Pair production is a prediction of practical QED, the applied science of quantum electrodynamics. It is the simultaneous creation of an electron and its antipaticle, the positron. It occurs wherever and whenever an extremely energetic photon with internal energies exceeding 1.02 MeV glances near an atomic nucleus. This flash of infinitesimal lightning strikes almost always happened at lightspeed. It vindicates the validity of Einstein’s energy and mass equivalence: m=E/c, the creation of mass from energy as the meaning of the phrase “light up to matter.” Conversely, the opposite meaning “matter down to light” will be discussed in a separate thread.

Pair production always obeys the laws of conservation, in this case, the law of energy conservation and the law of linear momentum conservation. Still, it could subtly hinted the law of angular momentum conservation but no experiment is refined enough to show it which might indicate a much finer working physics at the glancing of the nuclei. These energetic photons are technically classified as gamma rays. Together with X-rays they are the most powerful, the most energetic, and the most penetrating quantum of light found everywhere and everywhen in the entire universe. Gamma rays were first classified as one of the three components of radioactivity by Ernest Rutherford in 1903. The others are alpha rays and beta rays. Alpha rays are really energetic nuclei of helium while beta rays are simply energetic electrons. Furthermore, the extraterrestrial sources of gamma rays can be distinguished from the interstellar or extragalactic cosmic rays which are mainly energetic protons. The mysterious occurrence of celestial gamma ray bursts which occur once per day or so from completely random directions of the sky were thought to be explosions of very massive stars or galaxies far, far away and long, long time ago.