The Long Earth by Terry Pratchett and Stephen Baxter

This book solves a long-niggling problem for me! It's a silly problem, but it has seriously kept me awake at nights. You see, when I wake up in the middle of the night and my brain decides, hey, there's this idea I want to think about instead of sleeping, I often turn to one daydream. It's designed to relax me - I go through each of my senses, very carefully, and there's nothing unpredictable in the dream. Most often, I'm walking through a woods to a little cabin that is all mine, and when I get inside, I make tea and sit in front of a fire, reading. 

There are other variations on this theme, mostly depending on what's missing in my life. If I'm drowning in my dissertation and haven't seen friends enough, I'll go the same cabin, and have a party. The point is, I have a science fiction brain. And because in my head, this is always a different world, not our world at all, sometimes when I'm in the middle of relaxing, my science fiction brain will turn on and start asking questions like "then why are the trees the same?" "How long are the days and nights?" "How can things be so similar if you're on a different planet."

I realize this is dumb, but it seriously derails me getting back to sleep sometimes.  Pratchett and Baxter have solved that problem for me, with this idea of an infinite number of Earths in a row, to which you can pop over with the aid of a device and a potato.  The ones nearby are very similar, those further Earths away can be radically different.

An inventor releases the design for free on the internet, and suddenly a good portion of the population strikes out for further territories. The Earths nearest ours get built up, those further out attract the truly intrepid. The only thing is that iron and steel in their metallic form can't travel with you. 

Some people turn out to be natural steppers, not needing the potato or machine, while about a fifth of people can't stand to step at all. This creates dissatisfaction amongst those left behind, even though they're suddenly in much more abundant circumstances. 

Joshua is a natural stepper, indeed, he was stepped when he was just born, long before the invention was released or even thought of. He gets enlisted by a reincarnated Buddhist monk in an AI to go with him on a zeppelin through the worlds. Out there, they discover other humanoids - mostly peaceful singing trolls and bloodthirsty elves. Something is causing both of those races to stampede through the Long Earth, getting closer and closer to our Earth. Even if their intentions aren't bad, they can clearly panic.

Weirdly, when you combine Pratchett and Baxter, it reads a bit like Douglas Adams. Perhaps it's the potato and AI/Buddhist monk. I have only read one previous Baxter book, at least two decades ago, and despite the last name we have in common, did not like it at all. He has, it seems, gotten better over the intervening years, or maybe it's Pratchett's influence, but this was an easy read, an intriguing one, and as I know there are further books from here, I'm curious to find out where the series goes next.

At any rate, just its very existence may help me sleep better at night. Unless my science fiction brain finds something else to worry about.