From a New York Times interview with Brian Greene, physicist at Columbia University:
In your forthcoming book, “The Hidden Reality,” you ponder the possibility of a “multiverse” composed of many universes. But what kind of worlds are we talking about? Clumps of subatomic particles in space? Or universes with restaurants and museums?
Some might have museums and restaurants. Some might have copies of you and me having a conversation similar to this one. Yet other universes would be vastly different. They could involve a gigantic expansive space that might be filled with other forms of matter governed by other kinds of physical laws. In one such universe, when the apple is released by a tree, it might go up instead of down.