Abstract
Homogeneous and isotropic, nonsingular, bouncing world models are designed to evade the initial singularity at the beginning of the cosmic expansion. Here, we study the thermodynamics of the subset of these models governed by general relativity. Considering the entropy of matter, radiation and that the entropy of the apparent horizon is proportional to its area, we argue that these models do not respect the generalised second law of thermodynamics, also away from the bounce.
Highlights
The well-known, and partially successful, cosmological standard model, based on Einstein gravity, assumes a homogeneous and isotropic universe whose energy density is supplied by matter and fields that satisfy the strong energy condition [1]
The target of this paper is to explore whether the generalized second law (GSL) is satisfied by the nonsingular bouncing class of world models that obey general relativity, in their evolution outside the bounce itself
Assuming that the entropy of the universe is proportional to the area enclosing the dynamical apparent horizon, and taking into account the contributions by the matter and radiation, we investigated if nonsingular bouncing models satisfy the generalized second law of thermodynamics
Summary
The well-known, and partially successful, cosmological standard model, based on Einstein gravity, assumes a homogeneous and isotropic universe whose energy density is supplied by matter and fields that satisfy the strong energy condition [1]. Given the strong connection between gravity and thermodynamics [18,19,20,21], for a cosmological model that fits reasonably well the observational data it will be a bonus to comply with the laws of thermodynamics, especially the second law. The latter formalizes our daily experience that macroscopic systems, left to themselves, spontaneously tend to thermodynamic equilibrium or remain in it, if undisturbed.
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