Quark Hunters

The search for simplicity at the deepest levels of nature is one of the enduring themes of physics. Perhaps the greatest milestone in this quest has been the quark model of matter. In the early 1960s, theorists proposed that the scores of known subatomic particles were really composites, made up of just a handful of smaller particles. Even protons and neutrons, the major components of atomic nuclei, could be described as being made of these more fundamental objects, called quarks.

One physicist who laid the intellectual groundwork for this now mainstream theory, Caltech's Murray Gell-Mann, long ago won the Nobel Prize. But it was not until last week that the Royal Swedish Academy of Sciences honored the men who first detected the existence of quarks. Americans Jerome Friedman, 60, and Henry Kendall, 63, of M.I.T., and Richard Taylor, 60, a Canadian working at Stanford, share the physics award for discoveries made at the Stanford Linear Accelerator Center beginning in the late 1960s.

Their work closely paralleled the discovery of atomic nuclei. In 1910, Ernest Rutherford fired alpha particles (fragments of helium atoms) at targets of gold foil. Most passed through, but some bounced back, making it clear that there were dense concentrations of matter within the foil. In the Stanford experiments, electrons were fired at protons and neutrons. The way the electrons bounced off these particles showed that the latter were not uniformly dense but made up of tiny concentrations of matter -- the quarks.

Physicists now believe there are 18 kinds of quarks. That is not so simple, and so the search is on for even more basic objects. The machine most likely to find them is the giant superconducting supercollider, to be built in Texas. The controversial project will cost at least $8 billion, but the Nobel winners support it. Like the devices they used in their work, says Kendall, the SSC "represents the price of the restless curiosity of the human race to understand the physical universe we inhabit."