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/