Decoupling (cosmology)

In physical cosmology, decoupling is a transition from close interaction between a particle type and other matter to their substantial independence of each other.

The most often discussed such decoupling is at 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.

Another instance is 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.