Apparent Dark-Energy Evolution from Cosmic Inhomogeneities

TL;DR

This paper explores how cosmic inhomogeneities can mimic evolving dark energy by affecting light propagation and distance measurements, potentially aligning observations with a universe dominated by a cosmological constant.

Contribution

It models inhomogeneities in three ways and demonstrates their effects on cosmological observables, suggesting they could explain apparent dark energy evolution.

Findings

Inhomogeneities distort distance-redshift relations.

Models align with supernova and BAO data.

Inhomogeneity effects are comparable to deviations from a cosmological constant.

Abstract

A mildly inhomogeneous universe with a cosmological constant may look like it contains evolving dark energy. We show that could be the case by modelling the inhomogeneities and their effects in three different ways: as clumped matter surrounded by voids, as back-reaction of small-scale structure on the overall expansion of the Universe, and, finally, as a large-scale curvature inhomogeneity. In all of these cases, the propagation of light is affected, and differs from that in a homogeneous and isotropic universe. The net result is that cosmological observables, such as angular diameter and luminosity distances, become distorted. We find, in all three models, that the inclusion of these effects pushes the distance-redshift relation towards closer agreement with recent data from both supernovae Ia from the Dark Energy Survey, and from baryon acoustic oscillations from the Dark Energy Spectroscopic Instrument. The amount of inhomogeneity in these models might not be enough to explain the entirety of the deviation from a cosmological constant, but is found to be of a similar order of magnitude, hinting that these data may be consistent with a universe dominated by a cosmological constant.