Stephen Hawking (17 page)

Dicke soon realized that Penzias and Wilson had, in fact, detected the background radiation left over from the Big Bang. The Princeton detector, completed hurriedly a little later, confirmed the discovery, and soon radio astronomers around the world were getting in on the act. We now know that the Universe is indeed filled with a weak hiss of microwave background radiation, with wavelengths of around 1 millimeter, corresponding to a temperature of 2.73 K.

It was this discovery that opened the eyes of cosmologists to the reality of the Big Bang model: not just a model, after all, but also an accurate description of the real Universe we live in. First, the existence of the background radiation showed that there really had been a Big Bang; then, by using the precise
measurement of the temperature of that radiation today, it was possible to work backward to the Big Bang to calculate the exact temperature of the fireball itself. We got slightly ahead of our story in
Chapter 5
, when we described the first few minutes of the life of the Universe—the accuracy of that description, dating from the mid-1970s, depends in part on our present-day knowledge of the precise temperature of the background radiation. But there is something else significant about that description of the early stages of the Universe.
The First Three Minutes
was not written by a specialist in cosmology, or even an astronomer, but by a mainstream physicist, Nobel Prize winner Steven Weinberg.

Before 1965, cosmology was a quiet backwater of science, almost a little ghetto where a few mathematicians could play with their models without annoying anybody else. Today, a half century later, the study of the Big Bang is at the center of mainstream physics, and Big Bang cosmology is seen as offering the key to understanding the fundamental laws and forces by which the physical world operates. It is because of the measurements of the background radiation that we can be so confident about how nuclei were synthesized in the Big Bang. And it was the first calculations of this kind made after the discovery of the background radiation that convinced many physicists (not just cosmologists) that hot Big Bang cosmology had to be taken seriously as a description of the Universe.

These calculations were not something hurriedly cooked up in the light of the discovery of the background radiation; they
represented the culmination of more than ten years' work. In the 1950s, inspired by Fred Hoyle's lead, a team of British and American researchers had worked out how all the elements more complex than helium are synthesized inside stars. This was an astonishing
tour de force
. In essence, the process consists of sticking helium-4 nuclei together to build up more complex nuclei. Some of the complex nuclei then either spit out or absorb the odd proton, making nuclei of other elements.

As we mentioned in
Chapter 5
, though, there is a bottleneck for this process at its earliest stage. There is no stable nucleus that can be made by sticking two helium-4 nuclei together, and that is why nucleosynthesis stopped with helium in the Big Bang. Hoyle found a way around this bottleneck, via extremely rare collisions of three helium-4 nuclei almost simultaneously. This makes it possible to create a nucleus of carbon-12, but only if the energies (speeds) of the helium-4 nuclei are just right. The energies are just right inside stars, thanks to an unusual quantum effect known as a resonance. Nobody realized this until Hoyle explained how the crucial step in the chain must take place. He predicted the existence of the crucial resonance, which was then found during experiments here on Earth. Together with his colleagues, Hoyle went on to explain how
everything
is built up from hydrogen and helium inside stars—including the atoms in your body and in this book.

In one of the strangest decisions ever made by a Nobel committee, one of Hoyle's colleagues, Willy Fowler, later received a share of the 1983 Nobel Prize for Physics for this work. Fowler is a fine physicist in his own right and was a key member of the team. But he is the first to acknowledge that
Hoyle made the key breakthrough on carbon-12 production and was the inspiration for the team's efforts. Unfortunately, later in his career Hoyle espoused some decidedly unconventional ideas about the possibility that outbreaks of disease on Earth might be caused by viruses from comets. It seems that the Nobel committee, in its wisdom (?), decided not to give him a share of the physics prize with Fowler for fear of seeming to lend credence to what they regarded as his more cranky work. At least the British establishment, for once belying its stuffy image, acknowledged Hoyle's true worth with a knighthood. All that, however, lay far in the future in 1967, when Fowler, Hoyle, and their colleague Robert Wagoner put the icing on the nucleosynthesis cake.

The one problem with the story of stellar nucleosynthesis as developed in the 1950s was that it could not explain where helium came from. Starting out with stars in which 75 percent of the material was hydrogen and 25 percent helium, the theory could explain beautifully the presence of every other element and could even explain why some elements are more common than others and how much more common. But it all starts with the triple-helium/carbon-12 resonance; and without that initial 25 percent of helium, stars would not be able to cook up the rest of the elements. It was Wagoner, Fowler, and Hoyle who together showed that the kind of Big Bang that would leave a background radiation with a temperature of 2.73 K today would also produce a mixture of 25 percent helium and 75 percent hydrogen at the end of the first four minutes.

Their findings were unveiled at a meeting in Cambridge in 1967. One of us (J.G.) was present, as a very junior research
student, somewhat in awe of the occasion. He clearly recalls the deep questions being asked at the meeting by another member of the audience, a slightly older but still junior researcher, who seemed to have a slight speech impediment but whose words were listened to closely by the more eminent researchers on the platform. Stephen Hawking was already known to be someone worth listening to, even at this early stage of his career. And the reason for his keen interest in Big Bang cosmology soon became clear, when the results of the investigation he was carrying out with Roger Penrose were published.

