Stephen Hawking, His Life and Work

by Kitty Ferguson

  The Hawkings’ third child, Timothy, was born in April on Easter Sunday. To commemorate another birthday a hundred years before, Hawking and Werner Israel celebrated the anniversary of the birth of Albert Einstein (14 March 1879) by inviting colleagues to contribute articles to a book reflecting current research related to general relativity. The introduction foreshadowed the topic of Hawking’s Inaugural Lecture as Lucasian Professor, commenting on ‘Einstein’s dream of a complete and consistent theory that would unify all the laws of physics’.9

  Hawking received several major international awards and honorary doctorates in the mid- to late 1970s, including the Hughes Medal from the Royal Society honouring ‘an original discovery in the physical sciences’ for ‘distinguished contributions to the application of general relativity to astrophysics’, and, in 1978, the coveted Albert Einstein Award from the Lewis and Rosa Strauss Memorial Fund in the United States. That award is not given every year and is the most prestigious American award for a physicist. One of the honorary doctorates, in the summer of 1978, was from his alma mater, Oxford. Most significant of all for Hawking’s future, in the autumn of 1979 the University of Cambridge gave him the venerable title of Lucasian Professor of Mathematics. He at last got a private office. The impressive tome in which each new university teaching officer inscribes his or her name was brought to him there more than a year later. Somehow, this formality had been neglected earlier. ‘I signed with great difficulty. That was the last time I signed my name.’10

  In 1980, Hawking’s battle for independence reached a crisis point. Martin Rees was by then the holder of another prestigious chair at Cambridge, the Plumian Professorship of Astronomy. He had known the Hawkings since before their marriage and had witnessed at close hand both Stephen’s soaring success as a scientist and his inexorable physical decline. Some time in the late winter or early spring Rees asked Jane to come in for a chat with him at the Institute of Physics. Earlier that winter, when a bad cold had turned more serious and Jane had also been ill and slow to mend, Stephen, on the family doctor’s recommendation, had entered a nursing home for a short while until they both recovered. Rees feared that this would be the first of many times when the Hawkings would not be able to cope without additional help. He offered to find funding to pay for limited home nursing.11

  To Hawking, this was unthinkable. Agreeing to it would be giving in to his illness and would introduce an unwelcome, impersonal intrusion into his life. He would become a patient. After some consideration, however, he changed his mind. There would be advantages. He would be much freer to travel, not always having to depend on his wife, friends and students. What he had at first seen as a loss of independence might be a gain instead.

  N=8 Supergravity

  Hawking’s Inaugural Lucasian Lecture, ‘Is the End in Sight for Theoretical Physics?’, with which this book began, took place on 29 April 1980. In that lecture he chose N=8 supergravity as the front-running candidate for the Theory of Everything. It was not one of his own theories, but it seemed to him and many other physicists extremely promising. Supergravity grew out of the idea of supersymmetry, a theory that suggested that all the particles we know have supersymmetric partners, particles with the same mass but different ‘spin’.

  In A Brief History of Time, Hawking suggests it’s best to think of spin as meaning what a particle looks like when you rotate it. A particle with spin 0 is like a dot. It looks the same no matter from what direction you look at it and no matter how you turn it. A particle with spin 1 is like an arrow: you have to turn it around a full rotation (360 degrees) to have it look the same as when you started. A particle with spin 2 is like an arrow with two heads (one at each end of the shaft): it will look the same if you turn it only half a rotation (180 degrees). All seems fairly straightforward so far, but now we come to something slightly more bizarre, particles with spin ½. These have to complete two rotations in order to return to their original configuration.

  We saw in Chapter 2 that every particle we know in the universe is either a fermion (particles that make up matter) or a boson (a ‘messenger’ particle). Elementary fermions have spin ½. An electron, for example, has to finish two rotations in order to return to its original configuration. Bosons, on the other hand, all have whole number spins. The photon, W and Z bosons, and the gluon have spin 1, returning to their original configuration after one rotation (the single-headed arrow). The graviton theoretically has spin 2 (the double-headed arrow), returning to its original configuration after half a rotation.

