, Volume 39, Issue 10, pp 1519-1523,
Open Access This content is freely available online to anyone, anywhere at any time.
Date: 13 Jun 2007

Symmetries, horizons, and black hole entropy


Black holes behave as thermodynamic systems, and a central task of any quantum theory of gravity is to explain these thermal properties. A statistical mechanical description of black hole entropy once seemed remote, but today we suffer an embarrassment of riches: despite counting very different states, many inequivalent approaches to quantum gravity obtain identical results. Such “universality” may reflect an underlying two-dimensional conformal symmetry near the horizon, which can be powerful enough to control the thermal characteristics independent of other details of the theory. This picture suggests an elegant description of the relevant degrees of freedom as Goldstone-boson-like excitations arising from symmetry breaking by the conformal anomaly.

First Award in the 2007 Essay Competition of the Gravity Research Foundation.