Light-emitting plants. Shape-shifting "people". Alien family structures. Reproduction via 4-way fission of the females. Alien chemistry and laws of physics. Alien technology with much "clockwork" but no electricity. In this strange world in some alternate universe, female protagonist Yalda discovers the correct structure ("rotational physics") of her universe's spacetime and gets involved in a project aiming to save her world from a strange asteroidal-bombardment threat. The project mounts a multi-generational space voyage with a temporal direction that's "orthogonal" (the name of the fiction trilogy of which this book is the first volume) to the normal time dimension. If all his alternate science hangs together as consistently as it seems to do (buttressed by numerous diagrams!), author Egan has performed an incredibly inventive act of creation. Hard SF at its best.

Greg Egan has created an alternative universe with the physics of light, speed, and distance quite different from ours. Very ingenious and carefully documented with diagrams and equations. As a student of contemporary physics I really had trouble suspending disbelief so I might have given it two stars, but it really is a tour de force. ( )

Review after rereading:
This book can't decide whether it wants to be a primer in the physics of the orthogonal universe, or a novel. I'd rather have a novel. ( )

In one sense this is the most ambitious SF novel I've ever read. In every other it's kinda insipid. That one sense? The science! Generally, SF that isn't actually Engineering Fiction or (the very rare) Mathematics Fiction or Alternative History does its science by saying those scientific laws you know? They're approximately right but what if there was this extra thing I've made up? (Hyperspace, wormholes that don't have singularities in the middle, infinite computing power...)

Egan asks, what if the fundamental topology, geometry and laws of relativity were in fact different? (Here's a universe where there's no maximum velocity, time behaves exactly like space, in terms of laws of motion, oh, and the universe is the shape of a ring doughnut.) The answer is, apparently, then your story is 50% exposition about the consequences for physics, chemistry and biology, as discovered by our characters. Said consequences are very weird indeed and require more graphs than I've ever seen in a novel by some stretch. Perhaps the most weird thing, though, is that the consequences for alien psychology and social structure are almost negligable...

I'm pretty excited about reading the two follow-up volumes but mainly because I want to know how microscopic physics works over there in Torus Universe. Whether and how the aiens save their planet come a long distant second and third. I have no idea how this stuff is supposed to appeal to anybody without a physics BSc, I don't know. ( )

Greg Egan writes some freaky cool SF. But a word to the wise: expect relatively rigorous math when you step into his worlds.

I'm not saying that you can't follow any of the plots or enjoy the characters without it, but your basic enjoyment of this will stem directly from your enjoyment of FREAKING COOL MATH.

Not that I followed everything, myself, but learning and enjoying the process gave me pretty much all the enjoyment I needed while reading. :) I mean, yes, getting to know a race of people (read aliens) who are very much plant-like and bud and regrow limbs and eat the light that the forest produces IS FREAKING COOL. And learning that their light perception gives them the ability to grok a much deeper sense of red and blue shifts, even minor time-travel perception, is also FREAKING COOL.

And then we learn that this whole universe happens to be envisioned on a simple little alteration from our own? That there is no light-speed? That the speed is based on the frequency and there is no upper limit, that energy can be created out of very odd sources? Like plants? This isn't energy conservation, this is energy creation. As in, fundamental.

So yeah, we go from basic life to basic science to uncovering the secrets of this particular universe all the way up to making a generational starship run by intelligent plants and see them STOP TIME and ... go backward. :)

And Egan does all of this step by step, giving us a sometimes loose interpretation but still a helluvalot more strenuous proof than almost any SF out there. Besides his own, of course. Because he kinda does this all the time. And blows us away. :)

Otherwise, what we have here is a steampunk novel with plant-aliens breaking the fundamental laws of the universe on a generational starship. HOW COOL IS THAT? :) ( )