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Critical Essay by Michael Harwood
SOURCE: "The Universe and Dr. Hawking," in New York Times Magazine, January 23, 1983, pp. 16-19, 53-9, 64.
In the essay below, Harwood provides an overview of Hawking's life and works.
The theoretical physicist, although he deals in such arcane, modern concepts as curved time and space, is part of a philosophical and spiritual tradition older than recorded history. He seeks to know not just life as he experiences it but how the hidden parts of the universe work and fit together. Ultimately he hopes to learn if and how and why the universe began and if and how and why it will end.
These questions and the new knowledge to which they lead are so far from our daily round of getting, spending, surviving and reproducing that they demand a special language and symbolism in which to discuss them. That isolates the theoretical physicist from the intellectual mainstream, yet the rewards may be cosmic in scope, for the physicist seeks grand answers that will affect the lives of everyone—on spiritual and practical levels—forever after.
The seeking requires a certain amount of visible action—the communication of ideas with colleagues, the publication of papers. Mostly, however, it requires that the physicist think. "There's no other way to put it," says William Press, chairman ofthe astronomy department at Harvard. "He also thinks about the thinking process. If he has an idea that's not fully formed he has to try to isolate the idea in particular examples and then do detailed calculations to see whether those examples are self-consistent. It's a process of trying to build a large arch, where you work brick by brick, holding it up with a scaffolding, and you really don't know until you finally put in the keystone whether it's all going to support itself, or if when you take the scaffolding away it's all going to come crumbling down.
"This must have its equivalent in most artistic endeavors, where the struggle is with technique and detail but is in service of some grander plan, and you don't know whether it will all come together until all the pieces are together. Science really is art at this level, but it's art in service of finding objective truths about the universe."
The art demands an exceptional ability to concentrate, to remember, to make connections between ideas. It is perhaps significant, then, that Stephen W. Hawking, a physicist whose insights about gravity and matter are changing the way we look at the universe, should have attained his intellectual stature while his body was failing him, atrophying, shaping him increasingly into a cerebral being.
Hawking is attempting to unify two great theoretical break-throughs in 20th-century physics, seeking whether there is one bigger law from which all the other laws can be derived. The first, general relativity, deals with predictable events and huge objects, such as stars and planets. The other, quantum mechanics, deals with minute details inside the atom, an arena where we have not learned—and may never learn—to predict events precisely. He is trying to forge the links between this odd couple while at the same time trying to discover how the universe worked at its very beginning.
He has already provided strong proof that if Einstein's general relativity theory is correct the universe had a beginning—the "big bang." Since then, he has extensively explored a theoretical concept known as black holes, because black holes seem to contain clues to the nature of the big bang. Although astronomers are still only on the verge of proving by observation the existence of black holes in space, the theoreticians have drawn an increasingly detailed picture of what black holes ought to be like. Among Hawking's key contributions to this process was his finding that they are not simply black holes, cold and deadcollections of invisible matter, with gravitational power so strong that nothing radiates from them, but have temperature and some can be extremely active, bright and hot. As he has made his discoveries about them, he has on occasion managed to surprise even himself.
The Cambridge University building where Hawking has his office stands along Silver Street—an ancient, winding English byway about wide enough for three horses abreast, just off King's Parade in Cambridge. If you don't look sharp, you'll miss the entrance, an alley marked—apparently as an afterthought—by an unobtrusive sign over a mail slot on the brick building: DEPT of APPLIED MATHEMATICS AND THEORETICAL PHYSICS.
This leads into a homely courtyard and parking lot. At one end is a bright blue door with a glass window, alongside a brass nameplate identifying the place in a somewhat more distinguished fashion, but the atmosphere of the building within is again vaguely anonymous and haphazard. A zigzag hallway with closed doors on both sides leads to a large, high-ceilinged, scruffily furnished common room, off which are a few more offices—one of them Hawking's. The style is Universal Academic, I suppose, but it seems at first an unfitting arena for a man believed by many of his peers to be one of the most important theoreticians of this generation, whose intellect is sometimes compared to Albert Einstein's. Now 41 years old, Hawking holds the Lucasian professorship of mathematics at Cambridge—the very chair once held by Isaac Newton.
