Stephen Hawking

Toy Trains and Cosmology

Stephen Hawking, described accurately as “the most remarkable scientist of our time,” and inaccurately as a second Einstein (“perhaps an equal of Einstein,” according to Time magazine in 1978), was born in Oxford on January 8, 1942. On January 8, 1642, three hundred years earlier, Galileo Galilei died, and in December of the year 1642 Isaac Newton was born.

It was wartime when Stephen, the Hawkings’ first child, came into the world, and his mother, Isobel, had chosen an Oxford hospital for the delivery because the university town was safe from German bombing. (The German Luftwaffe agreed to spare Oxford and Cambridge if the Royal Air Force would do the same for Heidelberg and Gottingen.) Oxford was not a permanent haven, however. Isobel and her husband Frank lived in Highgate, a northern London suburb, where there was a real bomb threat; a near hit by a German V-2 rocket damaged the Hawking house but none of its inhabitants.

Frank and Isobel Hawking both came from the north, Frank from Yorkshire and Isobel from Glasgow. Both had been students in Oxford, but they did not meet there. Frank studied medicine and became a researcher in tropical medicine. “The vivacious and friendly Isobel,” as Hawking's biographers Michael White and John Gribbin describe her, met her future husband at the medical research institute where he was later employed. She had taken a secretHelvetica job there, “for which she was ridiculously overqualified.”

When Stephen was eight, the family moved twenty miles north of Highgate to the cathedral city of St. Albans. The Hawkings bought a large Victorian house there, “of some elegance and character,” as Hawking recalls. He continues: “My parents were not very well off when they bought it and they had to have quite a lot of work done on it before we could move in. Thereafter my father, like the Yorkshireman he was, refused to pay for any further repairs. Instead, he did his best to keep it going and keep it painted, but it was a big house and he was not very skilled in such matters. The house was solidly built, however, so it withstood this neglect.”

By St. Albans standards, the Hawkings were an eccentric family. Frank “cared nothing for appearances if this allowed him to save money,” Stephen writes. Isobel had been a member of the Young Communist League before the war. During one of Frank's extended research trips to Africa, Isobel took her three young children to the Mediterranean island of Majorca to join her friend Beryl Pritchard, who was the wife of the expatriate English poet and novelist Robert Graves. For many years, the Hawkings drove a retired London taxi, which had cost them fifty pounds. Finally they bought a new Ford, and the entire family, except for Stephen, who could not interrupt his schooling, embarked on a yearlong car trip to India and back.

In 1952, when he was ten, Stephen began his secondary education at the St. Albans School, connected with the cathedral and academically of high quality. Unlike many of the great physicists, Hawking did not turn in an outstanding classroom performance. He writes that he “was never more than about halfway up the class,” and reports that he “tended to do much better on tests and examinations than . . . on coursework.” His creative energy was spent on constructing working models of trains, boats, and airplanes, and on inventing immensely elaborate games. (One of his war games was played on a board with four thousand squares.) Hawking believes that the games and the model building foreshadowed his development as a scientist. “I think these games, as well as the trains, boats, and airplanes, came from an urge to know how things worked and to control them,” he wrote later in an autobiographical note. “Since I began my Ph.D., this need has been met by my research into cosmology. If you understand how the universe operates, you control it in a way.”

Hawking's father, Frank, was also an important influence in his life. “I modeled myself on him,” Stephen remarked in an interview. “Because he was a scientific researcher, I felt that scientific research was the natural thing to do when I grew up.” Stephen's preference was for mathematics and physics, but Frank disapproved of the mathematics, which he claimed was preparation only for teaching. Chemistry took the place of mathematics, and his limited mathematical training was a handicap in Hawking's subsequent research, based on the formidable mathematics of general relativity. But when he was later facing the adversities of disease, and increasingly unable to write in the formal language of mathematics (that is, with equations), he had to start all over again and find what was for him a better route to the physical message. “I don't care much for equations myself,” he says now. “This is partly because it is difficult for me to write them down but mainly because I don’t have an intuitive feeling for equations. Instead, I think in pictorial terms.”

Falling

In 1959, at age seventeen, Hawking went to Oxford on a scholarship to University College, his father's college. The physics course at Oxford was easy too easy. “The prevailing attitude at Oxford at that time was very anti work,” he writes. “You were supposed to be brilliant without effort, or to accept your limitations and get a fourth-class degree. To work hard to get a better class of degree was regarded as the mark of a gray man the worst epithet in the Oxford vocabulary.” The only examinations required were the final ones. Hawking estimates that he averaged about one hour of work a day. The predictable result for Hawking and many of his fellow students was boredom and a “feeling that nothing was worth making an effort for.”

One relief from the boredom was rowing, a sport with a long and serious tradition at Oxford. Hawking did not have the burly physique required to handle an oar, but with his loud voice and fascination with being in control of events, he was suited for the position of coxswain, the member of the team who sits in the stern of the boat, shouts instructions, and steers. Hawking's coach thought he was competent as a “cox,” but reckless and not so devoted to winning as he might have been.

