Testing Einstein : in 1959, just two years after the launch of Sputnik I, investigators began work on a space-based experiment to verify the general theory of relativity. Their efforts are about to come to fruition

Natural History, March, 2005 by Arthur Fisher

Ptolemy made a universe, which lasted fourteen hundred years. Newton also made a universe, which has lasted three hundred years. Einstein has made a universe, and I can't tell you how long that will last.--George Bernard Shaw (1930)

On April 20, 2004, at 9:57:24 A.M. local time--meeting a one-second launch window--a Delta II rocket rose from Vandenberg Air Force Base in California, bearing a payload with the less-than evocative name Gravity Probe B, or GP-B. Launched into a 97.5-minute, pole-crossing orbit 401 riffles above the Earth was a three-ton satellite designed to accomplish one of the most technologically challenging experiments in the history of physics. The launch, which proceeded flawlessly, was the culmination of forty-five years of effort by hundreds of physicists and engineers from Stanford University, Lockheed Martin in Sunnyvale, California, and NASA's Marshall Space Flight Center in Huntsville, Alabama. Its purpose: to perform two new tests of Einstein's general theory of relativity.

Publicly presented in 1915, the general theory of relativity was a spectacular intellectual feat. It interprets gravity not as a force but as a field distorting space and time. It holds that massive objects such as planets follow geodesics--paths that act as straight lines, or shortest "distances"--through a curved, four-dimensional generalization of geometry called space-time, which encompasses both space and time. As the physicist John Archibald Wheeler of Princeton University once wrote: "Spacetime grips mass, telling it how to move.... Mass grips spacetime, telling it how to curve."

"I do not consider the, main significance of the general theory of relativity to be the prediction of some tiny observable effect," Einstein remarked in 1930, "but rather the simplicity of its foundations and its consistency." One reason the theory gained rapid acceptance, however, is that it passed a couple of experimental tests with flying colors, proving it self superior to existing theories of the universe. No one doubts, by now, that it is a powerful theory. But undertaking new tests of its predictions is no idle exercise. Even if all they do is confirm Einstein's views, they could save physicists from exploring some theoretical blind alleys.

Long before Gravity Probe B bounced into orbit, the idea behind it was bounced around in a conversation among three naked professors sunbathing at a males-only Stanford University swimming pool. Leonard I. Schiff, executive head of the physics department, had been working out a way to use gyroscopes to test two obscure, minute effects predicted by the general theory of relativity. The experiment he had in mind would have to be performed in space because there the gyroscopes are weightless and better isolated from extraneous disturbances. He and his companions, William M. Fairbank, an authority on superconductivity, and Robert H. Cannon, an expert in gyroscopes, met at the pool in December 1959, to talk over the idea and its engineering difficulties. The three later learned that George E. Pugh, a Department of Defense scientist, had articulated the same idea independently in a November 1959 memo.

Nursed along for four decades, the project has cost nearly $700 million and has followed a turbulent path, suffering technical setbacks, suspensions, threatened cancellations, and intense political and academic criticism. In the intervening years, both Schiff and Fairbank have died, and Cannon is only indirectly involved. The principal investigator is C.W. Francis Everitt, who signed on in 1962, when he was just a twenty-eight-year-old postdoc from England. Now seventy, with a cascade of long gray locks, Everitt says, "I would never have joined GP-B if I'd had any idea of how long it would take."

The eminent English physicist Patrick M. S. Blackett, with whom Everitt had studied in London, once told him, "If you don't know what kind of physics you want to do, invent some new technology. It will always lead to new physics." Inventing the technology required for Gravity Probe B has turned out to be a supreme test for the ingenuity of the project's scientists and engineers. Happily, the technology is now doing its job, collecting data methodically and with exquisite sensitivity. Will it lead to new physics? If the experiment reveals that Einstein's calculations were even slightly off, the quest for a more exact theory could transform human understanding of the physical universe.

Einstein formulated two theories that interweave space and time. His special theory of relativity, published a hundred years ago this year, describes the behavior of objects moving close to the velocity of light; it also predicts the equivalence of mass and energy, according in the famous equation E = [mc.sup.2.] The special theory has been confirmed repeatedly, in the innards of particle accelerators, in nuclear power plants, and, of course, in atomic weapons. But it was Einstein's second theory, the 1915 general theory of relativity, that was first put to a public test, making the name "Einstein" a household word.