius"

"At closest approach to the Sun, while the front of Parker Solar Probe' solar shield faces temperatures approaching … 1,400° Celsius, the spacecraft's payload will be near room temperature, at about [29˚C.]."

http://parkersolarprobe.jhuapl.edu

Note: Dr Fox is NOT reporting from the Parker Solar Probe – just pictured in front of an image of the sun (Dr Fox's profile on NASA website)

Dr Fox, who is Director of NASA's Heliophysics [physics of the Sun] Division, was being interviewed about data released from an earlier close approach on a BBC Science in Action podcast.

Science in Action episode broadcast 2021-12-19

"The Parker Solar probe continues its mission of flying closer and closer to the sun. Results just published show what the data the probe picked up when it dipped into the surrounding plasma. NASA's Nicky Fox is our guide."

Item on BBC Science in Action

The project is framing that event as when, "For the first time in history, a spacecraft has touched the Sun". Although the visible surface of the sun has a temperature of about 6000K (incredibly hot by human standards), the temperature of the 'atmosphere' or corona around it is believed to reach several million Kelvins. On the programme, Dr Fox was asked about how the spacecraft could survive in the sun's corona, given its extremely high temperatures.

A teaching analogy?

In response she used an analogy from everyday experience:

"We talk about the plasma being at a couple of million degrees, it's like putting your hand inside an oven, and you don't touch anything. You won't burn your hand, you'll feel some heat but you won't actually burn your hand, and so the solar wind itself, or the corona, is a very tenuous plasma, there are just not that many particles there. So, even though the whole atmosphere is at about two million degrees, the number of particles that are coming into contact with the spacecraft are [sic] very small.

The temperatures that we have to deal with are about fourteen, fifteen hundred degrees Celsius, at the maximum, which is still hot, don't…let me kid you, that's still hot, but it is not two million degrees."

Dr Fox interviewed on Science in Action

Analogies are commonly used in science, science communication and science education as one means of 'making the unfamiliar familiar' by showing how something novel or surprising is actually like something the audience is already aware of and comfortable with.

Read about science analogies

Read about making the unfamiliar familiar

If the probe had been dipped in a molten vat of some hypothetical refractory liquid at two million degrees it would have quickly been destroyed. But because the Corona is not only a plasma (an 'ionised gas')3, but a very tenuous one, this does not happen. NASA sending the probe into the corona is similar to putting one's hand in the oven when cooking. If you touch the metal around the outside you will burn yourself, but you are able to reach inside without damage as long as you do not touch the sides – as although the air in the oven can get as hot as the metal structure, it has a very low particle density compared with a solid metal. So, your hand is in a hot place, but is not in contact with much of the hot material.

Do not try this at home – at least not unless you are quick

Of course, this is not the whole story. You can reach in the oven to put something in or (with suitable protection) take something out, but you cannot safely leave your hand in there for any length of time.

When two objects at different temperature are placed in contact, heating will occur with 'heat' passing from the hotter to colder object until they are in thermal equilibrium (i.e., at the same temperature). But this is not instantaneous – it takes time.4 If the Parker Solar Probe had been flown into the Sun's atmosphere and left there it would have been heated till it eventually matched the ambient temperature (not 'just' 1400˚C) regardless of how effective a heat shield it had been given. Or rather, it would have been heated till its substance reached the ambient temperature, as it would have lost structural integrity long before this point.

Of course, the probe has been designed to spend some time in the coronal atmosphere collecting data, but to only dip in for short visits, as NASA is well aware that it would not be wise to leave one's hand in the oven for too long.

Note:

1 This at least is the description based on Newtonian physics. There is an attractive, gravitational force between the Sun and the probe. As the spacecraft moves towards the sun it accelerates, and then its momentum takes it away, being decelerated by gravity.In this model gravity is a force between two bodies. (The path is actually more complex than this, as it has been designed to fly past Venus several times to adjust its trajectory round the Sun.)

In the model offered by general relativity the probe simply moves in a straight line through space which has a complex geometry due to the presence of matter/energy: a straight line which seems to us to be a shifting series of ellipses. Gravity here is best understood as a distortion from a 'flat' space. Perhaps it is clear why for most purposes scientists stick with the Newtonian description even though it is no longer the account considered to best describe nature.

