This is undoubtedly one of the best books I have ever read. One of the knockdown Christian arguments for the existence of god is that of the first mover; as it goes "effect requires cause / since the universe is in motion, it must have had a cause / therefore god." Of course, this argument merely passes the buck --- if the universe can't be started in motion, why can god? What was his mover? Permutation City is what happens when you bite the bullet and take that question _seriously._

This book follows a computer-simulated psychonaut in his quest to understand the nature of consciousness and reality. Egan really takes his time exploring the consequences of being able to make simulated copies of humans --- for example, what happens if you run their subjective experience backwards? Or if you remove a haunting memory? Are two indistinguishable copies the same person? Amazingly, every result here is both coherent and interesting, and I found myself pausing every few pages to think deeply about the consequences of some aspect of Permutation City's reality. Egan is a mathematician, and it shows.

Go read this book. If you appreciate hard science fiction and remarkably good world-building, you will love it.