Category: technical language

Explaining Y T cells stop working

Communicating oncology research

Keith S. Taber

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

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

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

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

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

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

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

Dan Theodorescu & Nick Petrić Howe speaking on the Nature Podcast

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

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

Communicating science

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

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

Read about science in public discourse and the media

The gist

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

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

The language used

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

Y-negative cells – a new technical term?

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

An immune evasive environment?

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

Paralysed, exhausted and tired T cells

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

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

Read about making the unfamiliar familiar

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

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

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

Read examples of similes used in discussing science

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

Read examples of metaphors used in discussing science

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

Images from Pixabay

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

Read about types of pseudo-explanations

Read examples of anthropomorphism in science discourse

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

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

Yi, Cox, & Zajac, 2010

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

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

Rejection – a dead metaphor?

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

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

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

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

Seated checkpoints: quo vardis, friend or foe?

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

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

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

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

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

Can tumours behave advertently?

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

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

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

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

Work cited:
Notes:

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

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

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

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

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

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

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

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

Read about anthropomorphism and science learning

5 So, we might suggest that

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

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

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

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

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

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

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

Read about ontology

Are these fossils dead, yet?

Non-living fossils and dead metaphors

Keith S. Taber

Fossil pottery?
(Images by by Laurent Arroues {background}) and OpenClipart-Vectors from Pixabay)

I was intrigued by some dialogue that was part of one of (physicist) Jim Al-Khalili's interviews for the BBC's 'The Life Scientific' series, where Prof. Al-Khalili "talks to leading scientists about their work, finding out what inspires and motivates them and asking what their discoveries might do for mankind".

The Life Scientific – interviews with scientists about their lives and work

This week he was talking to Dr Judith Bunbury of St. Edmund's College and the Department of Earth Sciences at Cambridge ('Judith Bunbury on the shifting River Nile in the time of the Pharaohs'). It was a fascinating interview, and in particular discussed work showing how the Nile River has repeatedly changed its course over thousands of years. The Nile is considered the longest river in Africa (and possibly the world – the other contender being the Amazon).

Over time the river shifts is position as it unevenly lay down sediment and erodes the river banks – (Image by Makalu from Pixabay)

The exchange that especially piqued my interest followed an account of the diverse material recovered in studies that sample the sediments formed by the river. As sediments are laid down over time, a core (collected by an auger) can be understood to have formed on a time-line – with the oldest material at the bottom of the sample.

Within the sediment, researchers find fragments of animal bone, human teeth, pottery, mineral shards from the working of jewels…

"Are you sure the Nile flows this far?" Using an auger to collect a core (of ice in this case) (Image by David Mark from Pixabay)

Dr Bunbury was taking about how changing fashions allowed the pottery fragments to be useful in dating material – or as the episode webpage glossed this: "pottery fragments which can be reliably time-stamped to the fashion-conscious consumers in the reign of individual Pharaohs".

This is my transcription of the exchange:

[JAK]: …a bit like fossil hunting
[JB]: well, I mean, we're just treating pottery as a kind of fossil
a kind of fossil, yeah, > no, absolutely >
< and it is a fossil <
yes, well quite, I can see the similarities.

Prof. Jim Al-Khalili interviewing Dr Judith Bunbury

Now Prof. Jim has a very gentle, conversational, interview style, as befits a programme with extended interviews with scientists talking about their lives (unlike, say, a journalist faced with a politician where a more adversarial style might be needed), so this exchange probably comes as close to a disagreement or challenge as 'The Life Scientific' gets. Taking a slight liberty, I might represent this as:

  • Al-Khalili: your work is like fossil hunting, the pottery fragments are similar to fossils
  • Bunbury: no, they ARE fossils

So, here we have an ontological question: are the pottery fragments recovered in archaeological digs (actually) fossils or not?

Bunbury wants to class the finds as fossils.

Al-Khalili thinks that in this context 'a kind of fossil' and 'like fossil hunting' are similes ("I can see the similarities") – the finds are somewhat like fossils, but are not fossils per se.

Read about science similes

So, who is right?

Metaphorical fossils

The term fossil is commonly used in metaphorical ways. For example, for a person to be described as a fossil is to be characterised as a kind of anachronism that has not kept up with social changes.

The term also seems to have been adopted in some areas of science as a kind of adjective. One place it is used is in relation to evidence of dampened ocean turbulence,

"The term 'fossil turbulence' refers to remnants of turbulence in fluid which is no longer turbulent."

Gibson, 1980, p.221

If that seems like a contradiction, it is explained that

"Small scale fluctuations of temperature, salinity, and vorticity in the ocean occur in isolated patches apparently caused by bursts of active turbulence. After the turbulence has been dampened by stable stratification the fluctuations persist as fossil turbulence."

