An idea often taken advantage of by proponents of creationism
that light has
been gradually slowing down with time. When one looks at galaxies that are
further away, the light that arrives is redshifted
. The further away the
galaxy, the greater the redshift. Cosmologists
explain this as the expansion
of the universe
, with things that are further away moving more rapidly.
The tired light theory, tries to explain this phenomenon by saying that the
objects are not moving away, but that light is slowing down, causing the
wavelength to red shift. However, this still does not explain the background
radiation levels of the universe, which have the spectral shape of a black body.
Furthermore, the speed of light is more than a quantity for light, its
a fundamental constant that enters into a number of other physical laws.