Matter creation

From Freepedia

Matter creation is process inverse to annihilation. It usually refers to pair creation, i.e., the conversion of photons into a fermion and antifermion pair, such as an electron and a positron. Since momentum conservation law prohibits the creation of a pair of fermions out of a single photon, pair creation involves at least two photons (or a single photon and one or more fermions). This, in turn, requires a high photon density to create a noticeable amount of matter.

Energy conservation law provides a lower limit for the photon energy required for creation of a pair of fermions. It must not be less than the rest energy of the fermions created. For example, to create an electron-positron pair (<math>2mc^2</math> = 1.04 MeV), the total energy of the photons must be greater than or equal to 1.04 MeV, corresponding to soft gamma ray photons. As another example, the creation of a proton-antiproton pair requires more than 1.88 GeV (hard gamma ray photons). Thus, to precipitate matter, a photon gas must not only be very dense but also very hot.

Matter creation during the early development of the universe (see Big Bang) is believed to be the source of fermionic matter in the visible universe, which consists predominantly of electrons and protons.