**Definition:**A

*variable speed of light cosmology*is a cosmological approach which involves allowing the speed of light to change in some specified way, in an attempt to solve the major cosmological issues in modern theoretical physics.

One of the major traits of Einstein's theory of relativity is that the speed of light in a vacuum is always a constant rate, *c*. However, the cosmological problems that led to the theoretical introduction of dark matter and dark energy into modern cosmology has motivated some physicists to look for solutions in other directions.

In 1992, John W. Moffat proposed an alternative model of inflation in which, during the early moments of the universe, the speed of light was very large, due to a breakdown in the Lorentz invariance (the symmetry of special relativity that keeps the speed of light constant).

In Moffat's viewpoint, this provided the benefit of taking care of all of the initial value problems in cosmology pretty nicely without the need for the more popular inflation models. Instead of space expanding quickly, the speed of light was incredibly fast ... the results are effectively the same in terms of explaining the physical properties set by the early universe.

In 1998, physicists Andreas Albrecht and Joao Magueijo published a paper on a similar variable speed of light cosmology, which they had developed completely independently of Moffat himself.

At present (2009), these approaches are still controversial among the cosmology and astrophysics communities, and are not widely accepted.

**Also Known As:**VSL Cosmology