There are lots of experimental results that seem to confirm Einstein’s General Theory of Relativity. For example, general relativity predicts that time passes slowly in the presence of strong gravitational fields and quickly in the presence of weak gravitational fields. The Global Positioning System confirms this prediction every second of every day.1 However, there are some fundamental assumptions of general relativity that are significantly more difficult to confirm.
One of those fundamental assumptions has to do with the very nature of gravity itself. General relativity says that what we perceive as the force of gravity isn’t really a force at all. It is merely a consequence of the way that mass warps spacetime, which is a four-dimensional construct that combines the three typical dimensions of space (length, width, and height) with time. While this assumption produces all sorts of testable predictions that have been confirmed experimentally, the assumption itself has never been directly confirmed…until now.
In April of 2004, Gravity Probe B started circling the earth from pole to pole. It did so for 15 months, and all the while, precise observations were made of four gyroscopes that were roughly the size of ping-pong balls. The gyroscopes were covered with a superconducting surface. Once they started spinning, they each produced a nice magnetic pointer. Those pointers were actually able to measure two effects that the earth’s mass has on the surrounding spacetime.