Gibson, 1980, p.221

So, 'fossil turbulence' is not actually turbulence, but more the afterglow of the turbulence: a bit like the aftermath of a lively party which leaves its traces: the the chaotic pattern of abandoned debris provides signs there has been a party although there is clearly no longer a party going on.

An analogy for 'fossil turbulence'

Another example from astronomy is fossil groups of galaxies, which are apparently "systems with a very luminous X-ray source …and a very optically dominant central galaxy" (Kanagusuku, Díaz-Giménez & Zandivarez, 2016). It seems,

"The true nature of fossil groups in the Universe still puzzles the astronomical community. These peculiar systems are one of the most intriguing places in the Universe where giant elliptical galaxies are hosted [sic]."

Kanagusuku, Díaz-Giménez & Zandivarez, 2016

('Hosted' here also seems metaphorical – who or what could be acting as a host to an elliptical galaxy?)

The term 'fossil group' was introduced for "for an apparently isolated elliptical galaxy surrounded by an X-ray halo, with an X-ray luminosity typical of a group of galaxies" (Zarattini, Biviano, Aguerri, Girardi & D'Onghia, 2012): so, something that looks like a single galaxy, but in other respsects resembles a whole group of galaxies?

Close examination might reveal other galaxies present, yet the 'fossil' group is "distinguished by a large gap between the brightest galaxy and the fainter members" (Dariush, Khosroshahi, Ponman, Pearce, Raychaudhury & Hartley, 2007). Of course, there is normally a 'large gap' between any two galaxies (space contains a lot of, well, space), but presumably this is another metaphor – there is a 'gap' between the magnitude of the luminosity of the brightest galaxy, and the magnitudes of the luminosities of the others.

Read about science metaphors

Dead metaphors

One way in which language changes over time is through the (metaphorical) death of metaphors. Terms that are initially introduced as metaphors sometimes get generally adopted and over time become accepted terminology.

Many words in current use today were originally coined in this way, and often people are quite unaware of their origins. References to the hands of a clock or watch will these days be taken as simply a technical term (or perhaps for those who only familiar with digital clocks, a complete mystery?) In time, this may happen to 'fossil turbulence' or 'fossil galaxy groups'.

What counts as a fossil?

But it seems reasonable to suggest that, currently at least, these are still metaphors, implying that in some sense the ocean fluctuations or the galactic groups are somewhat like fossils. But these are not actual fossils, just as tin-pot dictators are not actually fabricated from tin.

So, what are actual fossils. The 'classic' fossil takes the form of an ancient, often extinct, living organism, or a part thereof, but composed of rock which has over time replaced the original organic material. In this sense, Prof. Al-Khalili seems correct in suggesting bits of pottery are only akin to fossils, and not actually fossils. But is that how the experts use the term?

According to the British Geological Survey (BGS):

Fossils are the preserved remains of plants and animals whose bodies were buried in sediments, such as sand and mud, under ancient seas, lakes and rivers. Fossils also include any preserved trace of life that is typically more than 10 000 years old. 

https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils/ 1

Now, pottery is not the preserved remains of plants or animals or other living organisms, but the site goes on to explain,

Preserved evidence of the body parts of ancient animals, plants and other life forms are called 'body fossils'. 'Trace fossils' are the evidence left by organisms in sediment, such as footprints, burrows and plant roots.

https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils 1

So, footprints, burrows, [evidence of] plant roots 2…or shards of pottery…can be trace fossils? After all, unearthed pottery is indirect evidence of living human creatures having been present in the environment, and, as the BGS also points out "the word fossil is derived from the Latin fossilis meaning 'unearthed'."

However, if the term originally simply meant something unearthed, then although the bits of pot would count as fossils – based on that argument so would potatoes growing in farmers' fields. So, clearly the English word 'fossil' has a more specific meaning in common use than its Latin ancestor.

But going by the BGS definition, Dr Bunbury's unearthed samples of pottery are certainly evidence of organisms left in sediment, so might be considered fossils. These fossils are not the remains of dead organisms, but neither is 'fossil' here simply a metaphor (not even a dead metaphor).

