Electromagnetic redshift in anisotropic cosmologies

Sergio A. Hojman, Felipe A. Asenjo

Published 2018-01-16Version 1

Redshift of light is calculated for an anisotropic cosmological spacetime. Two different approaches are considered. In the first one, electromagnetic waves are modeled using the geometrical optics approximation. This approach considers light rays following null geodesics (which is equivalent to the motion followed by pointlike massless particles). It is shown that the redshift for this case depends, in general, on the direction of propagation, and it may even become dispersive (depending on the wavelength of light) if the light ray propagation coincides with one of the anisotropy axes. In the second approach electromagnetic waves are studied using the exact form of Maxwell equations, finding that redshift has dependence on the direction of propagation as well as on the wave polarization. The waves are dispersive and depend on the anisotropic temporal evolution. These results are discussed considering the Equivalence Principle. In general, both results are put into the context of recent astrophysical redshift observations for anisotropic cosmologies, and possible new measurements are suggested.