  Supersymmetry theory suggests a unification of matter and the forces of nature by proposing ‘supersymmetric partners’ for each of these particles, with every fermion having a boson for a partner, and every boson a fermion – a little like the procession at the end of an old-fashioned wedding uniting two formerly incompatible families, with every bridesmaid going out on the arm of a groom’s attendant from the other clan. There was a Latin flavour to the naming of the bosons’ partners. The photon’s theoretical supersymmetric partner was christened the photino. The graviton’s was named the gravitino. As for the fermions, their supersymmetric partners were all given names by adding an s. And so we have the selectron and the squark.

  There were several versions of supergravity around at the time of Hawking’s Lucasian Lecture. N=8 supergravity had the advantage of being the only one that worked in four dimensions (three of space and one of time), and though it called for a goodly number of as yet undiscovered particles, it did not call for an infinite number of them, as other attempts at theories of quantum gravity did. The name N=8 came from the fact that in this theory the graviton had not just one but eight supersymmetric partners. A little awkward for processing down the aisle, but it worked well in the theory.

  It was not long after his Lucasian Lecture that Hawking and others realized how stupendously difficult it was to do any calculations using what had seemed to be such a promising theory. In addition to the graviton and the eight gravitinos, there were 154 types of particles. The general conclusion was that it would take about four years to finish a calculation, even if you used a computer – making sure to account for all the particles, searching for infinities that might still lurk somewhere, and being sure not to make an error!

  Another problem was that none of the supersymmetric partners had ever been observed or looked likely to be. The theory says they have the same mass as their ‘normal’ partners, but this symmetry (in the world we can observe) is ‘broken’, leaving the supersymmetric partners hundreds, even thousands of times more massive. The energy required to discover them in a lab is tremendous. ‘Symmetry-breaking’ is something we’ll return to in another context.

  The ‘Higgs field’, proposed in 1964 by Peter Higgs at the University of Edinburgh, theoretically pervades the entire universe and is responsible for the symmetry-breaking that makes the supersymmetric partners so difficult to discover experimentally, and also for the masses of more familiar particles. If the theory is right, the Higgs field should show up as the ‘Higgs particle’, with spin 0. The Higgs particle itself is very massive and has never been observed, but, if it indeed exists, it may be discoverable with the high energies of the Large Hadron Collider at CERN on the Swiss–French border at Geneva. One of Hawking’s famous bets is that the Higgs particle will not turn up at all. He has become more interested in the possibility that the LHC may discover some of the supersymmetric partners, or perhaps produce a mini-black hole.

  In the spring of 1980, when Hawking gave his Lucasian Lecture, Jane was working towards her doctoral oral examination, scheduled for June. No one was surprised when she passed. She would not be officially graduated until April 1981, but with her degree now a certainty, she began to tutor local children in French, and then took a part-time position at the Cambridge Centre for Sixth Form Studies, helping students prepare for their sixth-form examinations and gain entrance to university.12 A little later, degree in hand, she became a teacher at sixth-form level. The beginning of her professio
nal career was something of an anticlimax after her years of labour to finish her thesis. There was still a dispiriting gap between her own considerable intellectual achievements and the much more conspicuous success of her husband. Nevertheless, ‘It is fulfilling a part of me,’ she said, ‘that I feel has been suppressed for a long time and the marvellous thing is that it is totally compatible with what goes on at home.’13

  Tim was a toddler, Robert was thriving at the Perse School, and Lucy had become a favourite at her primary school. The first I ever heard of any of the Hawkings was a comment from the head teacher at Newnham Croft Primary School that my six-year-old daughter reminded her of Lucy Hawking. This was obviously meant as a compliment. When I met Lucy, I found that it was. She by then had finished at the school but was back for a visit, helping with the small children in the playground. A radiant, clean-cut, blonde sixteen-year-old, she was brimming with intelligence and personality, with a thoughtfulness and composure beyond her years. She said her father was a physicist at Cambridge, but she hoped to go to Oxford instead because she had lived in Cambridge all her life and wanted a change of scene. Lucy told interviewers that she was not like her father. ‘I was never any good at science. I even managed to be hopeless at maths as well, which was slightly embarrassing.’14 But she was a fine student and cellist. It’s unlikely anyone has ever wagered a bag of sweets against her success or that of her brothers.

