I went to wikipedia to look up decoupling and ended up getting a pretty crappy result "In physical cosmology, the term decoupling is often used for the moment during recombination when the rate of Compton scattering became slower than the expansion of the universe. At that moment, photons nearly stopped their interactions with charged matter and "decoupled", producing the cosmic microwave background radiation as we know it. The term decoupling is also used to describe the neutrino decoupling which occurred about one second after the Big Bang. Analogous to the decoupling of photons, neutrinos decoupled when the rate of weak interactions between neutrinos and other forms of matter dropped below the rate of expansion of the universe, which produced a cosmic neutrino background." could someone answer me this; when it says "photons nearly stopped their interactions with charged matter and "decoupled" " what does it mean nearly,in reference to the cmb,has the cmb completely stopped interacting with matter?is it possible for it to be red/blue shifted enough to be absorbed by any matter at all? do the photons travel undisturbed completely? im just thinking this,if the cmb cant interact with matter in any way then how do we detect it?