Colliding Galaxies in a Virtual Universe

From Mica

Colliding Galaxies in a Virtual Universe

Although in extreme cases it has been supplanted by General Relativity, Newton's Theory of Universal Gravitation is an excellent description of how massive bodies interact in most circumstances. There's a problem, though. While the "two-body problem" of a planet orbiting a star, or of two stars orbiting each other, has a series of elegant solutions giving neat orbits, the three-body problem, or, more generally, the N-body problem (N meaning "a large number") cannot be solved in closed form. What happens you have a lot of objects orbiting around each other? What happens when two clusters collide with each other, and all of the stars interact with each other through their mutual gravitational attractions? Modern computers have given us the tools we need to answer these questions. Although we cannot solve the N-body problem on paper, we can use computers to do the huge number of calculations necessary to add up all of the gravitational interactions of all the interacting objets, over and over again, to figure out where they all go.