This paper by Andrew Strominger explores the black hole entropy in the context of black holes whose near-horizon geometries are locally AdS3 (three-dimensional anti-de Sitter space). Using the fact that quantum gravity on AdS3 is a conformal field theory, Strominger microscopically computes the black hole entropy by counting the asymptotic growth of states. The result precisely agrees with the Bekenstein-Hawking area formula for the entropy, demonstrating that the entropy can be explained statistically through the microstates near the black hole horizon. This derivation does not rely on string theory or supersymmetry but is based on general properties of diffeomorphism-invariant theories. The paper also reviews the work of Brown and Henneaux, which showed that quantum gravity on AdS3 is a conformal field theory with a central charge \( c = \frac{3}{2G\sqrt{-\Lambda}} \), where \( G \) is Newton's constant and \( \Lambda \) is the cosmological constant. The paper discusses specific examples, such as the BTZ black hole and black strings in six dimensions, and relates these to previous derivations of the black hole entropy, including those in string theory and topological theories. The discussion highlights the holographic principle and the role of the AdS3 boundary in describing the states that contribute to the black hole entropy.This paper by Andrew Strominger explores the black hole entropy in the context of black holes whose near-horizon geometries are locally AdS3 (three-dimensional anti-de Sitter space). Using the fact that quantum gravity on AdS3 is a conformal field theory, Strominger microscopically computes the black hole entropy by counting the asymptotic growth of states. The result precisely agrees with the Bekenstein-Hawking area formula for the entropy, demonstrating that the entropy can be explained statistically through the microstates near the black hole horizon. This derivation does not rely on string theory or supersymmetry but is based on general properties of diffeomorphism-invariant theories. The paper also reviews the work of Brown and Henneaux, which showed that quantum gravity on AdS3 is a conformal field theory with a central charge \( c = \frac{3}{2G\sqrt{-\Lambda}} \), where \( G \) is Newton's constant and \( \Lambda \) is the cosmological constant. The paper discusses specific examples, such as the BTZ black hole and black strings in six dimensions, and relates these to previous derivations of the black hole entropy, including those in string theory and topological theories. The discussion highlights the holographic principle and the role of the AdS3 boundary in describing the states that contribute to the black hole entropy.