Statistical physics of black holes as quantum-mechanical systems

Some basic features of black-hole statistical mechanics are investigated, assuming that black holes respect the principles of quantum mechanics. Care is needed in defining an entropy S₁₇ corresponding to the number of microstates of a black hole, given that the black hole interacts with its surroundings. An open question is then the relationship between this entropy and the Bekenstein-Hawking entropy S₁₇. For a wide class of models with interactions needed to ensure unitary quantum evolution, these interactions produce extra energy flux beyond that predicted by Hawking. Arguments are then presented that this results in an entropy S₁₇ that is smaller than S₁₇. Correspondingly, in such scenarios equilibrium properties of black holes are modified. We examine questions of consistency of such an inequality; if it is not consistent, that provides significant constraints on models for quantum-mechanical black hole evolution.