I'm no stranger to pop-science books but this book opened my mind to some amazing possibilities. How is it that the universe we inhabit has just the right properties for us to exist? The Anthropic principle says it must because we are here to observe it. Smolin suggests that, in a nutshell, in the beginning there was random nothing, then out of that came blind iteration - universes forming and collapsing again, until finally evolution emerged by chance (it had all the time in the world after all to do so) and one (or more) universes 'stuck', ie were just stable enough to give rise to offspring (in black holes). Each child universe inherits the properties of its parent, with some random mutation, and eventually one (or more) universe formed that is stable enough to give rise to us. This is the theory of cosmological natural selection. The idea that inside every black hole is another daughter universe of our own, and ours is, in turn, the guts of a black hole in some parent universe, is deeply attractive. This book expounds on this thought experiment in an highly accessible manner.