Great Physicists: The Life and Times of Leading Physicists from Galileo to Hawking

For about a century now, physicists have been occupied with fracturing atoms and sorting out the subatomic particles that are produced. The first experiments of this kind, leading to the discovery of the negatively charged electron, were done by J. J. Thomson in 1897. Rutherford's discovery of the atomic nucleus, and studies of radioactive elements by Rutherford, the Curies, Meitner, Fermi, and many others, penetrated further the mysteries of the subatomic realm. A wealth of energetic subatomic particles coming from outer space—so-called cosmic rays—has been observed in cloud chambers and other detectors. And experimentalists have learned how to create their own high-energy beams of subatomic particles in enormous accelerating machines. The beams are aimed at a target or another beam, and the particles produced are observed in highly sophisticated detectors. These experiments have produced so many different kinds of particles that at first theorists hardly knew what to do with them.

This part of the book introduces the three physicists who were most prominent in building the theories that brought order to the jungle of data from the domain of the subatomic. The first is Paul Dirac, who formulated one of the great theories of mathematical physics, ranking with Maxwell's theory of electromagnetism. Dirac's theory describes electrons moving at speeds high enough to demand the restrictions of Einstein's theory of special relativity. The theory shows that electrons have a kind of spin motion, and that they behave like tiny magnets, with north and south poles. Dirac also extracted from his theory the completely unexpected prediction that the electron has a positively charged counterpart, later called the “positron” after it was observed by Carl Anderson in a cloud chamber. The electron and the positron, which differ in other respects as well, are “antiparticles.” All other particles, from neutrons to neutrinos, also have their anti partners.

The second particle theorist is Richard Feynman, who came from the quantum generation following that of Dirac. Feynman's theory responded to the experimental discovery by Willis Lamb and Polykarp Kusch that Dirac's theory was slightly in error. The

-363-