New Theory: Speed of Light is Variable
According to a new theory, the speed of light is not necessarily a constant value approximately 3*10^8 m/s.
It is widely believed that the CMB is the energy left over from the early moments after the Big Bang. Although there are small pockets where the energy is varies, on a wide scale the CMB is mostly uniform possibly due to inflation of our universe.
The theory that the speed of light varies is in direct conflict with inflation, the idea that the universe rapidly ballooned in size. Inflation explains why the CMB is pretty stable. Different parts of the universe were influenced by each other and all expanded at the same rate, keeping the CMB nearly constant.