Background. Redshifts observed in light from distant cosmological objects has played a key role in measurement of apparent motion of these objects away from each other leading to Hubble's law and the expanding universe idea. Various scenarios may produce redshift observations, where simultaneous, proportional changes in spectral lines distinguish the phenomenon from a simple color change of the viewed object. For example, in the Doppler redshift, light received from receding objects displays increased wavelengths, shifting spectral lines in the red direction for common substances such as hydrogen. Another example may be a so-called cosmological redshift in which observed spectral features are said to be altered in a similar manner due to some sort of expansion of space itself between the light source and recipient.
Alternative hypothesis. If light speed is slower due to passage through substantial regions of lower partial vacuum density, is such a scenario distinguishable from the redshift effects supporting the expanding universe hypothesis? If not, the rate of expansion might be less than previously thought or possibly might even be zero.
Light speed in vacuum c is a key reference value in physics. Many texts emphasize that the redshift basis for the expanding universe hypothesis is different than decreased light speed in refraction, since the former involves light at constant velocity in "empty space" whereas the latter involves light travel through and interactions with the refractive material. However, the data in Fig. 1 suggests an almost opposite picture, namely that constant light speed in vacuum per Einstein's Special Relativity postulate actually requires a rather substantial density of energy quanta (1-state bits), so that the "vacuum" is far from "empty space" and that lower vacuum densities actually reduce light speed. In short, light speed invariance in vacuum appears to occur over a reduced vacuum density range than previously thought.
The author has previously discounted the notion that lower vacuum density regions might exist at present . After all, light is seen to arrive from all directions. Through billions of years of universe history, one might well assume that the vacuum has been sufficiently filled with 1-state bits to provide an extremely uniform transparent transmission media for light travel.
On the other hand, perhaps to coin a phrase (or not), "the universe is a big place". Hence, it might be premature to assume that significant variations in vacuum density across possibly vast volumes do not exist. Perhaps large enough regions of somewhat lower vacuum density slowing light speed do in fact exist and if so, the quantitative implications might be carefully evaluated in relation to the expanding universe theory.
If large regions of the universe do indeed have a lower vacuum density, further predictions of binary mechanics  are that much of the energy of light emitted by distant objects would be absorbed into bit cycles  in lower density regions traversed and therefore, the observed intensity of light from these objects would underestimate their brightness. If these predictions are correct, the continuing "filling" of lower density vacuum regions might be detectable (e.g., particular slow rates of increasing brightness of selected sources) and the distance of certain bright astronomical objects may have been significantly overestimated in astrophysics literature.
 Keene, J. J. "Light speed amendment" J. Bin. Mech. March, 2015.
 Keene, J. J. "Physics glossary" J. Bin. Mech. May, 2011.
 Keene, J. J. "Binary mechanics" J. Bin. Mech. July, 2010.
 Keene, J. J. "Proton and electron bit cycles" J. Bin. Mech. April, 2015.
© 2015 James J Keene