The balloon analogy is a good one. Rising raison bread is another good one, since the raisons in the bread all retreat from one another like galaxies in the universe.
But the more tightly you compare an analogy to the real thing the more likely the analogy is to break down. This is because the analogy is not the real thing at all, but just an aid to understanding that is effective because it is more familiar to us than the real thing in some important way.
In this case, the analogies of the balloon and the raison bread break down when you consider boundaries because the universe does not have hard boundaries. No matter where you go in our universe, all you will see is infinite space in all directions. There is no boundary that can be approached and discerned.
--Percy
™ Version 4.2