On Thursday 8th August 2002, a burst of Press publicity accompanied the publication of a paper in the prestigious scientific journal Nature. That article was authored by Professor Paul Davies, of Sydney's Macquarie University, and by two astrophysicists from the University of New South Wales, Dr. Charles Lineweaver, and graduate student Tamara Davis. The paper suggested that the speed of light was much higher in the past and had dropped over the lifetime of the universe. These conclusions were reached as a result of the observations of University of New South Wales astronomer Dr. John Webb made in 1999 and the more recent observations of one of his PhD students, Michael Murphy. These observations indicated a slight shift in the position of the dark lines that appear in the rainbow spectrum of metallic atoms deep in space when compared with their expected position. Because there are a number of factors to disentangle statistically, and because the effect is small (about 1 part in 100,000), there remains some doubt as to the validity of the primary conclusion, let alone the suspected causes of the effect.

The actual physical quantity that the observations are targeting is the fine structure constant. This constant links together four other atomic quantities, namely the speed of light, the electronic charge, Planck's constant and the electric property of free space called the permittivity. It is possible that any one of these quantities may be varying, or that there is synchronous variation between some or all of the components that make up the fine structure constant. Thus, one possible explanation for the observed effect is that the speed of light was higher the further back in time we look. But it is not the only explanation. Other possible explanations include a change in the value of the charge on the electron. However, the paper by Davies et al. rejects this possibility on the basis of what was expected to occur with black holes at the frontiers of the cosmos. Until I have seen a copy of the paper by Davies et al. I do not know if they have eliminated all other options.

However, since a major paper by Andreas Albrecht and Jao Magueijo in 1999, and another one by John Barrow in the same issue of Physical Review D, the speed of light has come under increasing scrutiny as a physical quantity that may be varying. These scientists are saying that if lightspeed was significantly higher at the inception of the cosmos (about 10⁶⁰ higher) then a number of astronomical problems can be readily resolved. Paul Davies statements echo that and he, like Barrow, considers that lightspeed has declined over the history of the universe. By contrast, Albrecht and Magueijo contained the lightspeed change to the earliest moments of the Big Bang and had it drop to its present value immediately afterwards. In that sense, this recent work is consolidating the belief that the drop in lightspeed has extended over the whole history of the universe. This is the position that the cDK research has advocated since the early 1980's.

The cause of the change in the speed of light has still to be determined, but according to Lineweaver, one of the prime suspects is that the structure of the vacuum has been changing uniformly across the cosmos. This is also the position that the cDK research has advocated since the early to mid 1990's and has been formalised in Behavior of the Zero Point Energy and Atomic Constants. It is also a key subject in "Exploring the Vacuum." Because there is an intrinsic energy in every cubic centimetre of the vacuum, this energy may manifest as virtual particle pairs like electron/positron pairs that flit in and out of existence. As a photon of light travels through the vacuum, it hits a virtual particle, is absorbed, and then shortly after is re-emitted. This process, while fast, still takes a finite time to occur. Thus, a photon of light is like a runner going over hurdles. The more hurdles over a set distance on the track the longer it takes for runners to reach their destination. Thus, if the energy content of space increased with time, more virtual particles would manifest per unit distance, and so the longer light would take to reach its destination.

Much was made of the potential problems that lightspeed changes would cause to Einstein's theory of Relativity. This matter has been discussed ever since Albrecht and Magueijo's paper in 1999. However, the cDK work examined this issue back in the 1980's and decided that Einstein's work will basically remain valid provided that energy is conserved in the process. This necessarily involves changes in a number of other constants as Trevor Norman and I outlined in the 1987 Report, The Atomic Constants, Light and Time, from SRI International and Flinders University. These matters are also discussed in further detail in the 2001 paper. I also had the opportunity to briefly pursue the issue of observed changes to other atomic constants with Prof. Albrecht in March 2002. He admitted that his proposal had problems with the observations of some constants. I mentioned that these problems could be overcome if energy was conserved in the process. He stated that they had looked at that but decided that they could not achieve all the effects they wanted to if energy was conserved, and so abandoned that position. Albrecht and Magueijo attempted to largely avoid these problems by isolating lightspeed changes to the earliest moments of the Big Bang. However, these more recent results are tending to confirm that the change has been occurring over the lifetime of the universe. Consequently, the issue of changing atomic constants must be opened again, and the validity of Einstein's equations linked in with it.

In summary, the scientific community is coming to believe that a drop in lightspeed has occurred over the lifetime of the cosmos from some initial value near 10⁶⁰ times its current speed. The cDK research has indicated that lightspeed has been dropping over the life of the universe from a maximum value around 10¹¹ times now. This is a more conservative estimate than others are proposing. The actual cause of the change in lightspeed is suspected as being related to changes in the structure of the vacuum by both secular scientists and those involved in the cDK research. Finally, Einstein's equations have been called into question. However, they can be shown to be basically correct provided that energy is conserved in the process of c variation, but some other atomic constants will vary synchronously in this case. Those other constants, which have been shown to be varying in this way from observational data, were examined in the 1987 Report and the 2001 paper and support the cDK position.

Barry Setterfield, 10th August 2002. Updated September 5, 2007