After a slightly disappointing venture into biology with Teranesia, Egan is back to his favoured territory of fundamental physics -- and back on form -- with Schild's ladder.
Taking as his starting point an experiment-gone-all-too-right, he creates, in effect, the story of a new-born universe with its own radically different physics. Expanding at half the speed of light, it spreads out across our own universe, devouring everything in its path. Against it he pits two competing groups of researchers, one trying to halt its progress, the other trying to destroy it.
This provides the backdrop for the classic Egan combination -- human emotions and mind-bending physics playing out an epic story for the highest stakes. The themes are familiar from Egan's other novels and short stories -- a threat to humanity's very existence, an impenetrable boundary, an epic journey into a vividly realised alternate universe -- but more boldly executed than before.
This will probably be viewed by many as Egan's best novel. I don't think it is -- it's just that the physics is harder in this one. The feat is superficially more impressive but ultimately it lacks some of the depth of Diaspora.
As ever with Egan, it's a good read and hard to put down. And it's packed with more new ideas than some SF writers manage in a career. But it has some flaws. The characterisation is less complete than in some of his other books and there are a few annoying flaws: his exotic physics, once you get inside it, is slightly less exotic than it might be; and in scenes where his characters venture outside their spaceship he doesn't seem to account for relativity -- despite the fact that the barrier is moving at half light speed.
But it's still a decent read, and one I'd recommend if you like your science hard but tempered with a little humanity.