WHAT ELSE CAN CAUSE REDSHIFT?
If the redshift of galaxies is not due to expansion velocity, then what might cause the redshift? Over the years, a surprising number of proposals have been made. A recent summary article lists 20 non-velocity redshift mechanisms.14 Basically, anything that causes light to lose energy will cause it to redshift. The trick is to have an energy loss mechanism that doesn't scatter the light. The absence of observed scattering is the main objection to the so-called "tired light" theory, in which intergalactic matter is supposed to be responsible for the energy loss of light.
One of many possibilities (the one favored by this author) is that one day we will discover the particle or wave serving as the carrier of the gravitational force. If such entities, dubbed "gravitons", exist, they must necessarily be of a much finer scale than current quantum particles. It therefore seems likely that they would have negligible scattering effects on light over cosmological distances, although light traveling through such a resisting medium of gravitons would necessarily lose energy and be redshifted. In such a case, we would expect to see light from galaxies redshifted in proportion to their distances from us, just as observed; yet there would be no expansion of the universe. The perfect cosmological principle would be obeyed.
This particular notion of gravitons also answers the dilemma for general relativity faced by Einstein -- Why doesn't the universe collapse from its own gravity? If these hypothetical gravitons have a finite cross-sectional area, then they can only travel a finite distance, however great, before colliding with another graviton. So the range of the force of gravity would necessarily be limited in this way. Curiously, if the mean flight distance between collisions for gravitons was about 2 kiloparsecs (about the diameter of the core of many galaxies), then the limited range of the force of gravity would give rise to a change in the inverse square force law over distances larger than 2 kiloparsecs. The predicted form of this change happens to imitate just what we observe in the behavior of galaxies that has led big bang astronomers to hypothesize the existence of "dark matter" in ever greater quantities to account for the rotation and clustering of galaxies on these large scales. In other words, if this graviton conjecture is correct, there would be no need of invisible dark matter to explain large-scale behavior of dynamical systems. More details of this alternative model are published elsewhere by this author.15
What of the cosmic microwave radiation and the light element abundance predictions, often touted as successful predictions of the big bang model? These points have been critiqued in detail elsewhere10,15,16, and that discussion is beyond the scope of this paper. To make a one-sentence summary about each point: The big bang made no quantitative prediction that the "background" radiation would have a temperature of 3 degrees Kelvin (in fact its initial prediction was 30 degrees Kelvin); whereas Eddington in 192617 had already calculated that the "temperature of space" produced by the radiation of starlight would be found to be 3 degrees Kelvin. And no element abundance prediction of the big bang was successful without some ad hoc parameterization to "adjust" predictions that otherwise would have been judged as failures.
As a final note on the question of the universe's expansion, it should not be forgotten that it is not even certain that the universe is presently expanding (as opposed to contracting) even within the context of the big bang theory. Sumner has recently argued that the new space introduced by the expansion must dilute the permittivity of the vacuum, which in turn must alter the frequency of electrons around atoms. This affects observed redshifts twice as strongly as the speed of expansion. When this consideration is factored into the equations, it turns out that the present universe is actually collapsing, not expanding, under big bang premises!18
So we see that, despite the widespread popularity of the big bang model, even its most basic premise, the expansion of the universe, is of dubious validity, both observationally and theoretically.