What if the Earth wasn’t the only one? What if there were millions more Earths beyond ours, formed every time in that history went one way or the other while moving along the trousers of time? What if ours was the only one where homo sapiens developed, leaving the others empty, unspoilt and there for the taking? What if all you needed to do to reach one was step to the side?
Parallel universes are nothing new to Science Fiction, but the idea is given a wonderful new spin in The Long Earth, a collaboration between Sir Terry Pratchett and Stephen Baxter.
(Please note: there are some minor spoilers to follow, but I won’t reveal any major plot points.)