Manifold Time

Humanity spread throughout the universe, but never found other intelligent life. Far into the future, matter having long since decayed away, the last descendants of humanity have survived by embedding themselves into a lossless computing substrate. They can theoretically survive indefinitely, but since there will never be new input, their thoughts are doomed to eventually begin repeating. A faction decides this was not meant to be and reaches back to the distant past...

The year is 2010. More than a century of ecological damage, industrial and technological expansion, and unchecked population growth has left the Earth on the brink of devastation. Strange, hyper-intelligent children are being born all over the globe. As the world's governments turn inward, Reid Malenfant campaigns for the exploration and colonization of space. Battling national sabotage and international outcry, as apocalyptic riots sweep the globe, he builds a spacecraft and launches it into deep space.

Part of Stephen Baxter's Manifold series.

This book provides examples of:

 * Absent Aliens: Despite coming to dominate the universe, humanity never found any other intelligent life.
 * Abusing the Kardashev Scale For Fun and Profit: In the distant future, descendants of humanity maintain vast Dyson nets around the supermassive black hole remnants of galaxies until they evaporate via Hawking radiation, accessing the power equivalent of multiple galaxies. And in the present, once the Blue children start tapping into this knowledge, things get a little crazy.
 * Alternate Continuity: To the other books in the Manifold series.
 * Apocalypse How:
 * Bizarre Baby Boom
 * Child Prodigy: "Prodigy" doesn't even begin to describe the Blues, who are under the influence of a civilization from the end of the universe. Humanity as a whole is considerably freaked out by them.
 * Fling a Light Into the Future: Well, into the past, but close enough.
 * Set Right What Once Went Wrong: The motivation of the downstreamers. In addition,.
 * To elaborate: what "went wrong" is.
 * Stable Time Loop: The notes Malenfant leaves for himself . Also, the strange matter nugget the Blues send back in time. But for the rest, the downstreamers really are changing the past.
 * Sufficiently Advanced Aliens / Humans Are Cthulhu: The Downstreamers are essentially gods. End of story. They can influence events in the past and have more energy at their disposal than entire galaxies, can travel to other universes, create other universes, and their plan is essentially . Space Battles seems to think they're the Ur Example of this trope.
 * Time Travel: In addition to the information the downstreamers send back, Malenfant goes on a tour of the universes that existed before this one;.
 * Xenofiction: A major subplot involves Malenfant using squid, modified to be more intelligent, as a space exploration force. This is told from the squids' perspective.
 * Zero-G Spot: It's mentioned that one spaceflight saw frequent zero-g orgies because the astronauts had no better way to pass their time.