Is the expansion of the universe accelerating? All signs still point to yes a local dipole anisotropy cannot explain dark energy

TL;DR

This paper reaffirms that the evidence for the universe's accelerating expansion remains strong, addressing recent claims that questioned its significance by correcting methodological errors in those analyses.

Contribution

It identifies and corrects errors in recent studies that challenged the significance of supernova data in confirming cosmic acceleration.

Findings

Corrected analysis shows dipole anisotropy has minimal impact on cosmological parameters.

Reaffirmed the robustness of supernova evidence for accelerating universe.

Addressed and fixed methodological flaws in recent conflicting studies.

Abstract

Type Ia supernovae (SNe Ia) provided the first strong evidence that the expansion of the universe is accelerating. With SN samples now more than ten times larger than those used for the original discovery and joined by other cosmological probes, this discovery is on even firmer ground. Two recent, related studies (Nielsen et al. 2016 and Colin et al. 2019, hereafter N16 and C19, respectively) have claimed to undermine the statistical significance of the SN Ia constraints. Rubin & Hayden (2016) (hereafter RH16) showed N16 made an incorrect assumption about the distributions of SN Ia light-curve parameters, while C19 also fails to remove the impact of the motion of the solar system from the SN redshifts, interpreting the resulting errors as evidence of a dipole in the deceleration parameter. Building on RH16, we outline the errors C19 makes in their treatment of the data and inference on cosmological parameters. Reproducing the C19 analysis with our proposed fixes, we find that the dipole parameters have little effect on the inferred cosmological parameters. We thus affirm the conclusion of RH16: the evidence for acceleration is secure.