Cosmological Constant and the Speed of Light

TL;DR

This paper investigates how a positive cosmological constant affects the speed of light, showing it becomes slower than in special relativity, and links this effect to anisotropy in gravitational fields.

Contribution

It demonstrates that a positive cosmological constant reduces the speed of light and connects this phenomenon to light anisotropy in gravitational fields.

Findings

Light speed is less than the special relativity value in presence of a positive cosmological constant.

The same reduction is confirmed using wave optics within geometrical optics validity.

The anisotropy in light velocity and the cosmological constant effect share a common mechanism.

Abstract

By exploring the relationship between the propagation of electromagnetic waves in a gravitational field and the light propagation in a refractive medium, it is shown that, in the presence of a positive cosmological constant, the velocity of light will be smaller than its special relativity value. Then, restricting again to the domain of validity of geometrical optics, the same result is obtained in the context of wave optics. It is argued that this phenomenon and the anisotropy in the velocity of light in a gravitational field are produced by the same mechanism.