Stephen Hawking, His Life and Work

by Kitty Ferguson

  A year and a half later, he had changed his mind. In an interview given shortly before September 11, he told the German periodical Focus that humans would be well advised to modify their DNA in order to avoid being outdistanced by super-intelligent computers that would eventually rule the world.2 Are computers really likely to become that intelligent? Hawking had previously commented that computers are ‘less complex than the brain of an earthworm, a species not known for its intellectual powers’.3 But he thought that ‘if very complicated chemical molecules can operate in humans to make them intelligent, then equally complicated electronic circuits can also make computers act in an intelligent way’.4 Intelligent computers will then design even more intelligent and complex computers.5

  His new position was controversial, but it was largely forgotten in the wake of the 9/11 attacks. The interviews that inevitably followed – for the media felt confident that Stephen Hawking would have wise words to offer on other topics besides physics – gave him the opportunity to introduce another issue that he had been considering. He told an interviewer from the Guardian: ‘although September 11 was horrible, it did not threaten the survival of the entire human race. The danger is that either by accident or design we may create a virus that destroys us.’6

  Hawking advised that plans be put in place as soon as possible with the long-range goal of colonizing space to ensure the survival of the human race. This was not an off-the-cuff notion, soon to be forgotten. Already in the millennial interview he had predicted a manned, ‘or should I say personned’, flight to Mars within the century. But that would be only the first stop. Mars isn’t suitable for human habitation. We need either to learn to live in space stations or travel to the next star, and that journey he was sure would not happen within the century. Because we can’t travel faster than light (no matter what science fiction claims), the trip would be slow, boring and arduous. Hawking would return to the advisability for humans to colonize space in the children’s books he would write with his daughter Lucy a few years later. This need seemed urgent enough for him to try to ingrain it in the minds of children who would be setting the agenda in the future.

  Not everyone appreciated pronouncements like these about issues beyond his own field of expertise. Most of Hawking’s critics called him not ‘wrong’ but ‘naïve’. Sir Brian Pippard, an eminent twentieth-century physicist, once apologized for himself and his colleagues for being ‘inclined to believe that their expertise absolves them from the duty of studying other branches of knowledge before contributing their own penn’orth of wisdom’.7 Hawking could perhaps be declared guilty, but he knew he had a golden opportunity to reach the public with ideas he strongly believes are important and ought to be heard. He possibly had enough clout to influence public policy.

  The TOE Revisited

  In his Lucasian inaugural lecture in 1980, Hawking had announced that the most promising candidate to unify the forces and particles was N=8 supergravity. In 1990 he had told me he suspected it might turn out to be superstrings, with his no-boundary proposal answering the question about the boundary conditions of the universe. Now, the close of the millennium had come and gone. Still no end to theoretical physics. Still no Theory of Everything. In April 2002, Hawking told a reporter that ‘I still think there’s a 50-50 chance that we will find a complete unified theory in the next twenty years’8 – a much more modest and tentative forecast than he had made in his Lucasian Lecture.

  As the months passed, Hawking hedged his bets even more. He was reconsidering one of the main thrusts of his scientific career, beginning to suspect that the fundamental, unified theory – if it exists at all – is at a level that will never be accessible to us. Our understanding will always resemble a patchwork quilt, with different theories holding in different regions, agreeing only in certain overlapping areas. If this is the case, then it would be ill advised to view what seem like inconsistencies among the theories as a sign that they are weak or incorrect. What we would be able to discover about the universe would inevitably be something like a jigsaw puzzle in which it is not so difficult ‘to identify and fit together the pieces around the edges’ – supergravity and the different string theories – but in which we will never be able to ‘have much idea what happens in the middle’.9 In a lecture for the Paul Dirac Centennial Celebration at Cambridge, in July 2002, he said, ‘Some people will be very disappointed if there is not an ultimate theory that can be formulated as a finite number of principles. I used to belong to that camp, but I have changed my mind.’10

