Redshift drift in an inhomogeneous universe: averaging and the backreaction conjecture

TL;DR

This paper derives an expression for average redshift drift in inhomogeneous universes, demonstrating that backreaction effects can mimic dark energy and influence observational measurements, challenging standard cosmological interpretations.

Contribution

It introduces a new formulation for redshift drift in inhomogeneous universes and explores how backreaction can produce effects similar to dark energy in observational data.

Findings

Backreaction can cause positive redshift drift at low redshifts.

Models without dark energy can mimic standard model redshift drift within measurement precision.

Local voids can cause deviations from the average redshift drift.

Abstract

An expression for the average redshift drift in a statistically homogeneous and isotropic dust universe is given. The expression takes the same form as the expression for the redshift drift in FLRW models. It is used for a proof-of-principle study of the effects of backreaction on redshift drift measurements by combining the expression with two-region models. The study shows that backreaction can lead to positive redshift drift at low redshifts, exemplifying that a positive redshift drift at low redshifts does not require dark energy. Moreover, the study illustrates that models without a dark energy component can have an average redshift drift observationally indistinguishable from that of the standard model according to the currently expected precision of ELT measurements. In an appendix, spherically symmetric solutions to Einstein's equations with inhomogeneous dark energy and matter are used to study deviations from the average redshift drift and effects of local voids.