Edwin Hubble and Georges Lemaître discovered the expansion of the Universe nearly a century ago. One way to test it is the surface brightness test: in an expanding cosmos, the light of a distant galaxy should fade like a pattern on a stretching film. The dependence of brightness on the light stretch factor z is given by the formula (1+z)−4.
Analysis of almost seven thousand galaxies from the photometric catalog ASTRODEEP-JWST, obtained by the James Webb Space Telescope, revealed that the actual drop in brightness is noticeably weaker. This contradicts the standard cosmological model Lambda-CDM.
The reason for the discrepancy is unknown. Perhaps galaxy evolution or unaccounted properties of dark energy play a role. But some scientists recall Fritz Zwicky, who back in the 1930s suggested that photons lose energy from 'tiredness' rather than expansion.
If light were to 'tire', galaxies would fade differently. That's exactly the difference the surface brightness test looks for, and the JWST data hint in favor of the forgotten hypothesis.