Thermodynamics of FRW Universe: Heat Engine

TL;DR

This paper models the non-flat FRW universe as a thermodynamic system, deriving entropy, temperature, and other thermodynamic quantities, and explores its behavior as a heat engine including Carnot and new engine cycles.

Contribution

It introduces a thermodynamic framework for the FRW universe using apparent horizon properties and analyzes its heat engine potential.

Findings

FRW universe obeys Joule-Thomson cooling behavior

Derived maximum efficiency for Carnot cycle in the universe

Identified inversion temperature and pressure for the universe

Abstract

We assume the non-flat Friedmann-Robertson-Walker (FRW) Universe as a thermodynamical system. We assume the cosmological horizon as a inner trapping horizon which is treated as dynamical apparent horizon of FRW Universe. We write the dynamical apparent horizon radius and temperature on the apparent horizon. We assume that the fluid pressure as thermodynamical pressure of the system. Using Hayward's unified first law, Clausius relation and Friedmann equations with cosmological constant, we obtain the entropy on the apparent horizon. We assume that the cosmological constant provides the thermodynamic pressure of the system. We obtain the entropy, surface area, volume, temperature, Gibb's Helmholtz's free energies, specific heat capacity of the FRW Universe due to the thermodynamic system. We study the Joule-Thomson expansion of the FRW Universe and by evaluating the positive sign of Joule-Thomson coefficient, we determine that the FRW Universe obeys the cooling nature. We also find the inversion temperature and inversion pressure. Next we demonstrate the thermodynamical FRW Universe as heat engine. For Carnot cycle, we obtain the work done and the maximum efficiency. Also for new engine, we study the work done and its efficiency.