Well-rounded

Einstein's general theory of relativity proposed that the all-encompassing blanket of space-time is warped, ever so slightly, by massive objects like the Earth. Al's theory was, you know, pretty genius. Still, so far there's been no way to measure these tiny distortions and actually prove his predictions. But a NASA/Stanford team of physicist- engineers might have finally found this proof.

In April 2004, the team launched the "Gravity Probe B"—a satellite-laboratory that contains the world's most precise gyroscopes. The satellite has been in orbit ever since, and the researchers are now starting to make sense of the data it collected. (Interestingly, the probe was first proposed in 1960, but funding and technological hurdles kept it from ever getting off the ground.)

To refresh your memory, a gyroscope is basically a wheel that's mounted within a ring so that it's free to spin in any direction. When the wheel is spun quickly (and in the absence of any pesky friction), it will keep its original plane of rotation no matter which way the ring is turned. Since gyroscopes always maintain equilibrium, they're used by experimentalists to define a fixed direction in space.

Gravity Probe B holds four super-accurate, 3-D gyroscopes, so accurate that they could detect a movement the width of a human hair from 20 miles away. Each gyroscope is made up of a spherical mass, about the size of a ping pong ball, spinning in a -271 degree-Celsius chamber of superfluid helium. The spheres are the most perfectly rounded objects ever made by hand—if blown up to the Earth's size, their biggest imperfections would form mountains only eight feet high.

If Newtonian physics is right, then the gyroscopes within Gravity Probe B should always point in the same direction. But if Einstein's relativity is correct, then the slight curvature of space should cause the spin axis of the gyroscope to change by a tiny, tiny bit (we're talking a difference of .0018 degrees in one year). As I mentioned, the data's still being analyzed...but preliminary results show the balls are indeed drifting. Way to go, Al.

Hat tip: Clive