With his one hour a day effort, Hawking found himself at the end of his three years at Oxford on the borderline between a first- and a second class degree. In an interview with the examiners who would make the final decision, Hawking said he wanted to do research. He would go to Cambridge, he said, if they gave him a first, and stay at Oxford if they gave him a second. He got a first.

At Cambridge, Hawking began his career as a theoretical astrophysicist and cosmologist. His intention was to obtain his Ph.D. under Fred Hoyle, then Britain's best-known cosmologist. Instead, he was assigned to Dennis Sciama, of whom he had never heard. At first, Hawking was annoyed not to be studying under the famous Hoyle, but then he began to appreciate the friendly and stimulating environment Sciama created for his students. Kip Thorne, a Caltech astrophysicist and contemporary of Hawking's, describes Sciama's selfless relationship with his research students: “Sciama was driven by a desperate desire to know how the universe is made. He himself described this drive as a sort of metaphysical angst. The universe seemed so crazy, bizarre, and fantastic that the only way to deal with it was to try to understand it, and the best way to understand it was through his students. By having his students solve the most challenging problems, he could move more quickly from issue to issue than if he paused to try to solve them himself.”

Soon after Hawking had joined Sciama and his talented band of students, he was devastated by the news that he had the incurable disorder known as amyotrophic lateral sclerosis (ALS), or (in the United States) as Lou Gehrig's disease, or (in Britain) as motor neuron disease. It attacks the nerve cells that control voluntary muscular activity. Thought and memory processes are unaffected, but muscles throughout the body atrophy, leading finally to general paralysis. The doctor who made the diagnosis gave him a grim prognosis two years to live and “washed his hands of me,” as Hawking puts it. “In effect, my father became my doctor, and it was to him I turned for advice.”

Hawking's first reaction to his disease was the most natural one: deep depression. Fortunately, he did not lose himself in drugs or alcohol. His escape was in isolation and the thundering operatic music of Wagner. He could see no sense in continuing with the Ph.D. program if he would not have the time to complete it. But he would not give in to self-pity. While he was in the hospital for tests, he saw a boy die of leukemia. “It [was] not a pretty sight,” he recalls. “Clearly there were people who were worse off than me. . . . Whenever I feel inclined to be sorry for myself, I remember that boy.”

Rising

Hawking lifted himself out of depression partly by the strength of his will and determination, and partly with the help of others. The help came mainly from Jane Wilde, an extraordinary young woman who became Hawking's fiancee. She too lived in St. Albans, and the couple met at a party in 1963, soon after Hawking's ALS symptoms began to appear. She was put off by his sometimes arrogant manner, but “there was something lost, he knew something was happening to him of which he wasn’t in control.” Their friendship grew and they became engaged. The partnership was based on love, and because of Stephen's condition, a serious sense of purpose. “I wanted to find some purpose to my existence,” Jane has said, “and I suppose I found it in the idea of looking after him. But we were in love.”

For his part, Hawking recognizes that without Jane in his life the disease would have soon destroyed him. He told an interviewer: “I certainly wouldn't have managed it without her. Being engaged to her lifted me out of the slough of despond I was in. And if we were to get married, I had to get a job and I had to finish my Ph.D. I began to work hard and found I enjoyed it. Jane looked after me single handedly as my condition got worse. At that stage, no one was offering to help us.”

By the summer of 1965, Hawking had completed his Ph.D. thesis and won a research fellowship in theoretical physics at Gonville and Caius College, Cambridge, always shortened to Caius (and, for some reason, pronounced “keys”). Jane and Stephen were married in July 1965. White and Gribbin describe the wedding photograph: “Hawking looks at the camera with a proud expression, a stare of deep-rooted determination and ambition a stance that says, ‘This is just the beginning.’ Jane smiles happily at the lens, equally sure, in her own gentler way, that they will make out and overcome all adversity.”

Hawking had an office at the Cambridge Department of Applied Mathematics and Theoretical Physics, and the couple needed to find nearby living accommodations, so Hawking, who was becoming increasingly disabled, could commute on his own. That proved to be a challenge, particularly when Hawking offended the college bursar (an administrative officer) by asking how much his fellowship paid. Finally, with the help of a woman who had noticed their plight, they found a small, ancient, but ideally located house on a picturesque street called Little St. Mary's Lane. One of Hawking's colleagues, Brandon Carter, describes the home as a lively place with friends on hand helping with the cooking and cleaning. Mahler and Wagner provided the musical accompaniment. And so it was in this remarkably normal way that the Hawkings began their married life. Their first child, Robert, was born in 1967.

The Most Perfect Objects

Hawking's first research project centered on black holes, those astonishing stellar objects Chandrasekhar called “the most perfect macroscopic objects there are in the universe.” Regardless of their size, “the only elements in their construction are our concepts of space and time.” A typical black hole might have a mass of ten solar masses and a radius of only ten to fifty kilometers. Astrophysicists now surmise that there are millions of such black holes in our galaxy. At the core of our galaxy and others there are evidently gargantuan black holes, some of them having the diameter of our solar system with a mass equivalent to several billions of solar masses. Theorists also speculate that vast numbers of miniature black holes populate the cosmos, each with the size of an atom and the mass of a mountain.

