Title: The cosmic asymmetry between matter and antimatter.
Abstract: }\I the fundamental constituents of matter come in matched pairs: for every kind of particle there is an antiparticle that is identical in mass but opposite in other properties, such as electric charge. The symmetrical pair ing of particles and antiparticles is re quired in order to unite the two great theories of 20th-century physics: relativ ity and quantum mechanics. The sym metry has been well verified by experi ment. Since 1932, when the positron, or antielectron, was discovered, the cata logue of antiparticles has grown apace with the catalogue of ordinary parti cles. Indeed, a particle and its antiparti cle have often been discovered simulta neously when the two were created as a pair by a high-energy collision in a parti cle accelerator. Such collisions always seem to yield matter and antimatter in equal quantities; indeed, it was long as sumed that the laws of nature express no preference for matter or antimatter. And yet in the world outside the labo ratory antimatter is almost never en countered. The atoms composing the earth consist of neutrons, protons and electrons, but never their antiparticles. Does this asymmetry prevail through out the universe? That is, does the entire universe consist predominantly of mat ter, with very little antimatter? If it does, has the asymmetry always existed, or did the universe begin with equal num bers of particles and antiparticles and somehow develop an imbalance later? Recent findings in cosmology and par ticle physics suggest answers to these questions. They suggest that in the first instant after the big bang, when the uni verse was much hotter and denser than it is now, there were equal amounts of matter and antimatter. Before the uni verse was 10-35 second old, however, violent collisions among particles cre ated conditions that led promptly to an asymmetry between matter and anti matter. The asymmetry has been locked into the universe ever since. The road
Publication Year: 1982
Publication Date: 1982-01-01
Language: en
Type: article
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