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07/09/2014

„Stephen Hawking. A Life in Science” – Fragmente 3


Din cartea: „Stephen Hawking. A Life in Science” – Michael White and John Gribbin. John Henry Press.2002.

Since his undergraduate days Hawking has been a keen follower of the philosopher Karl Popper. The main thrust of Popper’s philosophy of science is that the traditional approach to the subject, “the scientific method” as originally espoused by the likes of Newton and Galileo, is in fact inadequate.

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Popper stands this process on its head and suggests the following approach. Take a problem. Propose a solution or a theory to explain what is happening. Work out what testable propositions you can deduce from your theory. Carry out tests or experiments on these deductions in order not to prove them but to refute them. The refutations, combined with the original theory, will yield a better one.

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In Popper’s system, the scientist tries to disprove the theory in an attempt to find a better one.

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The science writer Dennis Overbye once asked him how his mind worked. In reply, Hawking said: Sometimes I make a conjecture and then try to prove it. Many times, in trying to prove it, I find a counter-example, then I have to change my conjecture. Sometimes it is something that other people have made attempts on. I find that many papers are obscure and I simply don’t understand them. So, I have to try to translate them into my own way of thinking. Many times I have an idea and start working on a paper and then I will realize halfway through that there’s a lot more to it. I work very much on intuition, thinking that, well, a certain idea ought to be right. Then I try to prove it. Sometimes I find I’m wrong. Sometimes I find that the original idea was wrong, but that leads to new ideas. I find it a great help to discuss my ideas with other people. Even if they don’t contribute anything, just having to explain it to someone else helps me sort it out for myself.

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– Page 133: The first pulsars were discovered by a research student, Jocelyn Bell, while testing a new radio telescope. The astonishing thing about these radio sources is that they flick on and off several times

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– Page 134: This is so much like an artificial signal, a kind of cosmic metronome, that, only half-jokingly, the first pulsars discovered were labeled “LGM 1” and “LGM 2”—the initials “LGM” stood for “Little Green Man.”

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– Page 137: 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.

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– Page 138: 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 quarter of a century later, the study of the Big Bang is at the center of mainstream physics,

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Stephen Hawking

Stephen Hawking

– Page 141: 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.

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– Page 142: 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 space-time itself simply disappears at the  singularity.

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– Page 142: 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.

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– Page 143: 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 space-time) 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 15 billion years of time.

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– Page 144: 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.

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– Page 144: The 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.

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– Page 153: Meanwhile Hawking was finding the mathematics of the work increasingly difficult to deal with. The equations for interpreting the physics of black holes are amazingly complex,

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– Page 154: Hawking is not unique in having this talent. In 1983 he dazzled students at a Caltech (California Institute of Technology) seminar when he dictated a forty-term version of an important equation from memory. As his assistant finished writing the last term, his colleague, Nobel laureate Murray Gell-Mann, who happened to be sitting in on the talk, stood up and declared that Hawking had omitted a term. Gell-Mann was also working from memory.

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– Page 159: Working on the equations in his head was difficult enough, but after months of intense work Hawking kept coming up with completely nonsensical results. According to the equations, black holes appeared to be emitting radiation. He, and everyone else at the time, believed this to be impossible. He was still convinced that he was really on to something but took the conscious decision not to discuss the problem with anyone until he had settled the matter one way or another.

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– Page 159: Finally, in January 1974 he took the plunge and confided in Dennis Sciama, who was organizing a conference at the time. To Hawking’s surprise, Sciama was very excited by the idea and, with Hawking’s permission, set about spreading the word.

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– Page 160: Going against all current ideas about black holes, by the power of mathematical reasoning, Hawking had been forced to the unarguable conclusion that not only did tiny black holes emit radiation, but under certain conditions they could actually explode. By late January one of his colleagues and friends from postgraduate days, Martin Rees, was convinced that Hawking had made a great discovery.

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– Page 160: He had a hunch, now supported by a number of his respected colleagues and peers, that he was on to something very big. At last he was wheeled to the front of the lecture theater, and his illustrations were projected on to the back wall while he delivered his talk in the almost unintelligible tones to which his colleagues had become accustomed. His final line was delivered. A stunned hush fell over the entire room. You could hear a pin drop as the audience of scientists tried to absorb the astonishing news. Then the backlash began.

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– Page 161: A month after the meeting outside Oxford, Hawking published in Nature his own paper describing the newly discovered phenomena. Within weeks, physicists all over the world were discussing his work, and it became the hot topic of conversation in every physics laboratory from Sydney to South Carolina. Some physicists went so far as to say that the new findings constituted the most significant development in theoretical physics for years. Dennis Sciama described Hawking’s paper as “one of the most beautiful in the history of physics.” The radiation that he had discovered could be emitted by certain black holes was from then on known as Hawking Radiation.

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– Page 164: Hawking’s achievements had been noticed by the scientific establishment. In March 1974, within weeks of the announcement of Hawking Radiation, he received one of the greatest honors in any scientist’s career. At the tender age of thirty-two, he was invited to become a fellow of the Royal Society, one of the youngest scientists in the society’s long history to be given such an honor.

