Quantum States of Black Holes

TL;DR

The paper surveys how string theory accounts for black hole entropy by counting microstates and shows that Hawking radiation can be described unitarily in a low-energy regime. It introduces a correspondence principle linking highly excited strings to black holes, with transitions governed by horizon scale and coupling, and provides precise entropy matches for supersymmetric and near-extremal black holes via D-brane bound states. Dualities (S-duality, IIB SL(2,Z), and M-theory connections) unify weak and strong coupling pictures, suggesting a unitary evaporation process across descriptions and hinting at spacetime arising from microscopic states. Collectively, these results bolster the view that black hole thermodynamics has a fundamental microscopic origin in string theory and point toward a deeper quantum structure of spacetime.

Abstract

I review the recent progress in providing a statistical foundation for black hole thermodynamics. In the context of string theory, one can now identify and count quantum states associated with black holes. One can also compute the analog of Hawking radiation (in a certain low energy regime) in a manifestly unitary way. Both extremal and nonextremal black holes are considered, including the Schwarzschild solution. Some implications of conjectured non-perturbative string ``duality transformations'' for the description of black hole states are also discussed.