On the adiabatic expansion of the visible space in a higher-dimensional Cosmology

TL;DR

This paper investigates how the expansion of our observable universe can occur adiabatically within higher-dimensional cosmologies, revealing modified energy laws and entropy production due to extra dimensions.

Contribution

It introduces a reinterpretation of stress-energy in higher dimensions, leading to new cosmological evolution models with entropy production.

Findings

Adiabatic expansion is possible with internal space dynamics.

Modified energy conservation laws due to extra dimensions.

Large-scale entropy production in four-dimensional cosmology.

Abstract

In the context of higher-dimensional cosmologies with isotropic visible and internal space and multi-perfect fluid matter, we study the conditions under which adiabatic expansion of the visoble external space is possible, when a time-dependent internal space is present. The analysis is based on a reinterpretation of the four-dimensional stress-energy tensor in the presence of the extra dimensions. This modifies the usual adiabatic energy conservation laws for the visible Universe, leading to a new type of cosmological evolution which includes large-scale entropy production in four dimensions.