First observational constraints on cosmic backreaction over an extended redshift range

TL;DR

This paper presents the first observational constraints on cosmic backreaction over a broad redshift range, using a novel method combining multiple cosmological observables, though the constraints remain weak.

Contribution

It introduces a new observational approach to constrain cosmic backreaction and provides the first direct constraints over an extended redshift range.

Findings

Constraints are consistent with zero backreaction within one standard deviation.

Constraints are weak, so significant backreaction cannot be excluded.

First direct observational constraints on cosmic backreaction over a large redshift span.

Abstract

In the recent preprint arXiv:2604.07244v1, the authors introduce a novel combination of redshift, distance, and expansion rate observables for constraining cosmic backreaction. The current work presents a first application of the method, yielding the first direct constraints on the total cosmic backreaction in our Universe over a significant redshift range. The constraints are consistent with vanishing backreaction within one standard deviation. However, the constraints are fairly weak and significant backreaction cannot be ruled out.