Work cited:
  • Dariush, A, Khosroshahi, H. G., Ponman, T. J., Pearce, F., Raychaudhury, S. & Hartley, W. (2007), The mass assembly of fossil groups of galaxies in the Millennium simulation, Monthly Notices of the Royal Astronomical Society, Volume 382, Issue 1, 21 November 2007, Pages 433-442, https://doi.org/10.1111/j.1365-2966.2007.12385.x
  • Gibson, Carl H. (1980) Fossil Temperature, Salinity, and Vorticity Turbulence in the Ocean. In Jacques C.J. Nihoul (Ed.) Marine Turbulence, Elsevier, pp. 221-257.
  • Kanagusuku, María José, Díaz-Giménez, Eugenia & Zandivarez, Ariel (2016) Fossil groups in the Millennium simulation – From the brightest to the faintest galaxies during the past 8 Gyr, Astronomy & Astrophysics, 586 (2016) A40, https://doi.org/10.1051/0004-6361/201527269.
  • Romero, I. C., Nuñez Otaño, N. B., Gibson, M. E., Spears, T. M., Fairchild, C. J., Tarlton, L., . . . O'Keefe, J. M. K. (2021). First Record of Fungal Diversity in the Tropical and Warm-Temperate Middle Miocene Climate Optimum Forests of Eurasia [Original Research]. Frontiers in Forests and Global Change, 4. https://doi.org/10.3389/ffgc.2021.768405
  • Zarattini, S., Biviano, A., Aguerri, J. A. L., Girardi, M. & D'Onghia, E. (2012) Fossil group origins – XI. The dependence of galaxy orbits on the magnitude gap, Astronomy & Astrophysics, 655 (2021) A103, DOI: https://doi.org/10.1051/0004-6361/202038722.
Notes:

1 "Fossils are the preserved remains of plants and animals whose bodies …". But this suggests that fungi do not form fossils. The same site points out that "We tend to think of fungi, such as mushrooms and toadstools, as being plants — but they are not. They neither grow from embryos nor photosynthesise and are put in a separate kingdom" (https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/plants-2/) – yet does not seem to mention any examples of fungi that have been fossilised (so the comment could be read to be meant to suggest that fossil fungi are found as well as fossil plants; but could equally well be read to mean that as fungi are not plants they do not fossilise).

The second quote here is more inclusive: "Preserved evidence of the body parts of ancient animals, plants and other life forms…" The site does also specify that "Remains can include microscopically small fossils, such as single-celled foraminifera…" (https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils/).

So, just to be clear, fossil fungi have been found.



Fungal spores found in Thailand – figure 3 from Romero et al, 2021. These fossils were recovered form lignite (a form of coal) deposited in the Miocene epoch.
Copyright © 2021 Romero, Nuñez Otaño, Gibson, Spears, Fairchild, Tarlton, Jones, Belkin, Warny, Pound and O'Keefe; distributed under the terms of the Creative Commons Attribution License (CC BY).

2 If the roots were themselves fossilised then these would surely be body fossils as roots are parts of plant. Presumably this is meant to refer to the channels in soil when the roots grow through the soil.


Of mostly natural origin

Is your shampoo of natural, unnatural, or supernatural origin?

Keith S. Taber

It seems that some of the ingredients of a well-known brand of hair care products are not of natural origin (Image by Stefan Keller from Pixabay)

A well know brand of hair products is being advertised on television with an explicit claim that the shampoo is 94% of natural origin. Clearly there is also an implicit claim here about the other 6%! This dubious claim does not seem to be a slip of the tongue, as similar references can be found in product details on line (including the examples below). The science teacher in me knew that it was this kind of nonsense which supports common misconceptions about 'natural' being inherently good, and there being a clear distinction between materials that are 'natural', and those that are not.

Shampoos from brands other than Herbal Essences are 100% of natural origin.

The other evening I was watching television, and there was a shampoo being advertised, and although I was not paying attention I thought I heard the claim that the shampoo contained products of 94% natural origin. Had I misheard – a quick 'rewind' suggested not.

My next assumption was that this was sloppy language being used by some advertising copywriter, and that the manufacturer who commissioned the commercial simply had not noticed the slip. So I had a look on line.1 It seems that the brand concerned, Herbal Essences, has a habit or topping up its products with material that is not of natural origin. The company claims it is using at least 90% materials of natural original in its latest products (see the examples below), and this is apparently seen as a positive point to stress in its marketing.

But this is just nonsense. If the shampoo was fabricated using 94% products of natural original, then 6% was not of natural origin. This leaves me to wonder where the rest originates. A shampoo, any shampoo, is 100% of natural origin.

Natural products chemistry

In chemistry there is a common term natural products which tends to be used for materials extracted from living organisms – one can extract vitamin C from oranges, and insulin for diabetics used to be extracted from pancreases from farm animals (although now it is produced by the activities of bacteria or yeast). In that sense salt (produced by evaporating sea water) and chalk (deriving from the shells debris from long dead sea organisms) are not natural products. But like everything else in the material world, salt and chalk are still of natural origin.

So what is a hair product which is not of natural origin, or which is only partially of natural origin? It seems there are two obvious contrasts to natural, which are 'unnatural' and 'supernatural'. Presumably the company was not suggesting it used ingredients of supernatural origin?

Do Herbal Essences employ a specialist formulation technologist to prepare the shampoo ingredients that are not of natural origin? (Image by pendleburyannette from Pixabay)

What makes something unnatural?

Assuming Herbal Essences products do not include material of supernatural origin, the other option would seem to be material of unnatural origin. But what makes a material unnatural.

