To Catch a Fleeting Gluon

Einstein's old dream of unity may yet come true

For much of the last half of his life, Albert Einstein was preoccupied with a lonely quest. He wanted to bring together under a single set of equations all of nature's basic forces. The master of relativity never achieved his grand unification, and many colleagues scorned him for wasting his precious time on such a farfetched intellectual exercise. Last week, at a major meeting of physicists at the Fermi National Accelerator Laboratory in Batavia, Ill., outside Chicago, Einstein's seemingly futile dream suddenly sounded far more realistic.

What caused the new optimism was a tiny, ephemeral bit of matter that has neither mass nor charge. Known whimsically as the gluon (pronounced glue-on), it is believed to carry the so-called strong force, which helps bind together the other tiny particles--some 200 at last count--that make up the minuscule world of the atomic nucleus. When physicists first postulated the sticky little gluons more than five years ago, they were only theoretical concepts: no one knew whether they really existed outside their equations or were just some more scribblings on the blackboard.

Now the doubts appear to be dwindling as a result of some extraordinary probings into what physicists fondly call their nuclear "zoo." Most of the inhabitants of that zoo are subatomic particles dubbed hadrons, a family that includes the familiar protons, pions and K mesons. Even so, hadrons are not the ultimate form of matter. They seem to be composed of still more basic particles called quarks. But how do quarks cling together? Answer: by tossing gluons back and forth among themselves.

To catch quarks in that playful activity, four separate teams of experimenters--involving 300 scientists from eight countries, including the U.S.--turned to West Germany's new PETRA colliding beam accelerator in Hamburg. The powerful machine accelerates electrons to energies of 15 billion electron volts and sends them barreling head-on into their antimatter opposites, particles called positrons, coming at high speed from the opposite direction. In the past, when such experiments have been tried with other accelerators operating at lower energies, the debris from the electron-positron collisions has consisted of only two "jets," or streams, of hadrons.

But this time the physicists saw three jets: as they interpreted the results, two were from a quark and its antimatter equivalent, the antiquark; the third apparently from a gluon.

All this was highly exciting news to the nearly 600 physicists from 38 countries gathered at the Fermi accelerator. If gluons really exist, they are the first strong proof of an esoteric yet extremely important new physical theory called quantum chromo dynamics, or QCD. Although more experimental work will be necessary to establish the existence of gluons, already some bold theorists are using QCD in an ambitious attempt to succeed by other means where Einstein failed. That could eventually mean a union of all four of nature's basic forces --gravitation, electromagnetism and the nuclear strong and weak forces. Predicted Israeli Theorist Haim Harari of the Weizmann Institute of Science: "Five years from now when we look back, we will all agree that the gluon was discovered in the summer of'79." sb

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