Gravity Probe B 
As Earth turns, it drags us and everything else on the surface along with it — a result of the planet’s gravitational pull. And it drags something else, too: space itself — an effect that was confirmed just last year.
Albert Einstein’s theory of gravity, known as General Relativity, says that massive bodies “warp” the space around them. For something as small and light as Earth, the effect is tiny. It’s more pronounced around more-massive objects, like stars, so it’s easier to detect.
Relativity also predicts that if a massive object is rotating, the warp in space rotates, too — the object actually drags space along with it.
A satellite launched in 2004, called Gravity Probe B, spent a year measuring the effect of Earth’s gravity on space. It did so with a set of ultra-precise gyroscopes, which were deflected by Earth’s pull on the space around it. After that, it took scientists five years to fully analyze the data. They announced their results last May: Earth does indeed drag the space around it — by exactly the amount predicted by Einstein’s equations.
And as with the warp in space, the dragging effect is much stronger around objects that are heavier and denser than Earth. In fact, the densest objects of all — black holes — may drag space at a good fraction of the speed of light — a gravitational maelstrom explained by Albert Einstein.
We’ll talk about another test of Einstein’s theory of gravity tomorrow.
Script by Damond Benningfield, Copyright 2012