It’s fun to play with “what ifs,” and this series is a doozy. What if there were an infinite number of Earths, with an infinite number of evolutionary permutations? What if (almost) anyone could go to them, with minimum effort?
Watching Pratchett and Baxter spin out the ramifications of these two relatively simple ideas is a pure joy. How would different countries react? How would individuals react? How would parallel Earths be worked into pre-existing national structures and conceptions?
And that’s when the book’s focused on our Earth. Once you get out into those evolutionary permutations, there’s all kinds of new questions. What else could have evolved? What kind of intelligent life? How would we recognize it? How would we deal with it? Could we deal with it? How would they adapt to new environments?
Personally, my favorite part is the “Jokers,” worlds that have evolved in super weird ways, like being populated entirely by butterflies.
It’s not Pratchett’s usual satire, and there are moments when the pioneer spirit becomes a bit grating. But it’s great fun.