All the rules of the universe, its light, heat, gravity, electromagnetism, its math, its history, its civilizations and people; all that was, is, and will ever be; exist within the pages of a book.
The book sits on a shelf next to other books. Some of the books on the shelf look like our book, except maybe one letter is different. Others tell stories, or are written in Chinese and Greek. Most of the books are complete chaos, letters mashed together by insane typewriters that spout nothing but gibberish at best and at worst are just a jumble of letters. Pages and pages are blank or contain only one character. Notes of music and vibration spring forth from others.
Rows of shelves go on and on into the distance, in a building with floor after floor of library space. Elevators and Stairs take you to new floors, some of them are underwater or on fire or upside down. Everything ever written or yet to be written or imagined or unimagined is contained within.
This is the Multiverse.