81. Edward Witten’s talk on 3D gravity
COND-MAT, HEP-TH/PH — By Dmitry Podolsky on November 7, 2008 at 4:00 pm
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Fascinating video of Edward Witten’s talk on 3D quantum gravity given at the Princeton Institute for Advanced Study.The picture that goes back to Deser, ‘t Hooft and Jackiw is the following. Since there are no dynamical (propagating) degrees of freedom in 3D gravity, the physics of the latter is completely defined by matter fields. Matter particle creates a conical singularity around it, and, in a sence, the 3D quantum gravity is the theory of scattering of these conical deffects on each other.
Later, Witten developed this picture and proposed that 3D quantum gravity is actually topological theory (namely, Chern-Simons). Now, he explains why his old picture of Chern-Simons topological gravity was wrong 
(the key word is black holes) and how monster group may appear in the context of string theory.
2 Comments
Dear Dmitry, I find these topics exciting and there’s a lot of true things here, especially the key importance of black hole microstates for the quantum theory.
However, the cool monster symmetry may only exist at the smallest radius of AdS3, see a proof by Davide Gaiotto.
http://arxiv.org/abs/0801.0988
This pretty much rules out that the right extrapolation of the extremal CFT continues to have the monster symmetry at flatter AdS3 spaces.
Hi Lubos
Thanks for the link! I have also found Distler’s analysis of Gaiotto’s paper who might be useful for us, lazies who don’t want to read the paper but still are willing to understand what happens.
Cheers,
Dmitry.
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