Thursday, January 12, 2006

Gold, Myrrh and Frankincense

I hope everyone had happy holidays and a great start into 2006! I haven't been posting here for a while, so this is going to be a bit like a rather delayed Santa's bag with something of everything in it.

First, I have been reading in a very interesting book during the last few weeks; I am speaking of G.E. Volovik's The Universe in a Helium Droplet. There are lots of material in there, most of which I am probably not able to appreciate properly, since my knowledge of superfluids is extremely limited. What I find most interesting are the analogies with the electroweak sector of the Standard Model and with General Relativity that occur in the effective theory of quasiparticles in superfluid 3He. While there are a lot of differences with the real universe (most importantly significant violations of the effective Lorentz symmetry), the possibility of having a "relativistic" QFT emerge from a non-relativistic condensed matter system is intriguing, and certainly suggests that the image that Volovik calls "anti-GUT", namely that instead of becoming simpler and more symmetric, nature becomes less symmetric at higher energies. Moreover, there is really no reason to believe that the sequence (effective QFT+GR) << (NRQM system) << (SM+GR) has to stop there, or in fact anywhere. If the Standard Model is an effective theory for something else (say strings, or whatever alternative you prefer), why should this something (just like the Helium atoms) not be reducible to another QFT, which is effective as well? This is a slightly disturbing image, without any truly fundamental physics (except for Quantum Theory, which occurs on, and remains the same at, all scales). But maybe that is how the universe really looks; but then, again, it is unlikely that we will ever know either way.

Second, as if the truly heroic feat of computing the O(α4) contributions to the leptons' anomalous magnetic moment was not enough, T. Kinoshita and collaborators have begun to calculate the O(α5) contributions! This needs some very advanced automation techniques; since my research revolves around automating perturbative calculations, I feel able to appreciate what they are doing, and all I can say is that it is truly impressive: Most people (or at least I) would not want to touch a four-loop diagram with a bargepole, whereas Kinoshita wade right into the midst of the five-loop diagrams. Did I say heroic? I really mean it.

Third, when entering "lattice qcd" into Google, a post on this blog turns up at number 15 of 626,000 -- flattering, but undeserved. It appears that with the current blogging craze, Google are overweighting hits from blogs in their results.

So this post wasn't something of everything, but just three things; so maybe it is more like the Magi's gifts. (Which is which? That's your guess.) And with that, a happy new year again to everyone!


Anonymous said...

[Georg: I found two editing mistakes that I somehow missed in previewing (which drives me nuts). Could I ask you to replace the previous revision of this comment with the following? Thanks.]

Does Volovik discuss the apparent circularity of the viewpoint he presents? My sense is that these are largely formal discoveries, and it is unclear how they should be interpreted.

At this juncture it certainly seems reasonable to view known fundamental physics—in some sense—as emergent from a substrate, but to say that the substrate might just as well be a non-relativistic condensed matter system, because such a system can emulate relativistic quantum fields at low energy, seems facile to say the least. I assume Volovik is really just posing a question—what does all this truly mean?—without committing himself to any clear position.

(For one notion of where this might be leading, see this bit of conceptual noodling and the following comments.)

Anonymous said...

More in a similar vein (via Christine Dantas):

Massive particles in acoustic space-times emergent inertia and passive gravity
(gr-qc/0601034; authors: Mordehai Milgrom)

Also, at Perimeter Institute (Nov 2005):
Emergence of Spacetime Workshop

Milgrom is well known in astrophysics as an originator of MOND.

Georg said...


Sorry, Blogger doesn't seem to allow editing of comments; I posted your new comment alongside the old one. (I can delete the old one, if you prefer, but I can't change the text of a comment).

As far as I understand him, Volovik doesn't propose that the substrate of reality might be a non-relativistic condensed matter system; all he proposes is the viewpoint which he calls "anti-GUT", namely that physics at higher energies may well be less (rather than more) symmetric than at low energies, and that many features of physics that we take as fundamental (general covariance, gauge invariance) may in fact be emergent.

The extrapolation to an infinite tower of effective theories is mine, not his; sorry if this wasn't clear from the original post. It isn't such a far-fetched idea, though, and has in fact been debated by philosophers of physics (cf. e.g. this paper and references therein).