Tests for the Expansion of the Universe

TL;DR

This paper reviews various independent cosmological tests to verify the universe's expansion, highlighting that some tests support expansion while others are inconclusive due to galaxy evolution effects.

Contribution

It provides a comprehensive review of recent cosmological tests, emphasizing the strengths and limitations of each in confirming the universe's expansion.

Findings

Some tests support an expanding universe

Other tests are inconclusive or favor a static universe

The Alcock--Paczynski test is independent of galaxy evolution effects

Abstract

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock--Paczy\'nski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock--Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.