I have a question about branes... #1: Why can't nongravitational fields escape this brane, and gravity can? I've read that some gravitons, and other particles, actually escape this brane. Where do they go? This implies an "outside" of this universe. Could this universe be a subuniverse? I also read something about something happening to the brane's surface, making it look like its expanding. Anyone know more about this?