Think of the universe like a deck of cards.
“Now, if you shuffle that deck, there’s just so many orderings that can happen,” Greene says. “If you shuffle that deck enough times, the orders will have to repeat. Similarly, with an infinite universe and only a finite number of complexions of matter, the way in which matter arranges itself has to repeat.” (Brian B. Greene)
Greene, the author of The Elegant Universe and The Fabric of the Cosmos, tackles the existence of multiple universes in his latest book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos.