Does the growth of structure affect our dynamical models of the universe? The averaging, backreaction and fitting problems in cosmology

TL;DR

This paper examines how small-scale structures in the universe influence large-scale cosmological models, focusing on the averaging and backreaction problems and their potential impact on understanding cosmic acceleration.

Contribution

It analyzes the significance of backreaction effects from small-scale structures on large-scale universe dynamics within general relativity.

Findings

Backreaction effects may influence cosmic acceleration estimates

Averaging over structures can alter the apparent cosmological constant

The averaging problem remains unresolved but crucial for precision cosmology

Abstract

Structure occurs over a vast range of scales in the universe. Our large-scale cosmological models are coarse-grained representations of what exists, which have much less structure than there really is. An important problem for cosmology is determining the influence the small-scale structure in the universe has on its large-scale dynamics and observations. Is there a significant, general relativistic, backreaction effect from averaging over structure? One issue is whether the process of smoothing over structure can contribute to an acceleration term and so alter the apparent value of the cosmological constant. If this is not the case, are there other aspects of concordance cosmology that are affected by backreaction effects? Despite much progress, this 'averaging problem' is still unanswered, but it cannot be ignored in an era of precision cosmology.