Could the universe have come into existence spontaneously out of nothing? Cosmologist and author Lawrence R. Krauss' defense of that possibility in his April 1 Op-Ed article, "A universe without purpose," prompted reader Ken Artingstall of Glendale to write:
"Krauss seems to make two contradictory statements: 'Our universe came from nothing' and, 'In its earliest moments … our universe … was contained in a volume smaller than the size of a single atom.' To a layman like me, that 'volume,' however infinitesimal, is not 'nothing.' Krauss never addresses where it came from, how (or by whom) it was created or why it 'decided' to explode.
"You do not have to be particularly religious to question the origin of that mysterious atom, but the notion of a creator is not easily dismissed while that question remains unanswered."
Lawrence R. Krauss replies:
I am sorry for the confusion. By "at its earliest moments," I meant shortly after the big bang, back to a time when we can safely extrapolate the known laws of physics, less than a billionth of a billionth a second after the "big bang." In this case, the "big bang" represents the moment when, if we extrapolate back, all of the universe was located at a single infinitely dense point.
Since we do not have a theory of quantum gravity that allows us to calculate exactly what happens before the very early time referred to above, we cannot say precisely what the appropriate quantum mechanical description of space was before that time.
In any theory of quantum gravity, however, space is likely to be a quantum mechanical variable. Therefore, space itself should be able to be spontaneously created from nothing by quantum processes.
To summarize, the "mysterious atom" Artingstall refers to describes the state of the universe shortly after the big bang. To go back earlier, to the precise moment when the universe "began" (or t=0), we can make plausible extrapolations based on what we know. Those extrapolations suggest quantum creation from nothing as viable and can produce a universe with the features we observe now. But we cannot argue beyond plausibility at this moment.