US: NASA’s Gravity Probe B (GP-B) mission confirmed two key predictions derived from Albert Einstein’s general theory of relativity, which the spacecraft was designed to test. One prediction, the geodetic effect, has it that time and space are warped around a gravitational body; the other, frame-dragging, concerns the effect of rotating objects on space-time. The findings are online in the journal Physical Review Letters.
The experiment, launched in 2004, used four ultra-precise gyroscopes to measure the hypothesised geodetic effect and frame-dragging. GP-B determined both effects with unprecedented precision by pointing at a single star, IM Pegasi, while in a polar orbit around Earth. If gravity did not affect space and time, GP-B’s gyroscopes would point in the same direction forever while in orbit. But in confirmation of Einstein’s theories, the gyroscopes experienced measurable, minute changes in the direction of their spin, while Earth’s gravity pulled at them.
“Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it’s the same with space and time,” said Francis Everitt, GP-B principal investigator at Stanford University. “GP-B confirmed two of the most profound predictions of Einstein’s universe, having far-reaching implications across astrophysics research. Likewise, the decades of technological innovation behind the mission will have a lasting legacy on Earth and in space.”