antimatter

A form of matter that is composed of particles that exhibit opposite quantum mechanical properties from particles of normal matter. As an example, positrons are the antimatter particles that correspond to electrons, which are made of regular matter. A positron is simply an electron with a positive, rather than negative, charge. When matter and antimatter particles encounter each other, they annihilate to become energy according to Einstein's famous equation E=mc^2. Pairs of matter and antimatter particles can also be created from energy. Most of the matter in the universe is normal matter; there has been very little antimatter present in the universe since the Big Bang.