A recent paper1 by Niayesh Afshordi and João Magueijo asserts that they have discovered a testable cosmology wherein during a “critical” cosmological phase of the early universe the maximal speed of propagation of matter (and hence light) was enormously much faster than the current speed of light (c) and faster than the speed of gravity, which in Einstein’s theory is the canonical speed c. They revisit what has become to be known as varying speed of light (VSL) models, in contrast to the now popular cosmic inflation models. They believe light travelled much faster just after the big bang than it does now and have developed a mathematical model of a big bang universe only a miniscule fraction of a second after the alleged hot beginning of the Universe.
The big bang model has many problems, but the biggest and most difficult to solve is what is known as the ‘horizon problem’.2 Cosmic inflation has been invoked to solve this problem. Afshordi and Magueijo agree that,
… the Big Bang model of the Universe remains an unfinished work of art. Many of its late-time successes can be traced to the initial conditions postulated for its early stages, and these are put in by hand, without justification, other than to retrofit the data. The main culprit for this shortcoming is the so-called horizon problem: the cosmological structures we observe today span scales that lay outside the ever-shrinking “horizons” of physical contact that plagued the early universe. This precludes a causal explanation for their initial conditions.1 (emphases added)
Cosmologist believe that structure in the universe was seeded from initial density variations in the early universe. But for structures (clusters of galaxies, for example) to naturalistically form gravity must propagate over the scale of any structure in the timescale available to it at the past epoch when the structures were allegedly built. In addition we observe a uniform temperature across all the sky in the cosmic microwave background (CMB) radiation, yet sources on opposite sides of the observable universe have not had time to exchange energy, at the constant speed of light c, in the time available in the big bang universe. That is, they have not had to time to come into thermal equilibrium. These limitations are what are known as ‘horizons’. The major problem with the big bang model is that cosmic inflation scenarios are inserted by hand, to overcome these ‘horizons’ but without any justification for why inflation started and why it stopped. Quite obviously if the speed of light were infinite there would exist no such ‘horizon’ to thermal equilibration of the Universe.