In spite of this diversity, black holes are among the simplest objects in the universe. A black hole can be as big as the solar system, or as small as an atom, or anything between; its behavior depends only on its mass and rate of spin (and on its electric charge, but that is generally comparatively small). Even though they are usually macroscopic in size, they are as standardized physically as elementary particles, which are also characterized by mass, spin, and charge. Black holes are not made out of rocks, like planets, or hot gases, like stars. They are, as Martin Rees, a contemporary of Hawking's and another one of Sciama's former students, writes, “made from the fabric of space itself.” It was this fundamental simplicity that fascinated Chandrasekhar.

Up to a point, black-hole theory follows from Einstein's theory of general relativity, which describes the gravitational extremity that exists within the hole. The theory reveals that the gravitational field in the hole is so powerful that anything, including light, coming closer than a certain critical radius called the “event horizon” falls into the hole and is lost forever. With care, a spaceship could safely orbit just outside the event horizon, but black hole interiors are not for exploration. A reckless astronaut passing beneath the event horizon could never escape, and could not even communicate his or her observations to the outside, because light and all other kinds of signals are confined within the hole.

General relativity tells us everything we need to know about black holes except for the physical situation at the center of the hole. There, relativity theory prescribes a point called a “singularity,” where the density and spacetime curvature are infinite. But infinities are unpopular with theoretical physicists because they are not valid numbers and are likely to indicate a flaw in the workings of the theory.

Hawking and Roger Penrose (Chandrasekhar's muse), sometimes working in collaboration, defined the problem of black-hole singularities during the period from 1965 to 1970. Hawking and Penrose worked well as team. Hawking has a penetrating physical intuition, while Penrose has the mastery of the mathematics of general relativity that Hawking lacks. As one solution to the problem, Penrose proposed a principle of “cosmic censorship”: a black-hole singularity is “censored” because it is “decently hidden,” as Hawking puts it, from outside observers by the event horizon. “Naked,” uncensored singularities are prohibited.

The theory of black holes was well established in the 1960s by Hawking, Penrose, and others, before any observations were reported that they actually existed. Then in the early 1970s a case was made that an x-ray emitting object called Cygnus X-1, located in the constellation Cygnus, was a black hole paired with a massive star. It was assumed that the black hole was drawing gas from the star and heating it to the point where it emitted x rays. (As the gas fell into the black hole's intense gravitational field, it lost gravitational energy and at the same time got hotter as it gained thermal energy.)

In 1974, Hawking and other astrophysicists were about 80 percent certain that Cygnus X-1 actually involved a black hole. As an “insurance policy,” Hawking made a bet with his Caltech colleague Kip Thorne that Cygnus X-1 did not harbor a black hole. Hawking's “insurance” if he lost the bet was a four-year subscription to the British magazine Private Eye. Thorne would receive a year's subscription to Penthouse magazine if he won. By 1990, confidence in the Cygnus X-1 black hole had risen to about 95 percent, and Hawking cheerfully paid off the bet.

Hawking's best known contribution to astrophysics is a theory that slightly contradicts the blackness of black holes: “Black holes ain't so black,” as Hawking puts it. The mechanism by which black holes shed their blackness relies on the concept, which originated with Dirac, that electrons have antielectron counterparts called positrons. When an electron meets a positron, they annihilate each other, and gamma ray photons are produced. The inverse of this process, in which a gamma ray photon obtained from some suitable energy source produces an electron positron pair, is also possible.

Quantum theory permits another version of the latter process, which is, as physicists like to say, “counterintuitive,” meaning weird. The energy for electron positron pair production can be “borrowed” from the empty space of a vacuum if an electron-positron annihilation follows that repays the energy “loan.” The sequence for an electron e^-- and a positron e⁺ is, first, pair production,

energy → e ^-- + e⁺,

quickly followed by pair annihilation,

e^-- + e⁺ → energy.

Heisenberg's uncertainty principle shows in detail how this can happen, and allows calculation of how long the electron and positron exist before they are lost in an annihilation. A similar story can be told for any kind of particle antiparticle pair. Particles and antiparticles involved in this coupling of pair production and pair annihilation are called “virtual” because they cannot be observed directly by a particle detector.

Hawking's idea was that the members of a virtual pair could become real and one of them observable if they were produced in the vicinity of a black hole. One might be captured by the hole and become a real particle or antiparticle, while the other, also real, might escape and be seen as emitted radiation. To the extent that these emissions occur, the hole is not literally black. Energy is required to create the particle antiparticle pairs, and that energy comes from the black hole's gravitational field. As the energy of the field is diminished, the hole shrinks in size and eventually disappears, possibly in an immense explosion with the strength of millions of hydrogen bombs.

But black holes are, after all, almost black. Emission of black hole radiation, called “Hawking radiation,” is a very inefficient, slow process. The time required for a black hole with the mass of the Sun to evaporate away all its mass is predicted by Hawking's theory to be 1065 years; the age of the universe as we observe it is vastly less than that roughly 1010 years.