Understanding the Dynamics of Collision and Near-Collision Motions in   the N-Body Problem
  Although rare, collisions of two or more bodies in the N-body problem are apparent obstacles at which Newton's Law of Gravity ceases to make sense. Without understanding the nature of collisions, a complete understanding of the N-body problem can not be achieved. Historically, several methods have been developed to probe the nature of collisions in the N-body problem. One of these methods removes, or regularizes, certain types of collisions entirely, thereby relating not only analytically, but also numerically, the dynamics of such collision motions with their near collision motions. By understanding the dynamics of collision motions in the regularized setting, a better understanding of the dynamics of near-collision motions is achieved. 
Lenanrd F. Bakker
math.DS