He is several minutes late for our first meeting. These past few months have been exceptionally hectic for him. He has organized and acted as host of a three week conference on the very early universe, has been to the United States three times to accept four honorary degrees (Princeton, Notre Dame, University of Chicago and New York University) and will leave with his wife in a few days on another visit to the United States to attend a conference at Santa Barbara, Calif. Before they go, they will give a party for a daughter—one of their three children—so the Hawking household is at sixes and sevens.
He comes around a corner into the common room—a slight figure folded into an electric wheelchair, left arm crossed over right to grip the control dial. He appears to be of medium height; at a guess, he doesn't weigh as much as 120 pounds. For virtually all his professional life, Stephen Hawking has been afflicted with a progressive and incurable motor-neuron disease, and although his mental capacities have obviously not been affected by the illness, driving his wheelchair is one of the few physical things he can still do for himself.
He has grown so weak that his speech—for many years difficult to understand—can now be interpreted only by those closest to him; to a stranger's ears it sounds like a soft, gravelly tenor hum sprinkled with m's and n's. So for the purposes of ourinterviews, he has arranged for a "translator," Don N. Page, an American physicist, a former post doctoral researcher in his department and now an assistant professor at the Pennsylvania State University, who returns each summer to visit and work with Hawking.
Page lets us into Hawking's office, which looks like the office of any busy university scholar—shelves bearing books and journals and stacks of papers, a desk heaped with work in progress. Hawking is a prolific author of papers and editor of conference proceedings. Without such production he would be anonymous, of course; publish or vanish is the operative law of scholarly success. Even so, his production seems remarkable. The manner in which something is done, the proper method for bringing off a solution, is a central problem in a theoretical physicist's intellectual existence, but Hawking has to struggle, at even the most basic level of getting things accomplished.
That sort of struggle, however, is not as important to him as it might appear at first. The face of his illness tends to mask him from the outsider; one sees the physical man virtually paralyzed and while trying to cope with that image, may fail to see beyond it. Most of us who remain upright and mobile are by instinct—empathy—frightened by what has happened to Hawking and inclined to think that his disability either somehow detracts from his effectiveness or makes him miserable. But neither seems to be the case, and after reading a draft of this article he remarked that I'd made too much of his physical condition. That was reminiscent of a remark by Einstein: "The essential in the being of a man of my type lies precisely in what he thinks and how he thinks, not in what he does or suffers."
Furthermore, Hawking travels all over the world by plane to attend conferences and visit universities, although he cannot go on such expeditions without one or two companions to help him manage the traveling and to feed and dress him. He and his wife, Jane, maintain a busy social life, giving parties and going out. And in terms of earthbound man in relation to the huge universe, there is virtually no difference between the restrictions on his mobility and the restrictions on anyone else's.
But to produce results he has certainly had to adapt to his circumstances. As we talk in his office, I ask, for instance, about his use of sources—the accessibility of other people's work. Most of us can take a book down from a shelf, flip through it, put it back, and try another one. That isn't possible for him. He can't hold a book, never mind rise to take it from a shelf. He does have a bookstand with an automatic page-turner, but someone has to fetch the book for him and put it in the stand. He doesn't use the page-turner much, anyway, he says, because he reads mostly papers from scientific journals. In that case, he has the paper he wants photocopied and spread out on the desk in front of him. His desk, as a result, is awash with papers, and from my own experience as a one-way correspondentwith Hawking, things quickly become buried there. He is unable to do something as simple as clean up his desk, or even to burrow in the pile after an article or a letter he read last week.
