Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe

by Lisa Randall

Underdense regions expand more rapidly than the Universe as a whole, whereas overdense regions expand more slowly.

The inner regions, which give rise to short period comets, are called the Kuiper belt and the scattered disk, while much farther out is the hypothesized Oort cloud, which produces long-period comets and to which I’ll soon (figuratively) return.