At first blush, a more unlikely pair of collaborators than Terry Pratchett and Stephen Baxter seems awfully distant, hovering like a mirage out there on some far-fetched, counterfactual literary horizon. Pratchett built his reputation mainly with his Discworld books, comic, slapstick fantasies; Baxter, with his Xeelee cycle, hard-edged, physics-saluting science fiction. Both are British, and both have indeed collaborated in the past with others, but only “like to like”: Baxter with Arthur C. Clarke, Pratchett with Neil Gaiman. So their new series — projected at first as a duology — might initially strike their separate fan bases as an awkward mismatch of talents.



Luckily, nothing could be farther from the truth. The two books — The Long Earth and The Long War — combine Baxter’s and Pratchett’s separate strengths into an organic hybrid: humor with real speculative vigor, or speculation laced with witty humor.



Surprisingly enough for a series that tips towards the SF end of the spectrum, the origin of the project lies with Pratchett. In 1986, before Discworld had decisively achieved fame and prominence in his catalogue, Pratchett wrote the seed from which the current project sprouted, a short story about interdimensional travel titled “The High Meggas.”



Now, interdimensional travel — or visits to parallel worlds or voyaging across the multiverse — is one of the essential tropes of science fiction. First handled rigorously (and non-magically) in the 1930s, the theme has been developed by such giants of the field, past and present, as Robert Heinlein, Clifford Simak, Keith Laumer, Brian Aldiss, Christopher Priest, Paul Melko, Ian McDonald, Steven Gould, and Neal Stephenson. Michael Moorcock, who brought the word multiverse into common parlance (after its obscure coinage in the philosophy of William James), has created an immense mythos concerning the interrelationships among sheaves of fictional timelines. So when we come to The Long Earth, the latest instance of the motif, we bring with us some expectations for new riffs on the theme. And indeed, our authors don’t let us down.



The two distinctive hallmarks of Pratchett-Baxter cross-continua travel are 1) all the parallel Earths, as far as humanity can travel, one tedious jump at a time, are bare of humans; and 2) the gadget for leaping off from the ground zero of “Datum Earth” — the Stepper — is so simple it can be made from Radio Shack components, and its blueprints instantly go viral, prompting a mass exodus from our overburdened planet. (This uncontrolled proliferation of dangerous tech finds previous expression in Baxter and Clarke’s The Light of Other Days, about the dangers of rogue time-viewers.)



Two other technical flourishes also shape the story: no ferrous metals can be carried across the reality barrier (goodbye guns, computers, cars, etc.), and each Earth — in the polar directions of “East” and “West” — differs slightly across an unfathomable “contingency tree.” Travel far enough, and things start to get weird. Oh, one last feature, probably courtesy of Pratchett: jumping across wordlines makes one violently sick in the stomach. Thus we have bold explorers uncontrollably vomiting before they can even utter, “One small step for man…”



From the two simple main ground rules and their codicils, Baxter and Pratchett construct an adventure that constantly surprises. It confers the mind-expanding feeling that Victorian readers must have experienced when encountering Wells’s The Time Machine.



The Long Earth starts the adventure rolling by following a number of protagonists in a deftly whipsawing, multivector fashion. We have our main hero, Joshua Valienté, a young fellow who can Step without machinery, thanks to the strange circumstances of his birth. Valienté is recruited for a big multiverse expedition by an entity dubbed Lobsang, an artificial intelligence, distributed across various platforms, which also claims to be the reincarnated-in-silicon soul of a lowly Tibetan motorcycle repairman. Then there’s Sally Linsay, another “natural Stepper” and daughter of the Stepper’s mysteriously vanished inventor, Willis Linsay; policewoman Monica Jansson; and frontiersman Jack Green and his daughter Helen.



