Humanity's understanding of the physical world is full of gaps. Not tiny little gaps you can safely ignore -- there are huge yawning voids in our basic notions of how the world works. Jorge Cham and Daniel Whiteson team up to explore everything we don't know about the universe, and while introducing the biggest mysteries in physics, they also helpfully demystify many complicated things we do know. And although the universe is full of weird things that don't make any sense, Cham and Whiteson make a case that the questions we can't answer are as interesting as the ones we can, and they invite us to see the universe as a possibly boundless expanse of uncharted territory that's still ours to explore.