A Beginner's Guide to Antimatter

In the GP-B experiment, gamma contributes to the slight tilt of the gyroscopes' spin axes, which are expected to drift about 6.6 arcseconds (0.00183 degrees) during the year-long data-gathering phase of the mission. This drift should allow scientists to measure gamma within about 0.01% of its true value -- and perhaps as good as 0.001%, Everitt says.

If gamma turns out to be slightly less than one, it would support the idea that a new force field exists, akin to gravity but much weaker. Physicists call it a "scalar field." This new field is a feature of some candidate Theories of Everything, including string theory. String theory is popular because of its elegance in explaining all known physical phenomena, from the subatomic to the cosmic. The problem is that string theory is very hard to test in the real world, and no experimental evidence of the unique predictions of string theory has yet been found.

Einstein, still making headlines...

"Finding that gamma is slightly less than one would support the idea of a scalar field, and thus could provide some of the first experimental support for string theory," Thibault says.

If gamma turns out to be slightly greater than one, however, it would be "back to the drawing board" for theorists. No existing theories predict that gamma should be larger than one, so physicists would have no idea how to explain such a finding. "Let's just say that every time I ask theorists what it would mean if gamma were larger than one, they change the subject," laughs Everitt, himself an experimentalist.

GP-B might also find that, within the experiment's limits of precision, gamma is equal to one--just as Einstein predicted. What would that mean? Perhaps the flaw, if it exists, is smaller than GP-B can sense. Or maybe the revolution's first shots will ring out elsewhere. No one knows.

Gravity Probe B is half-way through its one-year mission. One hundred years down, six months to go. Stay tuned for answers.