  Hawking asked his audience to recall the Austrian mathematician Kurt Gödel, who in 1931 had shown that mathematics was ‘incomplete’ because in any mathematical system complex enough to include the addition and multiplication of whole numbers, there are propositions that can be stated – and that we can even see are true – but that cannot be proved or disproved mathematically within the system. Hawking thought that it might also be the case in physics that there are things that are true but cannot be proved. Kip Thorne had spoken about the change in Hawking’s way of working, from an insistence on rigorous mathematical proof to a quest not for certainty but for ‘high probability and rapid movement towards the ultimate goal of understanding the nature of the universe’.11 Hawking had made large intuitive leaps, expecting others to fill in the gaps he was leaving behind. Was he now about to become even more daring, warning his listeners that things he was sure are true would be impossible to prove? No, even he had to join the human race at the brink of a chasm that no one could cross. Our theories are inconsistent or incomplete, he said, because ‘we and our models are both part of the universe we are describing … Physical theories are self-referential.’12

  The new and still elusive candidate he spoke about in his Dirac Centennial lecture was not ‘an ultimate theory that can be formulated as a finite number of principles’, but it might be the best we could ever do. It was M-theory. A particularly interesting version of that theory incorporated the brane theory that Townsend had suggested. Recall from our discussion of p-branes that when p = 1, that is a string. So strings could now be considered members of the larger clan that Townsend had named p-branes. Hawking was not throwing supergravity and string theory, his two earlier favourite candidates for the Theory of Everything, out of the window by any means. The five most promising superstring theories could be grouped in a family of theories that would also include supergravity. The superstring theories and supergravity were the pieces of the ‘patchwork quilt’, useful for considering different situations, but none of them applied in all situations. The unexpected network of relationships that physicists had found among them had led to the suspicion that these theories are all actually different expressions of a deeper, underlying theory – M-theory – which did not, as yet, have a single formulation. Hawking had begun to think it never would.

  In the M-theory network of mathematical models, spacetime has a total of ten or eleven dimensions. These are usually taken to be nine or ten space dimensions and one time dimension. You may be wondering why no one ever thinks there might be more than one time dimension, so I should tell you that some versions of the theory do allow more time dimensions, as long as the total stays the same.

  We, of course, experience only four dimensions. Where are the others? Hawking himself commented in 2001: ‘I must say that personally I have been reluctant to believe in extra dimensions. But as I am a positivist, the question “Do extra dimensions really exist?” has no meaning. All one can ask is whether mathematical models with extra dimensions provide a good description of the universe.’13

  The proposed answer to the question of why we don’t see them is that the extras are rolled up very small. Think of a garden hose. We know that a garden hose has thickness to it, but from a distance it looks like a line with length but no other dimension. If the extra dimensions were ‘rolled up’ like that we would miss noticing them, not only on human scales, but even on atomic or nuclear physics scales.

  Could we ever observe th
em? Suppose one or more of the extra dimensions is not so completely rolled up after all. That suggestion may be testable with a more advanced generation of particle accelerators or by measuring the gravitational force operating over extremely short distances.

  Meanwhile, M-theory and extra dimensions had staked out a claim in the future of theoretical physics and cosmology. That future would be the theme of a conference held to celebrate Hawking’s sixtieth birthday in 2002.

  Sixty or Bust!

  Hawking’s sixtieth-birthday party almost didn’t happen. He and his wheelchair ran into a wall a few days before the event. Hawking brushed this off in the opening of his lecture, ‘Sixty Years in a Nutshell’: ‘It was nearly 59.97 years in a nutshell. I had an argument with a wall a few days after Christmas, and the wall won. But Addenbrooke’s Hospital did a very good job of putting me back together again.’14

  There had been a moment when those planning the birthday party stopped dead and held their breath, but then it was learned that Hawking was working on his own birthday speech in his hospital bed. The preparations continued. No one had to cancel, at the last minute, the Marilyn Monroe impersonator who would fawn over Hawking and croon ‘I Want to be Loved By You’ … or tell all the physics luminaries gathering from around the world that they could come and give their talks, but the man they were celebrating would not be present. The party happened. Hawking thought sixty was well worth celebrating. Many people, he told interviewers, don’t welcome turning sixty, but for him it was an accomplishment. He had never expected to live so long.

