Lee Smolin presents an interesting hypothesis that attempts to explain why the fundamental physical constants seem to be "tuned" perfectly to allow stars, planets, and life to evolve. The best aspect of his hypothesis is that it is "falsifiable". This means that Smolin proposes a number of tests that if they fail, would mean that his hypothesis is wrong. And, the tests are not incredibly difficult. He includes observational tests--like measuring the masses of additional neutron stars--and theoretical tests; calculating the consequences of changing the values of certain physical "constants". So, Smolin's hypothesis is quite engaging, and should be considered seriously.

But most of the book is not about Smolin's hypothesis at all. It is really about reconciling various quantum theories and cosmology. The book is deeply philosophical, and the book makes clear which parts are pure speculation. Smolin mentions that he met Richard Feynman a few times. Each time he described his work to Feynman, he was criticized because Smolin's ideas were not sufficiently crazy!

So, much of the book contains some crazy ideas, and it is full of philosophical speculation. The book is not easy to read--not because of heavy technical explanations, but because the philosophical viewpoints are often quite subtle.