Question about the multiverse
The characters can only travel to realities where the (identical) box exists, so doesn't that mean that these realities must all be very similar? Dessen must exist in all of them and they must have peaceful societies with good education systems, advanced technology and chemistry, a stable climate and geology, the same laws of physics, etc. If these realities are very similar, wouldn't they all require a very similar history, and therefore be happening at roughly the same time? How it it possible that there's a box in a virgin rainforest, or buried underground, or a box existing in prehistory with dinosaurs (or whatever they were) wandering around?
I could be wrong, but I don't think the book had such outlandish alternate realities.