He can't take notes for himself, either. I ask him if he has a photographic memory for the material he reads. "Not a photographic memory, no I don't remember all the details, but I can remember the basic ideas." (Hawking's head rests against the back of the wheel chair. Don Page, sitting beside him, leans close to hear the indistinct words, mouths each phrase to be certain he has caught it, often pauses and asks for a repetition, speaks a phrase back to Hawking sometimes to make certain, corrects himself.)
But I have the impression, I tell him, based on various articles about him, that as he does experiments in his head—I am about to say he is alleged to do reams of computations, comparable to "Mozart composing an entire symphony in his head"—but he interrupts me, laughing: "I think you shouldn't believe what you read." He takes a deep breath to laugh, and his face, which at rest often appears pained and weary, is suddenly lighted by an enormous grin. His laughter is much muted by the paralysis—no ha-ha-ha, just a single long note sung on the exhalation of breath, yet it conveys so much delight one is propelled into laughing with him.
At some point, I ask him if he mustn't run through chains of equations or numerical proofs in his head. "I tend to avoid equations as much as possible," he replies. "I simply can't manage very complicated equations, so I have developed geometrical ways of thinking, instead. I choose to concentrate on problems that can be given a geometrical, diagrammatic interpretation. I can manage equations so long as they don't involve too many terms." Ten would be too many for me, I tell him. He laughs again. "And too many for me. Often I work in collaboration with someone else, and that is a great help, because they can do all the equations."
To be sure, such routine activities as eating go very slowly for Hawking and take up a great deal of his time. But no one asks him to chauffeur the children somewhere or to now the lawn. He cannot be seduced into taking an afternoon off to play golf. His responsibilities to his department at the university are limited: He administers the small "relativity group," and he advises four or five students. The physicist Kip S. Thorne of the California Institute of Technology, one of Hawking's closest friends, once asked him what the effect of his illness had been on his career, and Hawking said that "he thought it had enhanced his career … because he was not expected to give lectures on a regular basis—to teach courses. He had that much more time free simply to think about physics."
Hawking's affliction seems to have a beneficent effect on the distillation and expression of ideas. He writes by dictation, andhe does very little rewriting. "It's just too difficult," he says. "I have to impose on people enough just to dictate once, so to do a lot of revision would involve too much of other people." The pace of his delivery—the fact that he often has to repeat himself for listeners and that he must in any event dictate phrase by phrase, at the most a sentence at a time—may make his thoughts seem fragmented on first hearing. Yet as I transcribed, for example, my taped interviews with Hawking, I was struck by the clarity and precision of his sentences.
Later, I asked Don Page about this. "I found it very good training," Page told me, "during the three years I was a postdoc here. I lived with the Hawking family, and a lot of times I'd walk back and forth with him." Now as then, Hawking "commutes" by wheelchair from his home about half a mile away. "Of course, I couldn't write while I was walking, and sometimes he'd ask me something, and I'd try to think it out in my head. When you have to do it in your head, you have to get really to the heart of the matter and try to eliminate the inessential details." This, said Page, gives Hawking's papers "a great deal of elegance and beauty, because they really speak of the essential things, although sometimes it does have the unfortunate aspect that those of us who don't understand all the details may find some connecting arguments missing."
Attention to detail is not crucial to Hawking's contribution, as Page would be the first to agree. Harvard's William Press explains that at the frontiers of theoretical physics what is needed is not precision but "key overview ideas—great organizational principles, from which the details can follow. And then, of course, working out those details, ultimately to compare them with experiment, with reality—that involves technique and calculation and so forth. That's what Stephen leaves, by both necessity and choice, to his collaborators, and Stephen is the one who tries to come up with the great ideas that make these calculations possible. His track record on that is not just superb, it makes him one of the greatest physicists of our age."
