HAS THE SPEED OF LIGHT DECAYED?
by Lenny Flank
(c) 1995
One method of demonstrating the extreme age of the universe is done with a telescope. Using powerful reflecting telescopes (and now with the space-based Hubble Space Telescope), we are able to observe objects in space that are several million--even several billion--light years away. When we observe a quasar in our telescope that is a billion light years away, the light we are seeing now left that object a billion years ago and is just now reaching us. If the universe were only 6,000 years old, though, as the creationists claim, we would be quite unable to see anything more than 6,000 light years away from us, since the light from objects further away than that would not have had enough time to reach us by now. The fact that we are able to see objects several billion light-years away indicates that the universe itself must be at least several billion years old.
The creationists attempted to explain this inconsistency with a theory called "C-Decay", first put forth by the Australian creationist Barry Setterfield in 1981. Setterfield's thesis was a simple one: "The basic postulate of this article is that light has slowed down exponentially since the time of creation." (Setterfield, 1981, cited in Strahler, 1987, p. 116)
Setterfield cites figures for the speed of light (known to physicists and astronomers as "c") that were calculated at various times as far back as 1675. Back in the 17th century, the astronomers Roemer and Picard measured the speed of light at 299,270 km/sec, plus or minus 5 percent. Setterfield then took the higher value in this range, 301,300 km/sec, and compared it to the modern figure of 299.792.5 km/sec . (He ignored the fact that scientific instruments in 1675 were nowhere near the quality as modern ones and could not give a similar accuracy).
Setterfield then concluded that the speed of light had lessened or "decayed" from 1675 to the present, and if this trend were projected backwards, the speed of light would have been 1.5 million billion kilometers per second in the year 4040 BC (plus or minus twenty years), approximately 500 billion times faster than it is now. Thus, Setterfield concluded, the only reason why astronomical objects appear to be so far away today is because the speed of light has slowed down by a factor of half a trillion. In reality, says Setterfield, these objects are only several thousand light years away from us. "I propose," Setterfield concluded, "that this initial high value of c would have produced the appearence of great age to the universe in that one week (to those who look with eyes and minds fixed on the current value of c)." (Setterfield, 1981, cited in Strahler, 1990, p. 116)
The flaws in Setterfield's reasoning are obvious. There was no justification for assuming that the highest possible value of Picard and Roemer's experimental range was the correct value, other than the fact that it exaggerated the presumed "decay". The 1675 range of values, in fact, contains the current value of the speed of light, and there is thus no reason whatsoever to conclude that the speed of light in 1675 was any different than it is now.
When it was pointed out to Setterfield that the values for c that were measured in the early 1960's are identical with those made in the 1980's, he promptly concluded that the "decay" must have stopped shortly before that: "From these observations it would seem that beyond 1960 the speed of light had reached its minimum value and was constant thereafter". (cited in Robert P.J. Day, "The Decay of C-Decay", undated) Setterfield has never cited any reason why the speed of light should suddenly stop decaying after so many centuries (and, coincidentally, just at the time when technological methods were becoming precise enough to measure the speed of light very accurately).
Similarly, Setterfield made the assumption that the speed of light did not decay at all for some period of time after the original creation, but remained stable for a period. His "scientific reasoning" for this conclusion? "I will assume that this value held from the time of creation until the time of the Fall, as in my opinion the Creator would not have permitted it to decay during His initial work." (Setterfield, 1981, cited in Strahler, 1990, p. 116)
If, creationists point out, we assume that the value for c has varied over time, then some other consequences can be derived from that fact. As creationist Alan Montgomery points out, Setterfield's theory would "radically alter the dimensions of the age of the universe, eradicate the 'Big Bang', sink the Nebular hypothesis, undermine geological Uniformitarianism, and destroy Darwinism all at the same time." (Montgomery, "Creation Science", Creation Science Association of Ontario, Summer 1987) It is indeed unfortunate for the creationists that there is not a shred of evidence which indicates that the speed of light has ever varied.
By the late 1980's, the complete lack of scientific support for Setterfield's assertions caused even the ICR to publicly reject his theory, concluding that it was "not warranted by the data upon which the hypothesis rests." (Gerald Aardsma, ICR Impact, "Has the Speed of Light Decayed?", May 1988). "Even a cursory glance at the data," the ICR concluded, "reveals that the above analysis is inappropriate for the given data set, and, hence, the conclusions drawn from it are not valid . . . . This result says pretty clearly that there is no discernible decay trend in the data set." (Gerald Aardsma, ICR Impact, "Has the Speed of Light Decayed?", May 1988)