Stephen Baxter is an old favorite of mine. I discovered his writing on uchronia.net – the bibliography of alternate history: ”First to the Moon”, “Prospero One”, “Anti-Ice”, and of course the excellent novel “Voyage” made me follow his work.
I was surprised to learn that he has collaborated on a parallel Earths novel with Terry Pratchett. To me, Pratchett was the prototypical fantasy writer but then I remembered that he managed to write books about economy, politics and whatever else you can think of, all under the disguise of fantasy, and I was less surprised.
Eventually, I got my hands on a second-hand copy of the first book...
For more: http://scifiportal.eu/the-long-earth-by-terry-pratchett-and-stephen-baxter-a-review-by-valentin-ivanov/