The Long Earth by Terry Pratchett and Stephen Baxter (Amazon link)
I haven’t picked it up yet since I like to get books from my local indie bookstore when I can, but if Pratchett’s name is on it, I’m there.
The key to space-time travel seems to be the common potato (see diagram of the book’s “stepper” technology below on the left). In the original Hitchhiker’s Guide to the Galaxy television series, a nice hot cup of tea was used to create the Infinite Improbability Drive, but the actual Drive had something spinning inside it that certainly looked a lot like a potato (cheesy screen capture below right).
I’m waiting for the episode where the Doctor reveals the hidden spud in the center of the drive mechanism of the TARDIS.
These aren’t the only example of mysterious potato science…