It's not too hot, it's not too cold, and its forces act together in a way that's just right: why does the universe seem so perfectly tailor-made for life to exist? Paul Davies, one of the world's most acclaimed science writers, shows how everything from the humble carbon atom to the speed of light and the laws of physics themselves interact. He asks: is there a theory of everything within our grasp? If there was a big bang, what happened before it? Is there on universe or many? Could we exist within an endless time loop?