Thermodynamical Interpretation of the Second Law for Cosmology

TL;DR

This paper proposes a thermodynamical interpretation of the generalized second law in cosmology by relating holographic screen entropy to spacetime degrees of freedom and observer acceleration, extending thermodynamics beyond black holes.

Contribution

It introduces a novel approach to associate holographic screen entropy with spacetime degrees of freedom and observer acceleration, providing a thermodynamical framework for cosmological horizons.

Findings

Holographic screen area increases monotonically in cosmology.

Entropy of screens linked to spacetime degrees of freedom surface density.

Screens' temperature derived from Unruh temperature and acceleration.

Abstract

The area of a future holographic screen increases monotonically. Associating this area with entropy results in a generalized second law for Cosmology (GSLC). Unlike black hole horizons, screens relevant to Cosmology have no thermodynamical interpretation. We suggest relating the entropy of the screens to spacetime degrees of freedom surface density derived from a (seemingly) phase space. This construction enables us to identify the entropy of any holographic screen as the entropy detected by accelerating observers due to their acceleration. Using Unruh's temperature and the equivalence principle, this gives the holographic screens' temperature and yields a thermodynamical interpretation of the GSLC.