The Left Hand of God

After World War II, physicists in the United States and elsewhere were able to return to basic research. One group used balloons and other devices to lift photographic emulsions high in the atmosphere, where they recorded cosmic-ray tracks. Cosmic rays are the particles that bombard Earth from space or the particles that these primary particles knock out of the molecules that they encounter along the way in the atmosphere. Collisions between a cosmic ray and a molecule produce higher energies than the particle accelerators ("atom smashers") of the day were able to achieve. As Albert Einstein had shown in 1905, energy can be changed into mass. In fact, the result of these collisions at high energies is the production of new particles of masses greater than are observed in ordinary matter.
The new particles often behaved in very strange ways. In fact, Murray Gell-Mann, in the early 1950s, began to call one particular property strangeness, a name that has stuck. In physics, it is possible to specify completely whether a particle is "strange" or not. Among the strangest of the strange were particles that have undergone numerous name changes. These particles are the neutral K (kappa) mesons, also called kaons. In the 1950s, physicists called one variety of K meson tau and another theta (today tau refers to an entirely different particle). The problem with tau and theta was that every bit of evidence suggested that they should be exactly the same particle; but when, like all heavy particles, they decayed into lighter particles, tau decayed into three particles and theta decayed into two. Furthermore, the products of the two decays implied that the original particles had to be different in an essential property called parity. The fundamental wisdom of the time was that two otherwise identical particles could not have unequal parities.
Parity itself is a simple concept that is based on an either/or situation. The most common representations are in terms of numbers, usually + 1 and -1, or in terms of right and left. Since these two seemingly dissimilar ideas are mathematically identical, physicists often use the numbers + 1 and - 1, even when the actual physical operation is closer to right and left. Parity for particles is an example of this. The tau has a parity of - 1 while the theta has a parity of + 1. The experiment that finally explained "the tau-theta paradox," however, rested on the difference between right and left.
By 1956, this problem was a focal session for a physics conference in Rochester, NY. Physicits Martin Block and Richard Feynman were roommates at the meeting. Block suggested a radical idea to Feynman, which Feynman passed on to the conferees at the session on the tau-theta problem. Block's idea was that there is some fundamental difference between right and left. This was radical because the idea that right and left are essentially the same, called the law of conservation of parity, was one of the pillars of theoretical physics at the time. Frank Yang, one of the speakers at that session, and T.D. Lee met a month later at the White Rose Cafe near Columbia University and decided to work out the implications of Block's idea. In another month or so Yang and Lee were able to point to specific experiments that would resolve the question. Since they were theoreticians, others performed the experiments. By the end of the year, experiments conducted under the leadership of Chien-Shiung Wu had shown that parity is not conserved in interactions that involve the weak interaction, one of the fundamental forces of nature. Specifically, cobalt 60, whose atoms decay as a result of the weak interaction, preferentially decays toward the left, not the right.

The announcement of these results in January 1957 forced a major revision in the ideas of physicists. It was a revolution whose implications are not completetely resolved today. Wolfgang Pauli captured the idea best in a phrase calling God "a weak left-hander."He initially used those words to dismiss the results, and did not accept the fall of parity until he read papers produced by physicists who confirmed Wu's result in various other experiments.
This lack of symmetry in a world dominated by symmetry may be necessary for the universe to exist at all. In most reactions, matter and its exact opposite,anti-matter, are produced in equal amounts. Yet the existing universe, as far as we can tell, contains matter and not antimatter. Matter and antimatter interact to destroy each other whenever they meet. If equal amounts of matter and antimatter were produced in the creation of the universe, this reaction would have "uncreated" it. Physicists think that some asymmetrical reaction at the beginning of time must have prevented happening, or we would not be here to think about it.

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