The physical universe that you see is all in your mind. When you turn your mind off, or become unconscious, the physical universe, for you, disappears. Then, when you awaken your consciousness, the universe reappears magically. Quite simple really - no thoughts on your part, no physical world. As Walt Whitman succinctly stated: "The whole theory of the universe is directed unerringly to one single individual - namely to You." Without your mind to process it, the universe simply disappears into nothingness.