The Proceedings of the Eighth International Conference on Creationism (2018)

with the result predicted by an expanding universe model (four). Lubin and Sandage (2001) account for the discrepancy with a model for the evolution of galactic luminosity with redshift. From the perspective of a non-evolutionary cosmological model such as the one proposed here, the match to observations without additional considerations is a highly satisfactory result. In addition to resolving the distant starlight problem, such a model would have the potential to explain the anomalous rotation curves of galaxies without the need for either dark matter or a modification of Newtonian dynamics. The rotational velocities of stars are determined by the Doppler shift of the 21 cm hydrogen line, and as discussed above, a variation in c will result in a wavelength shift that would be falsely attributed to a Doppler shift if c is assumed to be constant. The gradients in the two effects have the same sign (both the velocity and the speed of light increase away from the center of the Galaxy), so it is quite likely that the combination of the two effects could be modeled using a Keplerian stellar velocity profile. Any mass estimates that are based on velocity measurements, such as the dynamical mass of clusters, would be similarly affected by a variation in the speed of light. An increase in c in expression (2) would imply a corresponding decrease in v for a given red or blue shift, thus reducing the dynamical mass estimate. A separate possibility for resolving the distant starlight problem is that light travels faster in regions of extremely low particle density. It is well known that the speed of light varies inversely with density (the apparent bending of a straw in a glass of water is due to light moving slower in the denser water than in air). The slowing down of light in dense materials is due to interactions between the light and the atoms or molecules making up the material. It may be that in the low density media where c has been measured there are residual interactions that determine the value of c 0 = 3 x 10 10 cm/s, and that these interactions are greatly reduced for the extremely low number of particles that are present in the interstellar medium (ISM) and galactic voids. While the physics of such hypothetical interactions would need to be elucidated, it is certainly the case that the application of c 0 to the speed of light in such low density media is an extrapolation that has not been confirmed by experiment. It would not be the first time that new physics understanding has been required for an unexplored regime of matter. Assuming the astronomical measurements of the speed of light that take place within the Solar System are valid, a change in c would only be noticed at densities lower than that of the interplanetary medium (IPM). A typical particle density in the IPM is 1 cm -3 , whereas in galactic voids it is 10 -6 cm -3 , or 1 m -3 . If the speed of light varies inversely with density, c = c 0 (1 + 1/ n ), (11) where n is particle number density in cm -3 , the speed of light in galactic voids would be 10 6 c 0 . In principle other functional forms for c ( n ) could be chosen to give arbitrarily large values for c. DISCUSSION This paper proposes the simple postulate that light travels faster in regions of low gravity or extremely low particle density as a solution to the distant starlight problem. I have only explored the bare outlines of a theory based on this idea, and much work remains to be done. The analogy between gravity and a spatially varying speed of light discussed above suggests that a robust physical model for c could be constructed in which c traces the gravitational potential of the visible matter in the universe. Such a model would remove the need for dark energy and has the potential to remove the need for dark matter as well. Future work along these lines should solve equation (6), or a related model based upon the ideas outlined in Barceló et al. (2011) and Dicke (1957), to determine the speed of light for actual observed (baryonic) stellar density distributions. A separate but related task would be to calculate redshifts based upon these speed of light variations and subtract their effect from dynamical mass estimates. Whether or not the speed of light varies in regions of extremely low density can in principle be experimentally tested. Assuming it is not technically feasible to achieve a sufficiently low density to see an increase in the speed of light in a terrestrial experiment, the most readily apparent opportunity for observing it would be to perform a light travel time measurement between a pair of space-based probes such as the Voyager space craft after they pass the solar bow shock and enter the ISM. The Voyager probes themselves are only about half-way to the bow shock, however, so such an experiment is not feasible in the near future. I will close with a final philosophical point. Attributing the cosmological redshift to a variation in the speed of light alone implies that Earth is near r = 0. This result clearly contradicts the Copernican Principle that is foundational to modern astronomy. Hubble (1937) himself noticed our apparent central location relative to the redshift distribution and rejected it as untenable (emphasis mine): Thus the density of the nebular distribution increases outwards, symmetrically in all directions, leaving the observer in a unique position. Such a favoured position, of course, is intolerable ; moreover, it represents a discrepancy with the theory, because the theory postulates homogeneity. Therefore, in order to restore homogeneity, and to escape the horror of a unique position , the departures from uniformity, which are introduced by the recession factors, must be compensated by the second term representing effects of spatial curvature. There seems to be no other escape…Well, perhaps the interpretation is correct and we do inhabit a rapidly expanding universe. Attributing the cosmological redshifts to a spatial variation in the speed of light thus entails a rejection of the expansion of the universe, dark energy, possibly dark matter, and the Copernican Principle. That is a lot to swallow, even for a creationist. As I discussed above, both effects (expansion and speed of light variation) could in principle be operating simultaneously. I have focused solely on a variation in the speed of light both for simplicity and for its relevance to the distant starlight problem, but one could imagine constructing a cosmological model that included both the Hubble expansion and a variation in the speed of light. There are several reasons to think that such a complication is not necessary, however, and that the simple model outlined above is preferable. 1) Reducing our level of ignorance regarding the contents of the universe from 96% to 23% (or possibly 0%) by removing the need for dark energy (and possibly dark matter) should speak for Johnson ◀ Young universe cosmology ▶ 2018 ICC 50