Electromagnetic redshift in anisotropic cosmologies

TL;DR

This paper investigates how electromagnetic redshift varies with direction and polarization in anisotropic cosmologies, using both geometrical optics and Maxwell equations, revealing dispersive effects and potential implications for the Equivalence Principle.

Contribution

It provides a detailed analysis of electromagnetic redshift in anisotropic universes through two approaches, highlighting directional and polarization dependencies and their astrophysical implications.

Findings

Redshift depends on propagation direction in anisotropic spacetimes.

Electromagnetic waves exhibit dispersive redshift depending on anisotropy.

Results suggest possible violations of the Equivalence Principle in such cosmologies.

Abstract

The 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 (high--frequency) approximation. This approach considers light rays following null geodesics, being equivalent to the motion followed by pointlike spinless massless particles. It is shown that the redshift for this case depends, in general, on the direction of propagation, and is dispersive (wavelength dependent) for light emitted from different points of an extended object. 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 electromagnetic waves are dispersive and depend on the anisotropic temporal evolution. In this last case, redshifts may become dispersive depending on the relative direction between the light ray propagation vector and the anisotropy axes. The relation of these results with a possible violation of the Equivalence Principle are discussed. In general, both results are set in the context of recent astrophysical redshift observations for anisotropic cosmologies, and new ways of determining redshifts are suggested.