Partially inflate the balloon and tie it off with string. Punch a series of holes in the paper and save the small paper dots. Use the rubber cement to glue the circles all over the balloon at varying distances. The paper circles represent the galaxies. The balloon represents the size of the universe.

To observe and notice

As you take off the string and blow up the balloon further, notice that the amount of space between the "galaxies" gets larger and larger, but the galaxies themselves don't grow. The same thing happens in the real universe: the expansion of the universe is the expansion of space.

Imagine yourself sitting on one of the paper galaxies as the balloon universe expands. You would observe all the other galaxies moving away from you. The nearby galaxies move away slowly, while the more distant ones rush away more rapidly. This, of course, is just what Edwin Hubble observed in the real universe!

Notice that this Hubble motion can be observed no matter which paper galaxy you call home. On every paper circle you would see the other circles moving away from you. No galaxy can be said to be at the "center" of the universe. Just as the surface of the balloon has no center or edge, the real universe also has no center or edge.