Einstein was Right About Space-Timeby Maggie Fox
News in Science, October 22, 2004
Einstein was right, again. Satellites that have been pulled slightly off their orbits show that the Earth is indeed twisting the fabric of space-time as it rotates, scientists said.
They said their findings are the first to directly measure and prove an important aspect of Albert Einstein's General Theory of Relativity: that a rotating body warps and twists the "fabric" that combines the three dimensions of space and the fourth dimension of time.
They reported their research in the current issue of the journal Nature.
"As the Earth turns, it is actually twisting space-time with it. Near Earth, the twisting is greater," said Dr Michael Salamon, a physicist at NASA
"This twisting of space-time, which is also referred to as frame-dragging, has never been directly observed before," Salamon said.
"This is the first real, solid, direct evidence we have for the twisting of space-time caused by the spinning of a rotating body."
Associate Professor Erricos Pavlis of the Joint Center for Earth System Technology at NASA and the University of Maryland and colleagues observed two satellites orbiting the Earth and found that they did shift as the planet pulled on space.
"We measured the distance from the Earth to the satellite with the accuracy of millimeters," Pavlis said.
The Laser Geodynamics Satellite, or LAGEOS I, a NASA spacecraft, and LAGEOS II, a joint NASA/Italian Space Agency satellite, are basically hunks of metal covered with reflectors that make them easy to follow and measure from the ground.
Their butterfly-shaped orbits are meant to simulate the movement of a spinning gyroscope.
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.
There is no proof that some other force is not acting on the satellites, Pavlis said, but it is unlikely.
"It would have to be a very smart force to exactly mimic general relativity," he said.
"We have eliminated all of the forces that we do know: tidal forces ... as well as gravitational model errors."
Pavlis likened the effect to a spoon twisting in a jar of molasses.
"Similarly, as the Earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near Earth," he said.
Salamon said indirect evidence has been seen of frame-dragging, but this was the first direct measurement.
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.
Einstein's relativity theory probed, News in Science 19 Apr 2004
Shedding new light on the speed of light, News in Science 12 Aug 2002
When two black holes come together, News in Science 2 Aug 2002
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