Antimatter resembles ordinary matter but with certain properties of its particles, such as electric charge, reversed. Both kinds of matter consist of elementary particles. The elementary particles of antimatter have the same mass as their counterparts in ordinary matter. For example, the positron is the antimatter counterpart to the electron. It has the same mass as an electron but a positive charge, rather than a negative one.
Antimatter particles can bind together just like ordinary particles. For example, a positron and antiproton (the antimatter counterpart of a proton) can combine to form an antihydrogen atom. In principle, particles of antimatter can combine to form antiatoms and antimolecules of all the ordinary atoms and molecules. However, up until the early 2000’s, only one type of antiatom, antihydrogen, and a few types of antinuclei had been created in experiments. In 2011, scientists working with the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory on Long Island, New York, reported the creation of antihelium (see Relativistic Heavy Ion Collider).
When matter and antimatter particles come into contact, they can convert into energetic photons or other particles in a process called pair annihilation. For this reason, antimatter on Earth is usually destroyed instantly, through contact with ordinary matter.The reverse process can also take place, in which a particle-antiparticle pair is created. In either case, antimatter and ordinary matter are created or destroyed in equal amounts.
Loading the player...Antimatter created in thunderstorms
The British physicist Paul Dirac predicted the existence of antimatter in 1931, based on an equation he discovered in 1928, describing how electrons behave. In 1932, the American physicist Carl D. Anderson discovered evidence for antiparticles. Although Dirac’s theory was incomplete, modern particle physics predicts that all elementary particles have antiparticle counterparts. Some electrically neutral particles serve as their own antiparticles.
The existence of antimatter raises questions regarding the big bang. The big bang was the massive cosmic explosion that marks the birth of our universe. Most matter was created in the first few seconds after the big bang. If identical quantities of ordinary matter and antimatter were created then, they would have destroyed each other entirely, leaving nothing but energy behind. However, we know that ordinary matter remains in the universe. This fact suggests that more matter than antimatter was present in the first fraction of a second following the big bang. Scientists do not yet know why more matter than antimatter was created.
Doctors use antimatter widely in positron emission tomography (PET). A PET scan uses gamma rays given off by electron-positron pair annihilation to produce three-dimensional images of the brain or other body parts (see Positron emission tomography (PET)). Scientists have also observed gamma rays that were produced by pair annihilation during thunderstorms. Some observers suspect that the antimatter created during the storms is a product of lightning strikes.
See also Anderson, Carl David; Dirac, Paul Adrien Maurice; Matter (Antimatter).
