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S.Daedalus is offline
Jun3-11, 07:26 AM
P: 210
I'm not very familiar with Wilczek's 'Grid' idea, but it seems to fit right in with what to me seems a recent (perhaps re-) emergence of, well, emergentist notions about 'fundamental' physics, where perhaps the core idea is that fundamental degrees of freedom really aren't, but are best thought of as collective excitations of some -- usually not further elaborated upon -- more fundamental stuff, typically thought of as a lattice of some sort, or an analogue to a condensed state of matter.

Such ideas have several pleasing properties, and some which make them somewhat unpalatable to a lot of physicists. One of the perhaps most striking features is that whatever emergentist framework one considers, you get a cosmological constant with relative ease -- in condensed matter systems, like, for instance, a cold quantum liquid, the pressure in general vanishes; however, if it is only a droplet, one gets surface corrections scaling as an inverse power of the droplet size, which indeed is the correct behaviour for a cosmological constant. Similarly, in the entropic gravity framework, dark energy is considered to be the entropic force exerted by the cosmological horizon, which again yields the right order of magnitude value.

On the other hand, generically, symmetries thought to be exact, such as Lorentz or gauge symmetry, turn out to be only approximate in condensed matter schemes, for instance -- there, considering a non-relativistic substrate, in the vicinity of Fermi points, quasiparticles with Lorentzian propagators emerge, but only at sufficiently low temperature. Indeed, one often finds what is dubbed an 'anti-GUT' behaviour in condensed matter systems: rather than 'breaking down' from more to less symmetry as the system cools, new symmetries emerge as it condenses, in stark contrast to the usual assumption that the higher the energy, the higher the symmetry (the GUT viewpoint).

One interesting feature about condensed matter models is their universality -- that at low energy, their behaviour is almost totally independent from their underlying constituents; rather, they fall within one of a small number of universality classes, some of which quite generically yield behaviour very much like what we observe in particle physics -- systems with Fermi points, for instance.

Currently, there are several distinct but related (or so it seems to me) approaches being pursued -- G. E. Volovik is perhaps the champion of straight-up condensed matter analogies, with his book 'The Universe in a Helium Droplet' providing an exhaustive (and, despite the somewhat droll name, serious and technical) overview of the field (the main ideas of which are also present in this short article), Xiao-Gang Wen's idea of string-net condensates (which I think is related, but I am not very knowledgeable about), 'emergent gravity' approaches of Sakharov and Jacobson/Padmanabhan/Verlinde, both of which may be argued to be extendible to other forces, as well, together with other analogue gravity models (e.g. Liberati et al, see also this video), and perhaps one might also mention the Causal Dynamical Triangulations approach to quantum gravity, due to Loll, Ambjorn et al, in this vein.

Oh, and yes, 'ether' is indeed a word that crops up often in this context, see for instance in this article by Jegerlehner, or this one by Levin/Wen.

This just to illustrate that there are indeed 'serious scientists' working on related approaches -- sorry if I went a bit overboard there with my free associations, it's just that it's a topic I'd been wanting to discuss for quite some time. Feel free to disregard this though if it's too off-topic...