Just when you thought there was nothing new to be said about evading the speed limit imposed by relativity, science fiction comes up with a completely original possibility. I just finished reading Karl Schroeder's Lockstep, which proposes yet another way to get around Einstein's cosmic speed limit. Lockstep was serialized in Analog about a year ago and has recently been published as a novel.
Science fiction has long played with the idea that space explorers could simply go into hibernation on long interstellar voyages. But what happens when they get home and find all of their friends and relatives dead, and the civilization they left behind changed beyond recognition? Lockstep provides a clever "out". The civilization invented by Schroeder goes into periodic hibernation -- everyone does, awakening for only one month out of every thirty years. Space travelers can time their voyages to take place during this hibernation period, and interstellar travel becomes as simple as a cross-country drive. Schroeder's world-building is a bit more subtle than this -- his "lockstep" worlds are mostly icy bodies, like those in the Kuiper belt around our own solar system, and their civilizations rely on robots to gather the scarce resources from these barren worlds while their inhabitants sleep. Meanwhile, the residents of more congenial worlds (like the Earth) never hibernate -- Schroeder calls these the "fast worlds."
Schroeder's novel is centered on the lockstep civilizations, but I think the most interesting possibilities concern the interactions between the lockstep planets and the fast worlds. Would the latter speed ahead of their hibernating counterparts technologically? The classic story of this kind is A.E. van Vogt's "Far Centaurus," in which astronauts on the first mission to Alpha Centauri come out of suspended animation only to discover that in the interim, humanity has developed faster-than-light travel and has already colonized the astronauts' destination! And what about biological evolution on the lockstep worlds -- it would be a shock to to wake up and discover that the pigs have taken over the farm (and everything else on the planet!) It will be interesting to see if Schroeder's idea becomes embedded in science fiction and used by other authors, much like Heinlein's generation ship.