Gravity probe results confirm theory of relativity

Posted by Kate Taylor

Einstein famously pointed out to an admirer that while a thousand experiments couldn't prove him right, a single one could prove him wrong.

But new results from NASA's Gravity Probe B (GP-B) mission have given the strongest possible backing to two predictions deriving from Albert Einstein's general theory of relativity.

The experiment, launched in 2004, used four gyroscopes - the most precise ever designed and produced. These have been measuring the geodetic effect - the warping of space and time around a gravitational body - and frame-dragging, the amount a spinning object pulls space and time with it as it rotates.

GP-B was pointed at a single star, IM Pegasi, while in a polar orbit around Earth. If gravity didn't affect space and time, its gyroscopes would point in the same direction forever while in orbit. But in confirmation of Einstein's theories, the gyroscopes experienced measurable, changes in the direction of their spin, caused by Earth's gravity.

"Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it's the same with space and time," says Francis Everitt, GP-B principal investigator at Stanford University.

"GP-B confirmed two of the most profound predictions of Einstein's universe, having far-reaching implications across astrophysics research. Likewise, the decades of technological innovation behind the mission will have a lasting legacy on Earth and in space."

GP-B is one of the longest running projects in NASA history, having kicked off in the fall of 1963. It was decommissioned in December 2010.

"The mission results will have a long-term impact on the work of theoretical physicists," says Bill Danchi, senior astrophysicist and program scientist at NASA Headquarters in Washington. "Every future challenge to Einstein's theories of general relativity will have to seek more precise measurements than the remarkable work GP-B accomplished."