Accelerated expansion from structure formation

Abstract

We discuss the physics of backreaction-driven accelerated expansion. Using the exactequations for the behaviour of averages in dust universes, we explain how large-scalesmoothness does not imply that the effect of inhomogeneity and anisotropy on theexpansion rate is small. We demonstrate with an analytical toy model how gravitationalcollapse can lead to acceleration. We find that the conjecture of the accelerated expansionbeing due to structure formation is in agreement with the general observational picture ofstructures in the universe, and more quantitative work is needed to make a detailedcomparison.