Most of us know M.C. Escher's artful and 'impossible' drawing constructions. One that I found very applicable to cosmology is Escher's Infinite Lattice. My son, Coburt, produced this replica of Esher's lattice in color. First 'enjoy the view' and then we will discuss it briefly.
Credit: Coburt 
This looks like a very static arrangement. Now, just suppose that every blue bar connecting two red cubes is stretching (increasing in length) at a steady rate, say at 1 meter every second. What will happen to the distance between the red cubes?
I think it is clear that the more bars there are between two red cubes, the faster they will be moving apart. Two bars between them and they move apart at 2 meters per second. Ten bars between then and they move apart at 10 meters per second.
This is effectively Hubble's law: the apparent recession speed of distant galaxies (from us) is directly proportional to the distance of those galaxies from us. Now this is not a hypothesis - Hubble measured it with good precision and then formulated his (empirical) law.
If you look at that bottom-left 'shaft' that goes down to (almost) invisibility, it represents the limit of our observational ability. There is actually an 'horizon' down there, where the red blocks are moving away from us (up here) so fast that light did not have time to reach us yet over all those stretching blue bars!
This is about as close as one can get to the real universe, as perceived today. It is a much better analogy than the historically favored 'balloon' analogy. Forget the balloon, consider Escher's infinite lattice!