Stephen Hawking, His Life and Work

by Kitty Ferguson

  Hawking would have none of that. He insisted that Hawking radiation could not serve as the escape vehicle back into the outside universe for information trapped in a black hole. If you tossed this book into a black hole, such reconstruction would be impossible. Hawking radiation is not the ‘ashes’ or the scrambled or chopped-up remains of what fell into the black hole. Recall that the ‘escaping’ member of the particle pair in Hawking radiation (the way it was explained in Chapter 6) doesn’t come from inside the black hole. It comes from just outside. The escaping particle carries with it no news whatsoever about whether the black hole is full of astronauts, unmatched socks, or Winnie the Pooh’s grandmother’s honeypot. It doesn’t know. Hawking radiation has no direct connection to whatever went into forming the black hole in the first place or what has fallen in. There are some physicists who held out hope that such information is somehow encoded in the Hawking radiation, but Hawking was not one of them. He thought that information does not escape and is completely lost when the black hole evaporates. You can’t restore it, not even in principle. Hawking christened the dilemma he had raised ‘the information paradox’.

  The problem looked likely to extend beyond black holes. In an interview on the BBC programme Horizon in 2005, Leonard Susskind, who was there in Erhard’s attic, remembers his shock at Hawking’s arguments and the realization that if Hawking was right – if information really is irretrievably lost in black holes – then that is not the only place it is going to be lost. Pieces of the universe must be missing. We can forget about predictability. Forget the dependability of cause and effect. Nothing we think we know in science can be trusted.23

  Hawking perceived that Susskind was probably the only person present who fully realized the implications of his arguments. ‘Leonard Susskind got very upset,’ he remembers. Scientists, and the rest of us, rely on the link between past and future, between cause and effect. That link is lost if information is lost. ‘We wouldn’t be able to predict the future. We can’t be sure of our past history either. The history books and our memories could be just illusions. It is the past that tells us who we are. Without it we lose our identity.’24 Kip Thorne pointed out that there was already speculation about the existence of black holes that are smaller than atoms that could be anywhere and everywhere, nibbling away bits of information.25

  The problem may not seem so disastrous to you or me. Granted, when anything falls into a black hole it carries information with it. The colour and size of a few unmatched socks? Perhaps the dimensions of the unfortunate astronaut? Not information that you or I find interesting or essential. However, this information is necessary, even for a more limited kind of prediction allowed by quantum mechanics.

  Hawking traces the discussion about being able to predict the future or the past to Pierre-Simon de Laplace, a mathematician who lived in the late eighteenth and early nineteenth centuries. Laplace’s famous proposal was that an omniscient being with unlimited powers of calculation, knowing the laws of the universe and the state of everything in it (that is, the positions and momenta of all the particles in the universe) at any given time, would be able to calculate the state of everything in the universe at any other time in the past or future. Though no one denied the stupefying practical difficulties of acquiring such knowledge and doing all the calculations, Laplace-style scientific determinism remained dogma through the nineteenth and early twentieth centuries. When I heard Hawking lecturing on the subject in Cambridge, he quoted Laplace in French and told us that since we were a Cambridge audience he would not insult our intelligence by offering a translation. One nevertheless soon slyly appeared on his slide screen.

  Laplace’s omniscient being had to have knowledge of the positions and momenta of all particles in the universe. You can’t leave out the particles in the toe of the sock. When the sock falls into the black hole, that information is lost from our region of the universe. If black holes exist for ever, well and good, then the lost information isn’t entirely lost. It is inaccessible, but still there. If black holes evaporate and disappear from the universe … trouble.

  Hawking and his colleagues in the attic knew that the ‘information paradox’ was not the first challenge to Laplace-style scientific determinism. In the mid-1920s when Werner Heisenberg published his ‘uncertainty principle’, it seemed all bets must be off … but only for a while. Arguments having to do with interpretations and implications of the uncertainty principle would go on for years and involve the finest minds in physics, but by the time Hawking studied black holes there was fairly general agreement that even Laplace’s omniscient being could not possibly know precisely a particle’s position and momentum at the same time.

  The uncertainty principle did not, however, ultimately succeed in undermining faith in the dogma of scientific determinism. It soon became clear that laws governing the quantum level of the universe are deterministic in a different way. You can predict what is called the ‘quantum state’, from which both positions and momenta can be calculated with a certain degree of accuracy. Laplace’s omniscient being, knowing the quantum state of the universe at any one moment in time, and the laws of science, could predict the quantum state of the universe at any other time, past or future.26fn1

  Now, Hawking had found a new problem, and it seemed to be a serious one. His earlier work had shown that black holes don’t last for ever. As Hawking radiation continues, the black hole gets smaller until eventually there is no black hole left. He was insisting that the information about whatever went into forming the black hole in the first place, and whatever fell in, is then irretrievably lost.

  Still … why all the angst about its loss? Couldn’t the universe make do with a little less of this rather arcane information?

