Thermodynamics of an accelerated expanding universe

TL;DR

This paper examines the thermodynamic laws in an accelerating universe influenced by dark energy, finding that the laws hold at the apparent horizon but break down at the event horizon, questioning its physical relevance.

Contribution

It demonstrates the validity of thermodynamic laws at the apparent horizon and shows the breakdown at the event horizon in a dark energy-driven universe.

Findings

Thermodynamics laws hold at the apparent horizon.

Thermodynamics laws break down at the event horizon.

Event horizon is unphysical from a thermodynamic perspective.

Abstract

We investigate the laws of thermodynamics in an accelerating universe driven by dark energy with a time-dependent equation of state. In the case we consider that the physically relevant part of the Universe is that envelopped by the dynamical apparent horizon, we have shown that both the first law and second law of thermodynamics are satisfied. On the other hand, if the boundary of the Universe is considered to be the cosmological event horizon the thermodynamical description based on the definitions of boundary entropy and temperature breaks down. No parameter redefinition can rescue the thermodynamics laws from such a fate, rendering the cosmological event horizon unphysical from the point of view of the laws of thermodynamics.