I believe that we can't define our universe as some sort of object. We might try to say that here is our universe and then point far away to the sky and say that somewhere out there it ends but that's what I think is wrong because after passing light years of nothing there might be some other object beyond it. If we travel at an unlimited speed and get past all the objects and there's nothing further and we're traveling the space then we will be forever in vacuum and if you believe that our universe is an objects then we would be enlarging it by moving further away from every other matter. We wouldn't ever find a magic wall, we would be always the furthest element of our universe and the further we would get the bigger our universe would be (for people seeing our universe as an object).