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Spinning Spheres Test Relativity's SubtletyPublication: EDN Magazine December 17, 2004 -- On April 20, 2004, a Boeing Delta II rocket launched from Vandenberg Air Force Base carried Gravity Probe B into orbit and so initiated the next step in a 40-year quest to verify a corollary of the General Theory of Relativity. First conceived in 1960, and initially funded in 1964 but delayed by financial, physics, and implementation challenges, this experiment embodies the ultimate in accurate measurement while canceling or eliminating error sources. As with so many engineering and science projects, GP-B (Gravity Probe B) is elegant in concept but brutal in details of its execution. We now accept Einstein's Theory of Relativity as fact—and with good reason. Since he put forth the Special Theory in 1905, and followed it in 1916 with the General Theory, which links space, time, and gravity, both theories have been confirmed by innumerable tests, observations, and their ability to predict and explain large- and atomic-scale phenomena. Special relativity, summarized by the elegant formula E=mc2, has the greatest impact on what most engineers and scientists do, along with quantum theory, of course. But one subtlety of the General Theory has evaded direct experimental confirmation (see sidebar "Is your frame dragging?"). The effect that the theory predicts is so subtle that only one observation, the Hulse-Taylor binary-pulsar discovery of the mid-1970s, has indirectly confirmed it. By Bill Schweber, EDN Executive Editor | |
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