Hawking had begun puzzling over the singularity at the beginning of time in the early 1960s but had soon been deflected, as we have seen, by the diagnosis of his illness, temporarily giving up his work. But by 1965, things were looking up. He had decided that he wasn't going to die quite so quickly as the doctors had predicted, after all; he had met and married Jane; and he was back at work with a vengeance. He was one of the few people, at that time, to take seriously the more extreme predictions of the general theory of relativity. Two years after the identification of the first quasar (but before its energy source was explained), and two years before the discovery of pulsars, only a handful of people believed in the possibility that black holes might exist or that the Universe really had been born out of a singularity.

One of the few other people who did take the notion of black holes seriously was a young mathematician, Roger Penrose,
working at Birkbeck College in London. It was Penrose who showed that every black hole must contain a singularity and that there is no way for material particles to slide past each other in the middle of the hole. Not just matter, but spacetime itself simply disappears at the singularity. At such a point the laws of physics break down, and it is impossible to predict what will happen next.

But as we have seen, this need not be too worrying, provided such bizarre objects are always safely hidden behind the horizon of a black hole. In this spirit, Penrose proposed a “cosmic censorship” hypothesis, suggesting that all singularities must be hidden in this way and that “nature abhors a naked singularity.” In other words, observers outside the horizon of the black hole are always protected from any consequences of the breakdown of the laws of physics at the singularity.

Hawking was intrigued by Penrose's work on singularities but saw that there was no way nature's abhorrence of a singularity could shield us from the singularity at the beginning of time—
if
it existed. In 1965, the two of them joined forces to investigate this puzzle.

Previously, researchers had expected that if you tried to wind back the equations describing the expanding Universe, things would get more and more complicated as you approached the Big Bang. Particles would collide and bounce off one another, producing a chaotic and confusing fireball. To many people this looked like the ideal way to make a model universe bounce at high densities, without encountering a singularity. But over the next few years, Hawking and Penrose developed a new mathematical technique for analyzing the
way that points in spacetime are related to one another. This did away with the confusion of the messy interactions between material particles and highlighted the underlying significance of the expansion (or collapse) of space itself.

The end result of this study was their proof that there must have been a singularity at the beginning of time, if the general theory of relativity is the correct description of the Universe. There is no way for particles in a contracting universe to slide past one another and avoid meeting in a singularity in the fireball, any more than it is possible to avoid the singularity inside a black hole. After all, when space shrinks to zero volume, there is literally no room left for particles to slip past one another. In other words, the expansion of the Universe away from the singularity in the beginning really is the exact opposite of the collapse of matter (and spacetime) into a singularity inside a black hole. The cosmic censor has slipped up, and there is at least one naked singularity in the Universe that we are exposed to, even if it is separated from us by 14 billion years of time.

While Hawking and Penrose were working all this out, the discovery of the background radiation was announced; pulsars were discovered; and Wagoner, Fowler, and Hoyle were explaining how helium had been made in the Big Bang. By the time the Hawking-Penrose theorems were published, John Wheeler had given astronomers the term “black hole,” and newspaper stories were being written about the phenomenon. What had started out as an esoteric (but erudite) piece of mathematical research had evolved by the end of the 1960s into a major contribution to one of the hottest topics in science at the time.

And yet this was Hawking's
first
real piece of research, stemming from his Ph.D. work—the journeyman piece for his scientific apprenticeship. What on earth would he come up with next? And what did it mean to say that there had been a definite beginning to time in the Big Bang? There seemed very little prospect, however, that the young researcher would come up with anything of comparable importance, and the deterioration in his physical condition seemed to rule out a long career.

8

THE BREAKTHROUGH YEARS

T
he 1960s ended with Hawking being forced to make a concession to his physical condition. After a great deal of persuasion from Jane and a number of close friends, he decided to abandon his crutches and take to a wheelchair. To those who had watched his gradual physical decline, this was seen as a major step and viewed with sadness. Hawking, however, refused to let it get him down. Although the acceptance of a wheelchair was a physical acknowledgment of his
affliction, at the same time he gave it not the slightest emotional or mental endorsement. In every other way, life went on as usual. And he could not deny that it did enable him to get around more easily. Never giving in to the symptoms of ALS more than he is physically compelled to is all part of the Stephen Hawking approach to life. As Jane said, “Stephen doesn't make any concessions to his illness, and I don't make any concessions to him.”
¹
That seems to be the way he has survived against all the odds for so many years and also how Jane managed to remain sane living with him.

Earlier, in 1968, Hawking had been invited to become a staff member at the Institute of Theoretical Astronomy housed in a modern building on the outskirts of Cambridge. Originally Fred Hoyle had headed it, but he resigned his post in 1972 after a final blazing row with the Cambridge establishment. This time the dispute was over the administration of British science in general and Cambridge science in particular. When Hoyle left, the institute was merged with the Cambridge Observatories and came under the control of Professor Donald Lynden-Bell. Under his leadership, “Theoretical” was dropped from the name, and it has been the Institute of Astronomy ever since. In the same year, a young radio astronomer, Simon Mitton, was appointed administrative head of the institute. He subsequently worked closely with Hawking during the years he spent there.