Antimatter

Antimatter is matter made of antiparticles, which have the same masses as corresponding particles but opposite electric charges and other quantum numbers. When a particle meets its antiparticle, they can annihilate into other forms of energy and particles.

Antiparticle: A particle with the same mass as a corresponding particle but opposite additive quantum numbers. Antimatter is built from these counterparts, including positrons and antiprotons.
Paul Dirac: A British theoretical physicist whose relativistic electron theory implied the existence of antiparticles. His 1928 equation provided antimatter’s first theoretical foundation.
Antihydrogen: The simplest antiatom, composed of an antiproton and a positron. It allows precision comparisons between atomic matter and antimatter.
Baryon asymmetry: The observed excess of baryons over antibaryons in the universe. It states the central cosmological puzzle: why ordinary matter dominates.
Ordinary matter: Matter composed mainly of particles such as electrons, protons, and neutrons. Its particles have opposite additive quantum numbers to their antimatter counterparts.
Pair production: The creation of a particle and its antiparticle from energy or another interaction. It is a direct way to create matter and antimatter together.
Positron: The electron’s antiparticle, with equal mass and positive electric charge. It was the first antiparticle discovered, in cosmic-ray tracks in 1932.
CERN Antiproton Decelerator: A CERN facility that slows antiprotons for experiments on antimatter. It supplies low-energy antiprotons for creating and testing antihydrogen.
Baryogenesis: The set of proposed processes that generated the universe’s excess of matter over antimatter. Its mechanisms must explain the cosmic imbalance left by the early universe.
Dark matter: A form of matter inferred from gravitational effects but not identified through emitted or absorbed light. It is not simply antimatter; its composition and relation to known particles remain uncertain.

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