The observable universe, the part we can see with telescopes, is incredibly vast. Yet recent theories suggest that there is far more to the universe than what our instruments record—in fact, it could be infinite. Colossal flows of galaxies, large empty regions called voids, and other unexplained phenomena offer clues that our own "bubble universe" could be part of a greater realm called the multiverse. How big is the observable universe? What it is made of? What lies beyond it? Was there a time before the Big Bang? Could space have unseen dimensions? In this book, physicist and science writer Paul Halpern explains what we know—and what we hope to soon find out—about our extraordinary cosmos.