Inelastic collapse in two dimensions

Molecular dynamic simulations show that a two-dimensional gas of inelastic disks, started from random initial conditions, has a finite time singularity in which a group of particles spontaneously forms a straight line. The inelastic disks then collide infinitely often in a finite time along their joint line of centers. The upshot of this process is a multiparticle collision that occurs through the accumulation of an infinite sequence of binary encounters.