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.