Outside the Universe?

One of my friends over on LiveJournal asked what's outside the universe. Thought it'd be fun to post my response here and see what y'all think.

The current model of the universe says that there isn't an "outside" to it in that if you keep going in one direction you can "leave" the universe. It's like if you look at a map of the Earth and ask what's past the edge - the Earth is round so you just come back to the other side of it. We're not convinced that our universe is finite in size (and therefore loops back on itself) or if it's instead infinite.

However, when you look at the flat map of the Earth, what that map fails to show is that since the Earth is a sphere, you *can* leave the Earth. If you could leave the universe, our best guess right now (via string theory) is that there are multiple "higher dimensional" universes called branes (short for membranes) that intersect to form universes like ours. So if we had hyperdimensional eyes, we'd see a bunch of sheets that cross each other, and at each crossing is another universe. I'm not sure if this idea is testable yet, or if it's still just a pipe dream though.