Timelike infinity by Stephen Baxter

Timelike Infinity

Set thousands of years in the future (5407AD), the human race has been conquered by the Qax, a truly alien turbulent-liquid form of life, who now rule over the few star systems of human space - adopting processes from human history to effectively oppress the resentful race.

Humans have encountered a few other races, including the astoundingly advanced Xeelee, and been conquered once before - by the Squeem - but successfully recovered.

A human-built device, the Interface project, returns to the solar system after 1,500 years. The project, towed by the spaceship Cauchy returns a wormhole gate, appearing to offer time traveldue to the time 'difference' between the exits of the wormhole (relativistic time dilation), with one end having remained in the solar system and the other traveling at near lightspeed for a century. The Qax had destroyed the solar system gate, but a lashed-up human ship (a great chunk of soil including Stonehenge, crewed by a group called the Friends of Wigner) passes through the returning gate, traveling back to the unconquered humanity of 1,500 years ago.

One of the crew of the Cauchy returns with the Friends, Miriam Berg. The Friends have a complex scheme, which does not include a simple military return-and-rescue - the 1,500 year technology gap makes this "risible". From the Wigner thought experiment they have postulated an unusual theory on the ultimate destiny of life in the universe. They believe that quantum wave-functions do not collapse like the Copenhagen interpretation holds, nor that each collapse actually buds off separate universes (like the quantum universes hypothesis holds) but rather that the universe is a participatory Universe: the entire universe exists as a single massive quantum superposition, and that at the end of time (in the open universe of the Xeelee Sequence, time and space are unbounded, or more precisely, bounded only at the Cauchy boundaries of "Time-like infinity" and "Space-like infinity"), when intelligent life has collected all information (compare the final anthropic principle and the Omega point), and transformed into an "Ultimate Observer", who will make the "Final observation", the observation which collapses all the possible entangled wave-functions generated since the beginning of the universe. They believe further that the Ultimate Observer will not merely observe, but choose which world line will be the true world-line, and that it will choose the one in which humanity suffers no Squeem or Qax occupations. However, the Ultimate Observer cannot choose between worldlines if no information survives to its era to distinguish worldlines- if the UO never knows of humanity, it cannot choose a worldline favorable to it. In other words, some way is needed to securely send information forward in time.

As a consequence of this necessity, they intend to turn Jupiter into a carefully formed singularity and use the precisely specified parameters as a method of encoding information. Miriam Berg is more concerned over the immediate fate of humanity, with the threat of the future Qax, and transmits a 'help' message to the gate designer Michael Poole.

The Qax, naturally, panic a little at the escape to the past. A complex, unavoidably fragile species in their huge living Spline spacecraft, the few Qax present are somewhat at a loss. They decide to build their own Interface, with major human-collaborator assistance (headed by Ambassador Jasoft Parz), to create a link to their future to gain aid in resolving the problem - with more modern GUT-engine spacecraft they can make a 500 year link in just eighteen months. A startling high-technology future vessel (in truth, one of the legendary Xeelee nightfighter, an advanced and long-range fast scout ship), with a future Qax comes through the gate. Its first act is to execute the Qax Governor of Earth and gather up Parz, before passing through the original portal after the Friends and all humanity. The future Qax takes two Spline ships (presumably leaving behind the nightfighter; this might be the nightfighter that is discovered by the crew of The Great Northern millennia later in Ring through the gate and on the journey reveals to Parz the reason behind its desire to completely destroy the human race.

The Ring

The future Qax tells Parz that over the centuries, the Qax had worn down humanity through constant oppression, and had eventually decided to completely eliminate its space-faring capabilities. But before they did, as economical traders, they wished to get as much value out of their human pilots as possible. So certain pilots were dispatched on a number of dangerous or quixotic missions.

One such pilot was a man named Jim Bolder. The Qax had come into possession of a Xeelee nightfighter, and had modified it to support human control. Bolder's mission was simple: go to the Great Atractor, the cause of most galactic drift and find out why and how it exists. Bolder travelled to the bottom of the gravitational well, and found- the Ring. A torusa thousand light year in diameter, constructed of an unknown substance, rotating at a large fraction of lightspeed. The Qax goes on to speculate that the torus created a Kerr metric, and that it allowed egress from the current universe, that it was in effect an escape route for the Xeelee. Before Parz, the Spline warship, and the Qax exit the wormhole, the Qax asks, "What do Xeelee fear, do you suppose?". Regardless, Bolder escaped the Great Attractor and returned to the Qax home system, where he was supposed to be taken into custody by dozens of Spline warships wielding gravity-wave based "starbreakers" and his priceless data on the god-like Xeelee's ultimate project secured. Bolder either did not, or somehow escaped; in the ensuing fight, the starbreakers were accidentally fired at the Qax system primary star, and true to their name, destabilized it, causing it to go nova.

The Qax were forced to hurriedly evacuate. Many died, and the power of the Qax trading empire (and by extension, their Occupation of Earth) ended.