One wonders where these key overview ideas come from. Are they produced like spiritual revelations? That's the way it seems when the public learns of a great breakthrough Hawking agrees there is "a certain similarity, in that there is no prescribed route to follow to arrive at a new idea You have to make an intuitive leap. But the difference is that once you've made the intuitive leap you have to justify it by filling in the intermediate steps in my case, it often happens that I have an idea, but then I try to fill in the intermediate steps and find that they don't work, so I have to give it up."
Hawking once told an interviewer that he wanted to know why the universe exists at all and why it is as it is. I quote that back to him and ask if his search has a religious component. "Isuppose so. But I would have thought that everyone would want to know that." Is the search in competition with religion? "If one took that attitude," he replies, "then Newton"—a very religious man—"would not have discovered the law of gravity.
"The whole history of human thought has been to try to understand what the universe was like. I think you can do that without prejudice as to the idea that God exists. Even if God created the universe, we want to know what it is like." I start to ask a clarifying question, but he interrupts me. "One attitude would be that God set up the universe in a completely arbitrary way, with all that anyone can say about anything is that it is just the will of God. But in fact, the more we examine the universe, we find it is not arbitrary at all but obeys certain well-defined laws that operate in different areas. It seems very reasonable to suppose that there may be some unifying principles, so that all laws are part of some bigger law. So what we are trying to find out is whether there is some bigger law from which all other laws can be derived. I think you can ask that question whether or not you believe in God."
For some people, I remind him, the existence of God is a satisfactory answer to all the questions he is dealing with. "Yes, but it is certainly not to me. I don't think that it answers anything. Whether you say that God created the universe does not really make any difference. I would regard it as a very meaningless statement, unless you're going to attach some other attributes to God. I'm not sure that I believe anything else about God. If that is the only attribute, then it is an unnecessary concept, because it doesn't have any consequences."
Yet man does need to explain the Beginning, the First Cause. How did it all start—and what existed to make a start possible? Science has not achieved that explanation, and the theoretical physicists are still searching. "I have an idea that people would feel happier with the idea of a big bang than of a universe that existed forever and ever," says Hawking. "The big bang may not be very like Genesis, but at least you can regard it as a creation, and you can invoke God as the creator. But if you had a universe that existed forever, people might feel there was not much room for God. I was at a conference on cosmology at the Vatican last year, and the Roman Catholic Church seems to be very happy with the idea of the big bang."
Does he himself think of time as having had a start? "The point is, the very meaning of time becomes very uncertain, very badly defined, when you go back to those very early times. I do think that you cannot have the ordinary concept of time going back indefinitely. So in that sense, time had a beginning. You might just say that time earlier than about 20,000 million years ago is simply not defined."
The search for the Beginning, be believes, will not be complete until we are able to understand the "boundary conditions," orwhat "preceded" the Beginning—what matter, what space, what time. "By the boundary conditions I mean the question of whether time had a beginning, and if so what the universe was like at the beginning of time, and if time does not have a beginning, what does determine the condition of matter in the universe."
In search of the answer to these questions, Hawking has followed a path marked by signposts that so far are invisible except to the imagination—ideas proposed by theoreticians but not yet supported by direct observation. One of these is black holes. Nearly two centuries ago, an English astronomer, John Michell, pointed out that a heavy star, if sufficiently compact, would have a gravitational field so strong that not even particles of light would have enough velocity to escape. In this century theoreticians have shown that the same effect would be produced by the collapse of a large celestial body—its density would become increasingly great as it fell in upon itself—and, further, that large stars must collapse when most of their nuclear fuel is spent.
In 1968, the American John A. Wheeler applied the term "black hole" to this idea of a self-hiding body. For some time, it was thought that the presence of a black hole could be discerned only through its gravitational effects on other bodies.
The effect on nearby objects can be fatal, as the black hole attracts and swallows more and more matter and grows in mass and size. In the heart of a black hole lies the second of the main signposts along Hawking's path, something known as a "singularity"—a point that might be fantastically, infinitely small, a theoretical edge of space and time. Toward that edge, that minuscule point, races at unimaginable speed all the matter sucked into the black hole, all the matter of a star or even a universe, to be crushed into a region of infinite density from which nothing escapes and where none of the known laws of physics apply.