  It was a many-faceted celebration. A serious four-day ‘fest schrift’ conference featured high-level papers presented by giants of theoretical physics and cosmology whose work touched on Hawking’s. The public was admitted for a day of popular-level lectures. The real partying took place in the evening, attended by a crowd of as many as 200 guests. There was ‘Marilyn’, whom Hawking dubbed ‘a model of the universe’. There was a choir of former and current graduate students and Hawking’s first wife Jane, conducted by her husband, Jonathan Hellyer Jones, and accompanied by the U2 guitarist, Edge. Because Hawking’s birthday fell close to the church Feast of St Stephen, they sang ‘Good King Wenceslas’ with new words written by Bernard Carr. ‘Page and Hawking, forth they went’ referred to Don Page. At one of the parties, in the Hall of Caius, Martin Rees – by this time Sir Martin Rees, Astronomer Royal – spoke glowingly about his old friend. A party in the Hall of Trinity College featured a sudden burst of colour and music as can-can dancers made a spectacular entrance. Television crews from Channel 4, the BBC, and America’s CBS were present, and there was a live webcast to the BBC’s website of Hawking’s public lecture and the audience’s rowdy, spontaneous, painfully off-key singing of ‘Happy Birthday’ that followed it – one of many renditions of it that week. The BBC later broadcast all the popular lectures as ‘The Hawking Lectures’.

  Hawking’s colleagues took advantage of the opportunity to rib him:

  Martin Rees: ‘Astronomers are used to large numbers, but few are as huge as the odds I would have offered then [when Hawking was a graduate student at Cambridge] against witnessing this marvellous celebration.’15

  Roger Penrose: ‘I am very glad to note that Stephen has now also officially become an old man, so that he can also get away with saying such outrageous things. Of course Stephen has always done that kind of thing, but he can perhaps feel a little bolder in this even than before.’16

  Bernard Carr: ‘I’ve often suspected that there must be more than one Stephen Hawking to have made so many important discoveries. I would like to wish all of them a very happy sixtieth birthday!’17

  Leonard Susskind: ‘Stephen, as we all know, is by far the most stubborn and infuriating person in the universe.’18

  Raphael Bousso: ‘It is a pleasure to help celebrate Stephen Hawking’s sixtieth birthday (not least because Stephen knows how to party).’19

  Gary Gibbons, praising ‘Stephen’s indomitable courage and daring optimism’,20 quoted Robert Browning: ‘Ah, but a man’s reach should exceed his grasp or what’s a heaven for?’

  Michael Green recalled the early 1970s in Cambridge, when he first met Stephen, and cosmology was held in such low regard that ‘it was considered a sub-branch of astrology and was not discussed at all!’21

  Neil Turok spoke of Hawking’s ‘real “lust for life” that keeps him going against all odds’.22

  Kip Thorne’s birthday present was a promise that ‘gravitational wave detectors – LIGO, GEO, VIRGO and LISA – will test your Golden-Age black-hole predictions, and they will begin to do so well before your seventieth birthday’.23

  The papers prepared for the sixtieth-birthday conference gave a splendid summing up of where things stood in theoretical physics and cosmology in 2002, and how they had got there, and, as the conference title suggested, provided a springboard for the future. It brought together the finest minds in the world on the topics that most interested Hawking and impinged on his own work, and also to a remarkable extent brought together the grey eminences of the field with energetic younger people who were going to carry it into the future, many of whom had been Hawking’s students. It all went on for a week … and why not? This was a birthday party no one for many of the sixty years had expected to attend. Elaine’s birthday gift was a thirty-minute flight in a specially designed hot-air balloon. When Hawking had dreamed of such a flight at the time of his tracheotomy in 1985, he had taken it as a symbol of hope. At the age of sixty, it seemed that this hope had been amply fulfilled.

