Variable Speed of Light Cosmology: An Alternative to Inflation

Abstract

It is generally believed that inflationary cosmology explains the isotropy, large scale homogeneity and flatness as well as predicting the deviations from homogeneity of our universe. We show that this is not the only cosmology which can explain successfully these features of the universe. We consider anew and modify a model in which local Lorentz invariance is spontaneously broken in the very early universe, and in this epoch the speed of light undergoes a first or second order phase transition to a value ~ 30 orders of magnitude smaller, corresponding to the presently measured speed of light. Before the phase transition at a time t ~ t_c, the entropy of the universe is reduced by many orders of magnitude, allowing for a semiclassical quantum field theory calculation of a scale invariant fluctuation spectrum. After the phase transition has occurred, the radiation density and the entropy of the universe increase hugely and the increase in the entropy follows the arrow of time determined by the spontaneously broken direction of the vev <ϕ^a>_0. This solves the enigma of the arrow of time and the second law of thermodynamics. A new calculation of the primordial Gaussian and adiabatic fluctuation spectrum is carried out, leading to a scale invariant scalar component of the power spectrum. We argue that there are several attractive features of VSL theory compared to standard inflationary theory, and that it provides an alternative cosmology with potentially different predictions.