Cosmic Antimatter; April 1998; Scientific American Magazine; by Tarlé, Swordy; 6 Page(s)

In 1928 the English physicist P.A.M. Dirac predicted the existence of antimatter. Dirac claimed that for every particle of ordinary matter there was an antiparticle with the same mass but an opposite charge. These antiparticles could join to form antiatoms, and the antiatoms could form antimatter counterparts to every object in the universe-- antistars, antigalaxies, even antihumans. What is more, if a particle of matter collided with a particle of antimatter, they would both be annihilated in an energetic burst of gamma rays. If a human and an antihuman shook hands, the resulting explosion would be equivalent to 1,000 one-megaton nuclear blasts, each capable of destroying a small city.

It was an extraordinary proposition. The theory was confirmed just four years later, when Carl D. Anderson, a physicist at the California Institute of Technology, detected the first antiparticle. While using a cloud chamber to study cosmic rays--high-energy particles that bombard the earth from space--Anderson observed a vapor trail made by a particle with the same mass as an electell much about the origins of antimatter. They may also indicate whether antistars and antigalaxies really exist.