On the Origin of Gravitational Thermodynamics

Vishnu JEJJALA

IHES

Mon, Mar. 10th 2008, 14:45

NOTE SPECIAL TIME AND LOCATION: IHES, Marilyn and James Simons hall.
We show that very heavy pure states in gravity can appear to be mixed
states to almost all probes. For half-BPS states, typical states are
described by a spacetime ``foam,'' the precise details of which are
invisible to almost all probes. We indicate how coarse-graining over
Planck scale fluctuations yields semiclassical geometries and propose
this as a mechanism for the origin of gravitational thermodynamics. By
working in perturbation theory with a small non-extremality parameter,
lessons from the supersymmetric situation can be adapted to the
microscopics of an almost extremal superstar. We match the counting of
the black hole entropy in semiclassical gravity to the degeneracy of
states in the dual field theory. Moreover, in certain decoupling
limits, the entropy is explained in terms of strings stretching
between D-branes.