Alex Vilenkin on a Universe Out of NothingMany Worlds in One: The Search for Other Universes (Macmillan: 2007), pp. 180, 185.
The concept of a universe materializing out of nothing boggles the mind. What exactly is meant by “nothing”? If this “nothing” could tunnel into something, what could have caused the primary tunneling event? And what about energy conservaton? … The initial state prior to the tunneling is a universe of vanishing radius, that is, no universe at all. There is no matter and no space in this very peculiar state. Also, there is no time. Time has meaning only if something is happening in the universe. We measure time using periodic processes, like the rotation of the Earth about its axis, or its motion around the Sun. In the absence of space and matter, time is impossible to define. ¶ And yet the state of “nothing” cannot be identified with absolute nothingness. The tunneling is described by the laws of quantum mechanics, and thus “nothing” should be subjected to these laws. The laws must have existed, even though there was no universe. … A quantum fluctuation of the vacuum assumes that there was a vacuum of some pre-existing space. And we now know that the “vacuum” is very different from “nothing”. Vacuum, or empty space, has energy and tension, it can bend a warp, so it is unquestionably something. As Alan Guth wrote, “In this context, a proposal that the universe was created from empty space is no more fundamental than a proposal that the universe was spawned by a piece of rubber. It might be true, but one would still want to ask where the piece of rubber came from.”