It’s potential. Matter can go there. Saying there is an end to the universe means that at some point, there is no possible expansion. It also means we are completely ignoring the tiniest infinitly small chance that our big bang wasn’t the only one. If you zoom out far enough, is there really zero chance that this “known universe” is actually just part of a greater whole?

imagining the universe as a contained thing with hard limits is what gives me the creep