I'm not going to pretend to know the physics behind it, but the idea, as proposed by the two notable physicists, is that the theory of general relativity predicts these existence of these bridges between points in space and time. I'm guessing it has something to do with gravity and the pull on space by large objects. But in any respect, the wormhole, doesn't last long, collapsing in on themselves quickly. And I'd hazard a guess that they would probably be a pretty rough place to set up a juice bar.
But the idea is out there. Here's a little vid for your enjoyment. Taken from an article on space.com