There is no boundary defined yet for universe.
For all we know, we might be as big that we MIGHT have n number of galaxies within ourselves. There may be some human life within you itself!
On the other hand, we might be as small that our milky way MIGHT be inside an ant!
To be a bit specific, the humans are nothing but a small world within a larger framework or we ourselves are one of the framework!
I don't question the existence of GOD! I believe that there is some power that is beyond our control. Some call it time, some call it luck, some idolize it and worship and some believe that there is no such a thing (which in itself something beyond you).
To me its mother nature who is the super power. If you see, all the above facts/factors I mentioned above are well confined within the control of Nature!
And Nature has no boundaries either!