Accelerating Universe via Spatial Averaging

TL;DR

This paper demonstrates that inhomogeneous universe models, specifically Tolman-Bondi solutions with mixed spatial curvatures, can exhibit accelerated expansion after averaging, providing insights into cosmic acceleration without dark energy.

Contribution

It introduces a model showing that spatial averaging of inhomogeneous universes can naturally lead to accelerated expansion, highlighting the role of curvature regions.

Findings

Averaged universe begins accelerated expansion after positive curvature re-collapses.

Deceleration parameter becomes negative in the averaged model.

The condition for acceleration depends on the spatial curvature distribution.

Abstract

We present a model of an inhomogeneous universe that leads to accelerated expansion after taking spatial averaging. The model universe is the Tolman-Bondi solution of the Einstein equation and contains both a region with positive spatial curvature and a region with negative spatial curvature. We find that after the region with positive spatial curvature begins to re-collapse, the deceleration parameter of the spatially averaged universe becomes negative and the averaged universe starts accelerated expansion. We also discuss the generality of the condition for accelerated expansion of the spatially averaged universe.