2 The movie poster gives a slight clue to the hazards involved in taking a manned mission to the Sun!

3 Plasma is considered a fourth state of matter: solid, liquid, gas, plasma. The expression that 'a plasma is an ionised gas' may suggest plasma is a kind of gas, but then we might also say that a gas is a boiled liquid or that a liquid is melted solid! So, perhaps what we should say is that a plasma [gas/liquid] is what you get when you ionise [boil/melt] a gas [liquid/solid].

4 In theory, modelling of such a process suggests it takes an infinite time for this to occur. 5 In practice, the temperatures become close enough that for practical purposes we consider thermal equilibration to have occurred.

5 This is an example of a process that can be understood as having a negative feedback cycle: temperature difference drives the heat flow, which reduces temperature difference, which therefore also reduces the driver for heat flow; so the rate of heat flow is reduced, so therefore the rate of temperature change is reduced… This is a similar pattern to radioactive decay – both follow an 'exponential decay' law.

Climate change – either it is certain OR it is science

Is there a place for absolute certainty in science communication?

Keith S. Taber

I just got around to listening to the podcast of the 10th October episode of Science in Action. This was an episode entitled 'Youngest rock samples from the moon' which led with a story about rock samples collected on the moon and brought to earth by a Chinese mission (Chang'e-5). However, what caused me to, metaphorically at least, prick up my ears was a reference to "absolute certainty".

BBC Science in Action episode, 10th October, 2021

Now the tag line for Science in Action is "The BBC brings you all the week's science news". I think that phrase reveals something important about science journalism – it may be about science, but it is journalism, not science.

That is not meant as some kind of insult. But science in the media is not intended as science communication between scientists (they have journals and conferences and so forth), but science communicated to the public – which means it has to be represented in a form suitable for a general, non-specialist audience.

Read about science in public discourse and the media

Scientific and journalistic language games

For, surely, "all the week's science news" cannot be covered in one half-hour broadcast/podcast. 1

My point is that "The BBC brings you all the week's science news" is not intended to be understood and treated as a scientific claim, but as something rathere different. As Wittgenstein (1953/2009) famously pointed out, language has to be understood in specific contexts, and there are different 'language games'. So, in the genre of the scientific report there are particular standards and norms that apply to the claims made. Occasionally these norms are deliberately broken – perhaps a claim is made that is supported by fabricated evidence, or for which there is no supporting evidence – but this would be judged as malpractice, academic misconduct or at least incompetence. It is not within the rules of that game

However, the BBC's claim is part of a different 'language game' – no one is going to be accused of professional misconduct because, objectively, Science in Action does not brings a listener all the week's science news. The statement is not intended to be understood as an objective knowledge claim, but more a kind of motto or slogan; it is not to be considered 'false' because it not objectively correct. Rather, it is to be understood in a fuzzy, vague, impressionistic way.

To ask whether "The BBC brings you all the week's science news" through Science in Action is a true or false claim would be a kind of category error. The same kind of category error that occurs if we ask whether or not a scientist believes in the ideal gas law, the periodic table or models of climate change.

Who invented gravity?

This then raises the question of how we understand what professional academic scientists say on a science news programme that is part of the broadcast media in conversation with professional journalists. Are they, as scientists, engaged in 'science speak', or are they as guests on a news show engaged in 'media speak'?

What provoked this thought with was comments by Dr Fredi Otto who appeared on the programme "to discuss the 2021 Nobel Prizes for Science". In particular, I was struck by two specific comments. The second was:

"…you can't believe in climate change or not, that would just be, you believe in gravity, or not…"

Dr Friederike Otto speaking on Science in Action

Which I took to mean that gravity is so much part of our everyday experience that it is taken-for-granted, and it would be bizarre to have a debate on whether it exists. There are phenomena we all experience all the time that we explain in terms of gravity, and although there may be scope for debate about gravity's nature or its mode of action or even its universality, there is little sense in denying gravity. 2

Newton's notion of gravity predominated for a couple of centuries, but when Einstein proposed a completely different understanding, this did not in any sense undermine the common ('life-world' 2) experience labelled as gravity – what happens when we trip over, or drop something, or the tiring experience of climbing too many steps. And, of course, the common misconception that Newton somehow 'discovered' gravity is completely ahistorical as people had been dropping things and tripping over and noticing that fruit falls from trees for a very long time before Newton posited that the moon was in freefall around the earth in a way analogous to a falling apple!

Believing in gravity

Even if, in scientific terms, believing in a Newtonian conceptualisation of gravity as a force acting at a distance would be to believe something that was no longer considered the best scientific account (in a sense the 'force' of gravity becomes a kind of epiphenomenon in a relativistic account of gravity); in everyday day terms, believing in the phenomenon of gravity (as a way of describing a common pattern in experience of being in the world) is just plain common sense.

