In the New York Times this week there’s an article* by Dennis Overbye on Erik Verlinde and his paper on the idea that gravity is not a force at all, but a consequence of thermodynamics. You can think of it as an extreme take on one of the directions a lot of the research (that I’ve mentioned a number of times has been going on in string theory) has been pointing, although I think it is safe to say that there’s a lot to be done on making the statement a concrete one that you can do physics with. I think it contains the germs of the right thing we’re all reaching for, but does not quite get there yet. We’re now quite routinely formulating some of the key physics of gravity entirely as physics of a completely non-gravitational dual theory – this is the content of what we call holography – and in particular the quantum physics of black holes in those settings get holographically mapped to the thermodynamics of the non-gravitational physics. This is the basis of the tools that we’ve been applying to studying aspects of phenomena showing up in various experimental systems in nuclear physics and cold atomic physics (and studies of phenomena relevant to various condensed matter systems are also being done). I’ve told you about a lot of this in various posts. (Some of them are listed below.) Running this the other way, the model non-gravitational systems (certain gauge theories at strong coupling and with large rank gauge groups) can be thought of as examples of how gravity (and space-time itself) is really an emergent phenomenon, appearing simply as an economical description of physics that has no gravity in it at all. If you like, gravity is simply a consequence of pragmatism. For moderate or small coupling, and/or small rank, there’d be no need for it in these systems – you’d simply do standard field theory computations – but at some point it becomes better and better to think in terms of the language of gravity in a nice smooth space-time that emerges in the limit of strong coupling. You can ask – is it real? Is the space-time really there, and is the gravity in it (i.e., its dynamics) really real? Is there secretly a black hole (however approximate) lurking in a little fifth dimension that opens up near the experiments that touch upon the regime that has these dual descriptions (at least qualitatively)? See my earlier post on that issue. Real is a funny word.
Verlinde is not simply restating this familiar (to many of us working in string theory) and highly useful quantum gravity phenomenon. He’s, as I understand it, trying to start at a more basic level and find a way of doing away with gravity in a much more general setting. Have a look at the article and the paper. My feeling is that we do need to take the hints and examples given to us by holography and gauge/gravity dualities and see if there is a way of saying something stronger and more generally applicable, and so Erik (and the many others who have been thinking about the issues over the years) is on the right track. But there is a lot of work to do.
*Thanks Shelley, Krzysztof.
Some Related Asymptotia Posts (not exhaustive):