Barry Setterfield

Barry Setterfield is a Young Earth creationist best known for promoting c-decay, the proposition that the speed of light was faster in the past and has been degrading ever since. He argues that the decreasing speed of light, along with 4 other quantities, point to a young earth: specifically, the fundamental physical constant 'c' -- the speed of light in a vacuum -- has decreased by several orders of magnitude and that Planck's constant 'h' has similarly changed, such that 'c h' is a true constant.

The Atomic Constants, Light, and Time
In his 1987 paper with Trever Norman, "The Atomic Constants, Light, and Time", Setterfield claims an observed decrease in the speed of light in measurements since the 17th century. Since atomic processes are limited by the speed of light, the paper concludes that atomic processes - such as e.g. atomic decay rates! - must have decreased in speed as well. The comparison is with "dynamic time", which is based on the rotational speed of the earth, which the two authors assume constant. One problem with this argumentation is that we can explain a decrease in the rotational speed of the earth (see The frequency of leap seconds indicates a young earth), whereas we have no explanation of why the speed of light should vary. Also notice that measurements of the speed of light is dependent on what is understood by a "kilometer", not only on what is understood by a "second". The meter (and therefore the kilometer) was first standardized in the early 19th century.

Like all good preachers of woo, he carefully tailors his ideas to avoid being verifiable or falsifiable. He claims that the decay curve just recently flat-lined. It was still decaying, honest, but we just missed it. Unfortunately for him, it has been demonstrated to be false.

Similar researchers
Setterfield is one of a gaggle of proposers of fanciful theories of varying speeds of light - including Joao Magueijo, Victor S Troitskii , JW Moffat , John D Barrow and John Webb.