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In their groundbreaking experiment at Brookhaven National Laboratory in Upton, N.Y., in 1964, the physicists examined two key laws of symmetry: 1) that in nuclear reactions all particles can be replaced by their antimatter opposites—for example, electrons by positrons; and 2) that nature does not distinguish between a reaction and its mirror image with respect to such processes as the decay (or breakup) of particles. Despite isolated variations, these rules taken together were presumed inviolable.
Fitch and Cronin discovered to their surprise that this is not always so. Experimenting with short-lived particles known as neutral K2-mesons, they found that in two of every 1,000 reactions these bits of matter would decay into a pair of µ-mesons (called pions) instead of the three pions that would be predicted on the basis of the combined symmetry rules. Such results indicated a possible violation of another basic presumption of symmetry known as time reversal: that reactions can run either forward or backward, like film in a movie projector. In effect, Fitch and Cronin showed that the universe was not as symmetrical as had been expected, a turn of events so profoundly disturbing that, as one member of the Nobel committee explained, "it would take a new Einstein to say what it means."
Lately, Fitch and Cronin's work has been studied intensely by cosmologists seeking an answer to a perplexing question. In the immediate aftermath of the Big Bang, the newborn universe was presumably symmetrical, consisting of equal amounts of matter and antimatter. But now it seems to be made largely of matter. Why? The Fitch-Cronin work suggests an answer: in those primordial moments, the production of ordinary matter slightly outpaced antimatter—by about one part in 10 billion. Then, as the universe cooled and particles collided, matter and antimatter largely annihilated each other. Just enough matter, however, was left over to keep the universe from destroying itself at birth.
CHEMISTRY: GENETIC ENGINEERS. The chemistry prize, in part, gives recognition to an experiment that almost did not take place. It was set up in 1971 by Biochemist Paul Berg of Stanford University, in an effort to understand why normal cells turn cancerous. He planned to insert the monkey virus SV40, which can cause tumorous growth in the cells of other animals, including laboratory cultures of human cells, into test tube versions of the common intestinal bacterium Escherichia coli. But the project was forestalled by the fears of Berg and some other scientists that it could accidentally plant a slow-ticking cancer time bomb in humans.
Last week's award made it clear that the Swedish Academy thought these fears were exaggerated. Berg, 54, who subsequently helped draw up federal guidelines for similar research, won half of the prize for this and other achievements in the fast-expanding field of genetic engineering. The other half was shared by Harvard's Walter Gilbert, 48, and Frederick Sanger, 62, of England's Cambridge University, for developing rapid methods of decoding genetic structure, a key tool in this biochemical revolution. It was Sanger's second Nobel in chemistry. His first prize came in 1958 for elucidating the structure of insulin, the body's molecule for breaking down sugar.