When and how did the universe begin? Why are we here? Why is there something rather than nothing? What is the nature of reality? Why are the laws of nature so finely tuned as to allow for the existence of beings like ourselves? And, finally, is the apparent “grand design” of our universe evidence of a benevolent creator who set things in motion—or does science offer another explanation?

The most fundamental questions about the origins of the universe and of life itself, once the province of philosophy, now occupy the territory where scientists, philosophers, and theologians meet—if only to disagree. In their new book, Stephen Hawking and Leonard Mlodinow present the most recent scientific thinking about the mysteries of the universe, in nontechnical language marked by both brilliance and simplicity.

In The Grand Design they explain that according to quantum theory, the cosmos does not have just a single existence or history, but rather that every possible history of the universe exists simultaneously. When applied to the universe as a whole, this idea calls into question the very notion of cause and effect. But the “top-down” approach to cosmology that Hawking and

Mlodinow describe would say that the fact that the past takes no definite form means that we create history by observing it, rather than that history creates us. The authors further explain that we ourselves are the product of quantum fluctuations in the very early universe, and show how quantum theory predicts the “multiverse”—the idea that ours is just one of many universes that appeared spontaneously out of nothing, each with different laws of nature.

Along the way Hawking and Mlodinow question the conventional concept of reality, posing a “model-dependent” theory of reality as the best we can hope to find. And they conclude with a riveting assessment of M-theory, an explanation of the laws governing us and our universe that is currently the only viable candidate for a complete “theory of everything.” If confirmed, they write, it will be the unified theory that Einstein was looking for, and the ultimate triumph of human reason.