The case for black hole thermodynamics, Part I: phenomenological thermodynamics

TL;DR

This paper systematically advocates for viewing black holes as thermodynamic systems, emphasizing classical thermodynamics, the membrane paradigm, and Hawking radiation, making the subject accessible without advanced quantum gravity knowledge.

Contribution

It provides a thorough, accessible presentation of black hole thermodynamics, highlighting classical concepts and the membrane paradigm, and clarifies the role of Hawking radiation in black hole thermal behavior.

Findings

Black holes can be modeled as thermodynamic systems with well-defined adiabatic processes.

The membrane paradigm extends black hole thermodynamics to local equilibrium.

Hawking radiation enables black holes to be in thermal contact and can be derived via multiple methods.

Abstract

I give a fairly systematic and thorough presentation of the case for regarding black holes as thermodynamic systems in the fullest sense, aimed at students and non-specialists and not presuming advanced knowledge of quantum gravity. I pay particular attention to (i) the availability in classical black hole thermodynamics of a well-defined notion of adiabatic intervention; (ii) the power of the membrane paradigm to make black hole thermodynamics precise and to extend it to local-equilibrium contexts; (iii) the central role of Hawking radiation in permitting black holes to be in thermal contact with one another; (iv) the wide range of routes by which Hawking radiation can be derived and its back-reaction on the black hole calculated; (v) the interpretation of Hawking radiation close to the black hole as a gravitationally bound thermal atmosphere. In an appendix I discuss recent criticisms of black hole thermodynamics by Dougherty and Callender. This paper confines its attention to the thermodynamics of black holes; a sequel will consider their statistical mechanics.