There’s a whole strand of science fiction built around simple “What If?” questions. The recipe: Start with something impossible according to our understanding of the universe, add it to a modern society, and extrapolate how the new information, plus personal and societal stresses, reveals the nature of humanity. First contact with aliens is a common what-if story seed, while the recent film Another Earth demonstrated a different form. Terry Pratchett and Stephen Baxter’s The Long Earth fits within the model: Its plot revolves around the near-future discovery that people can “Step” into an apparently infinite number of parallel earths.
For Pratchett, well known for the comedic fantasy of the Discworld series, it’s an interesting late-career switch. There are some recognizable Pratchett linguistic flourishes—one recycled joke describes the protagonist as the sort of person who “commences” instead of just starting—but the book is largely dramatic over comedic. Baxter usually writes hard science fiction, like The Time Ships and the Time Odyssey series he co-wrote with 2001 author Arthur C. Clarke. This collaboration doesn’t contain the outright silliness or wild far-future extrapolations of the authors’ other works, but it does have Pratchett’s compelling characterization and Baxter’s fascinating ideas.
The Long Earth focuses on Joshua Valienté, a rare human who can Step without a device, and without the nausea that makes Stepping a difficult process for most. He’s also a folk hero for saving dozens of children on the first day they Stepped. This brings him to the attention of a major corporation, which recruits him to explore deep into the Long Earth. Each alternate Earth down the line has had something change just slightly in its history, with the changes getting bigger and bigger the further away from the original Earth. Some of the most interesting sections of the book involve Joshua and his AI partner attempting to understand what made each planet special, or just describing the different plants and animals on each world: an extinct group of possibly sentient bipedal dinosaurs in one case, or the huge predatory fish of an ocean planet.
The Long Earth also features interlude chapters from side characters, adding further depth to the world by depicting how humanity has reacted to having an infinite number of worlds instead of one overcrowded one, as well as the new economic and social tensions between those who can Step easily and those who can’t do it at all. The story is filled with dozens of huge philosophical, scientific, and social questions, but it ends up short on answers. It lacks a strong plot, and asks, “What does it all mean?” and “What’s going to happen to humanity?” several times over its course, then ends with a promise of sequels. That promise is welcome, but The Long Earth suffers slightly from its own overpacked potential: It promises a satisfying meal, and delivers a tasty appetizer.