Black Holes, Equilibrium, and Cosmology

TL;DR

This paper reviews the development of black hole thermodynamics over fifty years, focusing on equilibrium, symmetry, and the challenges of extending these ideas to cosmological black holes in de Sitter spaces.

Contribution

It provides a comprehensive analysis of black hole thermodynamics, including interpretations of the first law and issues in cosmological contexts, highlighting open questions and proposed solutions.

Findings

Black hole thermodynamics relates closely to classical thermodynamics.

The first law's interpretation varies between mechanical and process-based views.

Formulating thermodynamics in de Sitter backgrounds presents significant difficulties.

Abstract

We trace the origins and development of black hole thermodynamics across the past half-century, emphasizing the framework's relation to classical thermodynamics, and the vital role played by the notions of equilibrium, stationarity, and symmetry. We discuss different interpretations of the first law of black hole mechanics, and assess the validity of its mechanical, process-based interpretation for evaporating black holes. We bring these ideas to the cosmological realm, and highlight the various difficulties that arise when formulating thermodynamics for black holes in asymptotically de Sitter backgrounds. We discuss a number of proposed solutions and the open questions that arise therein.