A NASA probe orbiting Earth has confirmed two key predictions of Albert Einstein’s general theory of relativity, which describes how gravity causes masses to warp space-time around them.
The Gravity Probe B (GP-B) mission was launched in 2004 to study two aspects of Einstein’s theory about gravity: the geodetic effect, or the warping of space and time around a gravitational body, and frame-dragging, which describes the amount of space and time a spinning objects pulls with it as it rotates.
Gravity Probe B used four ultra-precise gyroscopes to measure the two gravitational hypotheses. The probe confirmed both effects with unprecedented precision by pointing its instruments at a single star called IM Pegasi.
If gravity did not affect space and time, GP-B’s gyroscopes would always point in the same direction while the probe was in polar orbit around Earth. However, the gyroscopes experienced small but measurable changes in the direction of their spin while Earth’s gravity pulled at them, thereby confirming Einstein’s theories.