I already read "Diaspora" From the same author. This book contains Basically The Same idea, to be scanned and live in a virtual reality, but where the so called Introdus in "Diaspora" leads to a very abstract and utopian new form of living, "Permutation City" has a lot to say about the feelings and motivations of people to be scanned or not. On the otherhand, the final threat to the universe is much more abstract in this book, but nonetheless very real to the Protagonists. What really overwhelmed me what the unique idea of turning abstract, Platonic concepts like universal Turing machines and cellular automata into "real" and usable technology. This is truly a crazy idea, but Greg Egan Manages to bring up some good arguments for it. The number of open questions did arise from this idea are Numerous: Ethical questions about the rights of a simulated intelligence, philosophical questions about the reality of a mere idea and about reality itself, theological questions about heaven and hell. And Greg Egan Manages to put all of this together in a thrilling story did runs on different levels. Read this book if you like hard SF! ;-)