  Hawking’s colleagues and others who shared his birthday celebration were willing to accept his brushing off his wheelchair accident as something trivial, but it was in truth more serious than that. Wheeling along the uneven old pavement of Malting Lane near his home, accompanied by a nurse, he had lost control and crashed his chair into a wall, turning the chair over and breaking his hip. Neel Shearer, his graduate assistant, shrugged: ‘He was late for an appointment and running on Hawking time, as ever.’24 Hawking’s weakened condition precluded the use of a general anaesthetic when the doctors repaired him. With only an epidural anaesthetic, Hawking experienced the whole procedure, something ‘like hearing a Black and Decker drill’.25

  Hawking’s sixtieth-birthday year saw the publication of his carefully chosen compilation of excerpts from the writings of Copernicus, Galileo, Kepler, Newton and Einstein. On the Shoulders of Giants also featured biographical sketches of the five men and commentary by Hawking.

  Unpacking the CMBR

  As the new millennium got underway, a new generation of observers and observational instruments were gearing up to test the predictions made by inflation cosmology with unprecedented accuracy.26 In a continued search for experimental evidence that might, or might not, support inflation predictions, attention focused, not surprisingly, on the CMBR, the afterglow of the Big Bang. George Smoot’s discovery had shown that in the extraordinarily evenly dispersed microwave light, the temperature does vary from point to point. In 1998 (results released in 2000), balloon observations had measured the CMBR in detail in certain parts of the sky;27 and in 2001 the ground-based Degree Angular Scale Interferometer at the South Pole took similar measurements.

  Then, in June 2001, NASA launched WMAP, the Wilkinson Microwave Anisotropy Probe.fn1 Its mission: to map the CMBR more precisely than had ever before been possible. It was capable of measuring temperature differences varying by only a millionth of a degree and, because it was a satellite rather than a land-based instrument, take these measurements over the entire sky. The expectation was that WMAP would settle once and for all many of the arguments of the last few decades about the basic properties of the universe – its age, its shape, its expansion rate, its composition, its density. Different versions of inflation theory were telling slightly different stories about precisely how inflation happened and making predictions about what pattern of temperature variations we should find in the CMBR if we compare its temperature in diff
erent directions.28 WMAP data were expected to give scientists ways to test these different scenarios.29

  By February 2003, WMAP was brilliantly living up to its promise. Its data had allowed scientists to nail down precisely after many decades of controversy the age of the universe – 13.7 billion years – as well as the time in the universe’s history when patterns in the CMBR froze into place – 380,000 years after the Big Bang. WMAP results showed that space is flat and supported those who were insisting that most of the energy in the universe today is ‘dark energy’. WMAP measurements showed that the variations in temperature and density in the CMBR, observed across the sky – the variations that seeded the formation of galaxies – all had roughly the same amplitude regardless of their length, that all forms of energy had the same variation, and that the distribution of variations was random – just as predicted by the standard Big Bang inflationary model.30

  Nevertheless, important issues remained unresolved by that first February 2003 release of WMAP data. One key piece of evidence was missing: inflation theory makes predictions about what the patterns and characteristics of gravitational waves originating from the Big Bang should be like as they show up in the CMBR. WMAP had not yet found these gravitational wave footprints. Nor was it determined whether the dark energy was due to ‘vacuum energy’ – the cosmological constant – or ‘quintessence’. Interestingly, the observations that were fitting well with inflationary cosmology also fit a cyclical model where the universe expands from a big bang, eventually contracts again to a big crunch, and then reemerges in another big bang, in a cycle that keeps repeating itself – models which Neil Turok and Roger Penrose were favouring.31