The classic example of describing the expanding universe is the inflating balloon.

Imagine that you are on the surface of a half inflated balloon. As the balloon expands you see everything around you moving away even though you are not at the center. If you move around the balloon everything will still be moving away, there is no special center. The two dimensional surface of the balloon is expanding into a three dimensional space for ease of understanding. Likewise one could imagine our three dimensional space expanding into an embedded four dimensional space.

This analogy never really worked for me. I knew what the expanding universe meant but I don’t see how the balloon is the best way to explain it. I heard a better one recently in one of my classes.

Everyone in the room is standing (or sitting) on a particular floor tile. Imagine now that there is an explosion in the room that causes all the floor tiles to fly apart. If someone is at the center they would see everyone flying away from them. But someone sitting elsewhere in the room will see that same person flying away from them. Similarly everyone will see everyone else moving away from them while they are stationary. Except it is not the tiles that are moving apart but space itself.

Of course all of this would easier if we could easily visualize four dimensional space (like a hypercube or 3 sphere).