The Spitzer-Schwarzschild scattering mechanism is the process by which stars in the disk of our galaxy encounter interstellar clouds and are accelerated by them. Over time, this perturbs the stars, so that older disk stars have more elliptical orbits, larger velocity dispersions, and greater scale heights than younger disk stars. This mechanism cannot, however, explain the motions of stars in the galactic halo, which require the existence of dark matter.