The best analogy I've seen is imagine our universe as the surface of a balloon. Only the surface, we can't see or touch anything else.
If you inflate the balloon, our universe expands. Points get farther away from each other, proportionally to how far away they started. In this analogy, we're not expanding into anything we can see or feel or know anything about, the only real difference is that points are a bit farther apart.
If you inflate the balloon, our universe expands. Points get farther away from each other, proportionally to how far away they started. In this analogy, we're not expanding into anything we can see or feel or know anything about, the only real difference is that points are a bit farther apart.