Irreversible Thermodynamics of the Universe: Constraints from Planck Data

Abstract EN

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 three Planck data sets to constrain the thermal conductivity λ and the coupling parameter b 2 .

These constraints must be satisfied in order for GSLT to hold for universe bounded by apparent or event horizons.