Lincoln Wolfenstein reviews Helen Quinn and Yossi Nir’s The Mystery of the Missing Antimatter:
Each charged elementary particle has a counterpart with the opposite charge, which is known as an antiparticle. The antiparticle partner of the negative electron, for example, is the positive positron, which was predicted by Paul Dirac in 1930 and discovered by Carl Anderson in 1932; while for the proton it is the antiproton, which was discovered by Emilio Segrè and Owen Chamberlain in 1955. Just like normal particles, antiparticles can combine, forming atoms of “antimatter”. Dirac’s theory suggested that the laws of physics were exactly the same for matter and antimatter; so given this symmetry, why is our visible universe made of matter with no antimatter? This is the question addressed by Helen Quinn and Yossi Nir in The Mystery of the Missing Antimatter.
A surprising experimental discovery in 1964 suggested a possible answer. While experimenting with K-mesons, which belong to the class of “strange” particles that contain a single strange quark, Jim Cronin and Val Fitch at Princeton University found a small asymmetry between particles and antiparticles. Their experiments revealed that there is an interaction that is not the same for quarks and antiquarks — a phenomenon that now goes by the name of CP violation (where C is charge conjugation and P is parity).
This led the Russian theoretical physicist Andrei Sakharov — who later became famous as a campaigner for human rights — to propose that at the beginning of the universe there were equal numbers of particles and antiparticles, but then, at an early stage in the evolution of the universe, some reaction or decay process that involved CP violation led to the destruction of some of the antiparticles.