The cosmos, an endless expanse of luminiferous aether bathed in both darkness and light! Since Einstein's paper in 1905 on the special theory of relativity, the speed of light has been considered a fundamental constant of nature. So, if the speed of light is invariant, what happens when this light gets stretched or compressed? This phenomenon is described by the concepts of redshifting and blueshifting. It is these very concepts that allowed humanity to determine that the universe is not only expanding, but is accelerating in its expansion, a theory that also suggests the presence of dark matter and energy.
