Pull of Earth on Space-Time Supports Einstein’s Insight

A key prediction of Einstein’s general theory of relativity has been confirmed by an experiment showing that the Earth’s rotation drags the surrounding fabric of space-time along with it.

The phenomenon, known as frame-dragging, was one of the last untested predictions of general relativity.

“Frame-dragging is like what happens if a bowling ball spins in a thick fluid, such as molasses,” said Erricos C. Pavlis, of the Joint Center for Earth System Technology, one of the leaders of the international team of researchers that measured the effect. “As the ball spins, it pulls the molasses around itself .... Similarly, as the Earth rotates it pulls space-time in its vicinity around itself.”

Albert Einstein’s original insight held that gravity was a product of the way planets and stars warped space around them. It was predicted that in the same way, spinning bodies would create drag around them. Measuring Earth’s drag was difficult because it required separating the effect from the much larger effects of the Earth’s gravity.

Charting the path of two NASA satellites, researchers concluded that frame-dragging altered the satellites’ orbits by two meters per year.

Some scientists remain unconvinced, but Michael Salamon, a NASA physics expert, praised the team.

“These guys have doggedly done a very good experiment,” he said. “They’ve been working on it for decades.”

A NASA satellite, Gravity Probe B, was launched this year to test the same effect. The measurements of the probe, which are still a year away, are expected to be more exact.