recombination time

recombination time

The period in the Universe's history, according to the Big Bang theory, after which the temperature was low enough for atoms to form from free nuclei and electrons. This required a temperature of less than about 3000 K, which occurred when the Universe had expanded for about 300 000 years. At the time of recombination the radiation in the Universe began to propagate freely and ceased to interact with free electrons. This freely propagating radiation now resides in the microwave background. The name ‘recombination’ is a misnomer because neutral atoms are formed for the first time at the recombination era, never having existed previously.