Evaluating backreaction with the peak model of structure formation

TL;DR

This paper assesses how the formation of structures like voids affects the universe's expansion rate, finding a modest increase that does not lead to acceleration, using the peak model for structure formation.

Contribution

It introduces a realistic evaluation of backreaction effects on cosmic expansion using the peak model and spherical structures, highlighting the slow increase in expansion rate.

Findings

Expansion rate increases by 10-100 billion years

Void dominance causes the increase

No evidence of acceleration from backreaction

Abstract

We evaluate the average expansion rate of a universe which contains a realistic evolving ensemble of non-linear structures. We use the peak model of structure formation to obtain the number density of structures, and take the individual structures to be spherical. The expansion rate increases relative to the FRW value on a timescale of 10-100 billion years, because the universe becomes dominated by fast-expanding voids. However, the increase is not rapid enough to correspond to acceleration. We discuss how to improve our treatment. We also consider various qualitative issues related to backreaction.