Testing Einstein (again): 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.(Albert Einstein)

Publication: Natural History

Publication Date: 01-MAR-05

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COPYRIGHT 2005 Natural History Magazine, Inc.

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....

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