An Etymological Dictionary of Astronomy and Astrophysics

The production of → light elements, roughly three minutes after the → Big Bang when the temperature of the → Universe dropped from 10³² K to approximately 10⁹ K. In a short time interval → protons and → neutrons collided to produce → deuterium. Most of the deuterium then fused with other protons and neutrons to produce → helium and a small amount of → tritium. The element
→ lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei. According to the Big Bang nucleosynthesis theory, roughly 25% of the mass of the Universe consists of helium. It also predicts about 0.01% deuterium, and even smaller quantities of lithium. These predictions depend critically on the → baryon-photon ratio. Same as → primordial nucleosynthesis.

See also: → Big Bang; → nucleosynthesis.