Physicist: The three body problem is to exactly solve for the motions of three (or more) bodies interacting through an inverse square force (which includes gravitational and electrical attraction). The unsolvableness of the 3-body problem, rather than being an embarrassing hole in physics, an obvious but unsolved problem, is actually the norm. Answer gravy: First, this is how to solve the gravitational two body problem. “ ” is called “the relative position vector”, and all it does is point from the second body to the first body. In the 2-body problem all you have to worry about is the attraction between body 1 and body 2.