Hawking's first major contribution to our picture of the universe was his demonstration with a colleague, Roger Penrose, that the big bang began with a singularity. (Then the space in which the big bang started, I asked him, was at first no bigger than the proverbial head of the pin? "Yes," he said, "that's about right. We're not sure whether it came from absolute zero size, but we know that it must have been very small indeed.")
We can apparently never see a singularity. It gives off no information whatever to an observer outside. But through Hawking's work we now know that a black hole emits particles from the region around the entrance to the hole, and that makes some black holes theoretically visible. One might even watch a black hole explode and thus learn something about the big bang.
The belief in theoretical concepts, such as black holes, which cannot be observed at the time, has a long and honorable history in physics. Often a theoretician predicts the existence of something that is not found for years or decades. In one sense, however, this approach through the invisible has been elevated recently to become the center line of a major avenue along which physicists now search for the Beginning.
It represents a leap forward from Einstein's work, and the springboard for that leap is quantum theory, which describes the behavior of elementary particles—the component parts of the atom. Einstein, made major contributions to quantum theory, but he didn't really like the theory—he viewed it as a stepping stone to some better theory—because it depends on something called the "uncertainty principle." That principle says that an observer cannot precisely predict at any moment both the location and the speed of a particle within an atom. He can do one or the other; or he can predict both with poor precision. This introduces an element of chance for the human observer. He can know only half of what he wants to know about a particle; the other half is hidden. In classical physics—including. Newtonian theory and Einstein's theory of general relativity, which describes gravity—the observer can reliably predict both location and speed of an object in space at the same time. There is no apparent uncertainty, which is one of classical physics' attractive qualities. Einstein preferred that sureness, and complained of quantum theory: "I shall never believe that God plays dice with the world."
But quantum theory "works." It often does so in situations where classical physics does not, and an acceptance of uncertainty may prove necessary to a complete understanding of the way the universe operates. Hawking has used quantum theory to study black holes, and he found that in the vicinity of a black hole the uncertainty is particularly bad. There is no way to predict either the position or the speed of the particles emitted by a black hole. One can only predict "the probabilities that certain particles will be emitted." Hawking says this suggests "that God not only plays dice but also sometimes throws them where they cannot be seen."
Moreover, connecting links have been proven between quantum theory and every known physical field of force except gravity, so, as Hawking has said, consistency seems to require that general relativity theory be brought in under the tent of quantum theory. This is known as "quantizing gravity," and it is the knottiest problem in physics today. It has resisted solution for more than half a century.
The solution is important to an understanding of the Beginning. "The thing is," explains Hawking, "that in the very early stages of the universe"—by which he means a split second after the big bang began—"the length scales were all very small: Therefore, they were of particle physics dimensions, or less. So tounderstand the beginning of the universe, you have to understand how particle physics and gravity interact."
And that is what he is working on today.
Stephen Hawking grew up in London and in St. Albans, 20 miles north of the city, and prepared for university at St. Albans School. Some commentators have given the impression that he was an indifferent student then, rather as Einstein is said to have been, but according to Hawking, that picture has been over-drawn. "I wasn't at the top of my form," he concedes, "but it was a very high-powered-form." His father was a doctor who did research in tropical medicine, "so I always had a strong interest in science. I reacted against my father to the extent that I did not go into medicine. I felt that biology and medicine were too descriptive, not exact enough. Had I known about molecular biology I might have felt differently I wanted to specialize just in mathematics and physics, and my father was very unhappy about that, because he did not think there would be any jobs for mathematicians."
In British education such career choices are made when the student is 14 or 15. Hawking applied for admission to University College at Oxford, where he would read mathematics and physics.