At various times, in various cultural contexts, the divine right of kings, feudalism and slavery will have been seen as perfectly natural, as well the subservience of women to men. Certain sexual acts that are now widely (if not universally) considered part of the normal range of human behaviours have at various times in different societies been considered unnatural – indeed so unnatural that those found to have 'committed' them might be put to death.

Given that the question of 'what is human nature?' is not settled (didn't Immanuel Kant think this was the core task for philosophy?) the approach that is sometimes taken is to look instead to 'nature' herself (for nature is a 'she' as has long been established – in part justifying her domination and mistreatment by 'man'). If it happens in nature, then that's natural.

"The sun rises everyday but animals occasionally give birth to monsters. 'Natural is what occurs always or almost always', says Aristotle, generalizing from this experience."

Paul Feyerabend

So, by this criterion, saving lives with blood transfusions is not natural, and nor is hip replacement surgery, nor using an incubator to stop premature babies dying. However, cancer is natural. Pushing your siblings out of the nest, or pecking them to death, to get a greater share of the food your parents bring home is perfectly natural. Depositing your eggs in another creature, and paralysing it so that it acts as a defenseless (but alive, and so fresh) source of food when your offspring hatch out inside it, is natural.

"We can save you if you wish, but only by unnatural acts" (Image by Mohamed Hassan from Pixabay)

The man-made is not 'natural'

This depends upon demarcating humans as somehow outside of nature. This is difficult for a natural scientist to accept as 'ever since Darwin' (to borrow a phrase) it has been difficult to see how humans can be considered inherently distinct from the rest of the natural world, even if contingency has led to some obvious differences in terms of the development of culture. This argument then distinguishes the natural from the synthetic, the man-made.

A space rocket is not natural (in this sense) as it only exists because humans built it. Whether this is qualitatively different from technology elsewhere in nature – a badger's dam, a termite's nest, a honeycomb – rather than just a matter of a (admittedly impressive) difference of degree is an interesting question.

There are no doubt times where it is useful to distinguish between materials and objects that can be collected or extracted form 'natural' sources, and those that only exist because they have been synthesised by people – even if we do need to be wary of reading too much into the distinction. The Saturn V rocket did not exist 'in nature', and nor does a lemon coated in a wax so that it will stay 'fresh' longer – but one is the product of considerably less processing than the other. 2

Fluorine compounds (fluorides) are added to drinking water in many places to help protect teeth, but in other places the water supply already (i.e., 'naturally') contains fluoride at much higher levels – indeed, sometimes high enough to be considered a medical risk. This both reminds us that what is natural is somewhat arbitrary, and that what is considered natural is not necessarily desirable.

Natural and natural origin

The Saturn V rocket was synthetic – it was not found 'as is', growing in a swamp or being ejected from a volcano ('You Only Live Twice' style). But the materials it was made from were all of natural origin, even if some of them may have been the result of considerable processing of naturally occurring materials.

Everything you see here is of natural origin (From 'You Only Live Twice', Eon Productions)

Any material thing in our world is of natural origin. Some materials are used much as found 'in nature', sometimes some cleaning or tidying is needed (think of natural diamonds being 'cut' to best reflect light), some purifying (separating compounds from crude oil fractions), some extracting (metal from ore), some synthesising (ammonia from hydrogen and nitrogen)… The amount of processing may vary considerably, but everything material that goes into a manufactured product is ultimately of natural origin.

So Herbal Essences products are 100% of natural origin, just as are the products of all their competitors.

A vague distinction

Webpages advertising specific Herbal Essences product lines often simply report that they are of 9n% natural origin, as in the examples below (95%, 96%, 97%). However, I found a page where it was clarified that the 90+% of natural origin included "purified water and ingredient materials derived from a natural source and subjected to limited processing".

So Herbal Essences do not use natural ditch water, or natural swamp water, or even natural sea water in their products, but rather purified water. I am pleased – as I have used Herbal Essences products, and will likely do so again, and I would rather not use dirty water when I am seeking to clean my hair.

Water – easily sourced from nature, and used in hair products (Image by mac231 from Pixabay)

So, it seems that for Herbal Essences, being of natural origin actually means, natural materials found in a suitable form to be used directly, or ("natural derived") only needing a "limited" amount of processing. Limited processing is a good thing in 'green chemistry' terms (less waste, less energy needed) but it is both a vague notion (who is to decide what makes the processing 'limited', and how does a consumer know what Herbal Essences count as limited?), and of course it is simply a quite different concept to being of natural origin.

I guess the company wanted a way of saying they were basing their products on natural products (such as plant extracts) without being misleading by implying that they could simply go and collect all the component materials and use them without needing any further processing. These materials may be pressed, steamed, or separated and purified in other ways, but are not generally the outcomes of complex synthetic processes. I can see both why that would be attractive to consumers, and why it is not easy to get across in a simple catchy term.

