Death of a Law

The universe last week was just as substantial as it had ever been; the ground underfoot was just as firm. But for physicists who search for the inner secrets of matter, a new and tempestuous age had begun. One of their basic laws of nature had been proved not a law at all. From now on their erudite science would never be the same again.

The excitement started when Columbia University told about two experiments proving that the "parity law," one of the cornerstones of nuclear physics, is a man-made convention which does not bind nature except in special cases. According to the parity law, objects that are mirror images of each other must obey the same physical rules (see chart). Applied to nuclear physics about 30 years ago, this principle became extremely important. Theories that seemed to violate it were summarily rejected. Much of the structure of modern nuclear physics was erected on parity.

Tau-Theta Puzzle. Last summer two daring theorists, both of them Chinese, challenged parity. Professors Tsung Dao Lee of Columbia and Chen Ning Yang of the Institute for Advanced Study in Princeton were visiting Long Island's Brookhaven National Laboratory, whose pleasant summer climate and massive equipment attract vacationing physicists from all over the country. A leading topic at bull sessions, some of them held alfresco on Westhampton Beach, was the "tau-theta puzzle," which many leading physicists have been trying manfully to crack since 1953.

Physicists blame the tau-theta puzzle on the world's two most powerful atom-smashers, the Cosmotron at Brookhaven and the Bevatron at Berkeley, Calif. The atom-smashers have, in their few years of operation, raised more problems than they have solved. One of their most baffling stunts was to produce the K meson, a short-lived particle knocked out of atomic nuclei. In all significant ways K mesons are alike, but some of them, called "tau K mesons," decay into three pi mesons; others, called "theta K mesons," decay into only two pi mesons. For mathematical reasons which physicists can explain only to other physicists, this inconsistent behavior seemed to violate the sacred parity principle. What could be done about it? The experimental evidence was plain, but it was hard to accept. It was as if science found evidence of a material that is repelled rather than attracted by gravitation.

Most physicists tried vainly to solve the tau-theta puzzle in a way that preserved parity. Showing less respect for scientific propriety, Drs. Lee and Yang suggested last summer at Brookhaven that perhaps the trouble lay not with the K mesons but with parity itself. If parity could be violated on occasions, the odd behavior of the K mesons would be easy to explain.

Chilled Cobalt. In brilliantly reasoned papers Lee and Yang showed that it should be possible to get along without parity. They also suggested ways to test experimentally whether parity is really a basic principle of nature. By this time the whole world of theoretical physics was watching Lee and Yang, and the best facilities in the U.S. were offered for testing their theory.

Another Chinese physicist at Columbia, Associate Professor Chien-Shiung Wu, went to Washington. Working with a topflight team at the National Bureau of Standards, she arranged an elaborate deepfreeze apparatus to cool radioactive cobalt 60 to 0.01DEG above absolute zero ( -- 273.1DEG C.). The cobalt nuclei are known to be spinning, and they continue to spin in the deepfreeze, but their random "thermal" motions are reduced almost to nothing by the extreme cold. This accomplished. Dr. Wu and her helpers applied a powerful magnetic field that pointed the cobalt nuclei in one direction as if they were tiny magnets.

Temperature has no effect on radioactivity, so the chilled, lined-up cobalt atoms went right on disintegrating and emitting electrons. According to the parity principle, the electrons should shoot off in equal numbers in both directions along the spin axes of the lined-up nuclei. Any preference by the electrons for either direction would prove that parity is not a real law of nature.

Chinese Lunch. The chilled cobalt experiment proved extremely difficult, but by last fortnight Dr. Wu reported her results. The electrons were not shooting off equally in both directions. This looked bad for parity, and spirits rose high in the anti-parity camp.

For Columbia's physicists, Fridays are "Chinese lunch days," when Professor Lee, a gourmet as well as a physicist, takes a select group to a nearby Chinese restaurant, where he orders special dishes. During a very long Chinese lunch, Dr. Wu's progress in Washington was discussed excitedly. Dr. Lee turned to Associate Professor Leon M. Lederman. who works with Columbia's 385 million-volt cyclotron at Irvington, N.Y. "Why not try the mu mesons?" he asked.

The Columbia cyclotron (called affectionately a "pie factory") is arranged to generate a beam of pi mesons, which turn quickly into mu mesons. Using mu mesons to test parity had often been discussed, but had seemed too difficult. This time Dr. Lederman and Associate Richard L. Garwin had a new idea. Working at top speed with Graduate Research Assistant Marcel Weinrich, they set up an extremely simple experiment. In the path of the mu mesons streaming from the cyclotron, they placed a block of carbon about 6-in. square and 1-in. thick with a coil of wire wound around its perimeter.

Mu mesons disintegrate in two-millionths of a second, each forming an electron and two neutrinos, and this lifetime is too short to permit thermal motions in the carbon block to disturb them appreciably. When they lodge in the carbon, they are all spinning in the same direction, and under these conditions the parity principle requires that when they disintegrate, they must shoot out the same number of electrons in each direction along their common spin axis.

"You're In!" The mesons did no such thing. They shot out twice as many electrons in one direction. When a small current was passed through the coil the mesons turned around and shot their electrons in the other direction. This proved that mesons can be mirror twins (like right-hand and left-hand gloves) and still not behave in the same way. After the conclusive run of the experiment, says Dr. Lederman, "I called Lee on the telephone and told him, 'You're in!' " Parity was dead.

An experiment so simple could be copied elsewhere, so Columbia announced its success and the parallel success of the cobalt 60 experiment as quickly as was seemly.* As soon as the news got on the wires, questions and congratulations began to flow in from excited physicists all over the world.

Many physicists now feel that a new era has begun. The situation can be compared to the period of confusion after the Michelson-Morley experiment destroyed the "luminiferous ether" (1887). The physics of that time was dependent on the ether to carry the waves of light across airless space, and physicists for a while were sad to lose it. Then new and better theories (relativity and quantum theory) showed how light can travel handily without any medium to carry it. The luminiferous ether, a basically wrong idea, had been in 'fact an obstacle to man's exploration of the physical universe. When it was abolished, physics spurted ahead.

The abolition of parity may give the same kind of boost to those parts of physics that it affects. Nearly all physicists agree that since the end of World War II their science has fallen into deeper and deeper confusion. Great machines like the Cosmotron are spewing out all sorts of strange subatomic particles, and many of them, like the K meson, have "made no sense at all. Other new problems have been appearing faster than they can be solved. Many physicists felt that something radical would have to be done to bring any kind of order out of this runaway chaos.

Abolition of parity may prove to be this needed and violent reform. If Drs. Lee and Yang and their backers stand up against the attacks that will be made upon them, many physical theories will have to be rebuilt without the parity principle. The new, better theories may create new ideas about the universe. Matter and space as science now knows them may have a right-handed twist, like a screw with a right-hand thread. Matter in other galaxies may be lefthanded, or perhaps left-handed matter can be created or assembled on earth and prove to have different and startling properties.

*Another parallel experiment, by Dr. Valentine Telegdi and Jerome I. Friedman of the University of Chicago, was giving encouraging though preliminary results.

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