I have read several of Baxter's Xeelee Sequence books, but I never dived into his early novels set in this universe until now. At first, I thought I had read this before, but then I realized that was just an effect of Timelike Infinity having some of the same characters (like Michael Poole) and events of other books in the loose series. The Xeelee Sequence universe extents from the Big Bang to the end of the universe after all, with some 19 or so novels populating it.
This starts off around 5200 AD with the Earth and humanity suffering under the Qax, the second alien species to conquer humanity. The Qax, though few in number, control space in their massive, organic space ships and have largely shut down humanities space travel. Earth is now a giant farm producing food for export to other alien species while humans live on processed kelp and such. One of our main characters is a diplomat to the Qax (Parz), although he has never (like the rest of humanity) actually seen the Qax in the flesh if you will. Besides shutting down humanities space programs, the Qax also ended the treatments for human longevity, condemning humans to their natural lifespan once again.
Yet, 1500 years ago, Michael Poole, along with a team of engineers/scientists, created a 'wormhole' in Jupiter's orbit, with one end left there and its 'pair' dragged out toward the center of universe by a sublight spacecraft. This is were things get interesting! When the Qax conquered humanity, they destroyed the wormhole around Jupiter, but one day Parz is summoned by the Qax because the other end of the wormhole finally returned (it was expected). Further, despite the tyranny of the Qax, a ship left Earth and, using an alien hyperdrive, shot through the wormhole gate, in effect, traveling 1500 years back in time...
As the title suggests, the key feature of this story involves time travel. Now, most science fiction readers are familiar with the idea that when a spaceship reaches speeds close to light, time slows down on it relative to 'normal' time on a planet, say. Hence, we have subjective and objective time for those involved. When the wormhole returns, the people on the ship that towed it away have only aged 100 years subjective, even though on Earth it is 1500 years later.
Baxter tosses the reader for another loop here, however. What Poole created was basically a time machine. Ships passing through it when it came back to Earth will return to Earth 1500 years in the past. The rebels/terrorists (to the Qax at least) who shoot through the wormhole they have a plan and the Qax are worried. What will humans from 'today' do to impact the future, and as far as the Qax are concerned, them. Will Earth be 'ready' for them when they come to conquer humanity?
Time paradoxes are not my biggest thing, but Baxter does a great job here with the classic motif. This gets even more complicated when the Qax decide to force humanity to build yet another wormhole, with this one going into the future. The Qax hope to see what will happen on Earth and their occupation in order to thwart any rebellion in the 'now'. So, we have 'future' time, 'present' time, and 'past' all basically existing here; it is enough to make your head spin-- mine did!
Baxter, fairly typical of hard science fiction authors, focuses more on the tech and 'big ideas' rather than character development here, but given the 'big ideas' on display here, I was fine with that. We do learn a little more about the Xeelee, a mysterious 'race' doing unimaginable things in parts of the galaxy, like creating a massive black hole in order to facilitate their leaving 'this' universe to somewhere else. Baxter does not go into much detail here, but this is fleshed out in later works.
Quite a ride by Baxter! This is smaller than his later doorstops, but he packs enough science and ideas here that it feels like a much longer novel. Giant, organic spacecraft (which are sentient to a degree), interesting aliens, and a bleak future for humanity (at least in the present timeline). Few authors can blind you with science and still tell a gripping story. Good stuff! The ending? Well, I was not enchanted, hence, rounding down. 4.5 mind boggling stars!