The thermodynamics of self-gravitating systems in equilibrium is holographic

TL;DR

This paper demonstrates that classical thermodynamics of self-gravitating systems in equilibrium can be fully described by boundary variables, revealing a holographic nature without requiring quantum gravity insights.

Contribution

It shows that classical boundary variables suffice to specify the thermodynamics of gravitating systems, highlighting a holographic aspect at the classical level.

Findings

Thermodynamics of gravitating systems is determined by boundary geometry.

Holographic properties emerge without quantum gravity input.

Classical gravity symmetries encode boundary information.

Abstract

We show that, when we study the coexistence of general relativity with thermodynamics, some physical properties that are usually thought of as holographic and lying in the domain of quantum gravity can actually be accessed even at the classical level. In particular, we demonstrate that the thermodynamics of gravitating systems in equilibrium is fully specified by variables defined on the system's boundary, namely, the boundary's geometry and extrinsic curvature. Hence, information is non-trivially incorporated in boundary variables because of the structure (the symmetries) of the classical gravity theory, without any input from quantum theory (such as black hole entropy).