Thermodynamics of nonsingular bouncing universes

TL;DR

This paper examines the thermodynamic properties of nonsingular bouncing universe models within general relativity, finding that they violate the generalized second law of thermodynamics even away from the bounce point.

Contribution

It provides a thermodynamic analysis of nonsingular bouncing cosmologies, highlighting their incompatibility with the generalized second law.

Findings

Models violate the generalized second law of thermodynamics

Entropy of matter, radiation, and horizon are considered

Thermodynamic inconsistency persists away from the bounce

Abstract

Homogeneous and isotropic, nonsingular, bouncing world models are designed to evade the initial singularity at the beginning of the cosmic expansion. Here, we study the thermodynamics of the subset of these models governed by general relativity. Considering the entropy of matter, radiation and that the entropy of the apparent horizon is proportional to its area, we argue that these models do not respect the generalised second law of thermodynamics, also away from the bounce.