Material composed of antiparticles, which correspond
to ordinary protons, electrons, and neutrons but have
the opposite electrical charge and magnetic moment.
When matter and antimatter collide, both may be annihilated,
and other elementary particles, such as photons and
pions, are produced.
In 1932 Carl D Anderson, while
studying cosmic rays, discovered the positron or antielectron,
the first known as antiparticle.
Any antimatter in
our part of the universe is necessarily very short
lived because of the overwhelming preponderence of
ordinary matter, by which the antimatter is quickly