Dr Otto seemed to be suggesting that just as gravity is a phenomenon that we all take for granted (regardless of how it is operationalised or explained scientifically), so should climate change be. That might be something of a stretch as the phenomena we associate with gravity (e.g., dense objects falling when dropped, ending up on the floor when we fall) are more uniform than those associated with climate change – which is of course why one tends to come across more climate change deniers than gravity deniers. To the best of my knowledge, not even Donald Trump has claimed there is no gravity.

But the first comment that gave me pause for thought was:

"…we now can attribute, with absolute certainty, the increase in global mean temperature to the increase in greenhouse gases because our burning of fossil fuels…"

Dr Friederike Otto speaking on Science in Action
Dr Fredi Otto has a profile page at the The Environmental Change Unit,
University of Oxford

Absolute certainty?

That did not seem to me like a scientific statement – more like the kind of commitment associated with belief in a religious doctrine. Science produces conjectural, theoretical knowledge, but not absolute knowledge?

Surely, absolute certainty is limited to deductive logic, where proofs are possible (as in mathematics, where conclusions can be shown to inevitably follow from statements taken as axioms – as long as one accepts the axioms, then the conclusions must follow). Science deals with evidence, but not proof, and is always open to being revisited in the light of new evidence or new ways of thinking about things.

Read about the nature of scientific knowledge

Science is not about belief

For example, at one time many scientists would have said that the presence of an ether 3 was beyond question (as for example waves of light travelled from the sun to earth, and waves motion requires a medium). Its scientific characterisation -e.g., the precise nature of the ether, its motion relative to the earth – were open to investigation, but its existence seemed pretty secure.

It seemed inconceivable to many that the ether might not exist. We might say it was beyond reasonable doubt. 4 But now the ether has gone the way of caloric and phlogiston and N-rays and cold fusion and the four humours… It may have once been beyond reasonable doubt to some (given the state of the evidence and the available theoretical perspectives), but it can never have been 'absolutely certain'.

To suggest something is certain may open us to look foolish later: as when Wittgenstein himself suggested that we could be certain that "our whole system of physics forbids us to believe" that people could go to the moon.

Science is the best!

Science is the most reliable and trustworthy approach to understanding the natural world, but a large part of that strength comes from it never completely closing a case for good – from never suggesting to have provided absolute certainty. Science can be self-correcting because no scientific idea is 'beyond question'. That is not to say that we abandon, say, conversation of energy at the suggestion of the first eccentric thinker with designs for a perpetual motion machine – but in principle even the principle of conservation of energy should not be considered as absolutely certain. That would be religious faith, not scientific judgement.

So, we should not believe. It should not be considered absolutely certain that "the increase in global mean temperature [is due to] the increase in greenhouse gases because [of] our burning of fossil fuels", as that suggests we should believe it as a doctrine or dogma, rather than believe that the case is strong enough to make acting accordingly sensible. That is, if science is always provisional, technically open to review, then we can never wait for absolute certainty before we act, especially when something seems beyond reasonable doubt.

You should not believe scientific ideas

The point is that certainty and belief are not really the right concepts in science, and we should avoid them in teaching science:

"In brief, the argument to be made is that science education should aim for understanding of scientific ideas, but not for belief in those ideas. To be clear, the argument is not just that science education should not intend to bring about belief in scientific ideas, but rather that good science teaching discourages belief in the scientific ideas being taught."

Taber, 2017: 82

To be clear – to say that we do not want learners to believe in scientific ideas is NOT to say we want them to disbelieve them! Rather, belief/disbelief should be orthogonal to the focus on understanding ideas and their evidence base.

I suggested above that to ask whether "The BBC brings you all the week's science news" through Science in Action is a true or false claim would be a kind of category error. I would suggest it is a category error in the same sense as asking whether or not people should believe in the ideal gas law, the periodic table, or models of climate change.

"If science is not about belief, then having learners come out of science lessons believing in evolution, or for that matter believing that magnetic field lines are more concentrated near the poles of a magnet, or believing that energy is always conserved, or believing that acidic solutions contain solvated hydrogen ions,[5] misses the point. Science education should help students understand scientific ideas, and appreciate why these ideas are found useful, and something of their status (for example when they have a limited range of application). Once students can understand the scientific ideas then they become available as possible ways of thinking about the world, and perhaps as notions under current consideration as useful (but not final) accounts of how the world is."