  No, it seems it cannot. Not and still be the universe we think we know. The law of information conservation is one of the fundamental principles of physics. Information is never lost. It can be mixed and scrambled and transformed in ways that make it unrecognizable as the information you started with, but not ever lost. If this law is wrong, then the universe is in effect thumbing its nose at Laplace and all those who have been assuming that he was correct.

  Although Hawking’s colleagues in Erhard’s attic, in Susskind’s words, stood there in ‘stunned confusion’, most of them and other theoretical physicists would go right on believing that the present has evolved from the past and will go on evolving into the future, that cause and effect continue to operate, that it is meaningful to trace events into the past and into the future, that examining the debris from a collision in a particle accelerator can tell you what happened in the collision – as though Hawking had not hung a Sword of Damocles over all these assumptions. But Hawking stuck to his guns and the information paradox didn’t go away. Information, he continued to insist, is truly lost when black holes evaporate, and this means we can predict even less than we thought on the basis of quantum theory.

  Was there a fly in the ointment of quantum mechanics? Would the foundations of this well-established, dependable field have to shift? Hawking thought they would. As Kip Thorne has commented, Hawking is stubborn about insisting on his views of how nature works, and he likes to challenge others to show he’s wrong.27 Hawking had laid down the gauntlet. Susskind recalls that in Erhard’s attic ‘Stephen had a “Stephen” look on his face, a little smile that says, “You may not believe it but I’m right, no mistake about it.” We were absolutely sure Stephen was wrong but we couldn’t see why.’28

  fn1 Hawking’s ideas were not the only serious threat to determinism in the 1980s. An equally significant one came from chaos theory. Ilya Prigogine and Isobel Stengers presented this challenge in their 1985 book Order Out of Chaos, writing, ‘When faced with these unstable systems Laplace’s [omniscient being] is just as powerless as we.’ (Ilya Prigogine and Isobel Stengers, Order Out of Chaos, London: Heinemann, 1985.)

  9

  ‘The odds against a universe that has produced life like ours are immense’

  FOR HA
WKING, 1981 was a landmark year not only for his calling attention to the information paradox. He was turning his attention in a new way to the question of how the universe began and how it would end.

  At a conference at the Vatican in September, Pope John Paul II, addressing Hawking and other scientists, said that it was probably futile for humans to try to inquire into the moment of Creation: this knowledge ‘comes from the revelation of God.’fn1 Given the state of knowledge and theory at the time, which, thanks largely to Hawking, had the universe beginning in a singularity, no one could gainsay the Pope’s words. Most of Hawking’s colleagues probably would have reluctantly agreed with the first part of the Pope’s statement, while doubting God was ever going to lay down his cards. Hawking himself had recently told author John Boslough: ‘The odds against a universe like ours emerging out of something like the Big Bang are enormous. I think there are clearly religious implications whenever you start to discuss the origins of the universe.’1

  What the Pope and those who briefed him on science had failed to take into consideration was Hawking’s propensity for undermining his own previous discoveries. Hawking’s title for his presentation at this Vatican conference, ‘The Boundary Conditions of the Universe’, gave no forewarning that he would propose the possibility that there was no ‘beginning’ – ‘no boundary’ to the universe – leaving no necessary role or place for a creator. Had the Pope and his science advisors known, they might have been sufficiently wise and well informed to decide that the Pope should draw a parallel between Hawking’s ideas and the Judeo-Christian concept (from the Jewish philosopher Philo of Alexandria and the Christian philosopher St Augustine) of a God existing outside time – the ‘I Am’ of the Bible – for whom beginnings, endings or anything like our chronological time do not exist. That way of looking at time was to be a major part of Hawking’s ‘no-boundary proposal’. It was not new to philosophy or religion, but it was to physics.

  The work Hawking had done in the late 1960s, in his Ph.D. dissertation and afterwards, seemed to prove that the universe had begun as a singularity, a point of infinite density and infinite spacetime curvature. At that singularity all our laws of physics would break down, and it would be just as useless as the Pope thought to try to investigate the moment of creation. Any sort of universe could come out of a singularity. There would certainly be no way to predict that it would be a universe like ours. It was in this context that Hawking had said that discussing the origins of the universe inevitably had religious implications.2

  The ‘Anthropic Principle’

  Most of us have become convinced that the sun, the planets and everything else don’t revolve around the Earth. Science also tells us that the universe probably looks the same from any vantage point. Earth, with us as its favoured passengers, isn’t the centre of everything.

  Nevertheless, the more we discover on both the microscopic and the cosmic levels, the more we’re struck with the impression that some careful planning, some incredible fine-tuning, had to occur to make the universe a place where it’s possible for us to exist. In the early 1980s Hawking was saying, ‘If one considers the possible constants and laws that could have emerged, the odds against a universe that has produced life like ours are immense.’3

  There are many examples of this mysterious fine-tuning: Hawking points out that if the electric charge of the electron had been slightly different, stars either wouldn’t burn to give us light or wouldn’t have exploded in supernovae to fling back into space the raw material for new stars like our sun or planets like Earth. If gravity were less powerful than it is, matter couldn’t have congealed into stars and galaxies, nor could galaxies and solar systems have formed had gravity not been at the same time the weakest of the four forces. No theory we have at present can predict the strength of gravity or the electric charge of the electron. These are arbitrary elements, discoverable only by observation, but they seem minutely adjusted to make possible the development of life as we know it.

