One of the experimental evidence that supports the theory of big bang is cosmic microwave background radiation (CMBR). From what I've read is that CMBR is the left over radiation from an early stage of the universe.
My questions are:
Why are we able to detect this radiation at all?
As the nothing travels faster light, shouldn't this radiation have passed over earth long time ago?
Why is this radiation filling the universe uniformly?
Answer
This radiation was created 380,000 years after the Big Bang at every place of the Universe and from every place of the Universe, it was moving in every possible direction. So the density (per unit volume and per unit solid angle of motion) of photons at a particular place (x,y,z) and a particular direction of motion (kθ,kϕ) was always constant: ρ(x,y,z,kθ,kϕ)=const
As the Universe is getting older, we are observing CMB photons that were created at an increasing distance from the Earth. Note that ρ above also depends on ω∼|→k|, the frequency of the photons; this dependence is given by the black body curve while the temperature is dropping inversely proportionally to the linear distances between things in the Universe that keep on increasing.
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