Playing with space-time

There was a trampoline at our friends' house so I took the opportunity to demonstrate Einstein's vision of how gravity works. He thought of the 3 dimensions of space and the 1 dimension of time being inextricably joined to form 4 dimensional space-time. We can't visualise 4 dimensions so it is normal to picture it as a 2 dimensional rubber sheet - the trampoline. I stood in the middle pretending to be a large mass like the Sun. A large mass dents space-time. If you put on another object like the Earth (represented by the basketball) then that second object rolls down the dent. In other words, the Earth is attracted to the Sun. Einstein explains gravitational attraction by saying that masses dent space-time and that other masses roll down the dent towards them. If you fire the ball sideways, it rolls round the dent. This is orbital motion under gravity.