Taber, 2017: 90

But how do scientists cross the borders from science to science communication?

Of course many scientists who have studied the topic are very convinced that climate change is occurring and that anthropogenic inputs into the atmosphere are a major or the major cause. In an everyday sense, they believe this (and as they have persuaded me, so do I). But in a strictly logical sense they cannot be absolutely certain. And they can never be absolutely certain. And therefore we need to act now, and not wait for certainty.

I do not know if Dr Otto would refer to 'absolute certainty' in a scientific context such as a research paper of a conference presentation. But a radio programme for a general audience – all ages, all levels of technical background, all degrees of sophistication in appreciating the nature of science – is not a professional scientific context, so perhaps a different language game applies. Perhaps scientists have to translate their message into a different kind of discourse to get their ideas across to the wider public?

The double bind

My reaction to Dr Otto's comments derived from a concern with public understanding of the nature of science. Too often learners think scientific models and theories are meant to be realistic absolute descriptions of nature. Too often they think science readily refutes false ideas and proves the true ones. Scientists talking in public about belief and absolute certainty can reinforce these misconceptions.

On the other hand, there is probably nothing more important that science can achieve today than persuade people to act to limit climate change before we might bring about shifts that are (for humanity if not for the planet) devastating. If most people think that science is about producing absolute certain knowledge, then any suggestion that there is uncertainty over whether human activity is causing climate change is likely to offer the deniers grist, and encourage a dangerous 'well let's wait till we know for sure' posture. Even when it is too late and the damage has been done, if there are any scientists left alive, they still will not know absolutely certainly what caused the changes.

"…Lord, here comes the flood
We'll say goodbye to flesh and blood
If again the seas are silent
In any still alive
It'll be those who gave their island to survive…"

(Peter Gabriel performing on the Kate Bush TV special, 1979: BBC Birmingham)

So, perhaps climate scientists are in a double bind – they can represent the nature of science authentically, and have their scientific claims misunderstood; or they can do what they can to get across the critical significance of their science, but in doing so reinforce misconceptions of the nature of scientific knowledge.

Coda

I started drafting this yesterday: Thursday. By coincidence, this morning, I heard an excellent example of how a heavyweight broadcast journalist tried to downplay a scientific claim because it was couched as not being absolutely certain!

Works cited:

Notes

1 An alternative almost tautological interpretation might be that the BBC decides what is 'science news', and it is what is included in Science in Action, might fit some critics complaints that the BBC can be a very arrogant and self-important organisation – if only because there are stories not covered in Science in Action that do get covered in the BBC's other programmes such as BBC Inside Science.

2 This might be seen as equivalent to saying that the life-world claim that gravity (as is commonly understood and experienced) exists is taken-for-granted Schutz & Luckmann, 1973). A scientific claim would be different as gravity would need to be operationally defined in terms that were considered objective, rather that just assuming that everyone in the same language community shares a meaning for 'gravity'.

3 The 'luminiferous' aether or ether. The ether was the name given to the fifth element in the classical system where sublunary matter was composed of four elements (earth, water, air, fire) and the perfect heavens from a fifth.

(Film  director Luc Besson's sci-fi/fantasy movie 'The Fifth Element' {1997, Gaumont Film Company} borrows from this idea very loosely: Milla Jovovich was cast in the title role as a perfect being who is brought to earth to be reunited with the other four elements in order to save the world.)

4 Arguably the difference between forming an opinion on which to base everyday action (everyday as in whether to wear a rain coat, or to have marmalade on breakfast toast, not as in whether to close down the global fossil fuel industry), and proposing formal research conclusions can be compared to the difference between civil legal proceedings (decided on the balance of probabilities – what seems most likely given the available evidence) and criminal proceedings – where a conviction is supposed to depend upon guilt being judged beyond reasonable doubt given the available evidence (Taber, 2013).

Read about writing-up research

5 Whether acids do contain hydrated hydrogen ions may seem something that can reasonably be determined, at least beyond reasonable doubt, by empirical investigation. But actually not, as what counts as an acid has changed over time as chemists have redefined the concept according to what seemed most useful. (Taber, 2019, Chapter 6: Conceptualising acids: Reimagining a class of substances).

