Ars Mathematica

The three body problem in physics is the study of the trajectories of three bodies mutually attracted by (Newtonian) gravity. Unlike the two body problem, the three body problem cannot be solved in general, but some specific solutions are known. An article in the Notices of the AMS reports that a new (well, new circa 2001) solution has been found where all three bodies travel in the same orbit — a figure eight.

The figure eight orbit is stable, which means that it is robust under small perturbations. Since any actual physical system will be perturbed slightly by the gravitational pull of other bodies, stability is a prerequisite for a solution to actually be found in nature. So the figure eight orbit may someday be observed by astronomers.