C-decay

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The correct title of this article is c-decay. The initial letter is shown capitalized due to technical restrictions.

c-decay refers to a Young Earth Creationist proposal that the speed of light has been changing through time. By carefully selecting the decay rate, one can construct a universe that is billions of light years across, yet objects at these long distances are still visible even though the universe would be only a few thousand years old. It is an alternate to the Omphalos argument, which argues that the universe was created with the light already "in-flight", to the same end. Neither theory is widely accepted, even within the creationist community.

The concept was first proposed by Barry Setterfield in 1981 in an article for the Australian creationist magazine, Ex Nihilo. He selected a number of historical measurements of $c$ starting with the original measurement by Ole Rømer in 1667, and proceeding through a series of more recent experiments, culminating in "modern" measures in the 1960s. These showed a decreasing speed over time, which Setterfield claimed was in fact an exponential decay series that implied an infinite speed in the not distant past. The claim was later expanded to cover an apparent similar decay of several other physical constants.^[1] Similar charts have since been displayed in a number of creationist works.

Setterfield argues that this resolves the so-called "starlight problem". As Setterfield's original suggestion in Ex Nihilo notes, "If you propose that the universe and all in it is the product of an act of creation only 6-7000 years ago, many people ask - 'How is it that objects millions of light years away can be seen? Surely such light would take millions of years to reach us." If c is a constant, as is widely accepted, then this implies the universe is billions of years old due to the fact that we can see objects billions of light years away. However, if the speed was significantly faster in the past, as Setterfield argues, then the light would have traveled most of this distance in a short time. Setterfield proposes this as an alternative to mainstream physical cosmology and, as such, c-decay represents a unique creationist cosmology.

There are any number of problems with this claim, from the obvious to the subtle. One of the more obvious ones simply invokes Einstein's famous formula, $E = m c 2$ : If Setterfield is correct and the value of $c$ was much larger in the past, the energy released in chemical reactions would be much higher during this early epoch. When confronted with this argument, Setterfield claimed that the value of Planck constant was increasing to offset this effect. This would have equally noticeable effects on the universe, which are likewise unseen. In a more general sense, $c$ is so "ingrained" into basic physics that any macroscopic change would be likely to result in the universe not being able to exist in its current form at all. No convincing argument covering these issues has been proposed.

Observations taken since the concept was first proposed directly contradict the claim. For instance, measurements of the "light echo" from SN1987A show that the speed of light when the supernova occurred hundreds of thousands of years ago was within measurable accuracy of the figure today.^[2] Further, all modern measurements agree to a value that precludes the decay. In Setterfield's report he introduced a "cutoff date beyond which there is a zero rate of change", apparently to address this issue, making the theory unfalsifiable by new observations of $c$ . Further, he claims that the speed was also fixed for some time in this early epoch, apparently to avoid an infinite speed, but offers no strong argument why this would be. So the claim is that the speed was fixed at the beginning of time, is again today, but was decreasing measurably in an arbitrarily selected period between the two.

Just as worrying at a fundamental level is the apparent "cherry picking" of the data in order to fit the original curve. Many experiments measuring the speed of light, some of them famous, were left out of his analysis. When these are included the graph becomes much more "flat". Moreover, Setterfield's argument is most highly dependent on Rømer's original measurement, which is the outlier that defines the curve. His measure was copied from an issue of Sky and Telescope which he stated said the speed of light was "301,300 plus or minus 200 km/sec", about 0.5% above the current value. The article was actually an excerpt from The Astronomical Journal ^[3], which disagrees completely, and in fact states quite clearly that "The best fit occurs at zero where the light travel time is identical to the currently accepted value value".^[4] In other words Setterfield's own set of experiments contradict his claims if one examines what they really said. Recent versions of Setterfield's paper include these updated figures, using adjusted mathematics to rebuild the curve. These mathematics have been the object of ridicule.^[5]

There is no support for c-decay in the mainstream scientific community and, in fact, little support for it in the creationist community, including the Institute for Creation Research (ICR). Answers in Genesis (AiG), a leading creationist organization, says that this proposal has a number of problems that have not been satisfactorily answered. AiG currently prefers Dr. Russell Humphreys’ explanation for distant starlight.