@ Marco

Why does it have to be nonexplanable by science?

An alien from a society ten thousand years ahead of ours can do that. It doesnt take a God, as it wouldnt make them Gods simpyl because they can do things beyond our know-how or understanding.

This is again assuming that what is responsible for our existance IS a "God" and not simply a creator of vast knowledge and therefore power. A being can be very very powerful because of the knowledge he possesses, and still be bound by the laws of the logical (note that I didnt say physical) universe... meaning they dont have to be capable of turning water into wine (tho im sure with the right amount of study that too can be done).. they dont have to be capable of "magic" to be the one responsible for all things.