Dan Burns, a high school physics teacher in Northern California since 1992, explains how gravity and space-time warping work at a teaching workshop at Los Gatos High School.
Stretch a sheet of lycra over a drum shape made out of PVC and electrical conduit. Put a 2kg mass in the middle and roll marbles to show orbits. Put 2 large metal spheres on it and they will slowly attract. Put a large marble rolling with a smaller one next to it and it will orbit the larger marble mimicking the Earth-Moon system. Throw a handful of marbles going one way and a slightly larger handful going the other. They collide and fall in, leaving most of the survivors all going in the same direction, just like the formation of the solar system. Put 2, 2kg masses apart from each other and try and get a marble to do a figure 8 orbit around them both. Have a pole stick up from below creating a force of repulsion and you have Dark Energy.
Want to make your own Spacetime Simulator? Yeah you do, you beautiful nerd, you! Click here.