Can inhomogeneties accelerate the cosmic volume expansion?

TL;DR

This paper constructs exact inhomogeneous universe models demonstrating that inhomogeneities can temporarily accelerate cosmic volume expansion, highlighting the significance of non-linear relativistic effects.

Contribution

It introduces a novel class of inhomogeneous dust-filled universe models showing acceleration due to inhomogeneities, using exact solutions of Einstein's equations.

Findings

Acceleration occurs when contracting regions are comparable to the horizon radius.

Models show acceleration is possible with inhomogeneities, despite differences from observed universe.

Non-linear effects of inhomogeneities are crucial for accelerated expansion.

Abstract

If expanding and contracting regions coexist in the universe, the speed of the cosmic volume expansion can be accelerated. We construct simple inhomogeneous dust-filled universe models in which the speed of the cosmic volume expansion is accelerated for finite periods. These models are constructed by removing spherical domains from the Einstein-de Sitter universe and filling each domain with a Lemaitre-Tolman-Bondi dust sphere possessing the same gravitational mass as the removed region. This represents an exact solution of the Einstein equations. We find that acceleration of the cosmic volume expansion is realized in some cases when the size of the contracting region is comparable to the horizon radius of the Einstein-de Sitter universe though this model is very different from the universe observed today. This result implies that non-linear general relativistic effects of inhomogeneities are very important to realize the acceleration of the cosmic volume expansion.