written in 2001; first published in Reason
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Stephen Hawking seemed slightly worse, as always.

It is a miracle that he has clung to life for over twenty years with Lou Gehrig’s disease. Each time I see him I feel that this will be the last, that he cannot hold on to such a thin thread for much longer.

The enormous success of his A Brief History of Time has made Stephen a curious kind of cultural icon. Its huge success has made him a curious kind of world‑scale metaphor. He wonders himself how many of the starlets and rock stars who mentioned the book on talk shows actually read it.

With his latest book, The Universe in a Nutshell,  he aims to remedy the situation, with a plethora of friendly illustrations to help readers along. In it Hawking offers image-rich explanations for such complexities as superstring theory and the nature of time. The trick, of course, is translating equations to sentences, two very different languages. Pictures help enormously, though purists deplore them as oversimplified. I feel that any device is justified to span such an abyss of incomprehension.

As I entered, his office staff was wary of visitors, plainly suspecting I was a “civilian” harboring a crank theory of the universe. But I’d called beforehand, and then his secretary recognized me from years past. When I entered the familiar office his shrunken form lolled in his motorized chair, staring out, rendered goggle‑eyed by his thick glasses‑‑but a strong spirit animated all he said. You could sense the inner fire.

He had lost his vocal cords years ago to an emergency tracheotomy. His gnarled, feeble hands could not hold a pen. For a while after the operation he was completely cut off from the world‑‑an unsettling analogy with the fate of mathematical observers who plunge into black holes, their signals to the outside red‑shifted and slowed, by gravity’s grip, to dim, whispering oblivion.

A Silicon Valley firm had come to the rescue. Engineers devised tailored, user‑friendly software and a special keyboard for him. His frail hand now moved across it with crablike intent. The software is deft, and he could build sentences quickly. I watched him rapidly flit through the menu of often‑used words on his liquid crystal display, which hung before him in his wheelchair. The invention has been such a success that the Silicon Valley folk now supplied units to similarly afflicted people worldwide.

“Please excuse my American accent,” the speaker mounted behind the wheelchair said with a California inflection. He coded this entire remark with two keystrokes; his standard opening joke.

Though I had been here before, again I was struck that this man who had suffered such an agonizing physical decline had on his walls several large posters of a person very nearly his opposite: Marilyn Monroe. I mentioned her and he responded instantly, tapping one‑handed on his keyboard, so that soon his transduced voice replied, “Yes, she’s wonderful. Cosmological.“I wanted to put a picture of her in my latest book, as a celestial object.” I remarked that to me the book was like a French impressionist painting of a cow, meant to give a glancing essence, not the real, smelly animal. Few would care to savor the details. Stephen took off from this to discuss some ideas currently booting around the physics community about the origin of the universe, the moment just after the Big Bang.

Hawking’s great politeness paradoxically put me ill at ease; I was acutely aware of the many demands on his time, and after all, I had just stopped by to talk shop. I am an astrophysicist and have known Stephen since the 1970s.

“For years my early work with Roger Penrose seemed to be a disaster for science,” Stephen said. “It showed that the universe must have begun with a singularity, if Einstein’s general theory of relativity is correct. That appeared to indicate that science could not predict how the universe would begin. The laws would break down at the point of singularity, of infinite density.”

I recalled that I had spoken to him about mathematical methods of getting around this, one evening at a party in King’s College. There were analogies to methods in elementary quantum mechanics, methods he was trying to carry over into this surrealistic terrain.

“It now appears that the way the universe began can indeed be determined, using imaginary time.” We discussed this a bit. Stephen had been using a mathematical device in which time is replaced by imaginary time, as a notational convenience. This changes the nature of the equations, so he could use some ideas from the tiny quantum world. In the new equations, a kind of tunneling occurs, in which the universe, before the Big Bang, has many different ways to pass through the singularity. With imaginary time, one can calculate the chances for a given tunneling path into our early universe, after the beginning of time as we know it.

“Sure, the equations can be interpreted that way,” I argued, “but it’s really a trick, isn’t it?”

