I have heard people say there is no center to the expansion of the universe. I have also heard the expansion described as an ever expanding balloon with all galaxies as dots on the surface. These to statements seem contradictorily to me. If the expansion of the universe was like the above balloon example wouldn’t all galaxies be close to the edge or event horizon with a huge volume of empty space in the middle of which we could easily locate or at least mathematically define the center (e.g. we can determine the center of a balloon if we understand its size and dimensions). I get that my lack of understand likely stems from the shortfall of the metaphor but I was hoping someone could explain the expansion in terms that make sense to a non-physicist.