Characters in sci-fi movies and novels routinely encounter alien life somewhere in the universe. The crew of the USS Enterprise deals with Klingons, Q, and the Borg while Luke Skywalker works with Chewbacca the Wookiee and Ewoks to defeat the evil Galactic Empire. Sometimes the aliens come to Earth, as in Transformers, where Optimus Prime and his cohorts join elite military personnel on Earth to defend humanity against an attack by other villainous robots. Lois Lane encounters Superman, the Krypton native who gains great powers from the solar system’s yellow Sun. Yet despite the diversity of sci-fi aliens, no filmmaker or writer seems to be aware of the one alien that troubles cosmologists as they wrestle to understand the nature of the cosmos: the Boltzmann brain.