How a porcupine talks

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How a physicist talks:

[If you're not familiar with her work, Sabine Hossenfelder's blog, book, and videos are terrific.]

And some "behind the scenes outtakes", suggesting that Teddy Bear's "best of" video might be a bit selective:


  1. Philip Taylor said,

    January 1, 2021 @ 3:27 pm

    The porcupine was wonderful — I don't think I have ever seen film of such a placid specimen before. But the would-be physicist's "the sun is so much heavier than earth" ? Surely "the sun has a far greater mass than earth". I don't think that it is possible to compare the weights of two planets, is it ? If it were, how would one go about establishing a common gravitational field to which each was subject ?

  2. Nat J said,

    January 1, 2021 @ 5:15 pm

    Phillip Taylor – Excellent observation. Now, it’s not at all difficult, in the abstract, to subject the sun and earth to a common gravitational field. Just pick an arbitrary mass for your third body, and then pick an arbitrary distance between the center of mass of this third body and the sun. Use the same distance for the third body and earth. The calculation is trivial and you will always find that the weight of the sun is many times the weight of the earth.
    But while you could easily do this, I don’t doubt that you’re right and that Sabine. Hossenfelder intended to compare the masses of the sun and earth.

  3. Victor Mair said,

    January 1, 2021 @ 7:14 pm

    Teddy's quite a talker!

    Did anyone else see quill marks on the owner's hands and legs?

    I heard her say "ouch" once.

  4. ngage92 said,

    January 2, 2021 @ 4:53 am

    Philip's comment about "would-be physicist" reaches absolutely astronomical, Alan Partridge-like levels of self-satisfied obliviousness (as well as sexism_ – Sabine Hossenfelder has done post-doctoral work in particle physics so I'm quite sure she knew what she was talking about. Besides, "heavier" can plainly mean either "X has a greater weight than Y" AND "X has a greater mass than Y", so the comment fails with respect to English usage as well as physics.

  5. ~flow said,

    January 2, 2021 @ 4:56 am

    I think that what Ms Hossenfelder is talking about is exactly this kind of nitpicking of some people about weak points in the wording. Like in, "I want to lose weight"—"What you want to lose is mass, not weight" and so on. Since the inertia and the weight of mass are always, to the best of our understanding, coupled, we can take one for the other, can't we? Of course, to substitute weight for mass, we have to assume an infinitely homogeneous field of gravitation where to place the two bodies side by side without them influencing each other, and then weigh them using an appropriately sized balance which is somehow fixed in empty space…

  6. Philip Taylor said,

    January 2, 2021 @ 5:31 am

    I don't normally respond to personal attacks, but I do take exception to ngage92's comments above.

    From earlier discussions on this forum I now know that whilst the difference between mass and weight was drilled into British children of my generation at an early age, most modern American children are blissfully unaware of the difference. But if, as ngage92 asserts, Sabine Hossenfelder has done post-doctoral work in particle physics, then either she was patronising her audience by using a term that she thought they would understand (weight) in preference to one that she felt was too technical for a lay audience (mass) or she herself is unaware of the difference, something that would seem impossible if ngage92's assertion is correct.

    As to the accusation of sexism, I challenge ngage92 to adduce any evidence whatsoever to support his baseless accusation — I wrote of "this would-be physicist", not "this woman pretending to be a physicist" or any similar phrase that might have sought to draw attention to her sex in a negative way.

    As to «"heavier" can plainly mean either "X has a greater weight than Y" AND "X has a greater mass than Y" so the comment fails with respect to English usage as well as physics » — the statement itself is meaningless, since it seeks to contrast something with something else through its use of either, yet fails to inform the reader what that something else is by any corresponding use of "or". And from a scientific perspective, the statement is about as false as a statement can get — "heavier" means "weighs more" and tells us nothing at all about mass unless we can be certain that both weights were measured in an identical gravitional field. Science requires precision — lose the latter and the science goes out the window, leaving just amateurish arm-waving behind.

    Sorry, I felt that that needed to be said.

  7. Twill said,

    January 2, 2021 @ 5:49 am

    Ms Hossenfelder doesn't quite capture that the essence of pedantry is the context and attitude with which a correction or clarification is made rather than the information itself. A much better example that comes to mind is, in response to being wished a happy new year, to condescendingly remark that Jan 1 on the Gregorian calendar has on no astronomical basis any better claim for being the start of a new year than another, as though the wellwisher were making an empirical, astronomical claim that the Gregorian New Year is an objective fact and not participating in a cultural observance, and they were delivering a pertinent and informative insight.

  8. Twill said,

    January 2, 2021 @ 6:00 am

    *Dr. Hossenfelder's *video*, I really ought to say, though I can't claim to know if she does or doesn't embody the concept of pedantry.

