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What: |
Space Tests of General Relativity: Frame Dragging and Equivalence Principle |
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Who: |
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( Department of Physics, University of Marylan，College Park, Maryland, USA) |
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When: |
Tuesday morning, May 25th, 10:30 a.m |
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Where: |
Room 327, Office Block, 2 West Beijing Road (PMO, CAS) |
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Welcome to attend |
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( PMO Academic committee & academic circulating committee) |
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abstract
According to Einstein, a gyroscope in a 640-km polar orbit around the Earth is subject to two non-Newtonian precessions, a 6.6 arcsec/yr geodetic effect in the plane of the orbit and a 0.039 arcsec/yr frame-dragging effect due to the rotation of the Earth. GP-B has now successfully observed both. To measure these tiny effects has required developing a gyroscope 107 times better than the best Earth-based inertial navigation gyroscopes and a reference telescope 103 times better than any prior star tracker. A unique combination of cryogenics and space technologies made this possible.
Presently, the most accurate limits on the Equivalence Principle (EP) come from ground experiments, with one part in 1013 at ³ 104 km. Significant improvements in the tests of the EP are expected from dedicated space-based experiments. The low-g environment of space permits very soft superconducting magnetic suspension of the test masses. The signal is detected by a sensitive superconducting differential accelerometer formed by the suspended test masses. Combined with the full modulation of Earth’s gravity, an orbital mission promises a sensitivity of one part in 1018, five orders of magnitude improvement over the ground limits.
