“What is now proved was once only imagined.”- William Blake.
“To see a World in a Grain of Sand
And a Heaven in a Wild Flower,
Hold Infinity in the palm of your hand
And Eternity in an hour.”
When William Blake wrote those words in his “Auguries of Innocence” in 1803 he likely didn’t imagine we would one day have the technology to actually “see a world in a grain of sand” but with Gravity Probe B we pretty much do.
The Gravity Probe B was a satellite-based mission to test two unverified predictions of Einstein’s general theory of relativity:
- the geodetic effect and
- frame-dragging.
The mission was accomplished by measuring, very precisely, tiny changes in the tilting of the spin axis of gyroscopes contained in the Gravity Probe B satellite orbiting Earth at 650 km (400 mi) altitude, crossing directly over the poles. The gyroscopes were intended to be so free from disturbance that they would provide a near-perfect space-time reference system. This would allow them to reveal how space and time are “warped” by the presence of the Earth, and by how much the Earth’s rotation “drags” space-time around with it. (…