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– Page 169: Hawking, whose career has been founded on the study of black holes, made a bet with Kip Thorne of Caltech, that Cygnus X-1 does not contain a black hole. The form of the bet was that, if it were ever proved that the source is a black hole, Hawking would give Thorne a year’s subscription to Penthouse; but if it were ever proved that Cygnus X-1 is not a black hole, Thorne would give Hawking a four-year subscription to the satirical magazine Private Eye. In June 1990 Hawking decided that the evidence was now overwhelming, and paid up—although, being Hawking, he did so in a typically mischievous fashion, enlisting the aid of a colleague to break into Thorne’s office at Caltech. They extracted the document recording the bet and officially “signed” his admission of defeat with a thumbprint before returning the paper to the files for Thorne to discover later. Over the following months, Thorne duly received the promised issues of Penthouse.

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– Page 171: This basic truth about black holes was established in 1967, by the Canadian-born researcher Werner Israel. When he first developed the equations, Israel himself thought that because black holes had to be spherical, what the equations were telling him was that only a perfectly spherical object could collapse to form a black hole. But Roger Penrose and John Wheeler found that an object collapsing to form a black hole would radiate away energy in the form of gravitational waves—ripples in the fabric of space-time itself. The more irregular the shape of the object, the more rapidly it would radiate energy, and the effect of this radiation would be to smooth out the irregularities.

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– Page 171: So it was established by the early 1970s that a black hole could rotate, but it could not pulsate (Hawking played a small part in this work, too). The size and shape of a black hole depend only on its mass and the speed at which it rotates; the horizon, all that we can see from the outside Universe, carries no identifying features that can tell us what the hole was made of. Physicists call this lack of identifying features the “no hair” theorem. A black hole has no “hair” in the sense that it has no identifying features, and because all we can ever know about it is its mass and its rate of rotation, this makes the mathematical study of black holes much simpler than scientists had feared it would be.

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– Page 174: So Hawking’s dramatic realization, coming with such force that evening in November 1970, was to lead to the idea that the law which says that the area of a black hole can only stay the same or increase is equivalent to the law which says that the entropy of a closed system can only stay the same or increase. But even Hawking didn’t make that connection at first.

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– Page 175: But when a student at Princeton University, Jacob Bekenstein, suggested that the size of the horizon around the singularity might literally be a measure of the entropy of a black hole, he started an avalanche of  investigation which led Hawking to the discovery that black holes are not necessarily black after all—they explode.

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– Page 175: Hawking was annoyed by Bekenstein’s suggestion. Even a research student ought to have realized that there is a direct connection between entropy and temperature, so that if the area of a black hole were indeed a measure of entropy it would also be a measure of temperature. And if a black hole had a temperature, then heat would flow out of it, into the cold (–270°C) of the Universe. It would radiate energy, contradicting the most basic fact known about black holes,

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– Page 178: A black hole weighing about a billion tons, for example (the mass of a mountain here on Earth), would have a radius roughly the same as that of a proton. Less massive miniholes would be correspondingly smaller. And if you are dealing with objects as small as that, physicists knew, you have to use the quantum description of reality in order to understand what is going on.

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– Page 183: A hole smaller than a proton will not eat up much material from its surroundings, even if it happens to be inside a planet. To a hole that small, even solid matter is mostly empty space!

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– Page 186: In the second half of the 1970s he moved on to investigate the origin of the Universe itself, going back to the beginning of time.

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– Page 186: The 1970s were the years when he established himself as a world-class physicist, and they marked the beginning of two decades of startling success in the disparate worlds of arcane research and popular writing.

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– Page 189: …another physicist who was to play a significant role in collaborations and become one of Hawking’s lifelong friends—Don Page. Page, who was born in Alaska and graduated from a small college in Missouri, was working on his Ph.D. at the time of Hawking’s visit. The two of them immediately hit it off, and before Hawking’s year at Caltech was over they had written a black hole paper together.

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– Page 199: But she had a growing feeling that she was being ignored as a human being, as an intelligent woman who was academically successful in her own right. She was beginning to feel like nothing more than a sidekick to the great Stephen Hawking. As she has put it: Cambridge is a jolly difficult place to live if your only identity is as the mother of small children. The pressure is on you to make your own way academically.

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– Page 201: Jane was raised as a Christian and has very strong religious views. To one interviewer she has said: Without my faith in God, I wouldn’t have been able to live in this situation. I wouldn’t have been able to marry Stephen in the first place, because I wouldn’t have had the optimism to carry me through, and I wouldn’t be able to carry on with it.16 Hawking, for his part, is not an atheist; he simply finds the idea of faith something he cannot absorb into his view of the Universe. His outlook is not unlike that of Einstein, and he has been quoted as saying: We are such insignificant creatures on a minor planet of a very average star in the outer suburbs of one of a hundred thousand million galaxies. So it is difficult to believe in a God that would care about us or even notice our existence.17

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– Page 202: Equally, of course, there are a number of practicing scientists who have very strong Christian convictions, and some have claimed that Hawking is simply not qualified to make statements about religion because he knows nothing about it.

