Weak Interactions
Some of the particles participating in the big bang can undergo weak interactions as well as ones with
photons. Since at low temperatures
the strength of the weak interactions is much lower than for the electromagnetic
one, we may expect that the former decouple at an earlier time than the latter. Calculations show that
the weak interactions froze out only about 1 second after the big bang. Thus, they played a role in the
equilibrium only in the first instants and have been decoupled ever since.