The Sun would pull more on the Earth…

Bert's understanding of the reciprocal nature of forces 

Keith S. Taber

Bert was a participant in the Understanding Science Project. A key idea in school physics is that forces occur in pairs, when two bodies exert an equal magnitude force upon each other (as required by Newton's third law). However, this seems counter intuitive to pupils, who may expect that a larger (more massive, or greater charge etc.) object would exert a greater force on a smaller body than vice versa. In physics a distinction is made between the forces (always equal) and their effects (which depend upon the force applied, and the mass of the object being acted upon). This distinction is not always made by students.

When in Y11, Bert offered an example of one of the common alternative conceptions found among students – that the larger body will exert more force:

What about the Earth going round the Sun, that's an orbit as well is it?

Yeah.

…

So why does it go round?

Why does it go round?

Yeah.

Erm because erm, well one is the gravity of it pulling and the other is, I'm not so sure what the other force is.

That's gravity of what?

The Sun.

So the gravity of the Sun pulling on the Earth?

Yeah.

Do you think the Earth pulls on the Sun?

Yeah, I guess but not strongly enough to move the Sun. Because if there's an object with a small amount of mass then it's not going to give off as much pull as something ten times bigger as it. So the Earth would pull more on the Sun, I mean the Sun would pull more on the Earth.

Whereas the physics perspective is that a force is an interaction between bodies, Bert talks as though a force is something that emanates from one body to another ("give off … pull"), a way of talking quite common among students applying their intuitive understanding of force.

Many students conflate the force acting on a body, and its effect (the acceleration produced) – so here the Sun and Earth are subject to the same force, but the earth is much less massive so will accelerate much more subject to that force than the Sun would. (The Sun's acceleration would actually depend on the net force acting on it considering the various bodies in orbit around it.)

Common experience tells us that in interactions between contrasting bodies (e.g., consider a fly on a windshield) the larger object has more effect, which may seem naturally to mean it applies more force (how much force can the tiny fly impart? – surely the car must apply more force to the fly?) So there is an intuition here, which can act as a grounded learning impediment to learning the physics formalism.


Because they are laws these things have to be true

Keith S. Taber

Ralph was a participant in the Understanding Science project. When I interviewed him in Y10 he suggested that what was particular to science was that with science it will always be the same, i.e., that the nature of science was that it was universal rather than relative to a particular place. Ralph had commented that "because they're kind of like, they are laws so…these things have to be true".

I: So in say maths you have these laws that are what, universal?

R: Yeah.

I: And science you think is the same sort of thing?

R: Yeah.

So Ralph was asked about the universal nature of laws in science:

I: So what laws do you know in science then that will apply anywhere?

R: Erm, well there's kind of like the laws of gravity and things, which are always there. But they can, that is one exception, because that can be changed depending on what planet you are on, but that's kind of like very, far off so, if you went on the moon and did physics there it might be ever so slightly different, but I'm not sure because I haven't been to the moon though.

…

R: And chemistry it's so – reactions and things – but the environments can change those, but not to a large extent, so, so iron will always react with something, no matter what, and two of the same element will not react together because they're already the same and things like that.

I: Mm?

R: Erm, yep, and biology's because most is kind of like is an average so, it can be different as well, but they're kind of like, saying they're all universal laws and all actually the same is kind of a bit untrue, but if like, there are exceptions to the rule in different places, so biology you can kind of like have erm illnesses or disfigurements that change how you look at biology, and things, which is kind of complicated and you don't tend to do that in this kind of level of biology, 'cause that's more kind of like that's specialised, that's more in kind of medical biology and things.

I: So it's a kind of 'unless' law, so, you know, a dog will always have four legs,

R: Yeah.

I: unless one of them's been torn off

R: Yeah.

I: or unless it is a mutant and grown an extra one?

R: Exactly, unless there is some kind of other, erm, other … event which … changes how that will work, so … like a snail would normally have no legs, but if you put loads of radiation on it, I dunno, maybe it would grow an arm or something.

It seemed Ralph's notion of a law of gravity was not the universal law of Newtonian physics, but something linked to the local strength of the gravitational field. (Later in the interview Ralph explained that the law of gravity is that things will always move towards the centre, but it is different on the moon*). In chemistry, Ralph seemed to see ideas about which substances reacted together as laws, although he acknowledge that in some cases these patterns were dependent upon conditions. In biology, Ralph associated laws with the normal forms of organisms, which again he knew could be changed by environmental factors.

In general then, Ralph's notion of scientific laws did not match the scientific notion of a law, which would generally operate at a 'deeper' level (i.e., a higher level of abstraction from observations), but seemed more at the level of 'facts'.