Our universe might be really, really big — but finite. Or it might be infinitely big.
Both cases, says physicist Brian Greene, are possibilities, but if the latter is true, so is another posit: There are only so many ways matter can arrange itself within that infinite universe. Eventually, matter has to repeat itself and arrange itself in similar ways. So if the universe is infinitely large, it is also home to infinite parallel universes.
Does that sound confusing? Try this:
Think of the universe like a deck of cards.