In his previous novels, Greg Egan's hardcore scientific speculation has always seemed to be shoehorned, slightly awkwardly, into his decently imagined, elegantly written plots. A less brave writer might have reined in the science, and created a more conventional novel. Egan, instead, turns it up to 11, and may, in the process, have kickstarted an entirely new kind of writing.
Hundreds of years from now, 'humanity' is mostly a collective of self-generating, autonomous software running on underground computers. When an unexpected cosmic event kills off all remaining organic life on earth, and also shakes the foundations of known physics, it stirs this somewhat decadent posthumanity to launch these 'polises' on a grand quest to the stars, to find out what happened, whether it will happen again, and if there is any way of escaping it.
They find the rather bleak answers to their questions, and much more besides, in a tale so unlike anything else, that it can barely be called a novel. Instead, it's a travelogue through realms of incredible physics, concisely and, if you're prepared to make a bit of effort, very clearly explained.
A lot of the science is doubtless borderline gibberish (although you get a bibliography at the end which includes at least one scientific paper!), but that's not important. This is art, and what Egan has done is used the language of contemporary maths, physics and occasionally biology to conjure up artefacts so poetic, so beautiful in concept, that they demand to be believed.
And, bravely, he's left it at that, challenging the reader either to enjoy the exuberance of his worlds as much as he does, or go and do something else instead. There is, of course, a story to be told, but rather than using science as an adjunct to the story, it's inseparable form the story itself: his bizarre cosmology is as much a character as the actual characters.
Who, it must be said, occasionally lack substance. That they are all capable of adjusting their own personalities only goes so far as an excuse for not consistently giving them one at all, and bringing sixteen dimensional aliens into the mix is risky if some of your protagonists barely have two. He's still tubthumping over-hard for 'rationality', as well- the 'fleshers' who insist on corporeality for spiritual reasons are portrayed with more derision than they deserve, and their destruction is handled a little coldly.
Some flaws, then, but these are generally obscured by the light of wonderful, speculative science that discovers the beauty that can be created from the abstruse and technical concepts of theoretical physics.