Since for baryons and leptons, positive numbers represent matter and negative numbers represent antimatter, the consequence of ( I B i - I L i ) conservation is that baryons can convert into antimatter leptons and antimatter baryons can convert into matter leptons; for example, a proton could convert into a positron (antimatter electron). When the expansion of the universe dropped the photon energy below 1.022 MeV, electron/positron production ceased, nominally locking in the universe as being a bath of photons, electrons, and positrons. The universe would also contain neutrinos, the production of which is beyond this article, as well as a few protons and antimatter protons that were created by chance encounter by triplets of quarks or antiquarks. It predicted the existence of what we now call antimatter.[4] Antimatter is the opposite of matter.[5] When matter and antimatter are combined, they annihilate into a substantial amount of energy. [Extracted from the article]