If it's a page-turner you're looking for, Egan's Permutation City beats Connes' Noncommutative Geometry hands down.
— John Baez, sci.math
Paul uncovered his eyes, and looked around the room. Away from a few dazzling patches of direct sunshine, everything glowed softly in the diffuse light: the matte white brick walls, the imitation (imitation) mahogany furniture; even the posters — Bosch, Dali, Ernst, and Giger — looked harmless, domesticated. Wherever he turned his gaze (if nowhere else), the simulation was utterly convincing; the spotlight of his attention made it so. Hypothetical light rays were being traced backwards from individual rod and cone cells on his simulated retinas, and projected out into the virtual environment to determine exactly what needed to be computed: a lot of detail near the centre of his vision, much less towards the periphery. Objects out of sight didn't “vanish” entirely, if they influenced the ambient light, but Paul knew that the calculations would rarely be pursued beyond the crudest first-order approximations: Bosch's Garden of Earthly Delights reduced to an average reflectance value, a single grey rectangle — because once his back was turned, any more detail would have been wasted. Everything in the room was as finely resolved, at any given moment, as it needed to be to fool him — no more, no less.
Paul Durham keeps making Copies of himself: software simulations of his own brain and body which can be run in virtual reality, albeit seventeen times more slowly than real time. He wants them to be his guinea pigs for a set of experiments about the nature of artificial intelligence, time, and causality, but they keep changing their mind and baling out on him, shutting themselves down.
Maria Deluca is an Autoverse addict; she's unemployed and running out of money, but she can't stop wasting her time playing around with the cellular automaton known as the Autoverse, a virtual world that follows a simple set of mathematical rules as its “laws of physics”.
Paul makes Maria a very strange offer: he asks her to design a seed for an entire virtual biosphere able to exist inside the Autoverse, modelled right down to the molecular level. The job will pay well, and will allow her to indulge her obsession. There has to be a catch, though, because such a seed would be useless without a simulation of the Autoverse large enough to allow the resulting biosphere to grow and flourish — a feat far beyond the capacity of all the computers in the world.