I spotted the fourth in this sequence (The Long Utopia) in the Fnac in Belfort when I was hunting for books in English, but I couldn’t buy it because I hadn’t read these two, the first and second sequels to The Long Earth, which I’d read and quite enjoyed when it first came out.

But clearly I hadn’t enjoyed it enough to snap up these sequels as soon as they appeared.

The premise of this series is that it suddenly becomes possible to visit (or step into) multitudes of parallel worlds. The various narratives concern the consequences of such a discovery. When there are unlimited Earths, what happens to society, government, authority, culture? What becomes of scientific discovery and progress, space exploration, and so on?

Conveniently, or so it first appears, Homo Sapiens only seems to have occurred on the one Earth (known as Datum), so these worlds are empty, pristine, undeveloped. There are no pesky rival civilisations to deal with.

But there are hominids, smartish apes. Some, peaceful haries known as Trolls, resemble the Sasquatch or Yeti of legend; others, known as Elves or Kobolds, might resemble other mythical creatures. Whereas most humans need a special box to help them ‘step’ between worlds, these natives of the Long Earth are (like a very few humans) ‘natural steppers’.

The late Pratchett and Baxter have fun with their creations, imagining the various consequences back here on Datum, but also the multitude of variations of Earth that there might be out there: desert worlds, water worlds, worlds without moons, moons without worlds, dinosaur planets, giant sea creatures, smart dogs, and so on.

The Long War continues the story of The Long Earth, but takes us forward in time by a few years, so the protagonists are older, things are more (and less) settled, and the authorities of the USA Datum are trying to exert their influence and control over the equivalent land masses of the parallel worlds. The further you step from Datum, the more different the Earth tend to be. But you can step in two directions (known as East or West), so there is a West One and an East One, and so on.

There are stepping airships, and explorers, and a kind of rumbling conflict that builds up. The Long War is fairly gripping, only losing its way towards the end, when a couple of plot threads seem to be dropped and not picked up. The Long Mars begins, again, a few years later, but for me is a less successful sequel. (At the end of The Long War, the next in the series is advertised as The Long Childhood, but when it appeared, it was renamed The Long Mars. The problem here is that neither of the two titles is really suitable.) It’s really just more of The Long War, with an added side trip to Mars which is neither here nor there. The various plot threads no longer really hang together. The Mars trip had potential to be interesting and gripping, but was really told too briefly and just seemed like a throwaway idea.

The way these books are written, I would guess, is that each author writes their part of the narrative, and the two halves are edited together. But in The Long Mars, you get a much stronger sense that these are really two (or three) different plots, arbitrarily shuffled together without the various chapters ever meeting. You could rip out The Long Mars bits and not miss them at all. So one character, who previously interacted with some of the others, is just taken away. Meanwhile, in the other sections, a new type of human being seems to be emerging as a consequence of these parallel worlds and their various inhabitants, smarter humans, who at first seem to be remarkably stable and sensible, but are then suddenly portrayed as arrogant and lacking in empathy. Again, there’s a strong sense of various narrative threads not really weaving together as successfully as in the first two books.

So I’ve still yet to pick up The Long Utopia, book four, but it remains an option. These are readable, interesting, packed with ideas (as you’d expect from both authors) and also occasionally funny and slightly cynical (as you’d expect from at least one of them). In the end, though, there’s a problem that these types of book share. Putting The Long Earths together with Larry Niven’s Ringworld series and Bob Shaw’s Orbitsville series, we end up with a problem of scale.

The Ringworld, as it turned out, was so big that it couldn’t really be explored. To see all of it, you’d need to travel so fast that you wouldn’t really be able to experience it. Travel slowly enough to explore properly, however, and you end up only seeing a tiny part of it before you die of old age. There was so much room that there was almost no room for conflict. Niven, cleverly, responded to reader input to create conflict in the Ringworld’s instability, but he still ended up reducing his story to a fairly small scale, taking place in a very limited area of his vast world. As for Bob Shaw’s Dyson sphere, it was even bigger than the Ringworld, and, again, the characters could just disappear into that vastness and avoid all conflict, and no mortal person could hope to explore more than a small part of it. With the Long Earths, there is indeed conflict, but all anybody really has to do is disappear into some distant wilderness on Earth two million plus, and that’s that. And in telling these stories, all the authors can do is occasionally sample one of the millions of earths: and these are interesting ideas, sure enough, but it’s hard to see where the narrative can go. All these airships do is step and step and step, more and more rapidly, reaching further and further into randomised Earths which no longer resemble this one. Both writers are adept at creating situations and characters that make you angry at the injustice of something or other, but when the solution to such contrivances is simply to step away, every time, then your interest starts to flag.

Which is not to say that they aren’t entertaining and worth a look (especially as a holiday read), just that (as with Ringworld and Orbitsville) the ideas end up overwhelming the narrative.