at least nine-tenths of all the original reality ever created lies outside the multiverse, and since the multiverse by definition includes absolutely everything that is anything, this puts a bit of a strain on things.

Outside the boundaries of the universes lie the raw realities, the could-have-beens, the might-bes, the never-weres, the wild ideas, all being created and uncreated chaotically like elements in fermenting supernovas.

Just occasionally where the walls of the worlds have worn a bit thin, they can leak in.

Author: Terry Pratchett