# Towards statistically homogeneous and isotropic perfect fluid universes with cosmic backreaction

## TL;DR

This paper introduces a method to construct statistically homogeneous and isotropic perfect fluid universe models with notable cosmic backreaction, using a Swiss-cheese model with LTB structures, and evaluates their observational implications.

## Contribution

It presents a novel approach to model universe backreaction effects and assesses the accuracy of volume-averaged observational schemes in such contexts.

## Key findings

- Significant cosmic backreaction observed in the model.
- Poor agreement between exact and averaged redshift-distance relations.
- Deviations exaggerated by local expansion rate peculiarities.

## Abstract

A method for constructing statistically homogeneous and isotropic perfect fluid universe models with significant cosmic backreaction is proposed. The method is illustrated using a simplified model constructed as a Swiss-cheese model with Lemaitre-Tolman-Bondi structures. The model exhibits significant cosmic backreaction and is used to study methods proposed in the literature for relating volume averaged quantities with observations. The comparison shows a poor agreement between exact redshift-distance relations and the relations predicted by schemes based on volume averages. Most of these deviations are, however, clearly exaggerated by peculiarities of the example model, such as large local expansion rates.