the c constant, and the shape of the universe

For a while I was wondering why c was the speed limit for the universe. I knew that to answer that question, I needed a theory that quantified this speed limit with a physical property of the universe.

An idea struck me a little while ago. I was thinking about the shape of the universe, and mused with the idea that the universe was like a 4-d bubble, and that our 3-d space is on it's surface. The 4rth dimensioanlly inwards curvature of the surface of this "hyperbubble" causes gravity, as Einstein described. I then considered what would happen if something became so massive and curved space so far that it reached the cetner of the bubble (assuming the universe has a set radius), and therefor couldnt be any more massive. The distance to the center of this hyperbubble limits how much space-time curvature something can cause, and therefor limits it's mass, and therefor limits it's energy. That limit is the speed of light. Perhapse nothing can surpass the speed of light, because it's curvature has reached this maximum as a function of the G constant and the distance from the center--in other words, a function of the very topography of the universe! I really liked the idea. It explains why there can be a fastest possible speed in the universe, and why there are seemingly arbitrary thresholds of event horizons arround black holes. And all we have to assume to make this correct is that the universe is the shape that I described, which is not a very bold assumption.

please tell me what you think. I'd like to hear you're disagreements, and see if my theory can stand up to them!