Big Bounce and inhomogeneities

TL;DR

This paper investigates how inhomogeneities and gravitational waves affect the quantum bounce in Loop Quantum Cosmology, showing that the Big Bang singularity is replaced by a Big Bounce and that inhomogeneities can be amplified through this process.

Contribution

It demonstrates that inhomogeneous Gowdy spacetimes undergo a Big Bounce in Loop Quantum Cosmology, with inhomogeneities being amplified depending on the dynamical regime.

Findings

The Big Bang singularity is replaced by a Big Bounce.

The universe size at the bounce is comparable to the homogeneous background.

Inhomogeneities can be statistically amplified during the bounce.

Abstract

The dynamics of an inhomogeneous universe is studied with the methods of Loop Quantum Cosmology as an example of the quantization of vacuum cosmological spacetimes containing gravitational waves (Gowdy spacetimes). The analysis performed at the effective level shows that: (i) The initial Big Bang singularity is replaced (as in the case of homogeneous cosmological models) by a Big Bounce, joining deterministically two large universes, (ii) the universe size at the bounce is at least of the same order of magnitude as that of the background homogeneous universe, (iii) for each gravitational wave mode, the difference in amplitude at very early and very late times has a vanishing statistical average when the bounce dynamics is strongly dominated by the inhomogeneities, whereas this average is positive when the dynamics is in a near-vacuum regime, so that statistically the inhomogeneities are amplified.