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Frame dragging is a somwhat bizarre consequence of Einstein's theory of relativity. Also known as the Lense-Thirring effect, named after the two Austrian physicists, Joseph Lense and Hans Thirring who predicted it in 1918.

In the same way that a spinning bowling ball dropped into syrup will drag the liquid around in a swirling vortex, so a rotating mass will drag spacetime around into whirl.

This effect has been experimentally confirmed by observing some of the most massive objects in the universe, black holes and neutron stars. In 1997 the NASA Rossi X-ray Timing Explorer (RXTE) made detailed observations of the spinning accretion disks around two black holes, (GRS 1915+105 and GRO J1655-40), which showed the disks to be precessing, much like a spinning top as it slows down. In the case of GRO J1655-40, a seven solar mass hole, the rate of the precession is 30 times a second, and the only explanation that makes any sense, is frame dragging, caused by the huge space-time distortion of the spinning black hole.

Because these objects are so far away, and the black hole physics book is still being written, a better test would be to measure the frame dragging caused by the Earth's rotation. NASA's Gravity Probe B, (still in development as of 4/2001) which when orbiting the Earth, will contain 4 gyroscopes spinning in bath of 400 gallons of superfluid helium, will hopefully provide definitive evidence.

Frame dragging might lend weight to Mach's principle, help explain the jets shooting from quasars. In fact Einstein's theory is known to be incomplete, and precise measurements of frame dragging may highlight any discrepancies caused by the grand unification theories that must succeed it..

For more, see the Gravity Probe B web site http://einstein.stanford.edu/

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