State of matter at high density and entropy bounds

TL;DR

This paper challenges traditional entropy bounds by constructing a volume-proportional entropy model that exceeds black hole entropy and violates the covariant entropy bound in a cosmological setting.

Contribution

It introduces a simple volume-based entropy model that surpasses black hole entropy and demonstrates its violation of the covariant entropy bound in cosmology.

Findings

Volume-based entropy model exceeds black hole entropy.

Homogeneous cosmology with this gas violates covariant entropy bound.

Implications for understanding entropy limits in quantum gravity.

Abstract

Entropy of all systems that we understand well is proportional to their volumes except for black holes given by their horizon area. This makes the microstates of any quantum theory of gravity drastically different from the ordinary matter. Because of the assumption that black holes are the maximum entropy states there have been many conjectures that put the area, defined one way or another, as a bound on the entropy in a given region of spacetime. Here we construct a simple model with entropy proportional to volume which exceeds the entropy of a single black hole. We show that a homogeneous cosmology filled with this gas exceeds one of the tightest entropy bounds, the covariant entropy bound and discuss the implications.