Imagine that you live on the surface of a balloon in a two-dimensional universe. You would be absolutely flat, living on a flat-surface universe (similar to the way we are three-dimensional living in a three-dimensional universe.) Evenly spaced points cover the balloon surface, and one of these points is your home. As the inflating balloon expands, you observe that every other point moves away from you---the farther away the point, the faster away it moves.
Where is the edge of the balloon? What are the "inside" and "outside" of the balloon in two dimensions? The answers, at least from the perspective of a two dimensional being on the balloon's surface, are that every point appears to be at the center, and the universe has no edges, no inside, and no outside. The two-dimensional being experiences one continuous, never ending surface. We live in a universe of higher dimensionality, but the principal is the same:our universe has no center and no inside versus outside.
The balloon analogy is also useful because it can help us visualize another question that is often asked about the expanding universe: What is it expanding into? If you think about being on the balloon, you realize that you could start out in any direction and keep traveling. You might come back to where you started, but you would never come to an end. There would never be an "into." The surface of a balloon is an example of a system that is bounded (in two dimensions), but that has no boundaries.
THE EXPANDING-BALLOON ANALOGY OF THE UNIVERSE. ALL POINTS ON THE SURFACE OF THE EXPANDING BALLOON MOVE AWAY FROM EACH OTHER. THE FATHER APART THE POINTS, THE FASTER THEY MOVE APART!!!
