Entropy of gravitationally collapsing matter in FRW universe models

TL;DR

This paper studies the entropy evolution of a dust gas undergoing gravitational collapse in FRW universe models, showing entropy increases without needing an intrinsic gravitational entropy concept.

Contribution

It demonstrates that classical thermodynamic entropy increases during gravitational collapse when gravitational potential energy converts to thermal energy, without requiring a separate gravitational entropy.

Findings

Entropy increases during collapse at first order

Classical thermodynamics suffices to explain entropy change

No need for intrinsic gravitational entropy concept

Abstract

We look at a gas of dust and investigate how its entropy evolves with time under a spherically symmetric gravitational collapse. We treat the problem perturbatively and find that the classical thermodynamic entropy does actually increase to first order when one allows for gravitational potential energy to be transferred to thermal energy during the collapse. Thus, in this situation there is no need to resort to the introduction of an intrinsic gravitational entropy in order to satisfy the second law of thermodynamics.