You could ask, "If quantum mechanics works for objects we can see, but tells us that we can't be sure of their position and velocity at the same time, then how can I catch a football?" The answer is that the uncertainties about the position and velocity of the football are very small-the larger an object, the more exactly we can tell its position and velocity at the same time. General relativity is perhaps even harder to understand. Newton thought of gravity as a force of attraction. General relativity dosen't think of gravity as a force. Imagine a heavy bowling ball lying on a mattress. It will deform the mattress and anything near the bowling ball will sink toward it. Einstein's theory says that a heavy object like a star deforms space and time around it, and this causes the motion of the planets around it. It says space and time are curved by heavy objects.Even weirder!
