In the three days that the cosmic-ray detector hung 130,000 ft. over Sioux City, Iowa, it marked the passage of 75 heavy atomic particles hurtling in from outer space. One of the particles was distinctly different from the others. Its telltale track through a sandwich of three dozen sheets of plastic, nuclear emulsion and photographic film looked unfamiliar to cosmic-ray researchers. Last week, nearly two years after their equipment was brought back to earth, scientists from the universities of California and Houston finally offered an explanation. The unexpected particle, they said, was almost surely a magnetic monopole, the long-sought basic unit of magnetism.
If the new discovery is confirmed by further experiments, the American Institute of Physics and the University of California are both convinced that "it could rank as one of the major scientific events of the century." It would fill in some gaps in current scientific theory, modify present ideas about the basic building blocks of matter, and might eventually have significant practical applications in research, medicine and the generation of energy.
Magnetic Puzzle. At the very least, proof of the existence of the monopole would solve a mystery that has baffled scientists for more than a century. The elegant equations that Scottish Physicist James Clerk Maxwell worked out in 1865 described in detail the symmetrical relationship between electricity and magnetism. They accounted, for example, for the magnetic field formed by every electric current, and they predicted the electric currents that can be generated by moving magnetic fields. But they could not solve one puzzle. Complete symmetry between electricity and magnetism meant that there must be a monopole—a basic magnetic particle of one pole, either north or south. It would, in effect, be the equivalent of the positive proton or negative electron that exists independently in nature. But all magnetized objects, from subatomic particles to giant electromagnets, seemed to have inseparable north and south poles. Broken into the tiniest segments, each piece remained a "dipole." No isolated north or south monopole could be found.
British Physicist Paul A.M. Dirac attacked this dilemma in 1931 with the newly developed tool of quantum mechanics. His calculations showed that there should indeed be a magnetic particle (or family of particles) that carries a basic magnetic charge—either north or south. That charge, said Dirac, would be 68.5 times as strong as the charge on an electron. Or it would be some multiple of 68.5—say, 137. Scientists had good reason to respect Dirac's reasoning. He had earlier predicted the existence of a positron, or positively charged counterpart of the electron. The positron was subsequently discovered during cosmic-ray experiments in 1932, but the monopole proved more elusive. Physicists searched for it without success in everything from ocean-floor minerals to meteorites and moon rocks.