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"c-decay" is a term often used to refer to a hypothesis put by Barry Setterfield, a South Australian creationist who argues that the speed of light (c) had decayed from a much faster speed in the past down to its present speed.

If true, this would be a solution to the alleged "starlight problem" in the Biblical creation model. While the idea received initial support from other creationists, most creationists subsequently came to reject the hypothesis.[1]



Setterfield initially published his proposal in Creation,[2][3] the magazine of Creation Ministries International.[2] Further papers were published in the ministry's new Journal of Creation.[2] Setterfield, with Trevor Norman, then published an "Invited Research Report" for the Stanford Research Institute International.


Figure III from Norman and Setterfield, 1987, showing historic measurements and the plotted decay from 1740 to 1983.
Figure IV from Norman and Setterfield, 1987, showing the years 1870 to 1983 in more detail.

Setterfield used historical measurements of the speed of light dating back to 1675 to support his hypothesis that the speed of light had followed a decay curve that levelled out to the present speed of light in 1960.

The phase of decay is actually preceded and succeeded by phases of constant speed of light: It started out at 1.5 x 1017 km/s ("or roughly 5 x 1011 faster than it is now", as Setterfield points out) and is assumed to have stayed this way until after the Fall.[4] Around 1960, c then stopped decaying and is now constant again,[5] coincidentally just when lasers and digital counters were becoming available to provide a quantum leap in precision measuring the velocity of light.


Following publication of the hypothesis, reaction included anti-creationists objecting strongly to the proposal, including on the grounds that the speed of light was inviolable. However, their objections were often ideological, and this became especially clear when subsequently secular scientists proposed that the speed of light had changed, and although their hypothesis did not offer support for Setterfield's hypothesis, it did not incur the same reaction.[6]

However, other criticisms, including from other creationists, were more substantial, and most creationists ended up dropping the idea. As of December 2009, Setterfield still supports the claim and has not retracted his work.[7]


The theory has been criticized for various reasons. Some scientists rejected the possibility that the speed of light might have changed at all,[6][8][9] while others rejected such a drastic decay, citing the catastrophic effects of such a large change. In Setterfield's paper he introduced a "cutoff date beyond which there is a zero rate of change", effectively making the theory unfalsifiable by new observations of c.

Other than the potential effects of the theory, there was criticism of the way Setterfield arrived at his theory:

  • A gradual and asymptotic approach of data towards the current value is often a sign of refined methods and technique. Setterfield however interpreted this as a sign of decay.[10]
  • Setterfield used a non-weighted least squares fit to analyze his data. However, several of the values come with error bars (ranges of uncertainty as reported by the researchers), so the standard practice would be to give these values less weight in the calculation (the larger the error bar, the less weight should be assigned to the value). Using this standard method on the data gives a decay of 0.0000140 ± 0.0000596 km/s per year instead of the 38 km/s per year calculated by Setterfield.[10]
  • Most of the calculated decay is due to one indirect 1693 measurement by Cassini. In 1694, his experiment was strongly criticized by Halley. A similar contemporary measurement by Roemer gives a value for the speed of light significantly under the current value, which would cancel out any influence from Cassini's measurement. Setterfield "corrected" Roemer's value but left Cassini's alone.[10]

Other authors identify several problems with Setterfield's works:[11]

Setterfield’s published works are scientifically invalid for a number of reasons:

  1. Setterfield repeatedly depicts minority or even eccentric scientific viewpoints as well-established or proven. On issues such as the quantized redshift, the effect of ZPE on atomic structure, and calibration of Carbon-14 dating, he rarely acknowledges any evidence in favor of mainstream interpretations.92 His publications present a distorted view of science, ….
  2. After a quarter-century of work on c-decay, Setterfield has not presented a coherent functional form for the change in c over the full range of time. This makes it difficult for outsiders to critique his theory, or even to understand exactly what it consists of.
  3. Setterfield claims fundamental physical constants to be varying without acknowledging known systematic errors and reinterpretations of data that explain these variations. He generally ignores the error ranges of the measurements. He interprets the leveling-off of the recommended values as a physical effect, rather than acknowledging the correlation between the increasing stability of the values and the improving accuracy of the measurements. He claims to have found variations in m and h that track each other temporally in agreement with his theory, but the data do not support this claim. He ignores the fact that the measurements of these quantities are not independent. Errors in measurement of one quantity affect the others in a way that partially mimics his predictions, but this is a mathematical artifact rather than a physical reality.
  4. There are numerous non sequiturs, misstatements, and errors in his mathematical work.
  5. Astronomical observations of binary stars, pulsars, distant supernovae, and gamma ray bursts fail to show the slowing-down effect one would expect if his theory were correct. He claims that c-decay effects are not observable for objects within our galaxy, but this is inconsistent with his position that the Universe is 8,000 years old.
  6. His theory cannot explain the Earth’s ability to keep an atmosphere in the past, when atomic masses would have been much less.

In addition, William Dembski has pointed out, "[D]eeper problems confront Setterfield's proposal. The fundamental constants of nature seem finely tuned to one another so that even small changes in their values would fundamentally disrupt the universe (for example, by preventing the formation or stars, planets, or life).5 Perhaps the most famous scientific formula of all time is Einstein's E = mc2. The "c" here is the speed of light in a vacuum. This formula shows that energy is proportional to the speed of light. Thus, given a vastly increased speed of light in times past, chemical and physical reactions would have been much more energetic. It follows that increasing the speed of light would upset the fine-tuning of the universe."[12]

Creation Ministries International and Answers in Genesis have c-decay on their lists of arguments that creationists should not use. CMI lists it as a "doubtful argument" stating, "Although most of the evolutionary counter-arguments have been proven to be fallacious, there are still a number of problems, many of which were raised by creationists, which we believe have not been satisfactorily answered."[1]



  1. 1.0 1.1 Arguments we think creationists should NOT use (Creation Ministries International)
  2. 2.0 2.1 2.2 The magazine was then titled Ex Nihilo, the journal was then known as Ex Nihilo Technical Journal, and CMI was then known as the Creation Science Foundation.
  3. Setterfield, 1981
  4. From "The Velocity of light and the age of the universe": "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."
  5. From "The Velocity of light and the age of the universe": "From these observations it would seem that beyond 1960 the speed of light had reached its minimum value and was constant thereafter."
  6. 6.0 6.1 Sarfati, Jonathan, Have fundamental constants changed, and what would it prove?, Wed. 22nd August, 2001Wed. August 22nd, 2001 (Creation Ministries International)
  7. Setterfield, Barry, December, 2009, question and comment on the statistical use of the data
  8. Smith, Ken. "Creation Physics and the Speed of Light." In "Creationism" An Australian Perspective 4th ed. Bridgstock, Martin and Smith, Ken, eds. Austalian Skeptics: Roseville, NSW, 2001: p. 69.
  9. Plimer, Ian, Telling Lies for God, 1994, p. 40, Random House, ISBN 0 09 182852 X.
  10. 10.0 10.1 10.2 Gerald A. Aardsma: "Has the Speed of Light Decayed?"
  11. Jellison, G. P., and W. T. Bridgman. "Analysis of the Variable Lightspeed (c-Decay) Theory of Barry Setterfield." (2007).
  12. Dembski, William A., The End of Christianity: Finding a Good God in an Evil World, p. 67, B&H Academic, 2009; ISBN 9780805427431.
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