Black Hole Thermodynamics and Statistical Mechanics
Steven Carlip
TL;DR
The paper surveys the thermodynamic behavior of black holes, clarifying how Hawking radiation endows black holes with a temperature and an entropy proportional to horizon area. It then surveys a wide array of microscopic, statistical-mechanical approaches (string theory, fuzzballs, AdS/CFT, loop quantum gravity, induced gravity, entanglement) that reproduce the Bekenstein-Hawking entropy, emphasizing the puzzling universality of the area law despite diverse microphysics. A central theme is the search for universal horizon-based or conformal-symmetry explanations (via Cardy-type counting) that could unify these pictures. The discussion culminates in open questions about information loss, holography, and the nature of black hole microstates, highlighting holography as a guiding principle for quantum gravity.
Abstract
We have known for more than thirty years that black holes behave as thermodynamic systems, radiating as black bodies with characteristic temperatures and entropies. This behavior is not only interesting in its own right; it could also, through a statistical mechanical description, cast light on some of the deep problems of quantizing gravity. In these lectures, I review what we currently know about black hole thermodynamics and statistical mechanics, suggest a rather speculative "universal" characterization of the underlying states, and describe some key open questions.