Stephen said, “Yes, but perhaps an insightful trick.”

“We don’t have a truly deep understanding of time, so replacing real time with imaginary time doesn’t mean much to us.”

“Imaginary time is a new dimension, at right angles to ordinary, real time. Along this axis, if the universe satisfies the ‘no boundary’ condition, we can do our calculations. This condition says that the universe has no singularities or boundaries, in the imaginary direction of time. With the ‘no boundary’ condition, there will be no beginning or end, to imaginary time, just as there is no beginning or end to a path on the surface of the Earth.”

“If the path goes all the way around the Earth,” I said. “But of course, we don’t know that in imaginary time, there won’t be a boundary.”

“My intuition says there will be no blocking in that special coordinate, so our calculations make sense.”

“Sense is just the problem, isn’t it? Imaginary time is just a mathematical convenience.” I shrugged in exasperation at the span between cool mathematical spaces and the immediacy of the raw world; this is a common tension in doing physics. “It’s unrelated to how we feel time. The seconds sliding by. Birth and death.”

“True. Our minds work in real time, which begins at the Big Bang, and will end, if there is a Big Crunch—which seems unlikely, now, from the latest data showing accelerating expansion. Consciousness would come to an end at a singularity.”

“Not a great consolation,” I said.

He grins. “No, but I rather like the ‘no boundary’ condition. It seems to imply that the universe will be in a state of high order at one end of real time, but will be disordered at the other end of time, so that disorder increases in one direction of time. We define this to be the direction of increasing time. When we record something in our memory, the disorder of the universe will increase. This explains why we remember events only in what we call the past, and not in the future.”

“Remember what you predicted in 1980 about final theories, like this?” I chided him.

“I suggested we might find a complete unified theory, by the end of the century.” Stephen made the transponder laugh dryly. “Okay, I was wrong. At that time, the best candidate seemed to be N=8 supergravity. Now it appears that this theory may be an approximation to a more fundamental theory, of superstrings. I was a bit optimistic, to hope that we would have solved the problem by the end of the century. But I still think there’s a fifty‑fifty chance that we will find a complete unified theory in the next twenty years.”

“I’ve always suspected that the structure never ends, as we look to smaller and smaller scales‑‑and neither will the theories.”

“It is possible that there is no ultimate theory of physics at all. Instead, we will keep on discovering new layers of structure. But it seems that physics gets simpler, and more unified, the smaller the scale on which we look. There is an ultimate length scale, the Planck length, below which spacetime may just not be defined. So I think there will be a limit to the number of layers of structure, and there will be some ultimate theory, which we will discover if we are smart enough.”

“Does it seem likely we are smart enough?”

Another grin. “You will have to get your faith elsewhere.”

“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, space‑time is like the sea seen from an ocean liner, smooth and serene. Up close, though, it’s waves and bubbles. At extremely fine scales, pockets and bubbles of spacetime can form at random, sputtering into being, then dissolving. Arcane details of particle physics suggest that sometimes‑rarely, but inevitably‑‑these bubbles could grow.

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, Stephen 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 may be out forever‑‑the calculations are tough, guided by intuition rather than facts. Deciding whether they really 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 compensated 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 flat on such relatively tiny scales as our solar system, and even flat on the size range of our galaxy.

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 can’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’re cut off from us, after we made 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 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, of course. Such enclosed space‑times I had termed “onion universes,” since in principle they could have further locked‑away space‑times inside them, too, 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. Again, the image of mathematical physics as French impressionism.

“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 unbridgable. It is beyond physics because it is truly nothing, not physical at all.”

The mechanical laugh resounded. Stephen likes the tug of the philosophical, and seemed amused by the notion that universes are simply one of those things that happen from time to time.

His nurse appeared for a bit of physical cleanup, and I left him. Inert confinement to a wheelchair exacts a demeaning toll on dignity, but he showed no reaction to the daily round of being cared for by another in the most intimate way. Perhaps for him, it even helps the mind to slip free of the world’s rub.

