Our Milky Way galaxy is home to hundreds of billions of stars, yet Earth is the only planet known to harbor intelligent life. Why is that? In "The Reason Why," John Gribbin reveals what makes our planet unique. For the first time, he connects the series of cosmic events that led to the birth of our civilization—a unique set of circumstances that has not, and cannot, occur elsewhere. Gribbin is our most accessible guide to the big scientific questions. In this book, he explores the biggest questions of all: why do we exist, what does it mean to be alone in the universe, and do we have a future?