137 - Arthur I. Miller [117]
In mathematics, the law of parity conservation means that a physics equation must remain the same when right and left are exchanged. Parity invariance explains many properties of atomic systems and, at the time that Pauli began working on it, was taken as axiomatic; it had never been questioned.
By the mid-1930s physicists agreed that every charged particle must have a matching antiparticle. Charge conjugation (C) describes the mathematical process used to convert every particle into its antiparticle, and so matter into antimatter. In quantum mechanics it is considered to be an intrinsic property of every elementary particle (for example, an electron) along with parity.
In 1954, two years after he began working on mirror images, Pauli decided to look deeper into the whole subject. Instead of exploring charge conjugation (C), parity (P), and time reversal (T) separately, he looked at all three together—the whole combined operation of CPT. This entails the exchange of particle and antiparticle (C), right-left symmetry (P), and time reversal (T)—(particle antiparticle) x (left right) × (future past). CPT makes the astonishing assertion that a mirror universe—in which all matter is replaced with antimatter, all positions are their own reflections, and even time runs backward so that all speeds are reversed—would actually be indistinguishable from our own.
Explaining this complex concept to Jung, Pauli wrote, “The combination of CPT of all three parity operations…is correct under much more general assumptions (that is, deducible, demonstrable) than the operations C, P, and T taken individually.” The exclusion principle played a central role in his calculations because it required that collections of particles and antiparticles with half a unit of spin and those with a whole number of spin be treated differently. He proved that if the equations describing an atom remain unchanged under CPT, this was the same as requiring any of those equations to agree with relativity theory.
To date no violations of CPT symmetry have been found in the laboratory—that is, incorrect predictions of equations which can be traced to violating CPT, or what is the same, with violating relativity theory. It underlies every theory of elementary particles and is essential for studying the behavior of its three component symmetries—C, P, and T—in this increasingly bizarre world.
Pauli wrote up his conclusions in a milestone paper to be published in a volume to celebrate Niels Bohr’s seventieth birthday the following year, 1955. It was the capstone to a subject he had studied with a passion ever since he was a young man—relativity—and it finally set his greatest discovery, the exclusion principle, firmly in its embrace, along with another off shoot of the exclusion principle, spin. He began his paper on a historical note, recalling “a long and still continuing pilgrimage since the year 1922, in which so many stations are involved.”
It was precisely as he was writing this paper that he dreamed that curious dream about the Chinese woman and the reflections that were not reflections. But at the time he thought no more about it.
The father of the neutrino
In June 1956, the experimental physicists Frederick Reines and Clyde Cowan made an exciting discovery. They succeeded in finally verifying in the laboratory the neutrino, which Pauli had predicted twenty-six years earlier, actually existed. They immediately sent him a telegram. Pauli was at a symposium in CERN, the huge nuclear physics laboratory outside Geneva, at the time. Full of elation he read it out to the audience: “We are happy to inform you that we have definitely detected neutrinos from fission fragments from observing inverse beta-decay of protons. Observed cross-section agrees well with expected 6 × 10–44 cm2.”
Pauli was acclaimed worldwide as the “father of the neutrino” and was much called upon to