8. The speed of light

By applying modern astronomical knowledge to the creation account, we can infer that in the beginning light from the centre of what is now a galaxy of stars – the Milky Way – reached the earth almost instantaneously. Within hours the revolving earth was illuminated on one side and cast into shadow on the other, hemispheres of night and day. However, as measured by the current speed of light, the centre of the Milky Way is almost 25,000 light years away. If Genesis is true, the speed of light must have been much faster at Creation than now.

The speed of light (‘c’) is one of the fundamentals of physics. Until recently it was assumed to be invariable, but the possibility that it might have been faster in the past, albeit only in the very distant past, is now a point of discussion in the scientific community. Since its speed must be a function of the energy field through which it passes, we should not suppose that its present speed is just arbitrarily the value it is, or that is has always been that value.

Light has its canonical speed of approximately 300,000 km per second only when it passes through a vacuum. When photons pass through a medium, such as air or glass, they are absorbed and re-emitted by the intervening atoms, so that they slow down. Light consequently travels at a speed dictated by the medium it travels through. Since the vacuum is a sea of energy, not, as popularly conceived, empty space, possibly this may be what imparts energy to photons: the vacuum literally mediates the transmission of light. Photons continually recharge their energy by interacting with virtual particles in the vacuum, much as particles draw their mass from the vacuum. Thus, if the vacuum were emptied of its energy, the result would not be that light would travel at infinite speed but that it could not travel at all. Conversely, if the energy of the vacuum were higher, c would be higher. Because of the relation e = mc2, mass would then be lower. In the past c may have been millions of times higher and mass trillions of times lower. This may sound absurd, but gravity acts on the total energy of an object, not just its atomic mass. Gravity has the same force whatever the value of c.

Among the first to make the case that the speed of light has fallen over time was the Australian creationist Barry Setterfield, in 1987. On the basis of measurements taken with increasing accuracy since the 19th century, he argued that c had been falling during the last two hundred years (and by extrapolation, previously) at a decreasing rate, bottoming out in the 1980s. Numerous people have questioned the interpretation (recently Jellison & Bridgman 2007).

Crucially, there should also be evidence of a falling trend from before the period when c could be directly measured. Since the speed of light is proportional to the rates at which radioactive elements decay and these rates are used to give absolute dates to geological events, there is a direct relationship between astronomical chronology as measured on the basis of light travel times and geological chronology. Thus the assumption that the speed of light has always been the same can be tested by comparing the geological timescale against the direct evidence of depositional rates. As documented elsewhere on the website (indexed here), these rates appear to have been faster in the past. Depositional rates are causally linked to radioactivity in the mantle and primeval thermonuclear fusion in the core, because these phenomena produce heat. As a consequence the interior of the earth in the past was hotter, driving, through magmatism at the mid-oceanic ridges, both faster rates of chemical influx into the oceans (affecting, for example, the rate of limestone build-up) and faster rates of plate-tectonic movement (affecting the rate of mountain-building, erosion and sedimentation). Depositional rates suggest that geological processes have exponentially slowed down over time, levelling off towards present-day rates in the mid to late Holocene, a few thousand years ago.

The consequences for our understanding of geological history are immense. They are equally immense for our understanding of cosmological history. For example, the rate at which stars go through their lifecycle may also be linked to c. Stars derive their energy primarily from thermonuclear fusion, whereby hydrogen atoms fuse together to make helium atoms and energy is released as a by-product. If a star has sufficient mass, the temperature in its interior will be high enough for helium atoms, in turn, to fuse together to make heavier elements, all the way up to iron. Apart from temperature, the rate of thermonuclear fusion depends on the strength of the atomic forces that resist fusion – the forces that keep apart positively charged protons and negatively charged electrons. On the basis of present rates, stellar ages can be up to billions of years. However, the strength of the forces that resist fusion depend on particle mass, and thus on c. It may be, therefore, that the first stars to originate could have gone through their lifecycles much more quickly than those of comparatively recent origin.

Another implication arises from the fact that nothing can travel faster than the speed of light. As an object approaches this speed, its mass increases exponentially, such that c can never be reached. Conversely, if an object was moving at a speed close to c at a time when c was 1,000 times higher than now and thus moving at a speed far in excess of the present limit, then its speed would now be 1,000 times slower. This possibility is particularly important when considering cosmic events or processes which have involved travel distances amounting to millions of present light years, for example, the emission of a jet of gas from a galactic nucleus. If the jet was ejected at close to the speed of light and that speed was substantially higher than present-day c, the jet itself may have been ejected at speeds that would now break the speed limit. For a distance now measured at 100 million light years, the actual time taken to traverse the distance may have been nearer 50,000 years.

Redshift is also related to decreasing c.