Tests for the expansion of the Universe

The standard interpretation of the redshifts of galaxies is that they are due to the expansion of the universe plus peculiar motions, but there are other explanations, such as the “tired light” hypothesis, which assumes that the photon loses energy owing to some unknown photon-matter process or photon-photon interaction when it travels some distance. Different observational tests give different results, although none of them so far provides a strong proof in favour of a static universe. The discussion on anomalous redshifts is also inconclusive. Current status of the H_0 and growth tensions: theoretical models and model-independent