Abstract
The present work deals with irreversible universal thermodynamics. The homogenous and isotropic flat model of the universe is chosen as open thermodynamical system and nonequilibrium thermodynamics comes into picture. For simplicity, entropy flow is considered only due to heat conduction. Further, due to Maxwell-Cattaneo modified Fourier law for nonequilibrium phenomenon, the temperature satisfies damped wave equation instead of heat conduction equation. Validity of generalized second law of thermodynamics (GSLT) has been investigated for universe bounded by apparent or event horizon with cosmic substratum as perfect fluid with constant or variable equation of state or interacting dark species. Finally, we have used threePlanckdata sets to constrain the thermal conductivityλand the coupling parameterb2. These constraints must be satisfied in order for GSLT to hold for universe bounded by apparent or event horizons.
Highlights
This is well established that there is a profound relation between gravity and thermodynamics
As thermodynamical parameters such as temperature and entropy are characterized by the geometry of the event horizon of the black hole, it is legitimated to assume that black hole thermodynamics is deeply related to Einstein’s field equations
This assertion became true when Jacobson [4] in 1995 successfully derived Einstein equation from the first law of thermodynamics, δQ = TdS with δQ and T as the energy flux and Unruh temperature measured by an accelerated observer just inside the horizon, and subsequently Padmanabhan [5] derived the first law of thermodynamics from Einstein equations for general static spherically symmetric space time
Summary
This is well established that there is a profound relation between gravity and thermodynamics. Later Bardeen et al [3], in 1973, established that the four laws of black hole mechanics are analogous to four laws of thermodynamics As thermodynamical parameters such as temperature and entropy are characterized by the geometry of the event horizon of the black hole, it is legitimated to assume that black hole thermodynamics is deeply related to Einstein’s field equations. Jacobson [4] first noticed this when his attempt failed to reproduce Einstein’s equations from first law of thermodynamics in f(R) gravity In that case he assumed the horizon entropy to be proportional to a function of the Ricci scalar and this led to the breakdown of the local thermodynamical equilibrium. Wang and Liu [8] studied nonequilibrium thermodynamics for universe bounded by apparent horizon with dark energy in the form of perfect fluid with constant equation of state.
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