  Trouble in the Attic

  The year spent at the California Institute of Technology in 1974–5 had been such a success from Stephen Hawking’s point of view and that of his hosts that he began a habit of returning for a month almost every year. Caltech renewed and extended his Sherman Fairchild Distinguished Scholar appointment to make this possible.

  By 1980, Kip Thorne had noticed a change in Hawking’s attitude towards his research, summed up when Hawking told him: ‘I would rather be right than rigorous.’ This rather enigmatic statement referred to the fact that most mathematicians are satisfied with nothing less than a firm mathematical proof that they are correct. That had been Hawking’s attitude in the 1960s and 1970s. Now he was saying that such rigour is not necessarily the best way to arrive at ‘right’. It could lead one not to see the forest for the trees. He had become more speculative, happy to be perhaps 95 per cent sure of something and then move on. ‘Stubbornly intuitive’ was how New York Times columnist Dennis Overbye described him.15 Though Hawking’s intuition was often on target, for him the quest for certainty had changed to a quest for ‘high probability and rapid movement towards the ultimate goal of understanding the nature of the universe’.16

  Hawking’s experience of California had broadened to include more than Los Angeles and Pasadena. He liked the steep streets of San Francisco and the opportunities they offered for a dare-devil in a motorized wheelchair. He was just as reckless a driver now as he had been when he took Jane Wilde to the Trinity Hall May Ball in 1963. His colleague Leonard Susskind remembers him poised at the top of the steepest section of one of those hills, with an incline so severe that motorists shudder, fearing that their brakes must surely fail or the car somersault forward. Hawking flashed his companions one of his mischievous smiles and then disappeared, barrelling down the hill, almost in free fall. When they caught up with him at the bottom he was sitting there grinning with satisfaction and asked them to take him to a steeper hill.17

  In San Francisco in 1981, Hawking called attention to an issue that troubled some of his colleagues far more than his reckless disregard for the hazards of San Francisco streets. The venue was more than eccentric, the attic of the mansion of Werner Erhard, founder of a pop psychology called EST. EST targeted people who felt they were sadly lacking in self-confidence and were willing to pay fees of several hundred dollars for help. As many as a thousand at a time gathered for intensive two-week sessions in hotel ballrooms to submit to therapy that could be authoritarian, demeaning, and verbally and physically abusive. The claim was that they would experience at least temporarily a personal transformation and emerge enlightened, self-confident and outgoing. For some, it worked.

  This scheme had made a fortune for Erhard. He was also a physics aficionado and he used his wealth to cultivate the friendship of a number of theoretical physicists at the top of their profession and not at all lacking in self-confidence, including Richard Feynman. Erhard hosted elaborate gourmet dinners for them and equipped his mansion’s attic to accommodate small, exclusive physics conferences, funded out of his pocket. Though Erhard was the founding father of what his critics regarded as a hokey, violent pop psychology, he was a pleasant, interesting, extremely intelligent man. The elite of physics chose to ignore the first persona and enjoy the second, and did not say no to what he offered them.18

  When Stephen Hawking made his announcement at a conference in 1981 in Erhard’s attic, he was still able to speak with his own voice, but it had been several years since anyone except those who knew him best could understand him. His interpreter on this occasion was Martin Rocek, then a Junior Research Fellow at the DAMTP, later to make his name in physics in the areas of string theory and supersymmetry. Rocek travelled with Hawking on that trip to California, struggling more or less successfully to understand him and repeat his words clearly for others. Film clips made of this process show what a prodigious effort was involved. For most lectures, such as his Lucasian Lecture, Hawking’s graduate assistant would deliver the talk and ‘[Hawking] would just sit around and add brief comments if a student would say something wrong’.19 Whatever the Byzantine nature of the process involved, Hawking’s announcement in Erhard’s attic was clear enough.

