Video narration
Does the universe explode outward into empty space, with an edge racing ahead? Picture dots on an inflating balloon: as its surface stretches, each dot grows farther from the others. That shows distances growing as the surface stretches. But the balloon is only an analogy; the universe isn't a surface inside bigger space, with a center. Here's the flip: the universe isn't flying outward through space. Space itself is stretching. On the largest scales, faraway galaxies grow farther apart because the space between them grows, not because they're racing toward an edge. We can see only part of the universe: light from farther places hasn't reached us. That limit is what we can observe, not proof the universe ends there. The whole universe may extend beyond our view, perhaps without end; we don't know. So what is it expanding into? Nothing: space itself stretches.