Antimatter The existence of antimatter was postulated by Paul Dirac in 1928, and the first antimatter particle, the anti-electron called the positron, was discovered by Carl Anderson in 1932. Every type of matter particle is mirrored by an antimatter particle, that carries equal and opposite electric charge and also has opposite values of all the other internal properties of its matter partner. Matter and Antimatter in the Universe The opposite properties of matter and antimatter particles enable them to annihilate (a complete transformation of their mass into energy) when they come into contact, emitting radiation. The fact that we see no such radiation in the observable Universe suggests that it contains no large concentrations of antimatter. However, direct searches for antinuclei in the cosmic rays are being carried out by the AMS (Alpha Magnetic Spectrometer) and other experiments. For a survey of the history of antimatter and experiments to study it, look at the instructive CERN antimatter Website. A small difference Experiments on kaons and antikaons (certain types of elementary particles) in 1964 by James Cronin, Val Fitch and their collaborators showed that they do not decay in quite the same way. It was suggested by Andrei Sakharov that this small matter-antimatter difference might be linked to the dominance of matter over antimatter in the Universe today. Many experiments at particle accelerators now seek to understand better this small matter-antimatter difference, and might enable physicists to calculate the relative amounts of matter and radiation in the Universe. If there were much less matter than is known, the formation of galaxies and stars would have been impossible.

View into the Antiproton Decelerator's (AD) experimental hall at CERN, where antiprotons are produced and slowed to to 1/10 of the speed of light.