Timelike Infinity

Plot summary

By the year 5407, humanity has been subjugated by the Qax, a species of turbulent liquid that is profoundly alien. The Qax rule over a handful of star systems in human space, using methods borrowed from human history to keep the resentful population in check. Before the Qax, humans were conquered once by the Squeem but managed to recover. They have also encountered other species, including the immensely advanced Xeelee. A human project called the Interface, towed by the spaceship Cauchy, returns to the Solar System after 1,500 years. The project brings back a wormhole gate that seems to enable time travel because of the time difference between its two ends, a result of relativistic time dilation: one end stayed in the Solar System while the other traveled at near lightspeed for a century. The Qax had destroyed the gate that was in the Solar System, but a makeshift human ship—a large chunk of soil containing Stonehenge, crewed by a group known as the Friends of Wigner—passes through the returning gate and goes back in time to an era 1,500 years earlier, when humanity was still free. Miriam Berg, a crew member from the Cauchy, joins the Friends on this journey. The Friends do not plan a simple military rescue; the 1,500-year technological gap makes that idea risible. Instead, they have developed a complex theory about the ultimate fate of life, based on the Wigner thought experiment. They reject the Copenhagen interpretation of quantum mechanics, where wave-functions collapse, and also the quantum multiverse hypothesis, where each collapse creates separate universes. Their view is that the universe is participatory: it exists as a single, vast quantum superposition. At the end of time—in the open universe of the Xeelee Sequence, where time and space are unbounded except at the Cauchy boundaries of timelike infinity and spacelike infinity—intelligent life will gather all information, becoming an Ultimate Observer. This Observer will make a final Observation, collapsing every entangled wave-function that has existed since the universe began. The Friends further believe that the Ultimate Observer will not just observe but will choose which world line becomes the true one, and that it will select the world line where humanity never suffered occupation by the Squeem or the Qax.