Proposed to account for the observed redshift of distant galaxies, the ‘tired light’ model suggests that electromagnetic radiation (light) loses energy during its passage from distant objects.

There is currently no observational evidence to suggest that the energy of photons can be reduced in this way, as a change in energy would also mean a change in momentum resulting in the ‘blurring’ of distant objects. The tired light model also lacks support in the astronomical community as it does not predict the observed time dilation seen in high-redshift supernova light curves.

The currently accepted explanation of the redshifted distant galaxies and time dilated light curves, is that the Universe is expanding and we are observing a cosmological redshift due to this expansion.