He planned to measure how much the Earth (and by extension, all objects with mass) warps spacetime, a phenomenon known as the geodetic effect
. Everitt also wanted to measure the even feebler frame-dragging effect, in which the spinning Earth should yank and twist the surrounding spacetime.
The first, the "geodetic effect
," describes the dent that Earth's mass creates in the fabric of spacetime.
Gravity Probe B (GP-B), launched in 2004, used four ultra-precise gyroscopes to measure the hypothesized geodetic effect
, the warping of space and time around a gravitational body, and frame-dragging, the amount a spinning object pulls space and time with it as it rotates.
Its mission will be to measure two predicted effects by Einstein--frame dragging and the geodetic effect
. In short, the GP-B will aim to quantify how the presence of the Earth essentially bends or warps space-time and what effect, if any, does the rotation of our planet have on this fabric.
The results of this painstaking analysis, announced at a NASA press briefing May 4 and scheduled for publication in an upcoming Physical Review Letters, reconfirm the geodetic effect
with an error of about 0.2 percent.
There GP-B is poised to test rigorously two key predictions of general relativity: the geodetic effect
and frame dragging.