  9. Nat J said,

    January 2, 2021 @ 9:33 am

    I'm afraid that I overlooked the extraordinary phrase "would-be physicst" in my eagerness earlier. For anyone who watches the video there can be no doubt that Sabine Hossenfelder is perfectly aware of the difference between weight and mass. That is precisely her sixth point in the video! I assumed that she had simply made a small error. Of course, I should have paused to wonder whether it was more likely that she or I were making an error. For the sake of comparison, here is the would-be physicist Feynman. "Then there is that other, the μ-meson, the muon, which has a mass much higher, 206 times as heavy as an electron." (p 56, 6 Easy Pieces, 2011)

  10. Nat J said,

    January 2, 2021 @ 9:47 am

    I didn't notice any quill marks, but I was certainly struck by how nonchalant the owner was in petting the porcupine, and I flinched a bit. It seems that porcupines have some control over their spines, and I imagine that Teddy has his set in a safe, relaxed posture.

    After rewatching, I see marks on the owner's feet in the third video. They look pretty painful.

  11. John Shutt said,

    January 2, 2021 @ 11:08 am

    Theoretical physics does tend to emphasize, well, theory rather than practice. I've noticed this can result in sententious theory-based pronouncements about how people get things wrong that people are right about in practice. I remember a video explaining all about how people think if you get close to a mirror you can see more in it whereas, actually, this can be proven false with simple geometry. The trouble with that is, in practice, the closer you are to the mirror the more you can see by moving your head around (say, up and down or side to side by a few inches).

    When someone says "I want to lose weight", they're likely more concerned with downward pull on their body than with, say, their inertia when walking on ice; though… actually, they're likely more concerned with volume than with either weight /or/ mass.

  12. Matteo said,

    January 2, 2021 @ 11:40 am

    I believe P. Taylor's comment on "would-be-physicist" can be rapidly dismissed by considering how Hossenfelder is indeed a physicist (and one of the most renowned). I see no need to further analyse the matter.

  13. John Shutt said,

    January 2, 2021 @ 12:59 pm

    Hossenfelder says up-front she's demonstrating how to be just as annoying as a real physicist; the difficulty when studying the rest of the video is that she does such a good job of it, one can't tell whether she means what she's saying. Criticisms of the later material would be evidence of success on her part, but only if the thing criticized was intentional.

  14. Gregory Kusnick said,

    January 2, 2021 @ 1:03 pm

    Philip, perhaps you might look at Hossenfelder's blog as an opportunity to educate yourself about how real working physicists actually talk (as distinct from how you imagine they ought to talk).

  15. ~flow said,

    January 2, 2021 @ 2:03 pm

    In order to bring a modicum of relaxation onto this heated discussion, for those who have never heard of or listened to Frau Dr Hossenfelder, she can be surprisingly dead-pan. I think some in the audience may have mistaken her quotes of annoying party acquaintances as being seriously endorsed statements by herself. Secondly, as in Buddhism where one is taught about anātman/anattā or "no self, I, my, me", teachers still refer to themselves and associated things as "self, I, my, me", just to make them understood without contorting language. I think it's quite alright in everyday speech to refer to an object's mass using its weight as a stand-in, and that should be granted to physicists as well whenever there is no danger of misunderstanding.

    As for the claim that comparing the weights of two planets is not meaningful because "how would one go about establishing a common gravitational field to which each was subject"—well, being physically impossible hasn't kept physicists and metrologists from defining physical units; case in point: the recently obsoleted definition of the Ampere which relied on two parallel, infinitely long wires of infinitesimal thickness, placed one meter apart. I think if this counts, then planets do have a weight.

    There's a small wooden boat landing stage in the river not far from where I'm writing this, and some wise guy thought it expedient to give its maximum safe load as "5000N". Good luck figuring out how much that is in everyday units. "500kg" would have been wrong in the annoying-physicist way but "5000N" is wrong for everybody else.

  16. Philip Taylor said,

    January 2, 2021 @ 2:09 pm

    I have spent much of my professional life working with physicists, so can say with some confidence that I am quite familiar with how they "actually talk". Not one with whom I have worked would ever have spoken of the weight of the sun (or of a planet) when he or she was actually referring to its mass (all were British, which might in part explain this).

    In the context in which Dr Hossenfelder speaks of "the sun [being] much heavier than the earth", the very phenomenon to which she is referring (the force of gravity) is one of the two causes of weight (the other, of course, being mass), not an effect.

  17. Gregory Kusnick said,

    January 2, 2021 @ 3:20 pm

    An Ngram search for "heavy planet" shows that the phrase has been used by scientists (including Stephen Jay Gould and J.B.S. Haldane) for roughly two centuries.

  18. Philip Taylor said,

    January 2, 2021 @ 3:46 pm

    Google ngrams for "weight of a planet" v. "mass of a planet" and "weight of the sun" v. "mass of the sun" shew a marked preference for "mass" in both cases.