Yet the claim that 94% of your hair product is of natural origin, when a moment's thought should lead to the consumer realising that actually all products are of 100% natural origin, is a claim that (unlike the missing 6% of your Herbal Essences brand shampoo), does not have any substance.

a "limited" amount of processing

is both a vague notion and simply a quite different concept to

being of natural origin.

Appendix: Some examples of products that are not completely of natural origin

95% natural origin

The Herbal Essences Coconut Milk conditioner is, according to their website,

95% natural origin
73% purified water and 22% natural derived ingredients other 5% for a good usage experience & product stability.

https://herbalessences.co.uk/en-gb/products/coconut-milk/coconut-milk-shampoo/
96% natural origin

The Herbal Essences Coconut Milk conditioner is, according to their website

96% natural origin
88% purified water and 8% natural derived ingredients other 4% for a good usage experience & product stability.

https://herbalessences.co.uk/en-gb/products/coconut-milk/coconut-milk-conditioner/
96% natural origin

The Herbal Essences Bourbon & Manuka Honey shampoo, is,

96% natural origin
73% purified water and 23% natural derived ingredients other 4% for a good usage experience & product stability.

https://herbalessences.co.uk/en-gb/products/bourbon-manuka-honey/bourbon-manuka-honey-shampoo/
97% natural origin

Their Volumising White Strawberry & Sweet Mint shampoo, is

97% natural origin
84% purified water and 13% natural derived ingredients other 3% for a good usage experience & product stability.

https://herbalessences.co.uk/en-gb/products/white-strawberry-sweet-mint/white-strawberry-sweet-mint-shampoo/

At least 9/10ths natural origin

I learn from the company's website that

"All of our Herbal Essences bio:renew hair products have a 90% natural origin *"

https://herbalessences.co.uk/en-gb/whats-up-with-paraben-free-shampoo/

And they kindly explain that by natural origin they mean

"* includes purified water and ingredient materials derived from a natural source and subjected to limited processing"

Source cited:
  • Feyerabend, P. (2011) The Tyranny of Science. Cambridge: Polity Press

Footnote

1: All quotes are from the website pages cited as accessed on 22nd August 2021.

2. I note that Wikipedia suggests that

"Fruit waxing is the process of covering fruits (and, in some cases, vegetables) with artificial [sic] waxing material. Natural [sic] wax is removed first, usually by washing, followed by a coating of a biological or petroleum derived wax. Potentially allergenic proteins (peanut, soy, dairy, wheat) may be combined with shellac."

Shock! A typical honey bee colony comprises only six chemicals!

Is it half a dozen of one, or six of the other?

Keith S. Taber

Bee-ware chemicals!
(Images by PollyDot and Clker-Free-Vector-Images from Pixabay)

A recent episode of the BBC Inside science radio programme and podcast was entitled 'Bees and multiple pesticide exposure'. This discussed a very important issue that I have no wish to make light of. Researchers were looking at the stressors which might be harming honey bees, very important pollinators for many plants, and concluded that these likely act synergistically. That is a colony suffering from, say a drought and at the same time a mite infection, will show more damage that one would expect from simply adding the typical harm of each as if independent effects.  Rather there are interactions.

This is hardly surprising, but is none-the-less a worrying finding.

Bees and multiple pesticide exposure episode of BBC Inside Science

However,  my 'science teacher' radar honed in on an aspect of the language used to explain the research. The researcher interviewed was Dr Harry Siviter of the University of Texas at Austin. As part of his presentation he suggested that…

"Exposure to multiple pesticides is the norm, not the exception. So, for example a study in North America showed that the average number of chemicals found in a honey bee colony is six, with a high of 42. So, we know that bees are exposed to multiple chemicals…"

Dr Harry Siviter

The phrase that stood out for me was "the average number of chemicals found in a honey bee colony is six" as clearly that did not make any sense scientifically. At least, not if the term 'chemical' was meant to refer to 'chemical substance'. I cannot claim to know just how many different substances would be found if one analysed honey bee colonies, but I am pretty confident the average would be orders of magnitude greater than six. An organism such as a bee (leaving aside for a moment the hive in which it lives) will be, chemically, 'made up' of a great many different proteins, amino acids, lipids, sugars, nuclei acids, and so forth.

"the average number of chemicals found in a honey bee colony is six"

From the context, I understood that Dr Siviter was not really talking about chemicals in general, but pesticides. So, I am (not for the first time) being a pedant in pointing out that technically he was wrong to suggest "the average number of chemicals found in a honey bee colony is six" as any suitably informed listener would have immediately, and unproblematically, understood what he meant by 'chemicals' in this context.

Yet, as a teacher, my instinct is to consider that programmes such as this, designed to inform the public about science, are not only heard by those who are already well-versed in the sciences. By its nature, BBC Inside Science is intended to engage with a broad audience, and has a role in educating the public about science. I also knew that this particular pedantic point linked to a genuine issue in science teaching.

