Gravitation Cave Screen Saver is a physically correct 3D simulation of stars' movement under the force of gravity.

Different from the stars you see outside on a clear night, the stars in this screen saver don't have much space to move around (they are restricted by the walls of the cave), so they collide just like billiard-balls (also physically correct). The simulation is actually near the one just after the big-bang.

You can adjust the speed of the screen saver.