"His father was an old member of the college," said Robert Berman, who was to be young Hawking's physics tutor, "and was rather anxious that Stephen should get in. I am always rather wary in such instances. People shouldn't get in because they're old members' sons. But he took the entrance examinations. There were two papers in physics, and he got alpha on both of those. The math wasn't so good. Then he had a general interview." Berman referred to the notes he had taken on that occasion. "It just says, 'A—no other comment. Impressed us all.'"
Hawking began his studies at Oxford in 1959. "The first year, he read mathematics," said Berman. "There was an exam at the end of the year. He didn't do especially well. I mean, it was all right, but it wasn't sensational. He then took up physics, and he did very little work, really because anything that was doable he could do. It was only necessary for him to know that something could be done, and he could do it without looking to see how other people did it. Whether he had any books I don't know, but he didn't have very many, and he didn't take notes.
"Of course, his mind was completely different from all his contemporaries', and he did, I think, positively make an effort to sort of come down to their level and, you know, be one of the boys. If you didn't know about his physics and to some extent his mathematical ability, he wouldn't have told you. He coxed the college second eight, and he was very popular."
However he achieved the effect, naturally or consciously, the "common hearsay" about Hawking among his colleagues today is that he was a free spirit with a wide range of interests as an undergraduate.
His independent and casual method of working at Oxford had its drawbacks, Berman noted, because "he didn't do all that well in the final examination, and he was on the borderline between first and second-class honors." Anyone in such a situation took an oral exam, "and of course the examiners then were intelligent enough to realize they were talking to someone far cleverer than most of themselves."
By the time he was 20, Hawking had decided to become a cosmologist—literally, a student of the universe. Physicists in that discipline attempt to construct principles and images of the cosmos.
Hawking said he did consider other specialties in physics, "but it just seemed that cosmology was more exciting, because it really did seem to involve the big question: Where did the universe come from?
"At the time I entered it, cosmology was a very undeveloped field"—it is now well populated. "I didn't realize that when I chose to work in it, but it turned out there were lots and lots of problems that were waiting to be solved."
The first two years, however, were to be bad ones. Just as he started graduate work at Cambridge, he began to show symptoms of motor-neuron disease. The illness was diagnosed as amyotrophic lateral sclerosis, which is usually fatal within a short time. "It seemed to be developing very rapidly at first," he said, "and I was very depressed. I didn't think there was any point in doing any research, because I didn't feel I would live long enough to get my Ph.D."
But he did not, in fact, quit, nor did he go to pieces. For one thing, he had good resources to draw on—the buoyancy (call it adaptability, if you wish) for which he had been noted at Oxford and, more important, his engagement in a life of intellectual challenge, in an existence nourished by what happens in the mind. The disease was not the only thing distressing him in those first two years of research, because he was struggling with his studies. It appears from his present recollection that he spent as much energy and concentration on the intellectual difficulties he confronted as he did on the possible proximity of death. I asked him why he kept going at all after he became ill, and he replied, "I didn't really. At first, I was doing very little work. I had very little mathematical background, so that made it difficult to make any progress For the first two years as a research student, I got very little research accomplished."
That must be characteristic of theoretical physicists as aspecies. Hawking's thesis supervisor at Cambridge, Dennis Sciama, who is now at Oxford, reflected the same focus. I had remarked on Hawking's feelings of depression at the time he started his research—meaning as he faced imminent decline and death, and Sciama received the thought on another level. "That's probably true," he said, "because it's very difficult in these advanced fields to find a good thesis topic. Cosmology at that time was a bit fragmentary. It was not easy to say, 'Well, here's a problem. It will take you three years; now go on and do it.' So indeed he looked around for quite a bit. While he did quite interesting things, the real measure of his ability was hardly emerging yet, and I can imagine it was a bit frustrating for him."