  19. anonymouse said,

    January 2, 2021 @ 6:08 pm

    Dr. Hossenfelder obviously knows the difference between mass and weight because that topic is exactly what #6 is about. She is also not British (and probably not a native speaker of English) so Philip Taylor's comments about how British physicists speak would not apply. (As a tangent, I would be very interested in hearing how non-English languages distinguish between those two concepts.)

    My first take on the video was that Dr. Hossenfelder was obviously a physicist making fun of other physicists. It is so strange to me that Philip Taylor and others assumed that she was a "would-be" physicist or a "Ms." This is her long list of physics publications:, so it seems that I am right. Hmmm, why would someone assert, before doing a bare minimum of fact-checking, that a woman speaking about physics who was doing a spot-on job of parodying physicists was not in fact a physicist?

    But perhaps Philip Taylor is from 100 years ago, as evinced by his use of the word "shew." Just so you know, many physicists are women now. Also, it is generally considered polite to read the entire post or finish the entire video before commenting.

  20. Philip Taylor said,

    January 3, 2021 @ 3:12 am

    I think that continuing this debate is unhelpful. I would simply add that at no point did I refer to Dr Hossenfelder as "Ms", tho' I did assume that she was not a physicist — not because of her sex, but because she was setting out to parody physicists and I therefore assumed that she was a satirist or similar. In brief, my criticism was solely of her use of the word "weight" where "mass" was required, and I would have made exactly the same criticism had the speaker been a Nobel prize-winning bald white male Ph.D. D.Phil., D.Sci and bar, FRS of 90+ years.

  21. David L said,

    January 3, 2021 @ 11:39 am

    Philip Taylor: She did not use the word 'weight' where 'mass' was required. She referred to the Sun being 'heavier' than the Earth. As Anonymouse suggested, perhaps this was simply because she is not a native English speaker. I don't know enough German to say if that language has a convenient distinction between the two concepts.

    Kind of ironic, is it not, that the purpose of the video was to make fun of people who like to make a big deal about pedantic and fussy objections that really don't matter.

  22. Philip Taylor said,

    January 3, 2021 @ 12:12 pm

    You are quite right, David, she used the word "heavier" and not the word "weight"; I referred to "heavier" in my first comment, and then erred in my most recent. And indeed, the German word for "heavier" might also indicate "of greater mass" as well as "of greater weight" — not being a fluent German speaker, I do not know. I would respectfully suggest that an objection to the use of "heavier" where "of greater mass" is required is neither pedantic nor fussy, but as Dr Hossenfelder is not an L1 English speaker such a mistake can, and perhaps should, be overlooked.

  23. Dara Connolly said,

    January 3, 2021 @ 4:17 pm

    On the question of whether "heavier" can mean "more massive", as in "the sun is so much heavier than earth", consider heavy water (deuterium oxide), heavy metals (lead, mercury, gold, etc.), heavy elements (elements heavier than iron) and super-heavy elements (transactinic elements with atomic numbers >103).

    In all of these usages the term "heavy" relates to the atomic (or molecular) mass of the substance. Heavy elements are "heavy" independent of the presence or absence of an external gravitational field.

    If "heavier" can correctly be used to mean "more massive", then Ms Hossenfelder's usage is quite correct.

  24. Peter Erwin said,

    January 4, 2021 @ 7:47 am

    Dara Connolly pointed out the common use of "heavy" for more massive elements and molecules. A cursory search of the NASA Astrophysics Database (which indexes a large subset of physics in addition to pretty much everything astronomical) shows that "heavy" (and "light") are also used, at least on occasion, to describe black holes (e.g., Faccioni & Rossi 2017, "Light or heavy supermassive black hole seeds: the role of internal rotation in the fate of supermassive stars") and galaxies (Monari et al. 2018, "The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way").

    A full-text search for the exact phrase "heavier star" turns up over 75 hits, starting way back in 1911 with a meeting of the Royal Astronomical Society, in which you can read "Mr. Eddington" [I assume this is Arthur Eddington] discussing someone else's paper and continually referring to "heavy" and "light" stars, along with "heavy" and "light" gases, and even, I fear, using the dreadful term "weight" in this context ("a mixture of gases with molecules differing in weight").

    So I'm afraid that actual astronomers and astrophysicists are prone to using "heavy" and "light" to describe masses of astronomical objects, including stars. In keeping with the theme of probably unnecessary pedantry, I will point out that Dr. Hossenfelder is indeed German, and is a specialist in general relativity and quantum gravity, not particle physics or astronomy; nonetheless, her usage in the context of things like stars is not terribly unusual.

  25. Philip Taylor said,

    January 4, 2021 @ 8:19 am

    In the light of the above, and in the light of earlier related comments, I feel that I should (at least retrospectively) withdraw my initial comment and apologise to Dr Hossenfelder for the implied criticism therein.

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