Einstein's Relativity Theory confirmed
EINSTEIN WAS right after all. Satellites that have been pulled slightly off their orbits show that earth is indeed twisting the fabric of space-time as it rotates, scientists said recently.
This confirms one of the last untested predictions of general relativity by a reasonably accurate measurement of how the rotating earth warps the fabric of space. According to Einstein's General Theory of Relativity a rotating body warps and twists the `fabric' that combines the three dimensions of space and the fourth dimension of time.
``As the earth turns, it is actually twisting space-time with it. Near earth, the twisting is greater,'' said Michael Salamon, a physicist at NASA in Washington.
Frame-dragging
The space warp is a consequence of Einstein's General Theory of Relativity, which describes gravity as a curvature in space produced by objects sitting in it. The theory also implies that a rotating mass will drag space around it — an effect known as `frame-dragging.' Frame-dragging, has never been directly observed before.
The effect becomes important in understanding extreme situations like spinning quasars and the rotation of jets of gas around black holes. Though Austrian physicists Joseph Lense and Hans Thirring had first predicted this effect in 1918, scientists could not measure the tiny perturbations in the fabric of our Universe.
Two scientists charted the path of two NASA satellites, LAGEOS 1 (Laser Geodynamics Satellite) and LAGEOS 2, over a period of 11 years with laser range-finders with the precision of a few millimetres.
The effect dragged the satellite's orbits out of position by about 2 metres each year. Einstein's theory predicts that a nearby spinning body such as the earth will pull on space and cause a gyroscope to shift slightly on its axis.
Accordingly, the scientists find the satellite's orbits being dragged out of position by about 2 metres each year. The results were published in Nature. There is no proof that some other force is not acting on the satellites. But this is unlikely as the scientists had eliminated all of the forces that could have brought about this shift.
Pulling space-time
``Similarly, as the earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near earth,'' Erricos Pavlis of the University of Maryland in Baltimore and one of the scientist who studied the effect said.
But some scientists remain unconvinced. One of the difficulties is extracting the frame-dragging effect from the huge gravitational effect of the earth.
If the earth were perfectly symmetrical, frame-dragging would be easy to measure. But the uneven gravity field of the earth will move the satellites about far more than frame-dragging.
The two scientists took care of this uneven gravity field by using a map of the earth's gravity field as provided by the mission GRACE launched by NASA two years ago. GRACE relies on two satellites orbiting the earth about 220 km apart.
These satellites measure the tiny changes in gravity as they pass through different parts of the earth's gravity field.
The last major prediction of general relativity requiring confirmation is the existence of gravity waves. The LIGO experiment, run by theCalifornia Institute of Technology and the Massachusetts Institute of Technology, is already searching for these on earth, while NASA's LISA probes are expected to launch in 2010.
In April, NASA launched Gravity Probe B, a probe carrying four gyroscopes, which the scientists say should prove Einstein's theory with even higher accuracy when its results are reported next year.
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