  Shall we jump to the conclusion that Someone or Something had us in mind when things were set up? Is the universe, as astronomer Fred Hoyle phrased it, ‘a put up job’, a great conspiracy to make intelligent life possible? Or are we missing other possible explanations?

  ‘We see the universe the way it is because we exist.’ ‘Things are as they are because we are.’ ‘If it had been different we wouldn’t be here to notice it.’ All of these are ways of stating something called the ‘anthropic principle’.

  Hawking explains the anthropic principle as follows: picture a lot of different, separate universes, or different regions of the same universe. The conditions in most of these universes, or in these regions of the same universe, will not allow the development of intelligent life. However, in a very few of them, the conditions will be just right for stars and galaxies and solar systems to form and for intelligent beings to develop and study the universe and ask the question, why is the universe as we observe it? According to the anthropic principle, the only answer to their question may be that, if it were otherwise, we wouldn’t be around to ask the question.

  Does the anthropic principle really explain anything? Some scientists say that it doesn’t, that all it shows is how what seems like fine-tuning might instead be a random bit of good luck. It’s like the old story about giving enough monkeys typewriters so that by the laws of chance one of them would type the first five lines of Shakespeare’s Hamlet. Even if our sort of universe is highly unlikely, with enough universes around, one of them might very well be like ours.

  Does the anthropic principle rule out God? No. However, it does show that the universe could appear tailor-made for our good without there being a God.

  John Wheeler thought we might carry the anthropic principle a step further. Perhaps, he suggested, there can be no physical laws at all unless there are observers to work them out. In that case there won’t be all those alternate universes, because any universe that didn’t allow for the development of observers simply wouldn’t exist.

  If this is so, does it mean that if we become extinct, so will the universe? Will the stage crew come out and dismantle the set as the last member of the audience leaves the theatre? In fact, if we’re not around to remember that it existed, will it ever have existed? Does our having observed a brief slice of its existence give it the power to go on existing after we’re gone?

  A few physicists like to make a connection between an ‘observer-dependent’ universe and some of the ideas in Eastern mysticism: Hinduism, Buddhism and Taoism. They get no encouragement from Hawking, who says, ‘The universe of Eastern mysticism is an illusion. A physicist who attempts to link it with his own work has abandoned physics.’4

  Although he didn’t invent the idea, the anthropic principle is often associated with Hawking, along with other colleagues and particularly Brandon Carter, Hawking’s office-mate in the mid-1960s, who also worked with him trying to refute the ideas of Jacob Bekenstein about black holes and entropy in 1972. Hawking and most other physicists hoped that we wouldn’t have to turn to the anthropic principle as the only explanation for why we have the sort of universe we have and not another. ‘Was it all just a lucky chance?’ Hawking asks. ‘That would seem a counsel of despair, a negation of all our hopes of understanding the underlying order of the universe.’5 Those words would turn out to be prophetic.

  Meanwhile, the Pope had said it couldn’t be done. The anthropic principle said it was just a roll of the dice (one roll among an almost infinite number) that fell in our favour. Some were arguing that God had the power to change His mind and adjust things, including the laws of the universe, whenever He pleased. But Hawking didn’t think an all-powerful God would have any need to change his mind. He believed there are laws that held at the time that we call the beginning, or the Creation – that made our universe the way it is and not some other way – and that we are capable of understanding them. He wanted to know what those laws are. That meant that somehow he had to cut the ultimate Gordian knot: the si
ngularity.

  It would be a couple of years before Hawking would fully work out how to perform that heroic feat. Meanwhile, in October 1981, not long after the visit to the Vatican, he was also busy looking at the beginning of the universe through the eyes of a new theory, known as ‘inflation theory’.

  Big Bang Challenge

  Back in the 1960s, everything had seemed to be falling into place for those who favoured the Big Bang theory. In 1964–5 there was a particularly exciting step forward in the quest to understand the history of the universe and decide between the two competing models, the Big Bang and the Steady State. The story has become a classic. It was one of those relatively rare occasions in science when data turns up where no one is looking for it. At Bell Laboratories, in New Jersey, there was a horn antenna designed for use with the Echo I and Telstar communications satellites. The amount of background noise picked up by the antenna hampered the study of signals from space. Scientists working with the antenna had to make adjustments and resign themselves to studying signals that were stronger than the noise. It was an annoyance that most found it possible to ignore, but two young scientists, Arno Penzias and Robert Wilson, took the noise more seriously.

  Penzias and Wilson noticed that the level remained the same no matter in which direction they pointed the antenna. That wouldn’t be the case if the noise were a result of Earth’s atmosphere, since an antenna pointed towards the horizon faces more of the atmosphere than one pointed straight up. The noise had to be coming either from beyond the atmosphere or from the antenna itself. Penzias and Wilson thought pigeons nesting in the antenna might be the source, but evicting the pigeons and clearing away their droppings brought no improvement.