Maths HEP Lunchtime Seminars: Hydrodynamics of spacetime and vacuum viscosity
31 October 2008 13:00 in CM221
Recent work has shown that spacetime dynamics can be deduced from the non-equilbrium thermodynamics of all local causal horizons. In particular, by postulating an entropy balance law dS = dQ/T + d_i S connecting notions of horizon entropy, heat flux, temperature, and entropy production one can derive the Einstein equation. In this talk I will describe how this derivation can be reformulated in the language of hydrodynamics. I will argue that the vacuum thermal state ("thermal atmosphere") outside a local causal horizon can be treated as a fluid. The entropy balance law and Einstein equation then follow as a consequence of hydrodynamics. Interestingly, horizon fluid has universal properties: its entropy density is the Bekenstein-Hawking density and its shear viscosity to entropy density ratio is \hbar/4\pi. The \hbar/4\pi ratio also arises in gauge theory/gravity dualities, where it has received considerable attention recently. I will describe a possible relationship between the two pictures and discuss open questions.