  He had been focusing his attention on black holes for about fifteen years, arriving at equations of such simple clarity and elegance that he felt they had to be correct. Such results, he insisted, reveal a deep harmony underlying nature.20 By 1981, hardly anyone was treating Hawking radiation as a dubious concept. But Hawking had begun to realize, at least as early as his sabbatical in Pasadena in 1974–5, that at the heart of the equations surrounding that discovery lurked a paradox that threatened to undermine the whole of physics. It had to do with the loss of information in black holes and the threat this posed to a fundamental tenet of physics, the law of information conservation: information can never be lost from the universe. Don Page, in 1979, had been the first to disagree with Stephen’s conclusion, but Stephen had not budged.

  It’s important to understand what ‘information’ means in this context. You can think of this lost information as information about everything that went into making the black hole in the first place and everything that fell in later. But what does a theoretical physicist mean by ‘information’? The clue is in the words ‘information encoded in the particles that make up the universe’.

  Here, from the history of the study of black holes, is an example that helps explain what ‘information’ means to a theoretical physicist: in his book The Black Hole War, Leonard Susskind tells of an Einstein-like thought experiment performed by Jacob Bekenstein when he was considering the question of the entropy of a black hole. (Bekenstein’s proposals, you will recall, presented a challenge to Stephen Hawking in 1972.) It’s hard to imagine that anything could take much less information into a black hole than a single photon falling in, but, in fact, one photon does carry a good deal of information. Most significantly for Bekenstein, it carries into the black hole information about the location where it fell in.

  Bekenstein wanted to consider a smaller amount of information than that for his thought experiment. He wanted to reduce the amount of information to one ‘bit’, a unit of information suggested by John Wheeler that has the smallest possible size in the universe – a quantum distance calculated by Max Planck in the early twentieth century. In order to achieve this, Bekenstein made use of Heisenberg’s uncertainty principle and imagined ‘smearing out’ the location where the photon fell in. He imagined a photon of such long wavelength that the probability of its entry point would be spread out over the entire even
t horizon, making it as uncertain as possible, so that it would convey only a single ‘bit’ of information – that the photon was, in fact, inside the black hole. The photon’s presence would add to the mass of the black hole and, of course, to the area of the event horizon, by a minuscule amount, which Bekenstein proceeded to calculate.

  Obviously, ‘information’ in this story means something a little more subtle than what you and I normally think of as everyday ‘information’. It isn’t only information such as what channel John Wheeler’s television was tuned to when it fell into the black hole.

  The idea of information disappearing into a black hole and becoming inaccessible to those on the outside was not new to anyone at the conference. Locked-away information like that is not a violation of information conservation. The information in a black hole may be inaccessible to anyone on the outside, but it is still in the universe. Hawking was thinking of something more drastic. When a black hole has finally radiated all of its mass away and disappeared, what has actually happened to everything that went into forming the black hole and everything that later fell in?

  If you have been following this book carefully, you may be raising your hand to suggest that it would all have been recycled as Hawking radiation. That radiation, of course, would not look anything like, say, a hapless astronaut who fell in, but could it somehow be the solution to the problem? After all, the law of information conservation has it that information encoded in the particles of which everything in the universe is made up can be scrambled, chopped up, destroyed, but if the fundamental laws of physics as we now understand them are correct, it can always be retrieved from the particles that make it up. In principle, with the information in hand, anything can be restored.21

  For example, let’s say you burned this book. You might think you would never be able to finish reading it. However, in principle, if you could study the burning process carefully enough to trace all the molecular interactions that turned the book to ashes, then by running the process backwards you could have the book again. It would be a lot easier to go out and buy another copy, but in principle you could reconstruct it.22