In John Sclazi’s first series of science fiction novels, Old Man’s War and its several sequels and companion volumes, the Milky Way near earth (well, near in interstellar terms) teems with life and spacefaring civilizations. Humanity has to make its way in a galactic neighborhood that’s full of life, and nearly as full of war. The Collapsing Empire concerns an interstellar human civilization at the other end of the Drake equation: nobody here but us. In this setting, travel between solar systems proceeds thanks to the Flow, something like an extradimensional river that enables interstellar travel in a matter of weeks and months. Ships maneuver to an entry shoal that is more or less stable in space, translate themselves into the Flow, and follow it to an exit shoal in the destination system. Communication proceeds at the speed of travel, as it did on earth in the ages prior to the telegraph. Moreover, Flow connections are not symmetric: a route from A to B does not necessarily imply a route from B to A. The geometry of routes means that some systems are more important than others. Within the story, the ruling power set itself up about a thousand years before the book’s opening by controlling the most important set of Flow connections and building its empire outward from there.
Over that time span, the Flow has been stable with notably rare exceptions. Many centuries ago, the connection to earth was lost. This bit of narrative convenience gives Scalzi a much freer hand in shaping the overall setting for his space opera, which is likely to run for at least three books. (The second in the set, The Consuming Fire, is scheduled to be published in October 2018.) In a more recent century, the Flow to the planet Dalasýsla collapsed. Cut off from the rest of humanity, the settlement of some 20 million people on Dalasýsla also collapsed within decades.
Although the book’s title mentions an Empire, and one of the leading characters is the new Emperox, the star-spanning polity is actually known as the Interdependency. Not only is the universe of this story bereft of other forms of intelligent life, there is precious little habitable real estate in the systems connected by stable Flow links. Most of humanity lives in artificial habitats, either in space or under domes on planets that are otherwise inhospitable to human life. Rather than attempting to make every colony autonomous, an expensive and probably unattainable proposition, the leaders of human colonization chose to make the settlements dependent on one another. The resulting web of settlement is stronger and more prosperous than a string of autarkies would be, and they stand or fall together. For the better part of a thousand years, that has been an advantage.
At the book’s outset, there are signs that the Flow is not as stable over the very long term as humanity has assumed. Over the course of the book, these signs turn in to certainty, but plenty of power players are willing to overlook the fact that fundamental and inevitable change is coming to human civilization.