[In] the Narnia books it’s like that “main world” where it was just an infinite number of ponds and jumping into one shoots you out to some world … I think The Magicians kind of ripped off the idea.

Completely off-topic from symmetries and entropies, but I can’t pass up the opportunity to mention that the specific Narnia installment where we see this “main world” and branches is The Magician’s Nephew, the sixth out of seven books.