But "then things seemed to become more hopeful," Hawking told me. "The disease wasn't progressing so rapidly, and I got engaged to be married. So that was really the turning point. I realized that if I was going to get married, I would have to do some work—I'd have to get a job. About that time, I began to understand what I was doing as a mathematician."
This turning point, which Hawking describes in such a flat, cursory way, involved rather momentous developments. One was his falling in love with Jane Wilde, then an undergraduate in London, who now has a Ph.D. in languages. She proved willing to tie herself to a man whose future might be very short and difficult. He has said that she gave him "the will to live," and she was to do far more than that.
Jane Hawking is sott-voiced and affectionate, small and pretty, with straight dark brown hair. She is "very outgoing … a great professional asset" to her husband as a hostess, said Don Page. Hawking's Oxford tutor, Robert Berman, calls her "a remarkable woman. She sees that he does everything that a healthy person would to. They go everywhere and do everything."
At the same time that she came into Hawking's life, his thesis was rounding into shape, and one guesses he was beginning to sense his power. Dennis Sciama identified the academic turning point as having been the publication of an important paper by the theoretician Roger Penrose, now a professor at Oxford. The subject of the paper was singularities.
It had long been considered theoretically possible that when a dying star collapsed inward it could continue falling in on itself until all its mass was concentrated in a very small space that would have infinite density and therefore a gravitational field from which nothing could escape. Until Penrose wrote his paper, however, theoretical physicists had believed that—based on Newtonian principles—such a collapse to infinite density could not occur in the real universe, because the collapse of the star would have to be perfectly smooth, spherically symmetrical, and have no irregularities. Penrose showed, as Sciama put it, that in general relativity—the theory developed by Einstein to describe gravity—"new factors come into play, which guarantee that despite irregularities a singularity can occur."
Hawking took fire from that paper. "He conceived the idea," said Sciama, "that similar methods, suitably adapted, could be applied to the whole universe." Hawking knew that one theorist had shown that a universe could begin in a singularity, but only if it were a perfectly smooth universe, which ours is not. But our slightly asymmetric universe was observably expanding. If one ran the cosmic clock backward, one could demonstrate that, according to the principles of general relativity, the universe began with a singularity—a particle of infinite density.
In the last chapter of his thesis, and then in papers written as he began to move up the academic ladder at Cambridge, Hawking developed his singularity theorems of the universe and variations on the theorems—"which require very high-brow methods," said Dennis Sciama, "at least by the standards of theoretical physicists."
Theoretical physics is at one level a matter of methods, of approaches, of perspectives. If a given method seems to provide a useful way of solving a problem, it—or some part of it—may prove to be applicable to an allied or similar problem. Hawking had taken Penrose's approach to one question and adapted it for new purposes. Now he began to apply these new methods he had developed to an examination of the properties of black holes.
Perhaps this was not strictly "cosmology," though the exploration would shed light on the origins of the universe. One characteristic that sets Hawking apart from the main body of theoretical physicists is his readiness and ability to take up problems in a variety of specialties. I asked him if he would describe himself as a "cosmologist" now, and he answered, "That's partly right. That's one of the things I'd like to be. I'd call myself a theoretical physicist primarily interested in gravity—on all scales."
To say the least, that is a job description of considerable scope. The approaches in the different branches of physics, Don Page said, "are often quite a bit different. Stephen is certainly very good at understanding the principles behind the different ways of doing things. He may not know all the details of how particle physicists calculate certain complicated things. But he'll know the principles involved and be able to relate them to principles of another area. And he'll be able to take perhaps a part of a formula—say, from particle physics—and apply it in a different context—say, in cosmology or gravitation—in a way that persons working just in particle physics wouldn't be able to do."
So Hawking applied to the investigation of black holes the methods he used in his singularity theorems, and showed that asthe black hole swallows matter it can only get bigger—that when examining black holes with the tools provided by general relativity theory, there is no way to get a black hole to diminish in size, nor to have one black hole fission into two black holes. "That was just a fantastic result," said William Press. Until then, it would have been considered impossible to demonstrate that a black hole could not become two black holes, because the proof would be far too complicated. "Stephen's genius," said Press, "is in piercing through to the solution without having to calculate nonessential pieces. And, in fact, that theorem now can be taught to first-year graduate students."