A common alternative conception

The term chemical is not usually used in science discourse as such, but rather the term substance. Chemical substances are ubiquitous, although in most everyday contexts we do not come across many pure samples of single substances. Tap water is nearly all water, and table salt is usually about 99% sodium chloride, and sometimes metals such as copper or aluminium are used in more or less pure form. But these tend to be exceptions – most material entities we engage with are not pure substances ('chemicals'), rather being mixtures or even more complex (e.g., wood or carrot or hair).

In everyday life, the term chemical tends to be used more loosely – so, for example, household bleach may be considered 'a chemical'. More problematically 'chemicals' tends to be seen as hazardous, and often even poisonous. So, people object to there being 'chemicals' in their food – when of course their food comprises chemicals and we eat food to access those chemicals because we are also made up of a great many chemicals. Food with the chemicals removed is not food, or indeed, anything at all!

In everyday discourse 'chemical' is often associated with 'dangerous' (Image by Arek Socha from Pixabay)

So, science teachers not only have the problem that in everyday discourse the term 'chemical' does not map unproblematically on 'substance' (as it is often used also for mixtures), but even more seriously that chemicals are assumed to be bad, harmful, undesirable – something to be avoided and excluded. By contrast, the scientific perspective is that whilst some chemicals are potentially very harmful, others are essential for life. Therefore, it is unhelpful when science communicators (whether journalists, or scientists themselves) use the term 'chemical' to refer only to potentially undesirable chemicals (which even then tend to be undesirable only in certain contexts), such as pesticides which are found in, and may harm, pollinators.

I decided to dig into the background of the item.

The news item

I found a news item in 'the Conversation' that discuses the work.

Dr Siviter's Article in the Conversation

It began

"A doctor will always ask if you are on any other medication before they write you a prescription. This is because pharmaceuticals can interact with each other and potentially disrupt the treatment, or even harm the patient. But when agrochemicals, such as pesticides, are licensed for use on farms, little attention is paid to how they interact with one another, and so their environmental impact is underestimated."

Siviter, 2021

This seemed a very good point, made with an analogy that seemed very telling.

(Read about science analogies)

This was important because:

"We analysed data gathered in scientific studies from the last two decades and found that when bees are exposed to a combination of pesticides, parasites and poor nutrition, the negative impact of each is exacerbated. We say that the cumulative effect of all these things is synergistic, meaning that the number of bees that are killed is more than we would predict if the negative effects were merely added together."

Siviter, 2021

This seems important work, and raises an issue we should be concerned about. The language used here was subtly different from in the radio programme:

"Many agrochemicals, such as neonicotinoids, are systemic, meaning they accumulate in the environment over several months, and in some cases years. It is perhaps not surprising then that honeybee colonies across the US have on average six different agrochemicals present in their wax, with one hive contaminated with 39 [sic, not 42]. It's not just honeybees which are at risk, though: wild bees such as bumblebees are also routinely exposed."

Siviter, 2021

So, here it was not 'chemicals' that were being counted but 'agrochemicals' (and the average figure of 6 now referred not to the colony as a whole, but only to the beeswax.)

The meta-analysis

'Agrochemicals' was also the term used in the research paper in the prestigious journal Nature where the research had been first reported,

"we conducted a meta-analysis of 356 interaction effect sizes from 90 studies in which bees were exposed to combinations of agrochemicals, nutritional stressors and/or parasites."

Siviter, et al., 2021

A meta-analysis is a type of secondary research study which collects results form a range of related published studies and seeks to identify overall patterns.

The original research

Moreover, the primary study being referred to as the source of the dubious statistic (i.e., that "the average number of chemicals found in a honey bee colony is six") referred not to 'chemicals' but to "pesticides and metabolites" (that is, substances which would be produced as the bee's metabolism broke the pesticides down):

"We have found 121 different pesticides and metabolites within 887 wax, pollen, bee and associated hive samples….

Almost all comb and foundation wax samples (98%) were contaminated with up to 204 and 94 ppm [parts per million], respectively, of fluvalinate and coumaphos, and lower amounts of amitraz degradates and chlorothalonil, with an average of 6 pesticide detections per sample and a high of 39."

Mullin, et al., 2010

Translation and representation

Scientific research is reported in research journals primarily for the benefit of other researchers in the field, and so is formatted and framed accordingly – and this is reflected in the language used in primary sources.

A model of the flow of scientific to public knowledge (after McInerney et al., 2004)

Fig. 10.2 from Taber, 2013

It is important that science which impacts on us all, and is often funded from public funds, is accessible to the public. Science journalism, is an important conduit for the communication of science, and for his to be effective it has to be composed with non-experts in the public in mind.

(Read about science in public discourse and the media)

It is perfectly sensible and desirable for a scientist engaging with a public audience to moderate technical language to make the account of research more accessible for a non-specialist audience. This kind of simplification is also a core process in developing science curriculum and teaching.

