Spacetime and Spin


NASA’s long term Gravity Probe-B mission has proven that Einstein’s general relativity is, once again, accurate. The ambitious experiment showed that the space-time around the Earth appears indeed to be distorted, as it is described in his benchmark work on gravitation.

“We were just blown away”, said Clifford Will of Washington University Saint Louis, chair of the NASA committee that monitored and reviewed the results of Gravity Probe B (GP-B).

An expert in all things Einstein, Will was referring to the exactness of the iconic physicist’s calculations but also to the technical masterstroke that turned one year of data-taking and almost five years of analysis into a formidable success.

According to Einstein, “space-time” is a four-dimensional fabric around the Earth. With its mass, our planet causes something like a dimple in that fabric. Gravity, Einstein said further, is nothing but the motion of objects following the curvaceous lines of the dimple.

And here is where the effects of rotating bodies come into the picture: the Earth’s spinning, so Einstein, twists that dimple and pulls it around into a 4-dimensional swirl.

In 2004, GP-B ventured to space to check.

The idea behind the experiment is simple: put a spinning gyroscope into orbit around the Earth. Determine a fixed reference point, maybe a far-away star. Observe if the gyroscope’s spin axis drifts over time. Measure the twists of space-time. But "GP-B researchers had to invent whole new technologies to make this possible," Clifford Will pointed out to highlight the epic character of the GP-B endeavor.

If Einstein’s theories had proven deficient, new physics might have been found. For now, however, it looks as if he was all but distorted, and that the type of space-time vortex around the Earth may well exist elsewhere in the cosmos.

Picture ...Time... by Darren Tunnicliff on Flickr, courtesy of Creative Commons Licensing