Hubble tension and statistical processing of astronomical data

by Serge Parnovsky (Taras Shevchenko National University of Kyiv)

Wednesday 28 Sept 2022, 16:30 → 18:30 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

Many of you have either processed experimental data yourself or used the results of processing done by someone else. I want to demonstrate that processing, even standard processing, is not at all a simple procedure and can be a source of errors, in particular those caused by bias. This is what can explain Hubble tension, i.e. a statistically significant difference in the values of the Hubble constant obtained as a result of processing observations in the early and late Universe.

This report is based on my paper BIAS OF THE HUBBLE CONSTANT VALUE CAUSED BY ERRORS IN GALACTIC DISTANCE INDICATORS (arxiv 2109.09645, Ukrainian Journal of Physics,  Vol. 66 No. 11 (2021))

The bias in the determination of the Hubble parameter and the Hubble constant in the modern Universe is discussed. It could appear due to statistical processing of data on galaxies redshifts and estimated distances based on some statistical relations with limited accuracy. This causes a number of effects leading to either underestimation or overestimation of the Hubble parameter when using any methods of statistical processing, primarily the least squares method (LSM). The value of the Hubble constant is underestimated when processing a whole sample; when the sample is constrained by distance, especially when constrained from above, it is significantly overestimated due to data selection. The bias significantly exceeds the values of the error the Hubble constant calculated by the LSM formulae.
These effects are demonstrated both analytically and using Monte Carlo simulations, which introduce deviations in both velocities and estimated distances to the original dataset described by the Hubble law. The characteristics of the deviations are similar to real observations. Errors in estimated distances are up to 20%. They lead to the fact that when processing the same mock sample using LSM, it is possible to obtain an estimate of the Hubble constant from 96% of the true value when processing the entire sample to 110% when processing the subsample with distances limited from above.
The impact of these effects can lead to a bias in the Hubble constant obtained from real data and an overestimation of the accuracy of determining this value. This may call into question the accuracy of determining the Hubble constant and significantly reduce the tension between the values obtained from the observations in the early and modern Universe, which were actively discussed during the last year.