Horizons, Constraints, and Black Hole Entropy

TL;DR

This paper proposes that the universality of black hole entropy arises from symmetry behavior, with horizon constraints leading to a conformal field theory approach that reproduces Bekenstein-Hawking entropy without microscopic details.

Contribution

It introduces a symmetry-based explanation for black hole entropy, utilizing horizon constraints and conformal field theory techniques to derive the Bekenstein-Hawking entropy.

Findings

Symmetry algebra at the horizon is modified by the stretched horizon constraint.

Standard CFT methods can compute the density of states matching Bekenstein-Hawking entropy.

The approach does not rely on specific microscopic models.

Abstract

Black hole entropy appears to be ``universal''--many independent calculations, involving models with very different microscopic degrees of freedom, all yield the same density of states. I discuss the proposal that this universality comes from the behavior of the underlying symmetries of the classical theory. To impose the condition that a black hole be present, we must partially break the classical symmetries of general relativity, and the resulting Goldstone boson-like degrees of freedom may account for the Bekenstein-Hawking entropy. In particular, I demonstrate that the imposition of a ``stretched horizon'' constraint modifies the algebra of symmetries at the horizon, allowing the use of standard conformal field theory techniques to determine the asymptotic density of states. The results reproduce the Bekenstein-Hawking entropy without any need for detailed assumptions about the microscopic theory.