Leaping the Abyss

Stephen Hawking on black holes, unified field theory, and Marilyn Monroe.

Gregory Benford from the April 2002 issue

(Page 3 of 6)

"I can't keep up with the torrent of work on superstrings." Mathematical physics is like music, which a young and zesty spirit can best seize and use, as did Mozart.

"I try," he said modestly.

We began discussing recent work on "baby universes" -- bubbles in space-time. To us large creatures, space-time is like the sea seen from an ocean liner, smooth and serene. Up close, though, on tiny scales, it's waves and bubbles. At extremely fine scales, pockets and bubbles of space-time can form at random, sputtering into being, then dissolving. Arcane details of particle physics suggest that sometimes -- rarely, but inevitably -- these bubbles could grow into a full-fledged universe.

This might have happened a lot at the instant just immediately after the Big Bang. Indeed, some properties of our universe may have been created by the space-time foam that roiled through those infinitesimally split seconds. Studying this possibility uses the "wormhole calculus," which samples the myriad possible frothing bubbles (and their connections, called wormholes).

Averaging over this foam in a mathematical sense, smoothing its properties a bit, Hawking and others have tried to find out whether a final, rather benign universe like ours was an inevitable outcome of that early turbulence. The jury isn't in on this point, and it may be out forever -- the calculations are tough, guided by intuition rather than facts. Deciding whether they meaningfully predict anything is a matter of taste. This recalls Oscar Wilde's aphorism that in matters of great import, style is always more important than substance.

If this picture of the first split second is remotely right, much depends on the energy content of the foam. The energy to blow up these bubbles would be countered by an opposite, negative energy, which comes from the gravitational attraction of all the matter in the bubble. If the outward pressure just balances the inward attraction (a pressure, really) of the mass, then you could get a universe much like ours: rather mild, with space-time not suffering any severe curvature -- what astronomers call "flat." This seems to be so on such relatively tiny scales as our solar system, and flatness prevails even on the size range of our galaxy. Indeed, flatness holds on immense scales, as far as we can yet see.

It turns out that such bubbles could even form right now. An entirely separate space-time could pop into existence in your living room, say. It would start unimaginably small, then balloon to the size of a cantaloupe -- but not before your very eyes, because, for quite fundamental reasons, you couldn't see it.

"They don't form in space, of course," Stephen said. "It doesn't mean anything to ask where in space these things occur." They don't take up room in our universe but rather are their own universes, expanding into spaces that did not exist before.

"They're cut off from us after we make them," I said. "No relics, no fossil?"

"I do not think there could be."

"Like an ungrateful child who doesn't write home." When talking about immensities, I sometimes grasp for something human.

"It would not form in our space, but rather as another space-time."

We discussed for a while some speculations about this that I had put into two novels, Cosm and Timescape. I had used Cambridge and the British scientific style in Timescape, published in 1980, before these ideas became current. I had arrived at them in part from some wide-ranging talks I had enjoyed with Stephen -- all suitably disguised in the books, of course. Such enclosed space-times I had termed "onion universes," since in principle they could have further locked-away space-times inside them, and so on. It is an odd sensation when a guess turns out to have some substance -- as much as anything as gossamer as these ideas can be said to be substantial.

"So they form and go," I mused. "Vanish. Between us and these other universes lies absolute nothingness, in the exact sense -- no space or time, no matter, no energy."

"There can be no way to reach them," his flat voice said. "The gulf between us and them is unbridgeable. It is beyond physics because it is truly nothing, not physical at all."