Gravity Probe B

The probe's aim sounds deceptively simple: Test the forces generated by the fabric of space as it spins around the wheeling carousel of Earth. From its orbit, the gravity probe will measure the influence of gravity with the most accurate gyroscopes ever designed - a million times more precisely than can be achieved on Earth.

On the accuracy of those meticulously calibrated measurements, Einstein's theory of gravity could stand or fall.

"If you ask the most extreme question - is this experiment manifestly a totally crazy idea? - the answer is that it became fairly obvious to us it was not manifestly crazy," says Everitt, who has been involved in the project since its inception in 1971. "There is a sense in which we all know that Einstein's theory must be wrong, or must be incomplete."

The question, Everitt explains, arises from the troubling incompatibilities between general relativity and quantum mechanics, the other leading theory that describes the physical laws governing the universe. General relativity operates on the broad scale of planets, galaxies and the forces that bind them, while quantum physics addresses the microworld of subatomic particles. They should mesh at some level; yet they do not, as best anyone can tell at this point in time.

"The way that it doesn't fit with quantum mechanics is extremely, frustratingly deep. One or the other of these theories must be radically fixed," he says.

"It is true that there is no very convincing alternative theory to Einstein's. It is also true that we know the theory must break down somewhere. The difficulty is that nobody knows where or how it will break down."

That is the conundrum that set Stanford scientists on a collision course with one of the most influential figures in the history of science.

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