Hawking began to turn his attention to the question of little black holes that might have been formed in the birth of the universe. Big black holes can be described using general relativity theory, but little black holes cannot. The scale of little black holes puts them in the domain of the elementary particles, the domain where general relativity does not apply and where quantum mechanics—particle physics—takes over.
He was interested in work on black holes being done by the Russian theorist Yakov B. Zeldovich, who suggested that if a black hole is not stationary but rotates it should radiate its rotational energy and thus emit particles. According to Don Page, who had also been working on the same question, Hawking "liked the idea, but he didn't like the way it was derived, so he was going to derive it correctly."
The results surprised and dismayed Hawking. If his approach was right, when one examined black holes at the quantum-mechanical level they emitted particles even without rotating. In other words, black holes could lose mass and diminish in size. Eventually they could even evaporate. But Hawking's own relativity theorems of black holes forbade all that. Because he had characteristically reached this result by attacking the problem in a broad-brush way, perhaps some of the details he had left out were important and would wreck the quantum mechanical solution if they were added. He added them, but he got the same results. "It's a little bit unusual for Stephen," said Don Page, "in that this was a case where he didn't guess the correct answer beforehand and then work out the justification for it."
So Hawking had developed two very important and apparently contradictory ways of looking at black holes. In the regime of relativity or gravity theory, large black holes can only grow; in the regime of quantum theory, they can shrink.
The apparent contradiction did not mean either set of statements about black holes was useless. Indeed, the discovery of the apparent contradiction itself provided what may be a crucial clue in the quantum-gravity mystery. Hawking quickly realized, as Kip Thorne put it, that the supposedly contradictory results only reflected "two different aspects of a thermodynamic behavior of black holes, so they weren't contradictory at all. They were thesame thing. In fact, in different regimes." Thorne believes "they were the seeds of a great new insight about a unified law that applies in both regimes."
Colleagues expect that if anyone is to succeed at "quantizing gravity"—finding that fully unified law of gravity and quantum mechanics—Hawking will.
However, the possibility of failure is a key part of the enterprise.
"We're all risk takers," Kip Thorne told me. Part of the risk is that the theoretician can head off in an entirely wrong direction, a long blind alley, while others are solving the problem with different approaches. Physics is a very lively field at this moment, and there are more than a few brilliant individuals seeking insights about unifying laws and about the beginning and end of the universe. Not all of them agree that Hawking will lead the way to further important insights or is even on the right track.
What are Hawking's chances of solving the quantum gravity problem, bringing gravity in under the quantum tent with the rest of physics, and thereby producing (or at least inducing) a great theory that explains the behavior of all matter? Judging from his career to date, William Press suspects that Hawking will actually "come up with nothing so simple as the mere answer to that problem," but will go beyond it somehow, find a revolutionary way of restating or looking at it, and once again open previously unseen doors in theoretical physics, leading to new understanding of our universe.
One might wonder, of course, whether his disease puts him in a race against time now. I asked him about it, and his reaction seemed to typify his strikingly good-natured attitude toward the human condition, a characteristic that lifts him above the ordinary as much as his accomplishments in theoretical physics do. "I don't think of it that way at all," he says. "Any theoretical physicist is in a race against time, because as he gets older he gets less able to come up with new ideas. It's all a matter of mental agility. I think I'm probably over the hill anyway at 40. My supervisor, Dennis Sciama, held a party when he was 30 to celebrate being finished as a theoretical physicist."
I reminded him of the barracks song about old soldiers never dying, just fading away, and I asked what old physicists do. He laughed the long, sung, one-note laugh: "They try to quantize gravity."
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