Baxter and Pratchett use these various characters and many others to disclose a succession of marvels from their unflagging imaginations. Sentient hominid races known as trolls and elves and kobolds are revealed. The Gap is discovered: a continuum where the planet Earth is entirely vanished, removing any solid doppelgänger Terra and leaving a vacuum to be traversed. Timelines with ancient megafauna are reached. Finally, the unique intelligence known as First Person Singular is encountered, sending the expedition back to Datum Earth with a preliminary map of the riches that await humanity.



Baxter’s touch shows up in the brilliant extrapolations and impeccably logical unfolding of the Stepping tech, I think, while Pratchett’s hand is omnipresent in the whimsical characters and in many droll observations on culture and society. For instance, I take the invention of “The First Heavenly Church of the Cosmic Confidence Trick” to be a Pratchett bit, a smooth blend of Vonnegut-style tomfoolery with Asimovian analysis that goes down easy. As Lobsang explains, “They consider their religion to reflect the truth about the universe, which is its essential absurdity. True Victims believe that there is one Born Again every minute. And they must be fruitful and multiply, to create more human minds to appreciate the joke.”





The Long War opens ten years after the events of the first book. Joshua is married to Helen Green, with a family of his own, content to live as a simple homesteader out in the High Meggers, the (differently spelled) neighborhood at least one million Earths removed from Datum Earth. Lobsang is out of Joshua’s life, busy running the Black Corporation, which has a monopoly on many important new technologies, including the nonferrous dirigibles that keep all the iterations of Earth in contact, under a loose affiliation known as the Aegis. Joshua’s placid life gets a disruptive jolt with the reappearance of Sally Linsay, as prickly and unpredictable as ever. Sally is worried that the trolls — kindly, peaceful partners to humans — are being slaughtered or maltreated up and down the Long Earth, and she convinces Joshua to try to do something about it, launching him on a new odyssey, with his family along for at least part of the ride.



In addition, we get a passel of intriguing new characters and their quests, such as Captain Maggie Kauffman, who helms the USS Benjamin Franklin dirigible, tasked with enforcing Aegis authority up and down the Long Earth. Her conversion from an officious point of view to another frame of mind becomes a central theme. We also meet Christopher Pagel, an expert on trolls. Moreover, Sister Agnes, the Harley-riding nun who helped raise orphan Joshua (can we discern Pratchett’s hand here?) returns in a surprising manner.



Baxter and Pratchett don’t merely repeat the feel of the first book. Everything has evolved. Some twenty-five years after Step Day, their frontier is now morphing into “statehood,” with all the Realpolitik issues that condition implies. The plot of this volume reflects the extant complex conditions of a widely settled cosmos. The milieu is less Davy Crockett (a figure cited frequently in The Long Earth) and more John C. Frémont, Great Pathfinder turned politician. At one juncture, the authors illustrate these changes with a touching symbol: the markers that Helen Green and her family used on their long trek across the endless forests are now crumbling and abandoned. (Also conducive to more empire-building are the anti-nausea medicines that have normalized the Stepping procedure.) Additionally, whereas the first book concerned mainly the cognate USAs, we now experience what China has been doing in its associated dimensions, thanks to riding along with the East Twenty Millions Expedition involving pedagogue Jacques Montecute and his super-bright student Roberta Golding.



The Long War concludes on a very satisfactory note, after its patented amalgam of jesting and jousting, having explored topics such as the nature of consciousness (human and otherwise), cosmology, freedom, and the soul. But the last couple of chapters also form a trembling springboard to further adventures. Whether Terry Pratchett’s well-known health issues will permit any extensions remains in doubt. But should this entry terminate the series, readers will still feel blessed.



Like Greg Bear’s infinite corridor in his Eon series, Philip José Farmer’s overstuffed Riverworld, Larry Niven’s Ringworld, or Roger Zelazny’s feuding realms of Amber, or any of a dozen other allied venues, Pratchett and Baxter’s Long Earth is a quintessential SF construct tailored to offer an infinity of exploration and a bounty of fresh readerly joys.