Observations in statistically homogeneous, locally inhomogeneous cosmological toy-models without FLRW backgrounds

TL;DR

This paper investigates how redshift and redshift drift behave in cosmological models that are statistically homogeneous but locally inhomogeneous, showing potential for redshift drift to test backreaction effects.

Contribution

It introduces a method to compute redshift drift in inhomogeneous cosmological models without relying on FLRW backgrounds, highlighting its potential to distinguish local and global effects.

Findings

Spatial averages reproduce redshift-distance relations well in certain models.

Redshift drift differs from the drift of the mean redshift, indicating local vs. global effects.

Redshift drift can be a useful observational tool for testing backreaction.

Abstract

Observations are studied in toy-models constituting exact cosmological solutions to the Einstein equation which are statistically homogeneous but locally inhomogeneous, without an a priori introduced FLRW background and with "structures" evolving fairly slowly. The mean redshift-distance relation and redshift drift along 500 light rays in each of two models are compared to relations based on spatial averages. The relations based on spatial averages give a good reproduction of the mean redshift-distance relation, although most convincingly in the model where the kinematical backreaction is subpercent. In both models, the mean redshift drift clearly differs from the drift of the mean redshift. This indicates that redshift drift could be an important tool for testing the backreaction conjecture as redshift drift appears to distinguish between local and global effects. The method presented for computing the redshift drift is straightforward to generalize and can thus be utilized to fairly easily compute this quantity in a general spacetime.