This is probably a very dumb question for this forum, if so I'm sorry; but from what I know it does not make sense that the CMB is still visible and measurable today.
From what I understand, the CMB dates back to a time which has been calculated at being 380,000 years after the big bang, time at which photons in the primordial "particle soup" were able to escape.
But then photons move, unrestricted, at the speed of light (save for space time curvatures and collisions) so I would expect that this batch of photons which were able to escape would be long gone by now... Yet COBE, WMAP and Planck can still trace the origins back to the CMB. And save for the precision of measurements, due to the progress of technology, they pretty much all give the same picture.
I am at a loss. Especially since between COBE and WMAP the proof that the expansion of the universe is accelerating over time has been established.
I must be missing something fundamental here; why is it that this "batch of photons" is still visible today? Or does that mean that the CMB still has a physical existence somehow?