(Read about representing science in the curriculum)

However, in the case of 'chemical' I would suggest scientists take care with using the term (and avoid it if possible), as science teachers commonly have to persuade students that chemicals are all around of us, are not always bad for us, are part of us, and are essential. That pesticides and their breakdown products have been so widely detected in bee colonies is a matter of concern, as pesticides are substances that are used because of their detrimental effects on many insects and other organisms that might damage crops.

Whilst that is science deserving public attention, there are a good many more than 6 chemicals in any bee colony, and – indeed – we would want most of them to be there.

References:

Balding black holes – a shaggy dog story

Resurrecting an analogy from a dead metaphor?

Keith S. Taber

Now there's a look in your eyes, like black holes in the sky…(Image by Garik Barseghyan from Pixabay)

I was intrigued by an analogy in a tweet

Like a shaggy dog in springtime, some black holes have to shed their "hair."

The link led me to an item at a webpage at 'Science News' entitled 'Black holes born with magnetic fields quickly shed them' written by Emily Conover. This, in turn, referred to an article in Physical Review Letters.

Now Physical Review Letters is a high status, peer-reviewed, journal.

(Read about peer review)

As part of the primary scientific literature, it publishes articles written by specialist scientists in a technical language intended to be understood by other specialists. Dense scientific terminology is not used to deliberately exclude general readers (as sometimes suggested), but is necessary for scientists to make a convincing case for new knowledge claims that seem persuasive to other specialists. This requires being precise, using unambiguous technical language."The thingamajig kind of, er, attaches to the erm, floppy bit, sort of" would not do the job.

(Read about research writing)

Science News however is news media – it publishes journalism (indeed, 'since 1921' the site reports – although that's the publication and not its website of course.) While science journalism is not essential to the internal processes of science (which rely on researchers engaging with each other's work though  scholarly critique and dialogue) it is very important for the public's engagement with science, and for the accountability of researchers to the wider community.

Science journalists have a job similar to science teachers – to communicate abstract ideas in a way that makes sense to their audience. So, they need to interpret research and explain it in ways that non-specialists can understand.

The news article told me

"Like a shaggy dog in springtime, some black holes have to shed…
Unlike dogs with their varied fur coats, isolated black holes are mostly identical. They are characterized by only their mass, spin and electric charge. According to a rule known as the no-hair theorem, any other distinguishing characteristics, or "hair," are quickly cast off. That includes magnetic fields."

Conover, 2013

Here there is clearly the use of an analogy – as a black hole is not the kind of thing that has actual hair. This would seem to be an example of a journalist creating an analogy (just as a science teacher would) to help 'make the unfamiliar familiar' to her readers:

just as

dogs with lots of hair need to shed some ready for the warmer weather (a reference to a familiar everyday situation)

so, too, do

black holes (no so familiar to most people) need to lose their hair…

(Read about making the unfamiliar familiar)

But hair?

Surely a better analogy would be along the lines that just as dogs with lots of hair need to shed some ready for the warmer weather, so to do black holes need to lose their magnetic fields…

An analogy is used to show a novel conceptual structure (here, relating to magnetic fields around black holes) maps onto a more familiar, or more readily appreciated, one (here, that a shaggy dog will shed some of its fur). A teaching analogy may not reflect a deep parallel between two systems, as its function may be just to introduce an abstract principle.

(Read about science analogies)

Why talk of black holes having 'hair'?

Conover did not invent the 'hair' reference for her ScienceNews piece – rather she built her analogy on  a term used by the scientists themselves. Indeed, the title of the cited research journal article was "Magnetic Hair and Reconnection in Black Hole Magnetospheres", and it was a study exploring the consequences of the "no-hair theorem" – as the authors explained in their abstract:

"The no-hair theorem of general relativity states that isolated black holes are characterized [completely described] by three parameters: mass, spin, and charge."

Bransgrove, Ripperda & Philippov, 2021

However, some black holes "are born with magnetic fields" or may "acquire magnetic flux later in life", in which case the fields will vary between black holes (giving an additional parameter for distinguishing them). The theory suggests that these black holes should somehow lose any such field: that is, "The fate of the magnetic flux (hair) on the event horizon should be in accordance with the no-hair theorem of general relativity" (Bransgrove, Ripperda & Philippov, 2021: 1). There would have to be a mechanism by which this occurs (as energy will be conserved, even when dealing with black holes).

So, the study was designed to explore whether such black holes would indeed lose their 'hair'.  Despite the use of this accessible comparison (magnetic flux as 'hair'), the text of the paper is pretty heavy going for someone not familiar with that area of science:

"stationary, asymptotically flat BH spacetimes…multipole component l of a magnetic field…self-regulated plasma…electron-positron discharges…nonzero stress-energy tensor…instability…plasmoids…reconnection layer…relativistic velocities…highly magnetized collisionless plasma…Lundquist number regime…Kerr-schild coordinates…dimensionless BH spin…ergosphere volume…spatial hypersurfaces…[…and so it continues]"

(Bransgrove, Ripperda & Philippov, 2021: 1).

