BC-Axeman

I think of scale as a physical dimension by itself because forces are so different across it. Completely different realities exist at different scales. Time, gravity, light, everything, changes.
Also, note that as you go smaller there is a lot of emptiness. Then some theoretical stuff. Scale is infinite. There are probably things smaller.
At the upper limit it is the "observable universe." This is because it is expanding. At the observable limit it is expanding at the speed of light. We can't detect anything beyond that. It's there. Maybe without limit. Maybe not. Maybe there's a lot of nothing and then we find ourselves back at the small end.
This link is a great way to get into scale, the other dimension.