I think this is a really really good book. Right after finishing the book it feels as one of the best sci-fi books I have ever read when it comes to challenge the brain and think one step further... Sometimes it almost as if he wants to make sure that each idea that people are used with are challenged. If we struggle with nanotechnology, then femtotechnology is the obvious focus in this book, do you struggle with multiple dimensions, then the challenge of traveling between universes where the dimensions are configured in different ways.
I also like the fact that he has so many ideas and link them all together in a way that make sense for the overall story (so many journalists/authors today write books as soon as they have one idea, or even half of an idea).
The way he describes virtual worlds or confusion when moving between universes with different dimensions is really well written and I would love if someone could try to visualize Greg's ideas.
The story focus on three groups of beings: 1. The main characters are those living in "polises" as conscious software. 2 Others have robotic bodies that remain in contact with the physical world. 3. Finally there are "fleshers" who are physical human beings (most of them very genetically altered)
The best parts of the book is however not the – very good – descriptions of virtual worlds, alternate universes or different development paths for humanity, it is the way he captures the fundamental challenges of communication without really spending much time on it. The challenges include "normal" perspectives (from art and math to adults and children), a situation when genetic modifications of humans result in a situation when they are so different that they can't understand each other, a situation where different ways of living (body, robot, software) create societies that are very different, to the part where he spends the least time, how totally different intelligent beings communicate.
I look forward to read more books from Greg and recommend anyone interested in not just math, AI, sci-fi, alternative universes and technology but also communication and ethics to read this book.