Previously, we saw that the proper distance between two objects can increase or decrease with time depending on the function a(t) , even if the objects are "stationary". What if those two "objects" a...Previously, we saw that the proper distance between two objects can increase or decrease with time depending on the function a(t) , even if the objects are "stationary". What if those two "objects" are the crests of a light wave? As the light wave travels, then distance between those two crests can change. This causes the wavelength, and therefore the frequency, of the wave to change. We refer to this as cosmological redshift.
