[vacets-gen] [General relativity test: Einstein is proved right again ...]

[Hai Tran]

Fri 22 Oct 2004 

11:06am (UK)

Einstein Is Proved Right Again 

By John von Radowitz, Science Correspondent, PA News 

An experiment using two orbiting satellites has proved that as the Earth turns it drags space and time around itself, like a spinning top in treacle.

The result is yet another vindication of Albert Einstein’s genius. His theory of general relativity, published in 1916, said that material objects warped space and time around them.

In 1918, Joseph Lense and Hans Thirring used Einstein’s equations to predict that a rotating body will twist space-time enough to disturb a small object orbiting it.

Today scientists said they had succeeded in accurately measuring the Lense-Thirring Effect - also known as "frame dragging" - for the first time.

The American and Italian researchers made precise observations of two Earth-orbiting satellites, Lageos 1 and Lageos 2.

Dr Erricos Pavlis, from the Joint Center for Earth System Technology based at the American space agency Nasa’s Goddard Space Flight Center in Greenbelt, Maryland, said: "General relativity predicts massive rotating objects should drag space-time around themselves as they rotate.

"Frame dragging is like what happens if a bowling ball spins in a thick fluid such as molasses. As the ball spins, it pulls the molasses around itself. Anything stuck in the molasses will also move around the ball.

"Similarly, as the Earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near the Earth."

The scientists found that the satellites were shifted out of position by about six feet per year in the direction of the Earth’s rotation.

"Our measurement agrees 99% with what is predicted by general relativity, which is within our margin of error of plus or minus 5%," said Dr Pavlis.

"Even if the gravitational model errors are off by two or three times the officially quoted values, our measurement is still accurate to 10% or better."

Future measurements of the Lense-Thirring Effect by a new Nasa spacecraft, Gravity Probe B, should reduce this error margin to less than 1%.

The research is published in the latest edition of the journal Nature.

Frame dragging has recently been observed around distant objects with intense gravitational fields, such as black holes and neutron stars.

The Lageos satellites, launched in 1976 and 1992, are designed to test methods of accurately measuring distances using lasers.

 



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