The Gravity Probe B satellite has launched!
According to Einstein’s theory of relativity, any spinning massive body (like the Earth, the Sun, a black hole) will not only distort space, but will drag space along with it as it spins. This frame-dragging is a fairly small effect for a body like the Earth, but with the instruments aboard the Gravity Probe B, it should be measureable.
You might wonder why we need another test of Einstein’s theory. He’s a household name, afterall, and his theories have stood up against many other tests.
It’s true that Einstein’s theory has worked extremely well to explain, for example, the bending of starlight measured during solar eclipses and Mercury’s peculiar orbit and rotation. However, no matter how well a theory stands up, it is still open to further testing. That’s what science is all about.
Up to this point, frame dragging has not been directly measured, even though the effect has been known for over 50 years. The problem is that the best place to test frame dragging would be around a black hole, but we don’t have one handy. So we had to wait until we could develop sensitive enough instruments to test it on the Earth.
The results should prove interesting, but we’ll have to wait about a year for those.