Although elastic and inelastic collisions sound like they should have the same sort of effect, it is rather obvious that they are completely different. The basic contrast between the two is their associated steady states. Both inelastic and elastic collisions destroy the system's dipole moment. When atoms collide, their orientations are randomly altered. This change destroys the dipole moment. Elastic collisions conserve the normalization of the system, while inelastic collisions destroy it. If we had just examined the Bloch vector, then we could say that collisions in general have the same effect on the system. In both cases the populations of the upper and lower state are equal in the steady state: 0.0 for inelastic collisions and 0.5 for elastic collisions. In physical situations, for every inelastic collisions there are numerous elastic collisions; therefore, elastic collisions often dominate inelastic collisions.