Our understanding of ourselves and the cosmos has advanced immeasurably over the last five hundred years of modern science, yet many fundamental mysteries of existence persist. How did our Universe begin, if it even had a beginning? How big is it? What's at the bottom of a black hole? How did life on Earth arise? Are we alone? Is time travel possible?These mysteries define the threshold of the unknown. To explore that threshold is to gain a deeper understanding of just how far science has progressed. In The Known Unknowns, bestselling popular science writer Lawrence Krauss explores science's greatest known unknowns. Covering time, space, physical law, life and consciousness, Krauss introduces readers to the topics that will shape the state of science of the next few decades, and invites us to ponder and appreciate the universe in which we live.