Permutation City - Greg Egan
(Read originally in 1994).

"I was six years old when my parents told me that there was a small, dark jewel inside my skull, learning to be me"...

Learning to be me

With this starts off one of the most astonishing short stories I've ever read. If you haven't read it, I urge you to do so. Egan questions what it really means to be human in a way that it's quite unsurpassed in my mind.

I've just finished "Permutation City", and the feeling I got from reading it now is the same I got in 1994 when read it for the first time.

Is it possible to write a book exploring the dichotomy between a computer simulation of a person and a "real" person? More specifically, is it possible to focus on exploring one possible model of consciousness and reality? (YES, It's possible!!!)

The Dust Theory upon which the book works is based on Tegmark's mathematical universe hypothesis (MUH). The assertion states that our external physical reality is a mathematical structure. Without going into much detail, the following article is great to start grasping the concepts that underpin the book: 

MUH

Without the proper conceptual framework, I admit it's difficult to get into the book. But as one understands the questions lurking behind it, it's one hell of a ride.

Other Computer Science concepts needed to deeply appreciate the book:

1 - The assumption that human consciousness is Turing computable, ie, all aspects of genuine consciousness can be produced by a computer program. Egan tries successfully to deconstruct not only some standard notions of self, memory, and mortality, but also of physical reality;

2 - Cellular automata. In this book VR assumes the form of The Autoverse, which is basically a deterministic chemistry set, internally consistent and vaguely resembling real chemistry;

3 - VR making extensive use of heuristics to simulate completely immersion and convincing physical environments, but at a maximum of seventeen times slower than "real" time.

The three ideas above are at the core of the book. Not even William Gibson nor Neal Stephenson explore these concepts the way Egan does. His ideas are way, way bigger than Gibson's or Stephenson's. He's thinking way bigger. He's asking questions that start in the real world and run right past the border to metaphysics and philosophy using Computer Science constructs. I look back and wonder if there was ever a line at all.

Despite the fact that it makes some demands on the reader, namely Computer Science Literacy, the book feels absolutely real. 

Greg Egan is really one of a kind. He deserves a wider readership, not being pinned down to SF.

Computer Science apart, his work is so pure that it resonates. I'm going to reread all of his work. I'm in for a ride.