A Chi-Squared Analysis of the Measurements of Two Cosmological Parameters Over Time

TL;DR

This paper uses chi-squared tests on historical measurements of two key cosmological parameters, $\sigma_8$ and $H_0$, revealing that error bars are often underestimated, which may explain the Hubble tension.

Contribution

It provides a statistical analysis showing that measurement errors for these parameters are likely underestimated, impacting cosmological inferences.

Findings

Error bars are underestimated in over 20% of measurements.

The low Q-values suggest systematic errors are not properly accounted for.

Underestimated errors may explain the Hubble tension discrepancy.

Abstract

The aim of this analysis was to determine whether or not the given error bars truly represented the dispersion of values in a historical compilation of two cosmological parameters: the amplitude of mass fluctuations ($\sigma_8$) and Hubble's constant ($H_0$) parameters in the standard cosmological model. For this analysis, a chi-squared test was executed on a compiled list of past measurements. It was found through analysis of the chi-squared ($\chi^2$) values of the data that for $\sigma_8$ (60 data points measured between 1993 and 2019 and $\chi^2$ between 182.4 and 189.0) the associated probability Q is extremely low, with $Q = 1.6 \times 10^{-15}$ for the weighted average and $Q = 8.8 \times 10^{-15}$ for the best linear fit of the data. This was also the case for the $\chi^2$ values of $H_0$ (163 data points measured between 1976 and 2019 and $\chi^2$ between 480.1 and 575.7), where $Q = 1.8 \times 10^{-33}$ for the linear fit of the data and $Q = 1.0 \times 10^{-47}$ for the weighted average of the data. The general conclusion was that the statistical error bars associated with the observed parameter measurements have been underestimated or the systematic errors were not properly taken into account in at least 20\% of the measurements. The~fact that the underestimation of error bars for $H_0$ is so common might explain the apparent 4.4$\sigma$ discrepancy formally known today as the Hubble tension.