Anti-Matter EntityParticle Annihilation / Positron Emission

Anti-Matter Entity has your mass, the opposite charge, and no future in a room full of electrons.

Paul Dirac's 1928 equation for the electron had solutions he could not get rid of, with negative energy. By 1931 the reading that survived was that they described a new particle: the electron's twin, with positive charge. In 1932 Carl Anderson found one, a cloud-chamber track left by a cosmic ray that bent like a positive charge in a magnetic field but was far too light to be a proton. He called it the positron and received the 1936 Nobel Prize.

When a slow positron meets an electron, both can vanish. Their combined rest energy, 2mc², leaves as light. Momentum has to be conserved, and two particles nearly at rest have almost none, so the light usually leaves as two photons flying in opposite directions, each carrying one electron's rest energy: 511 keV. The number on this page is that energy.

Sometimes the pair first forms a brief atom, positronium. With their spins opposite, it annihilates into two photons in about a tenth of a nanosecond. With the spins parallel, a symmetry rule forbids two photons, so it has to make three, and it lasts roughly a thousand times longer.

Hospitals use this daily. In a PET scan, a tracer releases positrons inside the body; a ring of detectors catches the 511-keV pairs leaving back to back, and each pair draws a line through the point where it was made.

One question is open. The early universe should have made matter and antimatter in equal amounts, and they should have annihilated each other. Something tipped the balance slightly, and the leftover is everything you can see. Nobody yet knows what.

The Entity is not your opposite. It is you, with the signs flipped.