I sat in the common room outside his office, having tea and talking to some of his post‑doctoral students. They were working on similarly wild ideas and were quick, witty, keenly observant as they sipped their strong, dark Ceylonese tea. A sharp crew, perhaps a bit jelous of Stephen’s time. They were no doubt wondering who this guy was, nobody they had ever heard of, a Californian with an accent tainted by southern nuances, somebody who worked in astrophysics and plasma physics‑‑which was, in our age of remorseless specialization, quite a remote province from theirs. I didn’t explain; after all, I really had no formal reason to be here, except that we were friends.

Stephen’s secretary quietly came out and asked if I would join Stephen for dinner at Caius College. I had intended to eat in my favorite Indian restaurant, where the chicken vindaloo is a purging experience, and then simply rove the walks of Cambridge alone, for I love the atmosphere‑‑but I instantly assented. Dinner at college high table was one of the legendary experiences of England. I could remember keenly each one I had attended; the repartee is sharper than the cutlery.

We made our way through through the cool, atmospheric turns of the colleges, the worn wood and gray stones reflecting the piping of voices and squeaks of rusty bicycles. In misty twilight, student shouts echoing, his wheelchair jouncing over cobbled streets. He insisted on steering it himself, though his nurse hovered rather nervously. It had never occurred to me just how much of a strain on everyone there can be in round‑the‑clock care. A few people drifted along behind us, just watching him. “Take no notice,” his mechanical voice said flatly, “many of them come here just to stare at me.”

We wound among the ancient stone and manicured gardens, into Caius College. Students entering the dining hall made an eager rumpus. Stephen took the elevator and I ascended the creaking stairs. The faculty entered after the students, me following with the nurse.

The high table is literally so. They carefully placed Stephen with his back to the long, broad tables of undergraduates. I soon realized that this is because watching him eat, with virtually no lip control, is not appetizing. He follows a set diet that requires no chewing. His nurse must chop up his food and spoon feed him.

The dinner was noisy, with the year’s new undergraduates staring at the famous Hawking’s back. Stephen carried on a matter‑of-fact, steady flow of conversation through his keyboard.

He had concerns about physicists’ Holy Grail, a unified theory of everything. Even if we could thrash our way through a thicket of mathematics to glimpse its outlines, it might not be specific enough‑‑that is, we would still have a range of choices. Physics could end up dithering over arcane points, undecided, perhaps far from our particular primate experience. Here is where aesthetics might enter.

“If such a theory is not unique, one would have to appeal to some outside principle, which one might call God.”

I frowned. “Not as the Creator, but as a referee?”

“He would decide which theory was more than just a set of equations, but described a universe that actually exists.”

“This one.”

“Or maybe all possible theories describe universes that exist!” he said with glee. “It is unclear what it means to say that something exists‑‑in questions like, does there exist a man with two left feet in Cambridge. One can answer this by examining every man in Cambridge. But there is no way that one can decide if a universeexists, if one is not inside it.”

“The space‑time Catch‑22.”

“So it is not easy to see what meaning can be given to the question, why does the universe exist. But it is a question that one can’t help asking.”

As usual, the ability to pose a question simply and clearly in no way implied a similar answer‑‑or than an answer even existed.

After the dining hall, high table moved to the senior common room upstairs. We relaxed among long, polished table, comfortable padded chairs, the traditional crisp walnuts and ancient aromatic port, Cuban cigars. And somewhat arch conversation, occasionally skewered by a witty interjection from Stephen.

Someone mentioned Stephen Weinberg’s statement, in The First Three Minutes, that the more we comprehend the universe, the more meaningless it seems. Stephen doesn’t agree, and neither do I, but he has a better reason. “I think it is not meaningful in the first place to say that the universe is pointless, or that it is designed for some purpose.”

I asked, “No meaning, then, to the pursuit of meaning?”

“To do that would require one to stand outside the universe, which is not possible.”

Again the image of the separation between the observer and the object of study. The gulf. “Still,” I persisted, “there is amazing structure we can see from inside.”