On Cox vs. Swans

The other controversial thing this week that I shouldn’t get involved in is the debate over whether Brian Cox is talking nonsense in a recent discussion of the Pauli Exclusion Principle. Tom at Swans on Tea kicked this off with an inflammatory title, and Cox turned up in the comments to take umbrage at that. Sean Carroll provides a calmer and very thorough discussion, the comments to which include a number of well-known science popularizers duking it out.

My take on it is basically the same as Tom and Jim Kakalios in Sean’s comments: unless the two particles you’re talking about are within about a de Broglie wavelength of each other, Pauli exclusion doesn’t really matter. This was actually a question at my Ph.D. defense, because a big part of my thesis was about quantum statistical effects in ultracold collisions, where Pauli exclusion forbids certain types of collisions from taking place. When we think about that sort of thing, we require that the two colliding atoms be in an overall antisymmetric wavefunction, but we don’t worry about the state of other atoms of the same element elsewhere in the apparatus, because they’re so far away that they don’t change the energy states available to the colliding atoms in any significant way.

In Tom’s comments, Cox insists that hes right, and says that the whole thing is worked out in detail in his new book. I haven’t read the new book, though I’ve been offered a copy by a publicist, so we’ll see. I think Sean and Matt Leifer at comment #6 have covered pretty much all of the bases, though, so I’m inclined to think that Cox is just wrong. There may be a narrow philosophical sense in which he’s correct, but I don’t think it’s useful, and given that there are large numbers of people working scams based on woo-woo notions of quantum phenomena enabling paranormal abilities, I think this is a bad direction to take popular quantum mechanics.

Comments

  1. #1 Matt Leifer
    February 24, 2012

    Why do particle physicists write popular books about quantum theory, but experts in quantum theory don’t write popular books about particle physics?

    Which is to say, if you want to read a book in which the Feynman sum-over-paths formalism is treated as the “literal truth” about what is going on in the world according to quantum theory then you might enjoy Cox and Forshaw’s book. It is well-written, but its not saying anything you haven’t read in many other places.

    I should point out that Forshaw was my 1st year undergrad Tutor at Manchester, so I want to like the book, but I can’t seriously recommend it above dogphysics, or the imaginary perfect book about quantum theory that I will never write.

    Here’s another question: Why does every author of popular physics books feel the need to write a book about relativity and a book about quantum theory? (In case you are not aware, Cox and Forshaw’s previous book was about relativity — did you think I was talking about someone else?).

  2. #2 Chad Orzel
    February 24, 2012

    Here’s another question: Why does every author of popular physics books feel the need to write a book about relativity and a book about quantum theory?

    Cosmology. Don’t forget cosmology.

    In other news, I’m pleased to announce my next project, How to Teach Your Dog About the Origin and Eventual Fate of the Universe

    (Not really.)

  3. #3 Eric Lund
    February 24, 2012

    Why does every author of popular physics books feel the need to write a book about relativity and a book about quantum theory?

    Empirical evidence shows that such books (and, as Chad correctly points out, books on cosmology) generally sell better than equivalent books about other areas of physics. While I personally might be interested in a hypothetical How to Teach Your Dog Plasma Physics, I doubt it would find anywhere near the audience that Chad’s actual books have found, to say nothing about Stephen Hawking’s popular books.

  4. #4 Joerg Heber
    February 24, 2012

    Hi Chad

    My gut feeling, and it’s not more than that, sides with you. Brian Cox’ argument would require electrons across the universe to occupy energy states that are extremely finely separated. And in my view this is just against other principles such as Heisenberg. So I agree, if the separation of the electrons becomes too large the interpretation Cox its foreard doesn’t make sense. But the whole discussion really shows nicely how little we really understand about such fundamental questions…

    Joerg

  5. #5 RM
    February 24, 2012

    Why does every author of popular physics books feel the need to write a book about relativity and a book about quantum theory?

    Writing a pop-sci book is hard. If you’re going to the effort to write a book for the general public, why not write it on the fundamental, important things? And to paraphrase Rutherford, current physics is relativity, quantum mechanics, or stamp collecting. (Forget the reader, who wants to write “The Layman’s Guide to the Rydberg Constant”?)

    Also, relativity and quantum mechanics is hard to explain to the general public, so smart people look at previous popularization attempts and say “Those explanations are crap, and rely too heavily on suboptimal-conceptualization-A/don’t frame it under preferred-conceptualization-B. A german shepherd could do better!” There’s always room for more. I’ve read a number of popular science books on relativity/QM and am only marginally more informed than when I started.

    That’s also why you get the cosmology books. Big questions like “why are we here, and what’s the point of the universe, anyway?” are interesting to address. And we know so little there’s always room for another self-aggrandizer’s opinion on it.

  6. #6 Matt Leifer
    February 25, 2012

    But I would have thought that the market for books on relativity and quantum theory was saturated. I would also like to point out that it is not just physicists that do this. Science writers who are not specialists in physics also go for these areas, and they don’t have the excuse that they think they can present things more accurately than anyone else.

    As a case in point, consider the two books: “Uncertainty” by David Lindley and “Quantum” by Manjit Kumar. Both came out at roughly the same time and cover almost identical material. They are both decent books, but if we take a random selection of sentences from each book and play a game where you have to identify which book they come from, I suspect hardly anyone would do better than 50/50 success rate.

  7. #7 robert marischen
    February 26, 2012

    Recently read that Dr. Frank Wilczek of MIT has found that Time can be crystalized.

    Does this mean that Time has mass and can be converted to another phase like water can be converted to ice?

  8. #8 tcmJOE
    February 26, 2012

    I’d read “How to Teach Your Dog Plasma Physics”. A plasma can have two totally different temperatures at the same time for the ions and the electrons, how cool is that?!?

    I’d also (legitimately) be interested in a good layman’s solid state/condensed matter book–the field as a whole seems to be taught so poorly and there’s a point to be made that a lot of subtle, interesting physics lies in that slightly magnetized block of steel (or that finely made transistor) on my table.

  9. #9 tcmJOE
    February 26, 2012

    I’d read “How to Teach Your Dog Plasma Physics”. A plasma can have two totally different temperatures at the same time for the ions and the electrons, how cool is that?!?

    I’d also (legitimately) be interested in a good layman’s solid state/condensed matter book–the field as a whole seems to be taught so poorly and there’s a point to be made that a lot of subtle, interesting physics lies in that slightly magnetized block of steel (or that finely made transistor) on my table.

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