There is no way to tell if the universe is an atom at our current level of technology and knowledge (and yes, that was the original subject) Even if we could see out of the universe and see what was out there, we wouldn't be able to currently because of background radiation. If it were possible to theoretically prove that the universe has the same characteristics of an atom without any knowledge outside of the universe, then where would the protons, neutrons, and electrons be? Were the universe not an atom, but just an electron, or a quark, then about all we would find is the spin of the universe. As we can't see inside a quark or electron or outside the universe, the knowledge would do no good.