On the Cardy-Verlinde Entropy Formula in Viscous Cosmology

TL;DR

This paper extends the Cardy-Verlinde entropy formula to viscous cosmologies, exploring how bulk viscosity affects holographic principles and the definition of Casimir energy in non-conformally invariant universes.

Contribution

It proposes a formal generalization of the Cardy-Verlinde entropy formula to viscous cosmological models, questioning the physical interpretation of Casimir energy in such contexts.

Findings

Generalization of entropy formula to viscous universes

Discussion on the modification of Casimir energy definition

Insights into holographic principles in non-conformally invariant theories

Abstract

The results of the paper of Verlinde [hep-th/0008140], discussing the holographic principle in a radiation dominated universe, are extended when allowing the cosmic fluid to possess a bulk viscosity. This corresponds to a non-conformally invariant theory. The generalization of the Cardy-Verlinde entropy formula to the case of a viscous universe seems from a formal point of view to be possible, although we question on physical grounds some elements in this kind of theory, especially the manner in which the Casimir energy is evaluated. Our discussion suggests that for non-conformally invariant theories the holographic definition of Casimir energy should be modified.