Not to be confused with the 1985 novel Diasporah by W.R. Yates.
The novel provides examples of:
- Author Filibuster: The treatment of the conflict between Citizens and Fleshers in the early chapters is so one-sided that one gets the feeling Egan was trying to be the Ayn Rand of the transhumanists, or at least the Bizarro Leiji Matsumoto.
- Cessation of Existence: Generally presented as a voluntary option for any being which has achieved everything they might have set out to accomplish. In the end, having reached a kind of literal end of all things, Yatima and Paolo consider their choices. Paolo accepts Cessation; "That's not death. It's completion." Yatima chooses to spend the rest of eternity in abstract research. In the end, there was only mathematics.
- Chekhov's Gun: A sphere becoming a torus in five-dimensional space is the key to unlocking a path to other universes.
- Digital Avatar: How Citizens appear to one-another inside their Polises.
- Downer Ending: After unknown billions of years spent hunting through trillions of alternate universes, Paolo and Yatima utterly fail to find the Transmuters. They have no way home and realize that humanity would have evolved beyond all recognition in their absence anyway, so Paolo commits suicide and Yatima retreats into a virtual reality to study mathematics for all eternity.
- Everybody's Dead, Dave: Implied, though not confirmed; the last scene of the novel takes place billions of years after the previous one, Yatima and Paolo have traveled through trillions of alternate universes in pursuit of the Transmuters, and wound up empty-handed. It's unlikely that they'll be able to get back to their home universe, and even if they do, after billions of years, both Yatima and Paolo agree that humanity has almost certainly evolved into something completely unrecognizable, if it even still exists. They talk it over, and make their decisions: Paolo commits suicide, leaving Yatima the last recognizable descendant of the human race. Ve retreats into the Mines, a solipsistic virtual environment where ve will spend the rest of eternity studying mathematics.
- Formerly Sapient Species: The Dream Apes' ancestors deliberately removed their capacity for speech and most of their sapience in a wholesale renunciation of modern society.
- A Form You Are Comfortable With: When the Diaspora reaches the second macrosphere, two of the protagonists are approached by something that appears to be Hermann. Which freaks them the hell out, because Hermann didn't come with them. The "Contingency Handler", as it calls itself, explains that it chose this form precisely because it knew that they would know it couldn't actually be Hermann — it's actually a nonsentient AI designed to greet new arrivals in this universe.
- Invisible Aliens: Why can't we find any alien races in the Milky Way? They all ran away from the ensuing disaster.
- More than Three Dimensions: The protagonists discover that subatomic particles actually contain portals to a five-dimensional universe — whose subatomic particles contain portals to another three-dimensional universe, and so on.
- Speculative Fiction LGBT: Most of the characters are gender-neutral, although to be fair, that's because most of those characters exist as software and were created as such, having never been in an actual homo sapiens body.
- Starfish Aliens: Several species are so alien they can only be communicated with through 'bridgers': Citizens who clone themselves repeatedly, with minor alterations in each iteration, until they are themselves utterly alien. Messages are then sent back and forth down the line of clones, each one translating for the next in terms they can understand.
- Transhumanism: There are three main forms of humanity, each with several subgroups:
- Citizens are digital humans living in a collection of giant virtual reality universes, called Polises. The majority of the novel follows the actions of a small group of Citizens.
- Fleshers are biological humans, which include those who evolved naturally from Homo sapiens (called "statics") and a multitude of bio-engineered humans including "dream apes", which have had language capability engineered out of them.
- Gleisner Robots are digital humans living in the real world but separate from the fleshers. They inhabit robotic bodies and spend most of their time in space — or daydreaming on the Moon in one case.
- Translation Train Wreck: Yatima finds it very difficult to speak one-to-one with fleshers who have evolved completely alien viewpoints.
- Utopia: The Coalition of Polises... rather more like the Classical Greek polises wished they were like than they ever were actually like. A post-cyberpunk Crystal Spires and Togas. An extropian Galt's Gulch. All of the polises seen in the story were clearly designed to provide equal computing resources to all citizens thereof, and the polis hardware is unimpeachable in doing just that.
