Professor Greene explains what scientists envision when they talk about a multiverse: "Scientists have many proposals. In some, the other universes have the same laws of physics and the same particles making up matter. So except perhaps for some environmental differences, pretty much what we see here is what happens there. In some multiverse proposals, the other universes could be radically different from what we know, the particles could be different, the laws of physics could appear different. And in others—ones that frankly don’t compel me—even the kinds of mathematics that govern the physics in those realms might be different from the math that we are familiar with."