In the early universe as described by the big bang models: transition that occurs at cosmic time around 380 000 years. At this point, the universe has cooled down sufficiently for atomic nuclei and electrons to form atoms – without immediately being ripped apart by electromagnetic radiation. The etymology of recombination does not quite correspond to the physics – this is not a re-combination, it is the first such combination in the universe as we know it. In the process, the cosmic background radiation decouples from the material universe.