Is there a thought-picture that describes his conclusions about general relativity?
Gravity, he figured, was a warping of space and time. It can be described by using another thought experiment. Picture what it would be like to roll a bowling ball onto the two-dimensional surface of a trampoline. It curves the fabric as it moves. Then roll some billiard balls. They move toward the bowling ball not because it exerts some mysterious attraction (as Newton's theory had it), but because of the way it curves the trampoline fabric. Now imagine this happening in the four-dimensional fabric of space and time. O.K., it's not easy, but that's why we're no Einstein and he was. He was able to come up with a gravitational field equation that showed how matter curved space and how curved space told matter how to move.