there was never a time where nothing existed. if nothing ever existed there would have been nothing to create existence. The answer to the universe and its origin is simple, heres how: Take a handheld mirror hold at just the right angle facing a mirror placed on a wall. youll see that the image (most likely your face depending on the angle) will just keep on getting smaller and smaller and smaller and farther and farther and farther until it is to small to see. It is impossible for it to end, it just keeps getting smaller and smaller until its at a microscopic size. where even then it keeps going....forever. What you see in the mirror is (in my beliefs) the same way the universe and dimensions are, which is never ending.
OK, so there was a time when nothing existed. Maybe you created existence to exist in. Why So that you could experience what it is you are experiencing....... Simple ain't it.....
It's true, as said in Gen 1:2, the spirit of God moved upon the face of the waters, God always was and always will be.