Viscous Cosmology and Thermodynamics of Apparent Horizon

TL;DR

This paper demonstrates that the Friedmann equations for a viscous fluid-filled FRW universe can be expressed as a thermodynamic first law at the apparent horizon, confirming the generalized second law of thermodynamics.

Contribution

It shows the equivalence of Friedmann equations and thermodynamic laws in a viscous cosmological setting, extending previous work to include viscosity effects.

Findings

First law of thermodynamics holds at the apparent horizon with viscous fluid.

Generalized second law of thermodynamics is valid in this cosmological model.

Dominant energy condition is preserved at the apparent horizon.

Abstract

It is shown that the differential form of Friedmann equations of FRW universe can be recast as a similar form of the first law, $T_{h}dS_{h} = dE + WdV$, of thermodynamics at the apparent horizon of FRW universe filled with the viscous fluid. It is also shown that the generalized second law of thermodynamics holds at the apparent horizon of FRW universe and preserves dominant energy condition.