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– Page 203: His work deals with the origins and early life of the Universe. Could a subject be any more religious? He once stated: It is difficult to discuss the beginning of the Universe without mentioning the concept of God. My work on the origin of the Universe is on the borderline between science and religion, but I try to stay on the scientific side of the border. It is quite possible that God acts in ways that cannot be described by scientific laws. But in that case one would just have to go by personal belief.19

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– Page 203: When asked if there is any conflict between religion and science, Hawking tends to fall back on the same argument about personal belief and sees no real conflict. “If one took that attitude,” he replied, when asked whether he believed that science and religion were competing philosophies, “then Newton would not have discovered the law of gravity.”20 And what, in the light of Stephen’s and Jane’s dilemma, do we make of the famous last paragraph of A Brief History of Time?

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– Page 203: When asked if there is any conflict between religion and science, Hawking tends to fall back on the same argument about personal belief and sees no real conflict. “If one took that attitude,” he replied, when asked whether he believed that science and religion were competing philosophies, “then Newton would not have discovered the law of gravity.”20 And what, in the light of Stephen’s and Jane’s dilemma, do we make of the famous last paragraph of A Brief History of Time? However, if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the Universe exist. If we find the answer to that, it would be the ultimate triumph of human reason—for then we would know the mind of God.21

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– Page 211: By March 1977, however, the university had decided to offer him a specially created chair of gravitational physics, which would be his for as long as he remained in Cambridge; the same year he was awarded the status of professorial fellow at Caius, a separate professorship bestowed by the college authorities.  

Stephen Hawking

Stephen Hawking

 

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– Page 217: The size of these uncertainties is determined by Planck’s constant, which gives us basic “quanta” known as the Planck length and the Planck time. Both are very small. The Planck length, for example, is 10–35 of a meter, far smaller than the nucleus of an atom. According to the quantum rules, not only is it impossible in principle ever to measure any length more accurately than this (we should be so lucky!), but also there is no meaning to the concept of a length shorter than the Planck length.

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– Page 217: So if an evaporating black hole were to shrink to the point where it was just one Planck length in diameter, it could not shrink any more. If it lost more energy, it could only disappear entirely. The quantum of time is, similarly, the smallest interval of time that has any meaning. This Planck time is a mere 10–43 of a second, and there is no such thing as a shorter interval of time.

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– Page 219: What Hawking has tried to do is to develop a sum over histories describing the entire evolution of the Universe. Now this is, of course, impossible. Just one history of this kind would involve working out the trajectory of every single particle through spacetime from the beginning of the Universe to the end, and there would be a huge number of such histories involved in the “integration.”

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– Page 226: In 1978 Hawking was awarded one the most prestigious prizes in physics, the Albert Einstein Award given by the Lewis and Rose Strauss Memorial Fund, which announced the winner at a gala event in Washington. The citation claimed that Hawking’s work could lead to a unified field theory, “much sought after by scientists,”1 as one Cambridge newspaper put it. The Albert Einstein Award is considered to be the prestigious equivalent of a Nobel Prize and was undoubtedly the most important award Hawking had received up until that time.

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– Page 226: However, there are two reasons why Hawking is unlikely ever to receive a Nobel Prize. First, a cursory glance at the list of winners since the first prizes in 1901 shows very few astronomers. The reason for this, according to one story, is that the chemist Alfred Nobel, who created the awards, decreed that astronomers should be ineligible. Rumor has it that their exclusion was because his wife had an affair with an astronomer, and he subsequently felt only hatred for the whole profession. Despite this, Martin Ryle and Antony Hewish shared the 1974 Nobel Prize for Physics for their work in radio astrophysics and Subrahmanyan Chandrasekhar won it in 1983 for his theoretical studies on the origin and evolution of stars. These were awarded a good seventy years after the founder’s death, so perhaps the academy now views astronomers with greater sympathy.

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-Page 227: One of the academy’s rules states that a candidate may be considered for a prize only if her discovery can be supported by verifiable experimental or observational evidence. Hawking’s work is, of course, unproved. Although the mathematics of his theories is considered beautiful and elegant, science is still unable even to prove the existence of black holes, let alone verify Hawking Radiation or any of his other theoretical proposals.

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-Page 228: Hawking is well aware of his place in the history of science. He is fascinated by the fact that he was born on the three-hundredth anniversary of Galileo’s death on January 8, 1642. That year Isaac Newton was born in Woolsthorpe, a little village in Lincolnshire, and it was Isaac Newton who was appointed Lucasian professor at Cambridge in 1669, three hundred and ten years before Hawking.

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-Page 229: The appointment as Lucasian Professor of Mathematics at Cambridge University was one of the highlights of Hawking’s career. To be professor at one of the oldest and most respected universities in the world is a huge achievement in itself, but to have accomplished such a feat by the age of thirty-seven is remarkable. Newton was Hawking’s junior by ten years when he gained the chair, but in the seventeenth century there were far fewer academics and very little competition for such positions. Newton did also happen to be the youngest ever to be appointed Lucasian Professor at Cambridge.

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