In 1964, before the term ”black hole” was even coined, NASA began funding a project that would test the outer limits of the theory behind black holes, Einstein’s general theory of relativity. Last May, with the project, called Gravity Probe B (GP-B), looking like a US $650-million flop, a NASA review board recommended that all funding be cut off by the end of September.
Now, in a dramatic turnaround, the Gravity Probe B team has secured non-NASA funding to press forward with data analysis of an experiment that has been bogged down by unexpected sources of noise. With the latest round of stopgap funds in place, the group holds out hope that it will either be able to verify or refute one of the most extreme predictions of Einstein’s general theory of relativity.
GP-B is an orbiting set of precision gyroscopes measuring 6.4 meters long that was launched into low Earth orbit in April 2004. For nearly a year it studied the mild warping effect that Earth’s gravitational field has on the fabric of space. It has already confirmed one prediction of Einsteinian gravity to a 1 percent confidence level—that the fabric of space compresses inside a gravitational field such that circles actually measure slightly less than 360 degrees.
However, a more subtle effect, involving the tug of Earth’s rotation on space itself, has not yet been seen unequivocally. Because of an error in the gyroscopes’ manufacture, GP-B’s measurements have been riddled with wobbles that have made the ongoing data analysis for this ”frame dragging” effect tremendously challenging. GP-B’s final results were expected this year, but the GP-B team, based at Stanford University, appealed to NASA to continue funding through March 2010 to extract the precision measurements that team managers say still lie buried beneath a layer of noise.
With confidence in the project failing, NASA’s funding slowed to a trickle this year, dropping to $500 000—not quite enough to keep the data analysis moving forward. So with some careful negotiations, the GP-B team secured matching $500 000 donations from Stanford and Richard Fairbank, CEO of Capital One Financial Corp. and son of the late physicist William Fairbank, an early proponent of this often controversial experiment. Nevertheless, the clock on the $1.5 million stopgap ran out on 30 September.
As this story went to press, GP-B project head Francis Everitt notified IEEE Spectrum that ”a significant non-NASA agency” had committed $2.7 million to continue Gravity Probe B. This, Everitt hopes, will enable his group next year to reach a conclusion on a par with its original goal of testing the two Einsteinian effects down to the 1 percent confidence level.
The project was on very shaky ground, because even after years of data massaging, GP-B had weakly confirmed one of the effects, frame dragging, to only the 25 to 33 percent range. But as Everitt and GP-B spokesman Bob Kahn, of Stanford, told IEEE Spectrum via e-mail, a recent breakthrough in the modeling of behavior of the satellite’s instruments has increased the data’s accuracy ”by a factor of 5 to 10”. The new results are to be presented early this month at an International Space Science Institute workshop on the nature of gravity.
NASA’s science advisory committee for the project has called the recent effort ”heroic.” With this summer’s work, says the report, the GP-B team ”has brought the experiment from what seemed like a state of potential failure, to a position where the [committee] now believes that they will obtain a credible test of relativity, even if the accuracy does not meet the original goal. In the opinion of the SAC Chair [Washington University physics professor Clifford Will], this rescue warrants comparison with the mission to correct the flawed optics of the Hubble Space Telescope, only here at a minuscule fraction of the cost.”
Arguably the most sophisticated spacecraft ever flown, GP-B contains some of the most precisely machined objects in the history of humankind. Those objects were harnessed to test effects that Einstein and his acolytes predicted some 90 years ago.
Central to GP-B’s operations is a redundant set of four superconducting gyroscopes that each must point in precisely the same unwavering direction in space throughout the satellite’s orbit. For the experiment to work, these gyroscopes must drift no more than 0.00000000001 (a one hundred-billionth) degree per hour. Even advanced navigational gyroscopes in airplanes or guided missiles lack this precision by a factor of at least 1 million. GP-B’s required accuracy, three orders of magnitude better than the finest gyroscope technology before it, would be good enough to shine a laser from Earth to the moon’s surface and keep that laser light within a bull’s-eye just one-tenth of a millimeter across.
GP-B was a difficult experiment to build and, at $650 million, was also quite expensive. For these reasons, its development became the subject of acrimonious debate in the scientific community: Many physicists wanted it, while many astronomers thought it unnecessary. Like other California-based matters, it came to represent a focal point of discontent between those in the San Francisco area and those in the Los Angeles area. Many Stanford people, in the north, wanted it built, while some Caltech people, in the south, wanted it scrubbed. (An exception in the latter camp was the Caltech black-hole expert Kip Thorne, who consistently supported the mission and was present at GP-B’s launch.)