In 1918, two years after Einstein formulated general relativity, W. Lense and H. Thirring calculated that according to the theory a rotating massive body should slowly drag space and time around with it!
Startling and far-reaching as Lense & Thirring's discovery was, any verification of frame-dragging seemed hopeless. Nothing happened until 1959 when physicist George Pugh, an MIT professor working with the Institude for Defense Analyses proposed using orbiting gyroscopes in a drag-free satellite to test the effect. Independently, in late 1959, Leonard Schiff of Stanford University was also thinking of using gyroscopes to test the effects of general relativity, but in a ground-based system. After consulting with his colleages Bill Fairbank and Bob Cannon, it became clear that orbiting gyroscopes would provide both the pristine laboratory and the precision required to make the tests. According to Schiff's calculations a gyroscope in polar orbit at 400 miles should turn with the Earth through an angle amounting after one year to 42 milliarc-seconds.
This vitally important frame-dragging effect has never been seen. Gravity Probe B will measure it to a precision of 1% or better.
