At the latest count there are going to be five books.
From Jason's link to Locus Mag.
‘‘The Long Earth has eaten me up a bit, because we’ve agreed on a contract for five books now. At first we thought we’d do just one book, but the story was clearly too big for one book. The initial contract was for two books, but even there, it was still clearly too big. It’s a bit like my Xeelee universe: we can tell any kind of story we like in that setting. In fact, we can have any kind of Earth we like in there.
‘‘But Terry wants to end it on a James Blish note. He loves Blish, particularly the Cities in Flight sequence and the final novel, A Clash of Cymbals. He loves that – Mayor Amalfi, this practical guy, facing the end of the universe. Terry wants a big cosmic destination, so we’re working on that. I think in the end it’ll look as if the first two books are a two-part novel. Three and four set up this big climax in book five.”
‘‘In book three we go out to a quarter of a billion worlds. Two hundred and fifty million steps, when you’re getting to really strange stuff. Some of it is kind of logic from me, and some of it is more kind of fantasy from Terry.
‘‘And we also get into the physics. For me, with the Long Earth, it wasn’t like one of my regular ideas, where I usually start with the physics or ecology and work it through. This world was given to me by Terry, so it’s more like observation – I had to come up with a theory to fit the observed facts. I came up with some bonkers quantum mechanics stuff to explain the world, and bounced it off people like Ian Stewart, who’s very helpful. I’d been reading around about modern theories of multiple universes – very useful. In quantum mechanics, the world is supposedly splitting constantly into multiple copies – but maybe some of those copies can kind of braid into more coherent forms, so that you end up with a kind of tapestry of realities, like the Long Earth…. Multiple-universe ideas are all over modern physics. Some of these notions make specific predictions and are testable, but it’s really at the fringe of scientific thought.
‘‘I don’t think I believe any of it, though. The world just doesn’t feel like that. It doesn’t feel like you’re splitting into a million copies of yourself every second. I think reality’s a bit more robust. We’ll figure it out some day.’’
Read the complete interview, and biographical profile, in the January 2014 issue of Locus Magazine.
He willnae tak' a drink! I think he's deid! , on the other hand though A Midgie in yir hand is worth twa up yir kilt.