What's Antimatter? (It's not just in Star Trek)

"antimatter: a form of matter (atoms and stuff) in which each particle (for example an electron) has the opposite set of quantum properties (such as electic charge) to its counterpart. The classic example of a particle of antimatter (an antiparticle) is the antielectron (or positron), which has the same mass as an electron but a positive charge instead of a negative charge. The existance of antielectrons was predicted by Paul Dirac, at the end of the 1920's, when he found that the equation which represents a complete description of the electron in terms of both quantum mechanics and the special theory of relativity has two sets of solutions, one courresponding to negatively charged particles and one to positively charged particles. The exact meaning of this was not clear until 1932, when Carl Anderson discovered positrons form the traces they left in his cosmic ray detector.

Our visible Universe is almost entirely composed of matter, and very little antimatter has existed since the Big Bang in which the Universe was born. When an antiparticle meets its particle counterpart (for example, when a positron meets an electron), they annihilate, converting all of their rest mass into energy in line with Einstein's equation E=mc^2. Antiparticles can be made out of energy in the reverse of this process, but only if a particle counter part for every antiparticle is produced as well. This happens naturally in high-energy processes involving cosmic rays, and also in high-energy experiments in accelerators on Earth. Because the world is overwhelmingly made of matter, however, any antiparticle produced in this way soon meets up with a particle counterpart and annihilates."