Detecting a Twist of Space

A Stanford researcher may have found the long-sought monopole

Its existence was predicted in 1931 by British Theoretical Physicist Paul Dirac, and scientists have been looking for it ever since--on the ocean floor, in meteorites, Arctic ice and even moon rocks. Dirac, one of the fathers of quantum theory, said that magnetic particles might exist that are exclusively "north" or "south." Recent developments in quantum theory suggest that these single-poled units, or "monopoles," would have immense mass, about 10 million billion times that of a proton at rest. Placed on a table, a monopole would prove so heavy in relation to its size that it would fall through the table and plummet until it settled in the core of the earth. Described by scientists as "twists of space," monopoles are believed to have been formed during the Big Bang that marked the beginning of the universe.

Last week, at the annual meeting of the American Physical Society in Washington, D.C., scientists learned that the search for the elusive monopole may have paid off. A paper submitted to Physical Review Letters by Blas Cabrera, 35, an assistant professor of physics at Stanford University, reports an "event" that Cabrera thinks may have been caused by a monopole. If Cabrera is correct, his discovery could validate the various "grand unification theories," which postulate the existence of superheavy monopoles and hold that three natural forces--electro-magnetism, radioactivity and nuclear bonding--are manifestations of a single grand force. Monopoles might also account for the mass in the universe that cosmologists say is "missing" and would confirm current ideas about the basic building blocks of matter.

To detect a fugitive monopole, Cabrera used a kind of magnetic mousetrap, which was connected to a SQUID (superconducting quantum interference device). He turned a coil of niobium, a platinum-gray metallic element, into a superconductor of electricity by cooling it to within nine degrees of absolute zero (minus 460DEG F). Current thus moved through it without resistance, allowing the slightest twitch in the current's flow to be recorded. At 1:53 p.m. on Feb. 14, the magnetic flux in Cabrera's device jumped eight steps, exactly what was expected if a Dirac monopole passed through. Cabrera, a little skeptical, hit his device with a screwdriver to see if that blow too would register a significant reading. It did not. After examining every possible explanation, Cabrera concluded that a monopole had moved through his equipment. "The event is striking," says Cabrera. "We have not come up with an easy way to explain it."

Many other scientists were understandably cautious. In 1975 Berkeley Physicist P. Buford Price also thought he had found a monopole. Looking for cosmic rays, Price and three colleagues developed a multilayered plastic sandwich to record the tracks left by subatomic particles and launched the contraption over Iowa in a helium balloon. During three days, the particle detector recorded 75 hits, one much different from the rest. When Price published a paper claiming to have found a monopole "candidate," the scientific community's excitement soon gave way to skepticism. In the end, Price admitted he had been a bit hasty. Says Price of Cabrera: "His technique is extremely sophisticated. It looks just like a monopole going through the loop."

Nevertheless, some theoretical chinks remain. According to "Parker's Limit," a theory developed by University of Chicago Astrophysicist Eugene Parker, monopoles would draw energy from nearby magnetic fields as they traveled through the galaxy. Cabrera's one event in only 185 days is a very high rate of detection. It suggests that there are many more monopoles zipping around than our galaxy's magnetic field can properly support.

Cabrera and others are now rushing to build larger devices in the hope of expanding his approach. Armed with a three-coil device, Cabrera expects to record as many as 100 events in a year. Says Harvard Physicist Sheldon Glashow: "If Cabrera is right, this will be one of the most important physics discoveries in this century. It's been a long quest." qed

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