Why Does the World Exist: An Existentia - By Jim Holt Page 0,75

explain an event scientifically, Weinberg argues, is to show how it fits into the pattern of regularities encoded in some physical principle. And to explain that principle, in turn, is to show that it can be deduced from a more fundamental principle. (Thus, for example, the chemical properties of many molecules can be deduced from—and hence are explained by—the deeper principles of quantum mechanics and electrostatic attraction.) Eventually, according to Weinberg’s scheme, all such arrows of scientific explanation will converge at a single bedrock level, the deepest and most comprehensive of all—that of the final theory.

It is conceivable that future physicists will bring the existence of the universe itself into this grand deductive scheme. Perhaps, employing the final theory, they will be able to calculate that the seed of an inflationary multiverse was bound to quantum-tunnel out of nothingness. But what would be the meaning of such a calculation? Would it explain why there is Something rather than Nothing? No. It would merely show that the laws describing the regularities inside the world are incompatible with the nonexistence of that world. (If, for example, Heisenberg’s uncertainty principle says that the value of a field and its rate of change cannot both be precisely zero, then the world as a whole can’t very well consist of unchanging nothingness.) To the metaphysical optimist, that might not look like such a bad result. It would mean that the world is, in a sense, self-subsuming, since its existence is entailed, or at least rendered probable, by regularities within it. To the cynic, though, it looks like a vicious circle. Since the world is logically prior to the patterns within it, those internal patterns can’t be called on to explain the existence of the world.

My encounter with Weinberg had deepened my understanding of how scientific explanation works. But it had also left me in agreement with him that no such explanation could dispel the mystery of existence. The question Why is there something rather than nothing? lies outside the ambit even of the final theory. Notwithstanding the clever imaginative leaps of cosmologists like Stephen Hawking, Ed Tryon, and Alex Vilenkin, a satisfying answer, if there was one, would have to be sought elsewhere, beyond the precincts of theoretical physics.

Would the search prove futile? Perhaps. But that made it all the more noble, in a Sisyphean kind of way. After all, as Weinberg wrote at the very end of The First Three Minutes, “The effort to understand the universe is one of the very few things that lifts human life above the level of farce, and gives it some of the grace of tragedy.”

Interlude

A Word on Many Worlds

The existence of one world is mysterious enough. But what about the existence of many worlds? Such a wanton profusion of being would appear to make the quest for an ultimate explanation all the more hopeless. To the already intractable questions Why anything? and Why this?, it seems to adjoin a third: Why so much?

Yet the hypothesis of many worlds was evidently quite congenial to some of the thinkers I’d encountered. Steven Weinberg, despite his generally skeptical turn of mind, had not been shy about embracing it. Nor had (the rather less skeptical) David Deutsch. Both thought that the existence of multiple universes would render less mysterious certain deep features of our own universe: its otherwise inexplicable quantum behavior (Deutsch), and its improbable suitability for life (Weinberg).

Richard Swinburne, by contrast, had denounced the postulation of “a trillion trillion other universes” as “the height of irrationality.” And he is not alone in taking this dim view. The great science-popularizer and fraud-debunker Martin Gardner insisted that “there is not a shred of evidence that there is any universe other than the one we are in.” Theories of multiple universes, Gardner said, are “all frivolous fantasies.” And the physicist Paul Davies, carrying the debate to the op-ed page of the New York Times, declared that “invoking an infinity of unseen universes to explain the unusual features of the one we see is just as ad hoc as invoking an unseen Creator.” Each, Davies said, requires a “leap of faith.”

Should we or should we not believe in multiple universes? And does our decision have any bearing on the deeper question of why there is Something rather than Nothing?

Before getting to these matters, there’s a semantic point to be dealt with. If the universe is “everything there is,” then isn’t it true by definition that there is only one of these things? Well,