The renowned Harvard cosmologist and theoretical physicist explores a scenario in which a disk of dark matter—the elusive stuff in the universe that interacts through gravity like ordinary matter, but that doesn’t emit or absorb light—dislodged a comet from the Oort cloud that was ultimately responsible for the dinosaurs’ extinction. Dr. Lisa Randall teaches us an enormous amount about dark matter, our Universe, our galaxy, asteroids, and comets—and the process by which scientists explore new concepts.