"Come on Harry, you know full well that 'the characteristic minimum plasma density required to support the rotating magnetosphere is the Goldreich-Julian number density' [Bransgrove, Ripperda & Philippov, 2021: 2], so hand me that hyperspanner."
Image from Star Trek: Voyager (Paramount Pictures)

Spoiler alert

I do not think I will spoil anything by revealing that Bransgrove and colleague conclude from their work that "the no-hair theorem holds": that there is a 'balding process' – the magnetic field decays ("all components of the stress-energy tensor decay exponentially in time"). If any one reading this is wondering how they did this work, given that  most laboratory stores do not keep black holes in stock to issue to researchers on request, it is worth noting the study was based on a computer simulation.

That may seem to be rather underwhelming as the researchers are just reporting what happens in a computer model, but a lot of cutting-edge science is done that way. Moreover, their simulations produced predictions of how the collapsing magnetic fields of real black holes might actually be detected in terms of the kinds of radiation that should be produced.

As the news item explained matters:

Magnetic reconnection in balding black holes could spew X-rays that astronomers could detect. So scientists may one day glimpse a black hole losing its hair.

Conover, 2013

So, we have hairy black holes that go through a balding process when they lose their hair – which can be tested in principle because they will be spewing radiation.

Balding is to hair, as…

Here we have an example of an analogy for a scientific concept. Analogies compare one phenomenon or concept to another which is considered to have some structural similarity (as in the figure above). When used in teaching and science communication such analogies offer one way to make the unfamiliar familiar, by showing how the unfamiliar system maps in some sense onto a more familiar one.

hair = magnetic field

balding = shedding the magnetic field

Black holes are expected to be, or at least to become, 'hairless' – so without having magnetic fields detectable from outside the event horizon (the 'surface' connecting points beyond which everything, even light, is unable to 'escape' the gravitational field and leave the black hole). If black holes are formed with, or acquire, such magnetic fields, then there is expected to be a 'balding' process. This study explored how this might work in certain types of (simulated) black holes – as magnetic field lines (that initially cross the event horizon) break apart and reconnect. (Note that in this description the magnetic field lines – imaginary lines invented by Michael Faraday as a mental tool to think about and visualise magnetic fields – are treated as though they are real objects!)

Some such comparisons are deliberately intended to help scientists explain their ideas to the public – but scientists also use such tactics to communicate to each other (sometimes in frivolous or humorous ways) and in these cases such expressions may do useful work as short-hand expressions.

So, in this context hair denotes anything that can be detected and measured from outside a black hole apart form its mass, spin, and charge (see, it is much easier to say 'hair')- such as magnetic flux density if there is a magnetic field emerging from the black hole.

A dead metaphor?

In the research paper, Bransgrove, Ripperda and Philippov do not use the 'hair' comparison as an analogy to explain ideas about black holes. Rather they take the already well-established no-hair theorem as given background to their study ("The original no-hair conjecture states that…"), and simply explain their work in relation to it  ("The fate of the magnetic flux (hair) on the event horizon should be in accordance with the no-hair theorem of general relativity.")

Whereas an analogy uses an explicit comparison (this is like that because…), a comparison that is not explained is best seen as a metaphor. A metaphor has 'hidden meaning'. Unlike in an analogy, the meaning is only implied.

  • "The no-hair theorem of general relativity states that isolated black holes are characterized by three parameters: mass, spin, and charge";
  • "The original no-hair conjecture states that all stationary, asymptotically flat BH [black hole] spacetimes should be completely described by the mass, angular momentum, and electric charge"

(Read adbout science metaphors)

Bransgrove and colleagues do not need to explain why they use the term 'hair' in their research report as in their community it has become an accepted expression where researchers already know what it is intended to mean. We might consider it a dead metaphor, an expression which was originally used to imply meaning through some kind of comparison, but which through habitual use has taken on literal meaning.

Science has lots of these dead metaphors – terms like electrical charge and electron spin have with repeated use over time earned their meanings without now needing recourse to their origins as metaphors. This can cause confusion as, for example, a learner may  develop alternative conceptions about electron spin if they do not appreciate its origin as a metaphor, and assumes an electron spins in the same sense as as spinning top or the earth in space. Then there is an associative learning impediment as the learner assumes an electron is spinning on its axis because of the learner's (perfectly reasonable) associations for the word 'spin'.

The journalist or 'science writer' (such as Emily Conover), however, is writing for a non-specialist readership, so does need to explain the 'hair' reference.  So, I would characterise the same use of the terms hair/no-hair and balding as comprising a science analogy in the news item, but a dead metaphor in the context of the research paper. The meaning of language, after all, is in the mind of the reader.

Work cited: