Category Archives: Stephen W. Hawking

>Stephen W. Hawking – My Life in Physics

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I did my first degree in Oxford. In my final examination, I was asked about my future plans. I replied, if you give me a first class degree, I will go to Cambridge. If I only get a second, I will stay in Oxford. They gave me a first. I arrived in Cambridge as a graduate student in October 1962. I had applied to work with Fred Hoyle, the principal defender of the steady state theory and the most famous British astronomer of the time. I say astronomer because cosmology was at that time, hardly recognized as a legitimate field, yet that was where I wanted to do my research, inspired by having been on a summer course with Hoyle’s student, Jayant Narlikar. However, Hoyle had enough students already, so to my great disappointment, I was assigned to Dennis Sharma, of whom I had not heard. But it was probably for the best. Hoyle was away a lot, seldom in the department, and I wouldn’t have had much of his attention. Sharma, on the other hand, was usually around and ready to talk. I didn’t agree with many of his ideas, particularly on Mach’s principle, but that stimulated me to develop my own picture.
When I began research, the two areas that seemed exciting were cosmology and elementary particle physics. Elementary particles was the active, rapidly changing field that attracted most of the best minds, while cosmology and general relativity were stuck where they had been in the 1930s. Feynman has given an amusing account of attending the conference on general relativity and gravitation in Warsaw in 1962. In a letter to his wife, he said, “I am not getting anything out of the meeting. I am learning nothing. Because there are no experiments, this field is not an active one, so few of the best men are doing work in it. The result is that there are hosts of dopes here (126) and it is not good for my blood pressure. Remind me not to come to any more gravity conferences!”
Of course, I wasn’t aware of all this when I began my research. But I felt that elementary particles at that time, was too like botany. Quantum electro dynamics, the theory of light and electrons that governs chemistry and the structure of atoms, had been worked out completely in the 40s and 50s. Attention had now shifted to the weak and strong nuclear forces between particles in the nucleus of an atom, but similar field theories didn’t seem to work. Indeed, the Cambridge school, in particular, held that there was no underlying field theory. Instead, everything would be determined by unitarity, that is, probability conservation, and certain characteristic patterns in the scattering. With hind sight, it now seems amazing that it was thought this approach would work, but I remember the scorn that was poured on the first attempts at unified field theories of the weak nuclear forces. Yet it is these field theories that are remembered and the analytic S matrix work is forgotten. I’m very glad I didn’t start my research in elementary particles. None of my work from that period would have survived.
Cosmology and gravitation, on the other hand, were neglected fields that were ripe for development at that time. Unlike elementary particles, there was a well defined theory, the general theory of relativity, but this was thought to be impossibly difficult. People were so pleased to find any solution of the field equations, they didn’t ask what physical significance, if any, it had. This was the old school of general relativity that Feynman encountered in Warsaw. But the Warsaw conference also marked the beginning of the renaissance of general relativity, though Feynman could be forgiven for not recognizing it at the time.
A new generation entered the field and new centers of general relativity appeared. Two of these were of particular importance to me. One was in Hamburg under Pascal Jordan. I never visited it, but I admired their elegant papers which were such a contrast to the previous messy work on general relativity. The other center was at Kings College, London, under Hermann Bondi, another proponent of the steady state theory but not ideologically committed to it, like Hoyle.
I hadn’t done much mathematics at school or in the very easy physics course at Oxford, so Sharma suggested I work on astrophysics. But having been cheated out of working with Hoyle, I wasn’t going to do something boring like Faraday rotation. I had come to Cambridge to do cosmology, and cosmology I was determined to do. So I read old text books on general relativity and traveled up to lectures at Kings College, London each week with three other students of Sharma. I followed the words and equations, but I didn’t really get a feel for the subject. Also, I had been diagnosed with motor neurone disease, or ALS, and given to expect I didn’t have long enough to finish my PhD. Then suddenly, towards the end of my second year of research, things picked up. My disease wasn’t progressing much and my work all fell into place, and I began to get somewhere.
Sharma was very keen on Mach’s principle, the idea that objects owe their inertia to the influence of all the other matter in the universe. He tried to get me to work on this, but I felt his formulations of Mach’s principle were not well defined. However, he introduced me to something a bit similar with regard to light, the so called Wheeler Feynman electro dynamics. This said that electricity and magnetism were time symmetric. However, when one switched on a lamp, it was the influence of all the other matter in the universe that caused light waves to travel outward from the lamp, rather than come in from infinity and end on the lamp. For Wheeler Feynman electro dynamics to work, it was necessary that all the light traveling out from the lamp should be absorbed by other matter in the universe. This would happen in a steady state universe in which the density of matter would remain constant, but not in a big bang universe where the density would go down as the universe expanded. It was claimed that this was another proof, if proof were needed, that we live in a steady state universe. There was a conference on Wheeler Feynman electro dynamics and the arrow of time in Cornell in 1963. Feynman was so disgusted by the nonsense that was talked about the arrow of time that he refused to let his name appear in the proceedings. He was referred to as Mr. X, but everyone knew who X was.
I found that Hoyle and Narlikar had already worked out Wheeler Feynman electro dynamics in expanding universes and had then gone on to formulate a time symmetric new theory of gravity. Hoyle unveiled the theory at a meeting of the royal society in 1964. I was at the lecture, and in the question period, I said that the influence of all the matter in a steady state universe would make his masses infinite. Hoyle asked why I said that, and I replied that I had calculated it. Everyone thought I had done it in my head during the lecture, but in fact, I was sharing an office with Narlikar and had seen a draft of the paper. Hoyle was furious. He was trying to set up his own institute, and threatening to join the brain drain to America if he didn’t get the money. He thought I had been put up to it, to sabotage his plans. However, he got his institute and later gave me a job, so he didn’t harbor a grudge against me.
The big question in cosmology in the early 60s, was did the universe have a beginning? Many scientists were instinctively opposed to the idea, because they felt that a point of creation would be a place where science broke down. One would have to appeal to religion and the hand of God to determine how the universe would start off. Two alternative scenarios were therefore put forward. One was the steady state theory, in which as the universe expanded, new matter was continually created to keep the density constant on average. The steady state theory was never on a very strong theoretical basis because it required a negative energy field to create the matter. This would have made it unstable, to run away production of matter and negative energy. But it had the great merit as a scientific theory of making definite predictions that could be tested by observations. By 1963, the steady state theory was already in trouble. Martin Ryle’s radio astronomy group at the Cavendish did a survey of faint radio sources. They found the sources were distributed fairly uniformly across the sky. This indicated that they were probably outside our galaxy because otherwise, they would be concentrated along the Milky Way. But the graph of the number of sources against source strength did not agree with the prediction of the steady state theory. There were too many faint sources indicating that the density of sources was higher in the distant past. Hoyle and his supporters put forward increasingly contrived explanations of the observations, but the final nail in the coffin of the steady state theory came in 1965 with the discovery of a faint background of microwave radiation. This could not be accounted for in the steady state theory, though Hoyle and Narlikar tried desperately. It was just as well I hadn’t been a student of Hoyle, because I would have had to have defended the steady state.
The microwave background indicated that the universe had had a hot dense stage in the past. But it didn’t prove that was the beginning of the universe. One might imagine that the universe had had a previous contracting phase, and that it had bounced from contraction to expansion at a high, but finite density. This was clearly a fundamental question, and it was just what I needed to complete my PhD thesis.
Gravity pulls matter together, but rotation throws it apart. So my first question was, could rotation cause the universe to bounce? Together with George Ellis, I was able to show that the answer was no, if the universe was spatially homogeneous, that is, if it was the same at each point of space. However, two Russians, Lifshitz and Khalatnikov, had claimed to have proved that a general contraction without exact symmetry would always lead to a bounce, with the density remaining finite. This result was very convenient for Marxist Leninist dialectical materialism, because it avoided awkward questions about the creation of the universe. It therefore became an article of faith for Soviet scientists.
Lifshitz and Khalatnikov were members of the old school in general relativity. That is, they wrote down a massive system of equations and tried to guess a solution. But it wasn’t clear that the solution they found was the most general one. However, Roger Penrose introduced a new approach which didn’t require solving the field equations explicitly, just certain general properties such as that energy is positive and gravity is attractive. Penrose gave a seminar in Kings College, London, in January 1965. I wasn’t at the seminar, but I heard about it from Brandon Carter, with whom I shared an office in the then new DAMTP premises in Silver Street. At first, I couldn’t understand what the point was. Penrose had showed that once a dying star had contracted to a certain radius, there would inevitably be a singularity, a point where space and time came to an end. Surely, I thought, we already knew that nothing could prevent a massive cold star collapsing under its own gravity until it reached a singularity of infinite density. But in fact, the equations had been solved, only for the collapse of a perfectly spherical star. Of course, a real star won’t be exactly spherical. If Lifshitz and Kalatnikov were right, the departures from spherical symmetry would grow as the star collapsed and would cause different parts of the star to miss each other and avoid a singularity of infinite density. But Penrose showed they were wrong. Small departures from spherical symmetry will not prevent a singularity.
I realized that similar arguments could be applied to the expansion of the universe. In this case, I could prove there were singularities where spacetime had a beginning. So again, Lifshitz and Khalatnikov were wrong. General relativity predicted that the universe should have a beginning, a result that did not pass unnoticed by the Church.
The original singularity theorems of both Penrose and myself, required the assumption that the universe had a Cauchy surface, that is, a surface that intersects every time like curve once, and only once. It was therefore possible that our first singularity theorems just proved that the universe didn’t have a Cauchy surface. While interesting, this didn’t compare in importance with time having a beginning or end. I therefore set about proving singularity theorems that didn’t require the assumption of a Cauchy surface. In the next five years, Roger Penrose, Bob Geroch and I developed the theory of causal structure in general relativity. It was a glorious feeling, having a whole field virtually to ourselves. How unlike particle physics, where people were falling over themselves to latch onto the latest idea. They still are.
Up to 1970, my main interest was in the big bang singularity of cosmology, rather than the singularities that Penrose had shown would occur in collapsing stars. However, in 1967, Werner Israel produced an important result. He showed that unless the remnant from a collapsing star was exactly spherical, the singularity it contained would be naked, that is, it would be visible to outside observers. This would have meant that the break down of general relativity at the singularity of a collapsing star would destroy our ability to predict the future of the rest of the universe.
At first, most people, including Israel himself, thought that this implied that because real stars aren’t spherical, their collapse would give rise to naked singularities and break down of predictability. However, a different interpretation was put forward by Roger Penrose and John Wheeler. It was that there is Cosmic Censorship. This says that Nature is a prude and hides singularities in black holes where they can’t be seen. I used to have a bumper sticker, black holes are out of sight, on the door of my office in DAMTP. This so irritated the head of department, that he engineered my election to the Lucasian professorship, moved me to a better office on the strength of it, and personally tore off the offending notice from the old office.
My work on black holes began with a Eureka moment in 1970, a few days after the birth of my daughter, Lucy. While getting into bed, I realized that I could apply to black holes, the causal structure theory I had developed for singularity theorems. In particular, the area of the horizon, the boundary of the black hole, would always increase. When two black holes collide and merge, the area of the final black hole is greater than the sum of the areas of the original holes. This and other properties that Jim Bardeen, Brandon Carter and I discovered, suggested that the area was like the entropy of a black hole. This would be a measure of how many states a black hole could have on the inside, for the same appearance on the outside. But the area couldn’t actually be the entropy, because as everyone knew, black holes were completely black and couldn’t be in equilibrium with thermal radiation.
There was an exciting period culminating in the Les Houches summer school in 1972, in which we solved most of the major problems in black hole theory. This was before there was any observational evidence for black holes, which shows Feynman was wrong when he said an active field has to be experimentally driven. Just as well for M theory. The one problem that was never solved was to prove the Cosmic Censorship hypothesis, though a number of attempts to disprove it, failed. It is fundamental to all work on black holes, so I have a strong vested interest in it being true. I therefore have a bet with Kip Thorne and John Preskill. It is difficult for me to win this bet, but quite possible to lose, by finding a counter example with a naked singularity. In fact, I have already lost an earlier version of the bet by not being careful enough about the wording. They were not amused by the t-shirt I offered in settlement.
We were so successful with the classical general theory of relativity that I was at a bit of a loose end in 1973 after the publication with George Ellis, of The Large Scale Structure of Spacetime. My work with Penrose had shown that general relativity broke down at singularities. So the obvious next step would be to combine general relativity, the theory of the very large, with quantum theory, the theory of the very small. I had no background in quantum theory, and the singularity problem seemed too difficult for a frontal assault at that time. So as a warm up exercise, I considered how particles and fields governed by quantum theory would behave near a black hole. In particular, I wondered, can one have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe?
To answer this, I studied how quantum fields would scatter off a black hole. I was expecting that part of an incident wave would be absorbed, and the remainder, scattered. But to my great surprise, I found there seemed to be emission from the black hole. At first, I thought this must be a mistake in my calculation. But what persuaded me that it was real, was that the emission was exactly what was required to identify the area of the horizon with the entropy of a black hole. I would like this simple formula to be on my tomb stone.
Work with Jim Hartle, Gary Gibbons, and Malcolm Perry uncovered the deep reason for this formula. General relativity can be combined with quantum theory in an elegant manner, if one replaces ordinary time, by imaginary time. I have tried to explain imaginary time on other occasion with varying degrees of success. I think it is the name, imaginary, that makes it so confusing. It is easier if you accept the positivist view that a theory is just a mathematical model. In this case, the mathematical model has a minus sign whenever time appears twice. The Euclidean approach to quantum gravity, based on imaginary time, was pioneered in Cambridge. It met a lot of resistance, but is now generally accepted.
The Radiation from a black hole will carry away energy, so the black hole will lose mass, and shrink. Eventually, it seems the black hole will evaporate completely and disappear. This raised a problem that struck at the heart of physics. My calculation showed that the radiation was exactly thermal and random, as it has to be, if the area of the horizon is to be the entropy of the black hole. So how could the radiation left over carry all the information about what made the black hole? But if information is lost, this is incompatible with quantum mechanics. This paradox had been argued for thirty years without much progress, until I found what I think is its resolution. Information is not lost, but it is not returned in a useful way. It is like burning an encyclopedia. Information is not lost, but it is very hard to read. In fact, Kip Thorne and I had a bet with John Preskill on the information paradox. I gave John a baseball encyclopedia. Maybe I should have just given him the ashes.
Between 1970 and 1980, I worked mainly on black holes and the Euclidean approach to quantum gravity. But the suggestions that the early universe had gone through a period of inflationary expansion, renewed my interest in cosmology. Euclidean methods were the obvious way to describe fluctuations and phase transitions in an inflationary universe. We held a Nuffield work shop in Cambridge in 1982, attended by all the major players in the field. At this meeting, we established most of our present picture of inflation, including the all important density fluctuations which give rise to galaxy formation and so to our existence. This was ten years before fluctuations in the microwave were observed, so again in gravity, theory was ahead of experiment.
The scenario for inflation in 1982 was that the universe began with a big bang singularity. As the universe expanded, it was supposed somehow to get into an inflationary state. I thought this was unsatisfactory because all equations would break down at a singularity. But unless one knew what came out of the initial singularity, one could not calculate how the universe would develop. Cosmology would not have any predictive power.
After the work shop in Cambridge, I spent the summer at the Institute of Theoretical Physics, Santa Barbara, which had just been set up. We stayed in student houses and I drove in to the institute in a rented electric wheel chair. I remember my younger son, Tim aged three, watching the Sun set on the mountains, and saying, it’s a big country.
While in Santa Barbara, I talked to Jim Hartle about how to apply the Euclidean approach to cosmology. According to Dewitt and others, the universe should be described by a wave function that obeyed the Wheeler Dewitt equation. But what picked out the particular solution of the equation that represents our universe. According to the Euclidean approach, the wave function of the universe is given by a Feynman sum over a certain class of histories in imaginary time. Because imaginary time behaves like another direction in space, histories in imaginary time can be closed surfaces, like the surface of the Earth, with no beginning or end. Jim and I decided that this was the most natural choice of class, indeed the only natural choice. We had side stepped the scientific and philosophical difficulty of time beginning by turning it into a direction in space.
Most people in theoretical physics have been trained in particle physics rather than general relativity. They have therefore been more interested in calculations of what they observe in particle accelerators than in questions about the beginning and end of time. The feeling was that if they could find a theory that in principle, allowed them to calculate particle scattering to arbitrary accuracy, everything else would somehow follow. In 1985, it was claimed that string theory was this ultimate theory. But in the years that followed, it emerged that the situation was more complicated and more interesting. It seems that there’s a network called M theory. All the theories in the M theory network can be regarded as approximations to the same underlying theory, in different limits. None of the theories allow calculation of scattering to arbitrary accuracy, and none can be regarded as the fundamental theory of which others are reflections. Instead, they should all be regarded as effective theories, valid in different limits. String theorists have long used the term, effective theory, as a pejorative description of general relativity. However, string theory is equally an effective theory, valid in the limit that the M theory membrane is rolled into a cylinder of small radius. Saying that string theory is only an effective theory isn’t very popular, but it’s true.
Because they had the dream of a theory that would allow calculation of scattering to arbitrary accuracy, people rejected quantum general relativity and supergravity on the grounds that they were non renormalizable. This means that one needs undetermined subtractions at each order to get finite answers. In fact, it is not surprising that naïve perturbation theory breaks down in quantum gravity. One can not regard a black hole as a perturbation of flat space.
I have done some work recently on making supergravity renormalizable, by adding higher derivative terms to the action. This apparently introduces ghosts, states with negative probability. However, I have found this is an illusion. One can never prepare a system in a state of negative probability. But the presence of ghosts means that one can not predict with arbitrary accuracy. If one can accept that, one can live quite happily with ghosts.
This approach to higher derivatives and ghosts allows one to revive the original inflation model of Starobinski and other Russians. In this, the inflationary expansion of the universe is driven by the quantum effects of a large number of matter fields. Based on the no boundary proposal, I picture the origin of the universe as like the formation of bubbles of steam in boiling water. Quantum fluctuations lead to the spontaneous creation of tiny universes, out of nothing. Most of the universes collapse to nothing, but a few that reach a critical size will expand in an inflationary manner and will form galaxies and stars, and maybe beings like us.
It has been a glorious time to be alive and doing research in theoretical physics. Our picture of the universe has changed a great deal in the last 40 years, and I’m happy if I have made a small contribution. I want to share my excitement and enthusiasm. There’s nothing like the Eureka moment of discovering something that no one knew before. I won’t compare it to sex, but it lasts longer.

Stephen W. Hawking – My Life in Physics

I did my first degree in Oxford. In my final examination, I was asked about my future plans. I replied, if you give me a first class degree, I will go to Cambridge. If I only get a second, I will stay in Oxford. They gave me a first. I arrived in Cambridge as a graduate student in October 1962. I had applied to work with Fred Hoyle, the principal defender of the steady state theory and the most famous British astronomer of the time. I say astronomer because cosmology was at that time, hardly recognized as a legitimate field, yet that was where I wanted to do my research, inspired by having been on a summer course with Hoyle’s student, Jayant Narlikar. However, Hoyle had enough students already, so to my great disappointment, I was assigned to Dennis Sharma, of whom I had not heard. But it was probably for the best. Hoyle was away a lot, seldom in the department, and I wouldn’t have had much of his attention. Sharma, on the other hand, was usually around and ready to talk. I didn’t agree with many of his ideas, particularly on Mach’s principle, but that stimulated me to develop my own picture.
When I began research, the two areas that seemed exciting were cosmology and elementary particle physics. Elementary particles was the active, rapidly changing field that attracted most of the best minds, while cosmology and general relativity were stuck where they had been in the 1930s. Feynman has given an amusing account of attending the conference on general relativity and gravitation in Warsaw in 1962. In a letter to his wife, he said, “I am not getting anything out of the meeting. I am learning nothing. Because there are no experiments, this field is not an active one, so few of the best men are doing work in it. The result is that there are hosts of dopes here (126) and it is not good for my blood pressure. Remind me not to come to any more gravity conferences!”
Of course, I wasn’t aware of all this when I began my research. But I felt that elementary particles at that time, was too like botany. Quantum electro dynamics, the theory of light and electrons that governs chemistry and the structure of atoms, had been worked out completely in the 40s and 50s. Attention had now shifted to the weak and strong nuclear forces between particles in the nucleus of an atom, but similar field theories didn’t seem to work. Indeed, the Cambridge school, in particular, held that there was no underlying field theory. Instead, everything would be determined by unitarity, that is, probability conservation, and certain characteristic patterns in the scattering. With hind sight, it now seems amazing that it was thought this approach would work, but I remember the scorn that was poured on the first attempts at unified field theories of the weak nuclear forces. Yet it is these field theories that are remembered and the analytic S matrix work is forgotten. I’m very glad I didn’t start my research in elementary particles. None of my work from that period would have survived.
Cosmology and gravitation, on the other hand, were neglected fields that were ripe for development at that time. Unlike elementary particles, there was a well defined theory, the general theory of relativity, but this was thought to be impossibly difficult. People were so pleased to find any solution of the field equations, they didn’t ask what physical significance, if any, it had. This was the old school of general relativity that Feynman encountered in Warsaw. But the Warsaw conference also marked the beginning of the renaissance of general relativity, though Feynman could be forgiven for not recognizing it at the time.
A new generation entered the field and new centers of general relativity appeared. Two of these were of particular importance to me. One was in Hamburg under Pascal Jordan. I never visited it, but I admired their elegant papers which were such a contrast to the previous messy work on general relativity. The other center was at Kings College, London, under Hermann Bondi, another proponent of the steady state theory but not ideologically committed to it, like Hoyle.
I hadn’t done much mathematics at school or in the very easy physics course at Oxford, so Sharma suggested I work on astrophysics. But having been cheated out of working with Hoyle, I wasn’t going to do something boring like Faraday rotation. I had come to Cambridge to do cosmology, and cosmology I was determined to do. So I read old text books on general relativity and traveled up to lectures at Kings College, London each week with three other students of Sharma. I followed the words and equations, but I didn’t really get a feel for the subject. Also, I had been diagnosed with motor neurone disease, or ALS, and given to expect I didn’t have long enough to finish my PhD. Then suddenly, towards the end of my second year of research, things picked up. My disease wasn’t progressing much and my work all fell into place, and I began to get somewhere.
Sharma was very keen on Mach’s principle, the idea that objects owe their inertia to the influence of all the other matter in the universe. He tried to get me to work on this, but I felt his formulations of Mach’s principle were not well defined. However, he introduced me to something a bit similar with regard to light, the so called Wheeler Feynman electro dynamics. This said that electricity and magnetism were time symmetric. However, when one switched on a lamp, it was the influence of all the other matter in the universe that caused light waves to travel outward from the lamp, rather than come in from infinity and end on the lamp. For Wheeler Feynman electro dynamics to work, it was necessary that all the light traveling out from the lamp should be absorbed by other matter in the universe. This would happen in a steady state universe in which the density of matter would remain constant, but not in a big bang universe where the density would go down as the universe expanded. It was claimed that this was another proof, if proof were needed, that we live in a steady state universe. There was a conference on Wheeler Feynman electro dynamics and the arrow of time in Cornell in 1963. Feynman was so disgusted by the nonsense that was talked about the arrow of time that he refused to let his name appear in the proceedings. He was referred to as Mr. X, but everyone knew who X was.
I found that Hoyle and Narlikar had already worked out Wheeler Feynman electro dynamics in expanding universes and had then gone on to formulate a time symmetric new theory of gravity. Hoyle unveiled the theory at a meeting of the royal society in 1964. I was at the lecture, and in the question period, I said that the influence of all the matter in a steady state universe would make his masses infinite. Hoyle asked why I said that, and I replied that I had calculated it. Everyone thought I had done it in my head during the lecture, but in fact, I was sharing an office with Narlikar and had seen a draft of the paper. Hoyle was furious. He was trying to set up his own institute, and threatening to join the brain drain to America if he didn’t get the money. He thought I had been put up to it, to sabotage his plans. However, he got his institute and later gave me a job, so he didn’t harbor a grudge against me.
The big question in cosmology in the early 60s, was did the universe have a beginning? Many scientists were instinctively opposed to the idea, because they felt that a point of creation would be a place where science broke down. One would have to appeal to religion and the hand of God to determine how the universe would start off. Two alternative scenarios were therefore put forward. One was the steady state theory, in which as the universe expanded, new matter was continually created to keep the density constant on average. The steady state theory was never on a very strong theoretical basis because it required a negative energy field to create the matter. This would have made it unstable, to run away production of matter and negative energy. But it had the great merit as a scientific theory of making definite predictions that could be tested by observations. By 1963, the steady state theory was already in trouble. Martin Ryle’s radio astronomy group at the Cavendish did a survey of faint radio sources. They found the sources were distributed fairly uniformly across the sky. This indicated that they were probably outside our galaxy because otherwise, they would be concentrated along the Milky Way. But the graph of the number of sources against source strength did not agree with the prediction of the steady state theory. There were too many faint sources indicating that the density of sources was higher in the distant past. Hoyle and his supporters put forward increasingly contrived explanations of the observations, but the final nail in the coffin of the steady state theory came in 1965 with the discovery of a faint background of microwave radiation. This could not be accounted for in the steady state theory, though Hoyle and Narlikar tried desperately. It was just as well I hadn’t been a student of Hoyle, because I would have had to have defended the steady state.
The microwave background indicated that the universe had had a hot dense stage in the past. But it didn’t prove that was the beginning of the universe. One might imagine that the universe had had a previous contracting phase, and that it had bounced from contraction to expansion at a high, but finite density. This was clearly a fundamental question, and it was just what I needed to complete my PhD thesis.
Gravity pulls matter together, but rotation throws it apart. So my first question was, could rotation cause the universe to bounce? Together with George Ellis, I was able to show that the answer was no, if the universe was spatially homogeneous, that is, if it was the same at each point of space. However, two Russians, Lifshitz and Khalatnikov, had claimed to have proved that a general contraction without exact symmetry would always lead to a bounce, with the density remaining finite. This result was very convenient for Marxist Leninist dialectical materialism, because it avoided awkward questions about the creation of the universe. It therefore became an article of faith for Soviet scientists.
Lifshitz and Khalatnikov were members of the old school in general relativity. That is, they wrote down a massive system of equations and tried to guess a solution. But it wasn’t clear that the solution they found was the most general one. However, Roger Penrose introduced a new approach which didn’t require solving the field equations explicitly, just certain general properties such as that energy is positive and gravity is attractive. Penrose gave a seminar in Kings College, London, in January 1965. I wasn’t at the seminar, but I heard about it from Brandon Carter, with whom I shared an office in the then new DAMTP premises in Silver Street. At first, I couldn’t understand what the point was. Penrose had showed that once a dying star had contracted to a certain radius, there would inevitably be a singularity, a point where space and time came to an end. Surely, I thought, we already knew that nothing could prevent a massive cold star collapsing under its own gravity until it reached a singularity of infinite density. But in fact, the equations had been solved, only for the collapse of a perfectly spherical star. Of course, a real star won’t be exactly spherical. If Lifshitz and Kalatnikov were right, the departures from spherical symmetry would grow as the star collapsed and would cause different parts of the star to miss each other and avoid a singularity of infinite density. But Penrose showed they were wrong. Small departures from spherical symmetry will not prevent a singularity.
I realized that similar arguments could be applied to the expansion of the universe. In this case, I could prove there were singularities where spacetime had a beginning. So again, Lifshitz and Khalatnikov were wrong. General relativity predicted that the universe should have a beginning, a result that did not pass unnoticed by the Church.
The original singularity theorems of both Penrose and myself, required the assumption that the universe had a Cauchy surface, that is, a surface that intersects every time like curve once, and only once. It was therefore possible that our first singularity theorems just proved that the universe didn’t have a Cauchy surface. While interesting, this didn’t compare in importance with time having a beginning or end. I therefore set about proving singularity theorems that didn’t require the assumption of a Cauchy surface. In the next five years, Roger Penrose, Bob Geroch and I developed the theory of causal structure in general relativity. It was a glorious feeling, having a whole field virtually to ourselves. How unlike particle physics, where people were falling over themselves to latch onto the latest idea. They still are.
Up to 1970, my main interest was in the big bang singularity of cosmology, rather than the singularities that Penrose had shown would occur in collapsing stars. However, in 1967, Werner Israel produced an important result. He showed that unless the remnant from a collapsing star was exactly spherical, the singularity it contained would be naked, that is, it would be visible to outside observers. This would have meant that the break down of general relativity at the singularity of a collapsing star would destroy our ability to predict the future of the rest of the universe.
At first, most people, including Israel himself, thought that this implied that because real stars aren’t spherical, their collapse would give rise to naked singularities and break down of predictability. However, a different interpretation was put forward by Roger Penrose and John Wheeler. It was that there is Cosmic Censorship. This says that Nature is a prude and hides singularities in black holes where they can’t be seen. I used to have a bumper sticker, black holes are out of sight, on the door of my office in DAMTP. This so irritated the head of department, that he engineered my election to the Lucasian professorship, moved me to a better office on the strength of it, and personally tore off the offending notice from the old office.
My work on black holes began with a Eureka moment in 1970, a few days after the birth of my daughter, Lucy. While getting into bed, I realized that I could apply to black holes, the causal structure theory I had developed for singularity theorems. In particular, the area of the horizon, the boundary of the black hole, would always increase. When two black holes collide and merge, the area of the final black hole is greater than the sum of the areas of the original holes. This and other properties that Jim Bardeen, Brandon Carter and I discovered, suggested that the area was like the entropy of a black hole. This would be a measure of how many states a black hole could have on the inside, for the same appearance on the outside. But the area couldn’t actually be the entropy, because as everyone knew, black holes were completely black and couldn’t be in equilibrium with thermal radiation.
There was an exciting period culminating in the Les Houches summer school in 1972, in which we solved most of the major problems in black hole theory. This was before there was any observational evidence for black holes, which shows Feynman was wrong when he said an active field has to be experimentally driven. Just as well for M theory. The one problem that was never solved was to prove the Cosmic Censorship hypothesis, though a number of attempts to disprove it, failed. It is fundamental to all work on black holes, so I have a strong vested interest in it being true. I therefore have a bet with Kip Thorne and John Preskill. It is difficult for me to win this bet, but quite possible to lose, by finding a counter example with a naked singularity. In fact, I have already lost an earlier version of the bet by not being careful enough about the wording. They were not amused by the t-shirt I offered in settlement.
We were so successful with the classical general theory of relativity that I was at a bit of a loose end in 1973 after the publication with George Ellis, of The Large Scale Structure of Spacetime. My work with Penrose had shown that general relativity broke down at singularities. So the obvious next step would be to combine general relativity, the theory of the very large, with quantum theory, the theory of the very small. I had no background in quantum theory, and the singularity problem seemed too difficult for a frontal assault at that time. So as a warm up exercise, I considered how particles and fields governed by quantum theory would behave near a black hole. In particular, I wondered, can one have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe?
To answer this, I studied how quantum fields would scatter off a black hole. I was expecting that part of an incident wave would be absorbed, and the remainder, scattered. But to my great surprise, I found there seemed to be emission from the black hole. At first, I thought this must be a mistake in my calculation. But what persuaded me that it was real, was that the emission was exactly what was required to identify the area of the horizon with the entropy of a black hole. I would like this simple formula to be on my tomb stone.
Work with Jim Hartle, Gary Gibbons, and Malcolm Perry uncovered the deep reason for this formula. General relativity can be combined with quantum theory in an elegant manner, if one replaces ordinary time, by imaginary time. I have tried to explain imaginary time on other occasion with varying degrees of success. I think it is the name, imaginary, that makes it so confusing. It is easier if you accept the positivist view that a theory is just a mathematical model. In this case, the mathematical model has a minus sign whenever time appears twice. The Euclidean approach to quantum gravity, based on imaginary time, was pioneered in Cambridge. It met a lot of resistance, but is now generally accepted.
The Radiation from a black hole will carry away energy, so the black hole will lose mass, and shrink. Eventually, it seems the black hole will evaporate completely and disappear. This raised a problem that struck at the heart of physics. My calculation showed that the radiation was exactly thermal and random, as it has to be, if the area of the horizon is to be the entropy of the black hole. So how could the radiation left over carry all the information about what made the black hole? But if information is lost, this is incompatible with quantum mechanics. This paradox had been argued for thirty years without much progress, until I found what I think is its resolution. Information is not lost, but it is not returned in a useful way. It is like burning an encyclopedia. Information is not lost, but it is very hard to read. In fact, Kip Thorne and I had a bet with John Preskill on the information paradox. I gave John a baseball encyclopedia. Maybe I should have just given him the ashes.
Between 1970 and 1980, I worked mainly on black holes and the Euclidean approach to quantum gravity. But the suggestions that the early universe had gone through a period of inflationary expansion, renewed my interest in cosmology. Euclidean methods were the obvious way to describe fluctuations and phase transitions in an inflationary universe. We held a Nuffield work shop in Cambridge in 1982, attended by all the major players in the field. At this meeting, we established most of our present picture of inflation, including the all important density fluctuations which give rise to galaxy formation and so to our existence. This was ten years before fluctuations in the microwave were observed, so again in gravity, theory was ahead of experiment.
The scenario for inflation in 1982 was that the universe began with a big bang singularity. As the universe expanded, it was supposed somehow to get into an inflationary state. I thought this was unsatisfactory because all equations would break down at a singularity. But unless one knew what came out of the initial singularity, one could not calculate how the universe would develop. Cosmology would not have any predictive power.
After the work shop in Cambridge, I spent the summer at the Institute of Theoretical Physics, Santa Barbara, which had just been set up. We stayed in student houses and I drove in to the institute in a rented electric wheel chair. I remember my younger son, Tim aged three, watching the Sun set on the mountains, and saying, it’s a big country.
While in Santa Barbara, I talked to Jim Hartle about how to apply the Euclidean approach to cosmology. According to Dewitt and others, the universe should be described by a wave function that obeyed the Wheeler Dewitt equation. But what picked out the particular solution of the equation that represents our universe. According to the Euclidean approach, the wave function of the universe is given by a Feynman sum over a certain class of histories in imaginary time. Because imaginary time behaves like another direction in space, histories in imaginary time can be closed surfaces, like the surface of the Earth, with no beginning or end. Jim and I decided that this was the most natural choice of class, indeed the only natural choice. We had side stepped the scientific and philosophical difficulty of time beginning by turning it into a direction in space.
Most people in theoretical physics have been trained in particle physics rather than general relativity. They have therefore been more interested in calculations of what they observe in particle accelerators than in questions about the beginning and end of time. The feeling was that if they could find a theory that in principle, allowed them to calculate particle scattering to arbitrary accuracy, everything else would somehow follow. In 1985, it was claimed that string theory was this ultimate theory. But in the years that followed, it emerged that the situation was more complicated and more interesting. It seems that there’s a network called M theory. All the theories in the M theory network can be regarded as approximations to the same underlying theory, in different limits. None of the theories allow calculation of scattering to arbitrary accuracy, and none can be regarded as the fundamental theory of which others are reflections. Instead, they should all be regarded as effective theories, valid in different limits. String theorists have long used the term, effective theory, as a pejorative description of general relativity. However, string theory is equally an effective theory, valid in the limit that the M theory membrane is rolled into a cylinder of small radius. Saying that string theory is only an effective theory isn’t very popular, but it’s true.
Because they had the dream of a theory that would allow calculation of scattering to arbitrary accuracy, people rejected quantum general relativity and supergravity on the grounds that they were non renormalizable. This means that one needs undetermined subtractions at each order to get finite answers. In fact, it is not surprising that naïve perturbation theory breaks down in quantum gravity. One can not regard a black hole as a perturbation of flat space.
I have done some work recently on making supergravity renormalizable, by adding higher derivative terms to the action. This apparently introduces ghosts, states with negative probability. However, I have found this is an illusion. One can never prepare a system in a state of negative probability. But the presence of ghosts means that one can not predict with arbitrary accuracy. If one can accept that, one can live quite happily with ghosts.
This approach to higher derivatives and ghosts allows one to revive the original inflation model of Starobinski and other Russians. In this, the inflationary expansion of the universe is driven by the quantum effects of a large number of matter fields. Based on the no boundary proposal, I picture the origin of the universe as like the formation of bubbles of steam in boiling water. Quantum fluctuations lead to the spontaneous creation of tiny universes, out of nothing. Most of the universes collapse to nothing, but a few that reach a critical size will expand in an inflationary manner and will form galaxies and stars, and maybe beings like us.
It has been a glorious time to be alive and doing research in theoretical physics. Our picture of the universe has changed a great deal in the last 40 years, and I’m happy if I have made a small contribution. I want to share my excitement and enthusiasm. There’s nothing like the Eureka moment of discovering something that no one knew before. I won’t compare it to sex, but it lasts longer.

>Life in the Universe

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Life in the Universe

A PUBLIC LECTURE BY PROF.STEPHEN HAWKING
In this talk, I would like to speculate a little, on the development of life in the universe, and in particular, the development of intelligent life. I shall take this to include the human race, even though much of its behaviour through out history, has been pretty stupid, and not calculated to aid the survival of the species. Two questions I shall discuss are, ‘What is the probability of life existing else where in the universe?’ and, ‘How may life develop in the future?’
It is a matter of common experience, that things get more disordered and chaotic with time. This observation can be elevated to the status of a law, the so-called Second Law of Thermodynamics. This says that the total amount of disorder, or entropy, in the universe, always increases with time. However, the Law refers only to the total amount of disorder. The order in one body can increase, provided that the amount of disorder in its surroundings increases by a greater amount. This is what happens in a living being. One can define Life to be an ordered system that can sustain itself against the tendency to disorder, and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form, like food, sunlight, or electric power, into disordered energy, in the form of heat. In this way, the system can satisfy the requirement that the total amount of disorder increases, while, at the same time, increasing the order in itself and its offspring. A living being usually has two elements: a set of instructions that tell the system how to sustain and reproduce itself, and a mechanism to carry out the instructions. In biology, these two parts are called genes and metabolism. But it is worth emphasising that there need be nothing biological about them. For example, a computer virus is a program that will make copies of itself in the memory of a computer, and will transfer itself to other computers. Thus it fits the definition of a living system, that I have given. Like a biological virus, it is a rather degenerate form, because it contains only instructions or genes, and doesn’t have any metabolism of its own. Instead, it reprograms the metabolism of the host computer, or cell. Some people have questioned whether viruses should count as life, because they are parasites, and can not exist independently of their hosts. But then most forms of life, ourselves included, are parasites, in that they feed off and depend for their survival on other forms of life. I think computer viruses should count as life. Maybe it says something about human nature, that the only form of life we have created so far is purely destructive. Talk about creating life in our own image. I shall return to electronic forms of life later on.
What we normally think of as ‘life’ is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous. One can speculate that one might have life with some other chemical basis, such as silicon, but carbon seems the most favourable case, because it has the richest chemistry. That carbon atoms should exist at all, with the properties that they have, requires a fine adjustment of physical constants, such as the QCD scale, the electric charge, and even the dimension of space-time. If these constants had significantly different values, either the nucleus of the carbon atom would not be stable, or the electrons would collapse in on the nucleus. At first sight, it seems remarkable that the universe is so finely tuned. Maybe this is evidence, that the universe was specially designed to produce the human race. However, one has to be careful about such arguments, because of what is known as the Anthropic Principle. This is based on the self-evident truth, that if the universe had not been suitable for life, we wouldn’t be asking why it is so finely adjusted. One can apply the Anthropic Principle, in either its Strong, or Weak, versions. For the Strong Anthropic Principle, one supposes that there are many different universes, each with different values of the physical constants. In a small number, the values will allow the existence of objects like carbon atoms, which can act as the building blocks of living systems. Since we must live in one of these universes, we should not be surprised that the physical constants are finely tuned. If they weren’t, we wouldn’t be here. The strong form of the Anthropic Principle is not very satisfactory. What operational meaning can one give to the existence of all those other universes? And if they are separate from our own universe, how can what happens in them, affect our universe. Instead, I shall adopt what is known as the Weak Anthropic Principle. That is, I shall take the values of the physical constants, as given. But I shall see what conclusions can be drawn, from the fact that life exists on this planet, at this stage in the history of the universe.
There was no carbon, when the universe began in the Big Bang, about 15 billion years ago. It was so hot, that all the matter would have been in the form of particles, called protons and neutrons. There would initially have been equal numbers of protons and neutrons. However, as the universe expanded, it would have cooled. About a minute after the Big Bang, the temperature would have fallen to about a billion degrees, about a hundred times the temperature in the Sun. At this temperature, the neutrons will start to decay into more protons. If this had been all that happened, all the matter in the universe would have ended up as the simplest element, hydrogen, whose nucleus consists of a single proton. However, some of the neutrons collided with protons, and stuck together to form the next simplest element, helium, whose nucleus consists of two protons and two neutrons. But no heavier elements, like carbon or oxygen, would have been formed in the early universe. It is difficult to imagine that one could build a living system, out of just hydrogen and helium, and anyway the early universe was still far too hot for atoms to combine into molecules.
The universe would have continued to expand, and cool. But some regions would have had slightly higher densities than others. The gravitational attraction of the extra matter in those regions, would slow down their expansion, and eventually stop it. Instead, they would collapse to form galaxies and stars, starting from about two billion years after the Big Bang. Some of the early stars would have been more massive than our Sun. They would have been hotter than the Sun, and would have burnt the original hydrogen and helium, into heavier elements, such as carbon, oxygen, and iron. This could have taken only a few hundred million years. After that, some of the stars would have exploded as supernovas, and scattered the heavy elements back into space, to form the raw material for later generations of stars.
Other stars are too far away, for us to be able to see directly, if they have planets going round them. But certain stars, called pulsars, give off regular pulses of radio waves. We observe a slight variation in the rate of some pulsars, and this is interpreted as indicating that they are being disturbed, by having Earth sized planets going round them. Planets going round pulsars are unlikely to have life, because any living beings would have been killed, in the supernova explosion that led to the star becoming a pulsar. But, the fact that several pulsars are observed to have planets suggests that a reasonable fraction of the hundred billion stars in our galaxy may also have planets. The necessary planetary conditions for our form of life may therefore have existed from about four billion years after the Big Bang.
Our solar system was formed about four and a half billion years ago, or about ten billion years after the Big Bang, from gas contaminated with the remains of earlier stars. The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, some of these atoms came to be arranged in the form of molecules of DNA. This has the famous double helix form, discovered by Crick and Watson, in a hut on the New Museum site in Cambridge. Linking the two chains in the helix, are pairs of nucleic acids. There are four types of nucleic acid, adenine, cytosine, guanine, and thiamine. I’m afraid my speech synthesiser is not very good, at pronouncing their names. Obviously, it was not designed for molecular biologists. An adenine on one chain is always matched with a thiamine on the other chain, and a guanine with a cytosine. Thus the sequence of nucleic acids on one chain defines a unique, complementary sequence, on the other chain. The two chains can then separate and each act as templates to build further chains. Thus DNA molecules can reproduce the genetic information, coded in their sequences of nucleic acids. Sections of the sequence can also be used to make proteins and other chemicals, which can carry out the instructions, coded in the sequence, and assemble the raw material for DNA to reproduce itself.
We do not know how DNA molecules first appeared. The chances against a DNA molecule arising by random fluctuations are very small. Some people have therefore suggested that life came to Earth from elsewhere, and that there are seeds of life floating round in the galaxy. However, it seems unlikely that DNA could survive for long in the radiation in space. And even if it could, it would not really help explain the origin of life, because the time available since the formation of carbon is only just over double the age of the Earth.
One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated. The fact that life happened to occur on Earth, is not however surprising or unlikely. It is just an application of the Weak Anthropic Principle: if life had appeared instead on another planet, we would be asking why it had occurred there.
If the appearance of life on a given planet was very unlikely, one might have expected it to take a long time. More precisely, one might have expected life to appear just in time for the subsequent evolution to intelligent beings, like us, to have occurred before the cut off, provided by the life time of the Sun. This is about ten billion years, after which the Sun will swell up and engulf the Earth. An intelligent form of life, might have mastered space travel, and be able to escape to another star. But otherwise, life on Earth would be doomed.
There is fossil evidence, that there was some form of life on Earth, about three and a half billion years ago. This may have been only 500 million years after the Earth became stable and cool enough, for life to develop. But life could have taken 7 billion years to develop, and still have left time to evolve to beings like us, who could ask about the origin of life. If the probability of life developing on a given planet, is very small, why did it happen on Earth, in about one 14th of the time available.
The early appearance of life on Earth suggests that there’s a good chance of the spontaneous generation of life, in suitable conditions. Maybe there was some simpler form of organisation, which built up DNA. Once DNA appeared, it would have been so successful, that it might have completely replaced the earlier forms. We don’t know what these earlier forms would have been. One possibility is RNA. This is like DNA, but rather simpler, and without the double helix structure. Short lengths of RNA, could reproduce themselves like DNA, and might eventually build up to DNA. One can not make nucleic acids in the laboratory, from non-living material, let alone RNA. But given 500 million years, and oceans covering most of the Earth, there might be a reasonable probability of RNA, being made by chance.
As DNA reproduced itself, there would have been random errors. Many of these errors would have been harmful, and would have died out. Some would have been neutral. That is they would not have affected the function of the gene. Such errors would contribute to a gradual genetic drift, which seems to occur in all populations. And a few errors would have been favourable to the survival of the species. These would have been chosen by Darwinian natural selection.
The process of biological evolution was very slow at first. It took two and a half billion years, to evolve from the earliest cells to multi-cell animals, and another billion years to evolve through fish and reptiles, to mammals. But then evolution seemed to have speeded up. It only took about a hundred million years, to develop from the early mammals to us. The reason is, fish contain most of the important human organs, and mammals, essentially all of them. All that was required to evolve from early mammals, like lemurs, to humans, was a bit of fine-tuning.
But with the human race, evolution reached a critical stage, comparable in importance with the development of DNA. This was the development of language, and particularly written language. It meant that information can be passed on, from generation to generation, other than genetically, through DNA. There has been no detectable change in human DNA, brought about by biological evolution, in the ten thousand years of recorded history. But the amount of knowledge handed on from generation to generation has grown enormously. The DNA in human beings contains about three billion nucleic acids. However, much of the information coded in this sequence, is redundant, or is inactive. So the total amount of useful information in our genes, is probably something like a hundred million bits. One bit of information is the answer to a yes no question. By contrast, a paper back novel might contain two million bits of information. So a human is equivalent to 50 Mills and Boon romances. A major national library can contain about five million books, or about ten trillion bits. So the amount of information handed down in books, is a hundred thousand times as much as in DNA.
Even more important, is the fact that the information in books, can be changed, and updated, much more rapidly. It has taken us several million years to evolve from the apes. During that time, the useful information in our DNA, has probably changed by only a few million bits. So the rate of biological evolution in humans, is about a bit a year. By contrast, there are about 50,000 new books published in the English language each year, containing of the order of a hundred billion bits of information. Of course, the great majority of this information is garbage, and no use to any form of life. But, even so, the rate at which useful information can be added is millions, if not billions, higher than with DNA.
This has meant that we have entered a new phase of evolution. At first, evolution proceeded by natural selection, from random mutations. This Darwinian phase, lasted about three and a half billion years, and produced us, beings who developed language, to exchange information. But in the last ten thousand years or so, we have been in what might be called, an external transmission phase. In this, the internal record of information, handed down to succeeding generations in DNA, has not changed significantly. But the external record, in books, and other long lasting forms of storage, has grown enormously. Some people would use the term, evolution, only for the internally transmitted genetic material, and would object to it being applied to information handed down externally. But I think that is too narrow a view. We are more than just our genes. We may be no stronger, or inherently more intelligent, than our cave man ancestors. But what distinguishes us from them, is the knowledge that we have accumulated over the last ten thousand years, and particularly, over the last three hundred. I think it is legitimate to take a broader view, and include externally transmitted information, as well as DNA, in the evolution of the human race.
The time scale for evolution, in the external transmission period, is the time scale for accumulation of information. This used to be hundreds, or even thousands, of years. But now this time scale has shrunk to about 50 years, or less. On the other hand, the brains with which we process this information have evolved only on the Darwinian time scale, of hundreds of thousands of years. This is beginning to cause problems. In the 18th century, there was said to be a man who had read every book written. But nowadays, if you read one book a day, it would take you about 15,000 years to read through the books in a national Library. By which time, many more books would have been written.
This has meant that no one person can be the master of more than a small corner of human knowledge. People have to specialise, in narrower and narrower fields. This is likely to be a major limitation in the future. We certainly can not continue, for long, with the exponential rate of growth of knowledge that we have had in the last three hundred years. An even greater limitation and danger for future generations, is that we still have the instincts, and in particular, the aggressive impulses, that we had in cave man days. Aggression, in the form of subjugating or killing other men, and taking their women and food, has had definite survival advantage, up to the present time. But now it could destroy the entire human race, and much of the rest of life on Earth. A nuclear war, is still the most immediate danger, but there are others, such as the release of a genetically engineered virus. Or the green house effect becoming unstable.
There is no time, to wait for Darwinian evolution, to make us more intelligent, and better natured. But we are now entering a new phase, of what might be called, self designed evolution, in which we will be able to change and improve our DNA. There is a project now on, to map the entire sequence of human DNA. It will cost a few billion dollars, but that is chicken feed, for a project of this importance. Once we have read the book of life, we will start writing in corrections. At first, these changes will be confined to the repair of genetic defects, like cystic fibrosis, and muscular dystrophy. These are controlled by single genes, and so are fairly easy to identify, and correct. Other qualities, such as intelligence, are probably controlled by a large number of genes. It will be much more difficult to find them, and work out the relations between them. Nevertheless, I am sure that during the next century, people will discover how to modify both intelligence, and instincts like aggression.
Laws will be passed, against genetic engineering with humans. But some people won’t be able to resist the temptation, to improve human characteristics, such as size of memory, resistance to disease, and length of life. Once such super humans appear, there are going to be major political problems, with the unimproved humans, who won’t be able to compete. Presumably, they will die out, or become unimportant. Instead, there will be a race of self-designing beings, who are improving themselves at an ever-increasing rate.
If this race manages to redesign itself, to reduce or eliminate the risk of self-destruction, it will probably spread out, and colonise other planets and stars. However, long distance space travel, will be difficult for chemically based life forms, like DNA. The natural lifetime for such beings is short, compared to the travel time. According to the theory of relativity, nothing can travel faster than light. So the round trip to the nearest star would take at least 8 years, and to the centre of the galaxy, about a hundred thousand years. In science fiction, they overcome this difficulty, by space warps, or travel through extra dimensions. But I don’t think these will ever be possible, no matter how intelligent life becomes. In the theory of relativity, if one can travel faster than light, one can also travel back in time. This would lead to problems with people going back, and changing the past. One would also expect to have seen large numbers of tourists from the future, curious to look at our quaint, old-fashioned ways.
It might be possible to use genetic engineering, to make DNA based life survive indefinitely, or at least for a hundred thousand years. But an easier way, which is almost within our capabilities already, would be to send machines. These could be designed to last long enough for interstellar travel. When they arrived at a new star, they could land on a suitable planet, and mine material to produce more machines, which could be sent on to yet more stars. These machines would be a new form of life, based on mechanical and electronic components, rather than macromolecules. They could eventually replace DNA based life, just as DNA may have replaced an earlier form of life.
This mechanical life could also be self-designing. Thus it seems that the external transmission period of evolution, will have been just a very short interlude, between the Darwinian phase, and a biological, or mechanical, self design phase. This is shown on this next diagram, which is not to scale, because there’s no way one can show a period of ten thousand years, on the same scale as billions of years. How long the self-design phase will last is open to question. It may be unstable, and life may destroy itself, or get into a dead end. If it does not, it should be able to survive the death of the Sun, in about 5 billion years, by moving to planets around other stars. Most stars will have burnt out in another 15 billion years or so, and the universe will be approaching a state of complete disorder, according to the Second Law of Thermodynamics. But Freeman Dyson has shown that, despite this, life could adapt to the ever-decreasing supply of ordered energy, and therefore could, in principle, continue forever.
What are the chances that we will encounter some alien form of life, as we explore the galaxy. If the argument about the time scale for the appearance of life on Earth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before the Earth. So why is the galaxy not crawling with self designing mechanical or biological life forms? Why hasn’t the Earth been visited, and even colonised. I discount suggestions that UFO’s contain beings from outer space. I think any visits by aliens, would be much more obvious, and probably also, much more unpleasant.
What is the explanation of why we have not been visited? One possibility is that the argument, about the appearance of life on Earth, is wrong. Maybe the probability of life spontaneously appearing is so low, that Earth is the only planet in the galaxy, or in the observable universe, in which it happened. Another possibility is that there was a reasonable probability of forming self reproducing systems, like cells, but that most of these forms of life did not evolve intelligence. We are used to thinking of intelligent life, as an inevitable consequence of evolution. But the Anthropic Principle should warn us to be wary of such arguments. It is more likely that evolution is a random process, with intelligence as only one of a large number of possible outcomes. It is not clear that intelligence has any long-term survival value. Bacteria, and other single cell organisms, will live on, if all other life on Earth is wiped out by our actions. There is support for the view that intelligence, was an unlikely development for life on Earth, from the chronology of evolution. It took a very long time, two and a half billion years, to go from single cells to multi-cell beings, which are a necessary precursor to intelligence. This is a good fraction of the total time available, before the Sun blows up. So it would be consistent with the hypothesis, that the probability for life to develop intelligence, is low. In this case, we might expect to find many other life forms in the galaxy, but we are unlikely to find intelligent life. Another way, in which life could fail to develop to an intelligent stage, would be if an asteroid or comet were to collide with the planet. We have just observed the collision of a comet, Schumacher-Levi, with Jupiter. It produced a series of enormous fireballs. It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out. It is difficult to say how often such collisions occur, but a reasonable guess might be every twenty million years, on average. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.
A third possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, in the external transmission phase. But at that point, the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true. I prefer a fourth possibility: there are other forms of intelligent life out there, but that we have been overlooked. There used to be a project called SETI, the search for extra-terrestrial intelligence. It involved scanning the radio frequencies, to see if we could pick up signals from alien civilisations. I thought this project was worth supporting, though it was cancelled due to a lack of funds. But we should have been wary of answering back, until we have develop a bit further. Meeting a more advanced civilisation, at our present stage, might be a bit like the original inhabitants of America meeting Columbus. I don’t think they were better off for it.
That is all I have to say. Thank you for listening.
 
………….STEPHEN HAWKING

Life in the Universe

Life in the Universe

A PUBLIC LECTURE BY PROF.STEPHEN HAWKING
In this talk, I would like to speculate a little, on the development of life in the universe, and in particular, the development of intelligent life. I shall take this to include the human race, even though much of its behaviour through out history, has been pretty stupid, and not calculated to aid the survival of the species. Two questions I shall discuss are, ‘What is the probability of life existing else where in the universe?’ and, ‘How may life develop in the future?’
It is a matter of common experience, that things get more disordered and chaotic with time. This observation can be elevated to the status of a law, the so-called Second Law of Thermodynamics. This says that the total amount of disorder, or entropy, in the universe, always increases with time. However, the Law refers only to the total amount of disorder. The order in one body can increase, provided that the amount of disorder in its surroundings increases by a greater amount. This is what happens in a living being. One can define Life to be an ordered system that can sustain itself against the tendency to disorder, and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form, like food, sunlight, or electric power, into disordered energy, in the form of heat. In this way, the system can satisfy the requirement that the total amount of disorder increases, while, at the same time, increasing the order in itself and its offspring. A living being usually has two elements: a set of instructions that tell the system how to sustain and reproduce itself, and a mechanism to carry out the instructions. In biology, these two parts are called genes and metabolism. But it is worth emphasising that there need be nothing biological about them. For example, a computer virus is a program that will make copies of itself in the memory of a computer, and will transfer itself to other computers. Thus it fits the definition of a living system, that I have given. Like a biological virus, it is a rather degenerate form, because it contains only instructions or genes, and doesn’t have any metabolism of its own. Instead, it reprograms the metabolism of the host computer, or cell. Some people have questioned whether viruses should count as life, because they are parasites, and can not exist independently of their hosts. But then most forms of life, ourselves included, are parasites, in that they feed off and depend for their survival on other forms of life. I think computer viruses should count as life. Maybe it says something about human nature, that the only form of life we have created so far is purely destructive. Talk about creating life in our own image. I shall return to electronic forms of life later on.
What we normally think of as ‘life’ is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous. One can speculate that one might have life with some other chemical basis, such as silicon, but carbon seems the most favourable case, because it has the richest chemistry. That carbon atoms should exist at all, with the properties that they have, requires a fine adjustment of physical constants, such as the QCD scale, the electric charge, and even the dimension of space-time. If these constants had significantly different values, either the nucleus of the carbon atom would not be stable, or the electrons would collapse in on the nucleus. At first sight, it seems remarkable that the universe is so finely tuned. Maybe this is evidence, that the universe was specially designed to produce the human race. However, one has to be careful about such arguments, because of what is known as the Anthropic Principle. This is based on the self-evident truth, that if the universe had not been suitable for life, we wouldn’t be asking why it is so finely adjusted. One can apply the Anthropic Principle, in either its Strong, or Weak, versions. For the Strong Anthropic Principle, one supposes that there are many different universes, each with different values of the physical constants. In a small number, the values will allow the existence of objects like carbon atoms, which can act as the building blocks of living systems. Since we must live in one of these universes, we should not be surprised that the physical constants are finely tuned. If they weren’t, we wouldn’t be here. The strong form of the Anthropic Principle is not very satisfactory. What operational meaning can one give to the existence of all those other universes? And if they are separate from our own universe, how can what happens in them, affect our universe. Instead, I shall adopt what is known as the Weak Anthropic Principle. That is, I shall take the values of the physical constants, as given. But I shall see what conclusions can be drawn, from the fact that life exists on this planet, at this stage in the history of the universe.
There was no carbon, when the universe began in the Big Bang, about 15 billion years ago. It was so hot, that all the matter would have been in the form of particles, called protons and neutrons. There would initially have been equal numbers of protons and neutrons. However, as the universe expanded, it would have cooled. About a minute after the Big Bang, the temperature would have fallen to about a billion degrees, about a hundred times the temperature in the Sun. At this temperature, the neutrons will start to decay into more protons. If this had been all that happened, all the matter in the universe would have ended up as the simplest element, hydrogen, whose nucleus consists of a single proton. However, some of the neutrons collided with protons, and stuck together to form the next simplest element, helium, whose nucleus consists of two protons and two neutrons. But no heavier elements, like carbon or oxygen, would have been formed in the early universe. It is difficult to imagine that one could build a living system, out of just hydrogen and helium, and anyway the early universe was still far too hot for atoms to combine into molecules.
The universe would have continued to expand, and cool. But some regions would have had slightly higher densities than others. The gravitational attraction of the extra matter in those regions, would slow down their expansion, and eventually stop it. Instead, they would collapse to form galaxies and stars, starting from about two billion years after the Big Bang. Some of the early stars would have been more massive than our Sun. They would have been hotter than the Sun, and would have burnt the original hydrogen and helium, into heavier elements, such as carbon, oxygen, and iron. This could have taken only a few hundred million years. After that, some of the stars would have exploded as supernovas, and scattered the heavy elements back into space, to form the raw material for later generations of stars.
Other stars are too far away, for us to be able to see directly, if they have planets going round them. But certain stars, called pulsars, give off regular pulses of radio waves. We observe a slight variation in the rate of some pulsars, and this is interpreted as indicating that they are being disturbed, by having Earth sized planets going round them. Planets going round pulsars are unlikely to have life, because any living beings would have been killed, in the supernova explosion that led to the star becoming a pulsar. But, the fact that several pulsars are observed to have planets suggests that a reasonable fraction of the hundred billion stars in our galaxy may also have planets. The necessary planetary conditions for our form of life may therefore have existed from about four billion years after the Big Bang.
Our solar system was formed about four and a half billion years ago, or about ten billion years after the Big Bang, from gas contaminated with the remains of earlier stars. The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, some of these atoms came to be arranged in the form of molecules of DNA. This has the famous double helix form, discovered by Crick and Watson, in a hut on the New Museum site in Cambridge. Linking the two chains in the helix, are pairs of nucleic acids. There are four types of nucleic acid, adenine, cytosine, guanine, and thiamine. I’m afraid my speech synthesiser is not very good, at pronouncing their names. Obviously, it was not designed for molecular biologists. An adenine on one chain is always matched with a thiamine on the other chain, and a guanine with a cytosine. Thus the sequence of nucleic acids on one chain defines a unique, complementary sequence, on the other chain. The two chains can then separate and each act as templates to build further chains. Thus DNA molecules can reproduce the genetic information, coded in their sequences of nucleic acids. Sections of the sequence can also be used to make proteins and other chemicals, which can carry out the instructions, coded in the sequence, and assemble the raw material for DNA to reproduce itself.
We do not know how DNA molecules first appeared. The chances against a DNA molecule arising by random fluctuations are very small. Some people have therefore suggested that life came to Earth from elsewhere, and that there are seeds of life floating round in the galaxy. However, it seems unlikely that DNA could survive for long in the radiation in space. And even if it could, it would not really help explain the origin of life, because the time available since the formation of carbon is only just over double the age of the Earth.
One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated. The fact that life happened to occur on Earth, is not however surprising or unlikely. It is just an application of the Weak Anthropic Principle: if life had appeared instead on another planet, we would be asking why it had occurred there.
If the appearance of life on a given planet was very unlikely, one might have expected it to take a long time. More precisely, one might have expected life to appear just in time for the subsequent evolution to intelligent beings, like us, to have occurred before the cut off, provided by the life time of the Sun. This is about ten billion years, after which the Sun will swell up and engulf the Earth. An intelligent form of life, might have mastered space travel, and be able to escape to another star. But otherwise, life on Earth would be doomed.
There is fossil evidence, that there was some form of life on Earth, about three and a half billion years ago. This may have been only 500 million years after the Earth became stable and cool enough, for life to develop. But life could have taken 7 billion years to develop, and still have left time to evolve to beings like us, who could ask about the origin of life. If the probability of life developing on a given planet, is very small, why did it happen on Earth, in about one 14th of the time available.
The early appearance of life on Earth suggests that there’s a good chance of the spontaneous generation of life, in suitable conditions. Maybe there was some simpler form of organisation, which built up DNA. Once DNA appeared, it would have been so successful, that it might have completely replaced the earlier forms. We don’t know what these earlier forms would have been. One possibility is RNA. This is like DNA, but rather simpler, and without the double helix structure. Short lengths of RNA, could reproduce themselves like DNA, and might eventually build up to DNA. One can not make nucleic acids in the laboratory, from non-living material, let alone RNA. But given 500 million years, and oceans covering most of the Earth, there might be a reasonable probability of RNA, being made by chance.
As DNA reproduced itself, there would have been random errors. Many of these errors would have been harmful, and would have died out. Some would have been neutral. That is they would not have affected the function of the gene. Such errors would contribute to a gradual genetic drift, which seems to occur in all populations. And a few errors would have been favourable to the survival of the species. These would have been chosen by Darwinian natural selection.
The process of biological evolution was very slow at first. It took two and a half billion years, to evolve from the earliest cells to multi-cell animals, and another billion years to evolve through fish and reptiles, to mammals. But then evolution seemed to have speeded up. It only took about a hundred million years, to develop from the early mammals to us. The reason is, fish contain most of the important human organs, and mammals, essentially all of them. All that was required to evolve from early mammals, like lemurs, to humans, was a bit of fine-tuning.
But with the human race, evolution reached a critical stage, comparable in importance with the development of DNA. This was the development of language, and particularly written language. It meant that information can be passed on, from generation to generation, other than genetically, through DNA. There has been no detectable change in human DNA, brought about by biological evolution, in the ten thousand years of recorded history. But the amount of knowledge handed on from generation to generation has grown enormously. The DNA in human beings contains about three billion nucleic acids. However, much of the information coded in this sequence, is redundant, or is inactive. So the total amount of useful information in our genes, is probably something like a hundred million bits. One bit of information is the answer to a yes no question. By contrast, a paper back novel might contain two million bits of information. So a human is equivalent to 50 Mills and Boon romances. A major national library can contain about five million books, or about ten trillion bits. So the amount of information handed down in books, is a hundred thousand times as much as in DNA.
Even more important, is the fact that the information in books, can be changed, and updated, much more rapidly. It has taken us several million years to evolve from the apes. During that time, the useful information in our DNA, has probably changed by only a few million bits. So the rate of biological evolution in humans, is about a bit a year. By contrast, there are about 50,000 new books published in the English language each year, containing of the order of a hundred billion bits of information. Of course, the great majority of this information is garbage, and no use to any form of life. But, even so, the rate at which useful information can be added is millions, if not billions, higher than with DNA.
This has meant that we have entered a new phase of evolution. At first, evolution proceeded by natural selection, from random mutations. This Darwinian phase, lasted about three and a half billion years, and produced us, beings who developed language, to exchange information. But in the last ten thousand years or so, we have been in what might be called, an external transmission phase. In this, the internal record of information, handed down to succeeding generations in DNA, has not changed significantly. But the external record, in books, and other long lasting forms of storage, has grown enormously. Some people would use the term, evolution, only for the internally transmitted genetic material, and would object to it being applied to information handed down externally. But I think that is too narrow a view. We are more than just our genes. We may be no stronger, or inherently more intelligent, than our cave man ancestors. But what distinguishes us from them, is the knowledge that we have accumulated over the last ten thousand years, and particularly, over the last three hundred. I think it is legitimate to take a broader view, and include externally transmitted information, as well as DNA, in the evolution of the human race.
The time scale for evolution, in the external transmission period, is the time scale for accumulation of information. This used to be hundreds, or even thousands, of years. But now this time scale has shrunk to about 50 years, or less. On the other hand, the brains with which we process this information have evolved only on the Darwinian time scale, of hundreds of thousands of years. This is beginning to cause problems. In the 18th century, there was said to be a man who had read every book written. But nowadays, if you read one book a day, it would take you about 15,000 years to read through the books in a national Library. By which time, many more books would have been written.
This has meant that no one person can be the master of more than a small corner of human knowledge. People have to specialise, in narrower and narrower fields. This is likely to be a major limitation in the future. We certainly can not continue, for long, with the exponential rate of growth of knowledge that we have had in the last three hundred years. An even greater limitation and danger for future generations, is that we still have the instincts, and in particular, the aggressive impulses, that we had in cave man days. Aggression, in the form of subjugating or killing other men, and taking their women and food, has had definite survival advantage, up to the present time. But now it could destroy the entire human race, and much of the rest of life on Earth. A nuclear war, is still the most immediate danger, but there are others, such as the release of a genetically engineered virus. Or the green house effect becoming unstable.
There is no time, to wait for Darwinian evolution, to make us more intelligent, and better natured. But we are now entering a new phase, of what might be called, self designed evolution, in which we will be able to change and improve our DNA. There is a project now on, to map the entire sequence of human DNA. It will cost a few billion dollars, but that is chicken feed, for a project of this importance. Once we have read the book of life, we will start writing in corrections. At first, these changes will be confined to the repair of genetic defects, like cystic fibrosis, and muscular dystrophy. These are controlled by single genes, and so are fairly easy to identify, and correct. Other qualities, such as intelligence, are probably controlled by a large number of genes. It will be much more difficult to find them, and work out the relations between them. Nevertheless, I am sure that during the next century, people will discover how to modify both intelligence, and instincts like aggression.
Laws will be passed, against genetic engineering with humans. But some people won’t be able to resist the temptation, to improve human characteristics, such as size of memory, resistance to disease, and length of life. Once such super humans appear, there are going to be major political problems, with the unimproved humans, who won’t be able to compete. Presumably, they will die out, or become unimportant. Instead, there will be a race of self-designing beings, who are improving themselves at an ever-increasing rate.
If this race manages to redesign itself, to reduce or eliminate the risk of self-destruction, it will probably spread out, and colonise other planets and stars. However, long distance space travel, will be difficult for chemically based life forms, like DNA. The natural lifetime for such beings is short, compared to the travel time. According to the theory of relativity, nothing can travel faster than light. So the round trip to the nearest star would take at least 8 years, and to the centre of the galaxy, about a hundred thousand years. In science fiction, they overcome this difficulty, by space warps, or travel through extra dimensions. But I don’t think these will ever be possible, no matter how intelligent life becomes. In the theory of relativity, if one can travel faster than light, one can also travel back in time. This would lead to problems with people going back, and changing the past. One would also expect to have seen large numbers of tourists from the future, curious to look at our quaint, old-fashioned ways.
It might be possible to use genetic engineering, to make DNA based life survive indefinitely, or at least for a hundred thousand years. But an easier way, which is almost within our capabilities already, would be to send machines. These could be designed to last long enough for interstellar travel. When they arrived at a new star, they could land on a suitable planet, and mine material to produce more machines, which could be sent on to yet more stars. These machines would be a new form of life, based on mechanical and electronic components, rather than macromolecules. They could eventually replace DNA based life, just as DNA may have replaced an earlier form of life.
This mechanical life could also be self-designing. Thus it seems that the external transmission period of evolution, will have been just a very short interlude, between the Darwinian phase, and a biological, or mechanical, self design phase. This is shown on this next diagram, which is not to scale, because there’s no way one can show a period of ten thousand years, on the same scale as billions of years. How long the self-design phase will last is open to question. It may be unstable, and life may destroy itself, or get into a dead end. If it does not, it should be able to survive the death of the Sun, in about 5 billion years, by moving to planets around other stars. Most stars will have burnt out in another 15 billion years or so, and the universe will be approaching a state of complete disorder, according to the Second Law of Thermodynamics. But Freeman Dyson has shown that, despite this, life could adapt to the ever-decreasing supply of ordered energy, and therefore could, in principle, continue forever.
What are the chances that we will encounter some alien form of life, as we explore the galaxy. If the argument about the time scale for the appearance of life on Earth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before the Earth. So why is the galaxy not crawling with self designing mechanical or biological life forms? Why hasn’t the Earth been visited, and even colonised. I discount suggestions that UFO’s contain beings from outer space. I think any visits by aliens, would be much more obvious, and probably also, much more unpleasant.
What is the explanation of why we have not been visited? One possibility is that the argument, about the appearance of life on Earth, is wrong. Maybe the probability of life spontaneously appearing is so low, that Earth is the only planet in the galaxy, or in the observable universe, in which it happened. Another possibility is that there was a reasonable probability of forming self reproducing systems, like cells, but that most of these forms of life did not evolve intelligence. We are used to thinking of intelligent life, as an inevitable consequence of evolution. But the Anthropic Principle should warn us to be wary of such arguments. It is more likely that evolution is a random process, with intelligence as only one of a large number of possible outcomes. It is not clear that intelligence has any long-term survival value. Bacteria, and other single cell organisms, will live on, if all other life on Earth is wiped out by our actions. There is support for the view that intelligence, was an unlikely development for life on Earth, from the chronology of evolution. It took a very long time, two and a half billion years, to go from single cells to multi-cell beings, which are a necessary precursor to intelligence. This is a good fraction of the total time available, before the Sun blows up. So it would be consistent with the hypothesis, that the probability for life to develop intelligence, is low. In this case, we might expect to find many other life forms in the galaxy, but we are unlikely to find intelligent life. Another way, in which life could fail to develop to an intelligent stage, would be if an asteroid or comet were to collide with the planet. We have just observed the collision of a comet, Schumacher-Levi, with Jupiter. It produced a series of enormous fireballs. It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out. It is difficult to say how often such collisions occur, but a reasonable guess might be every twenty million years, on average. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.
A third possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, in the external transmission phase. But at that point, the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true. I prefer a fourth possibility: there are other forms of intelligent life out there, but that we have been overlooked. There used to be a project called SETI, the search for extra-terrestrial intelligence. It involved scanning the radio frequencies, to see if we could pick up signals from alien civilisations. I thought this project was worth supporting, though it was cancelled due to a lack of funds. But we should have been wary of answering back, until we have develop a bit further. Meeting a more advanced civilisation, at our present stage, might be a bit like the original inhabitants of America meeting Columbus. I don’t think they were better off for it.
That is all I have to say. Thank you for listening.
 
………….STEPHEN HAWKING

>STEPHEN HAWKING (விஞ்ஞானி "ஸ்டீபன் ஹாக்கிங்" )

>

STEPHEN HAWKING

I am quite often asked: How do you feel about having ALS? The answer is, not a lot. I try to lead as normal a life as possible, and not think about my condition, or regret the things it prevents me from doing, which are not that many.
It was a great shock to me to discover that I had motor neurone disease. I had never been very well co-ordinated physically as a child. I was not good at ball games, and my handwriting was the despair of my teachers. Maybe for this reason, I didn’t care much for sport or physical activities. But things seemed to change when I went to Oxford, at the age of 17. I took up coxing and rowing. I was not Boat Race standard, but I got by at the level of inter-College competition.
In my third year at Oxford, however, I noticed that I seemed to be getting more clumsy, and I fell over once or twice for no apparent reason. But it was not until I was at Cambridge, in the following year, that my father noticed, and took me to the family doctor. He referred me to a specialist, and shortly after my 21st birthday, I went into hospital for tests. I was in for two weeks, during which I had a wide variety of tests. They took a muscle sample from my arm, stuck electrodes into me, and injected some radio opaque fluid into my spine, and watched it going up and down with x-rays, as they tilted the bed. After all that, they didn’t tell me what I had, except that it was not multiple sclerosis, and that I was an a-typical case. I gathered, however, that they expected it to continue to get worse, and that there was nothing they could do, except give me vitamins. I could see that they didn’t expect them to have much effect. I didn’t feel like asking for more details, because they were obviously bad.
The realisation that I had an incurable disease, that was likely to kill me in a few years, was a bit of a shock. How could something like that happen to me? Why should I be cut off like this? However, while I had been in hospital, I had seen a boy I vaguely knew die of leukaemia, in the bed opposite me. It had not been a pretty sight. Clearly there were people who were worse off than me. At least my condition didn’t make me feel sick. Whenever I feel inclined to be sorry for myself I remember that boy.
Not knowing what was going to happen to me, or how rapidly the disease would progress, I was at a loose end. The doctors told me to go back to Cambridge and carry on with the research I had just started in general relativity and cosmology. But I was not making much progress, because I didn’t have much mathematical background. And, anyway, I might not live long enough to finish my PhD. I felt somewhat of a tragic character. I took to listening to Wagner, but reports in magazine articles that I drank heavily are an exaggeration. The trouble is once one article said it, other articles copied it, because it made a good story. People believe that anything that has appeared in print so many times must be true.
My dreams at that time were rather disturbed. Before my condition had been diagnosed, I had been very bored with life. There had not seemed to be anything worth doing. But shortly after I came out of hospital, I dreamt that I was going to be executed. I suddenly realised that there were a lot of worthwhile things I could do if I were reprieved. Another dream, that I had several times, was that I would sacrifice my life to save others. After all, if I were going to die anyway, it might as well do some good. But I didn’t die. In fact, although there was a cloud hanging over my future, I found, to my surprise, that I was enjoying life in the present more than before. I began to make progress with my research, and I got engaged to a girl called Jane Wilde, whom I had met just about the time my condition was diagnosed. That engagement changed my life. It gave me something to live for. But it also meant that I had to get a job if we were to get married. I therefore applied for a research fellowship at Gonville and Caius (pronounced Keys) college, Cambridge. To my great surprise, I got a fellowship, and we got married a few months later.

The fellowship at Caius took care of my immediate employment problem. I was lucky to have chosen to work in theoretical physics, because that was one of the few areas in which my condition would not be a serious handicap. And I was fortunate that my scientific reputation increased, at the same time that my disability got worse. This meant that people were prepared to offer me a sequence of positions in which I only had to do research, without having to lecture.
We were also fortunate in housing. When we were married, Jane was still an undergraduate at Westfield College in London, so she had to go up to London during the week. This meant that we had to find somewhere I could manage on my own, and which was central, because I could not walk far. I asked the College if they could help, but was told by the then Bursar: it is College policy not to help Fellows with housing. We therefore put our name down to rent one of a group of new flats that were being built in the market place. (Years later, I discovered that those flats were actually owned by the College, but they didn’t tell me that.) However, when we returned to Cambridge from a visit to America after the marriage, we found that the flats were not ready. As a great concession, the Bursar said we could have a room in a hostel for graduate students. He said, “We normally charge 12 shillings and 6 pence a night for this room. However, as there will be two of you in the room, we will charge 25 shillings.” We stayed there only three nights. Then we found a small house about 100 yards from my university department. It belonged to another College, who had let it to one of its fellows. However he had moved out to a house he had bought in the suburbs. He sub-let the house to us for the remaining three months of his lease. During those three months, we found that another house in the same road was standing empty. A neighbour summoned the owner from Dorset, and told her that it was a scandal that her house should be empty, when young people were looking for accommodation. So she let the house to us. After we had lived there for a few years, we wanted to buy the house, and do it up. So we asked my College for a mortgage. However, the College did a survey, and decided it was not a good risk. In the end we got a mortgage from a building society, and my parents gave us the money to do it up. We lived there for another four years, but it became too difficult for me to manage the stairs. By this time, the College appreciated me rather more, and there was a different Bursar. They therefore offered us a ground floor flat in a house that they owned. This suited me very well, because it had large rooms and wide doors. It was sufficiently central that I could get to my University department, or the College, in my electric wheel chair. It was also nice for our three children, because it was surrounded by garden, which was looked after by the College gardeners.
Up to 1974, I was able to feed myself, and get in and out of bed. Jane managed to help me, and bring up the children, without outside help. However, things were getting more difficult, so we took to having one of my research students living with us. In return for free accommodation, and a lot of my attention, they helped me get up and go to bed. In 1980, we changed to a system of community and private nurses, who came in for an hour or two in the morning and evening. This lasted until I caught pneumonia in 1985. I had to have a tracheotomy operation. After this, I had to have 24 hour nursing care. This was made possible by grants from several foundations.

Before the operation, my speech had been getting more slurred, so that only a few people who knew me well, could understand me. But at least I could communicate. I wrote scientific papers by dictating to a secretary, and I gave seminars through an interpreter, who repeated my words more clearly. However, the tracheotomy operation removed my ability to speak altogether. For a time, the only way I could communicate was to spell out words letter by letter, by raising my eyebrows when someone pointed to the right letter on a spelling card. It is pretty difficult to carry on a conversation like that, let alone write a scientific paper. However, a computer expert in California, called Walt Woltosz, heard of my plight. He sent me a computer program he had written, called Equalizer. This allowed me to select words from a series of menus on the screen, by pressing a switch in my hand. The program could also be controlled by a switch, operated by head or eye movement. When I have built up what I want to say, I can send it to a speech synthesizer. At first, I just ran the Equalizer program on a desk top computer.
However David Mason, of Cambridge Adaptive Communication, fitted a small portable computer and a speech synthesizer to my wheel chair. This system allowed me to communicate much better than I could before. I can manage up to 15 words a minute. I can either speak what I have written, or save it to disk. I can then print it out, or call it back and speak it sentence by sentence. Using this system, I have written a book, and dozens of scientific papers. I have also given many scientific and popular talks. They have all been well received. I think that is in a large part due to the quality of the speech synthesiser, which is made by Speech Plus. One’s voice is very important. If you have a slurred voice, people are likely to treat you as mentally deficient: Does he take sugar? This synthesiser is by far the best I have heard, because it varies the intonation, and doesn’t speak like a Dalek. The only trouble is that it gives me an American accent.
I have had motor neurone disease for practically all my adult life. Yet it has not prevented me from having a very attractive family, and being successful in my work. This is thanks to the help I have received from Jane, my children, and a large number of other people and organisations. I have been lucky, that my condition has progressed more slowly than is often the case. But it shows that one need not lose hope.
                                                                                                           by Stephen Hawking

STEPHEN HAWKING (விஞ்ஞானி "ஸ்டீபன் ஹாக்கிங்" )

STEPHEN HAWKING

I am quite often asked: How do you feel about having ALS? The answer is, not a lot. I try to lead as normal a life as possible, and not think about my condition, or regret the things it prevents me from doing, which are not that many.
It was a great shock to me to discover that I had motor neurone disease. I had never been very well co-ordinated physically as a child. I was not good at ball games, and my handwriting was the despair of my teachers. Maybe for this reason, I didn’t care much for sport or physical activities. But things seemed to change when I went to Oxford, at the age of 17. I took up coxing and rowing. I was not Boat Race standard, but I got by at the level of inter-College competition.
In my third year at Oxford, however, I noticed that I seemed to be getting more clumsy, and I fell over once or twice for no apparent reason. But it was not until I was at Cambridge, in the following year, that my father noticed, and took me to the family doctor. He referred me to a specialist, and shortly after my 21st birthday, I went into hospital for tests. I was in for two weeks, during which I had a wide variety of tests. They took a muscle sample from my arm, stuck electrodes into me, and injected some radio opaque fluid into my spine, and watched it going up and down with x-rays, as they tilted the bed. After all that, they didn’t tell me what I had, except that it was not multiple sclerosis, and that I was an a-typical case. I gathered, however, that they expected it to continue to get worse, and that there was nothing they could do, except give me vitamins. I could see that they didn’t expect them to have much effect. I didn’t feel like asking for more details, because they were obviously bad.
The realisation that I had an incurable disease, that was likely to kill me in a few years, was a bit of a shock. How could something like that happen to me? Why should I be cut off like this? However, while I had been in hospital, I had seen a boy I vaguely knew die of leukaemia, in the bed opposite me. It had not been a pretty sight. Clearly there were people who were worse off than me. At least my condition didn’t make me feel sick. Whenever I feel inclined to be sorry for myself I remember that boy.
Not knowing what was going to happen to me, or how rapidly the disease would progress, I was at a loose end. The doctors told me to go back to Cambridge and carry on with the research I had just started in general relativity and cosmology. But I was not making much progress, because I didn’t have much mathematical background. And, anyway, I might not live long enough to finish my PhD. I felt somewhat of a tragic character. I took to listening to Wagner, but reports in magazine articles that I drank heavily are an exaggeration. The trouble is once one article said it, other articles copied it, because it made a good story. People believe that anything that has appeared in print so many times must be true.
My dreams at that time were rather disturbed. Before my condition had been diagnosed, I had been very bored with life. There had not seemed to be anything worth doing. But shortly after I came out of hospital, I dreamt that I was going to be executed. I suddenly realised that there were a lot of worthwhile things I could do if I were reprieved. Another dream, that I had several times, was that I would sacrifice my life to save others. After all, if I were going to die anyway, it might as well do some good. But I didn’t die. In fact, although there was a cloud hanging over my future, I found, to my surprise, that I was enjoying life in the present more than before. I began to make progress with my research, and I got engaged to a girl called Jane Wilde, whom I had met just about the time my condition was diagnosed. That engagement changed my life. It gave me something to live for. But it also meant that I had to get a job if we were to get married. I therefore applied for a research fellowship at Gonville and Caius (pronounced Keys) college, Cambridge. To my great surprise, I got a fellowship, and we got married a few months later.

The fellowship at Caius took care of my immediate employment problem. I was lucky to have chosen to work in theoretical physics, because that was one of the few areas in which my condition would not be a serious handicap. And I was fortunate that my scientific reputation increased, at the same time that my disability got worse. This meant that people were prepared to offer me a sequence of positions in which I only had to do research, without having to lecture.
We were also fortunate in housing. When we were married, Jane was still an undergraduate at Westfield College in London, so she had to go up to London during the week. This meant that we had to find somewhere I could manage on my own, and which was central, because I could not walk far. I asked the College if they could help, but was told by the then Bursar: it is College policy not to help Fellows with housing. We therefore put our name down to rent one of a group of new flats that were being built in the market place. (Years later, I discovered that those flats were actually owned by the College, but they didn’t tell me that.) However, when we returned to Cambridge from a visit to America after the marriage, we found that the flats were not ready. As a great concession, the Bursar said we could have a room in a hostel for graduate students. He said, “We normally charge 12 shillings and 6 pence a night for this room. However, as there will be two of you in the room, we will charge 25 shillings.” We stayed there only three nights. Then we found a small house about 100 yards from my university department. It belonged to another College, who had let it to one of its fellows. However he had moved out to a house he had bought in the suburbs. He sub-let the house to us for the remaining three months of his lease. During those three months, we found that another house in the same road was standing empty. A neighbour summoned the owner from Dorset, and told her that it was a scandal that her house should be empty, when young people were looking for accommodation. So she let the house to us. After we had lived there for a few years, we wanted to buy the house, and do it up. So we asked my College for a mortgage. However, the College did a survey, and decided it was not a good risk. In the end we got a mortgage from a building society, and my parents gave us the money to do it up. We lived there for another four years, but it became too difficult for me to manage the stairs. By this time, the College appreciated me rather more, and there was a different Bursar. They therefore offered us a ground floor flat in a house that they owned. This suited me very well, because it had large rooms and wide doors. It was sufficiently central that I could get to my University department, or the College, in my electric wheel chair. It was also nice for our three children, because it was surrounded by garden, which was looked after by the College gardeners.
Up to 1974, I was able to feed myself, and get in and out of bed. Jane managed to help me, and bring up the children, without outside help. However, things were getting more difficult, so we took to having one of my research students living with us. In return for free accommodation, and a lot of my attention, they helped me get up and go to bed. In 1980, we changed to a system of community and private nurses, who came in for an hour or two in the morning and evening. This lasted until I caught pneumonia in 1985. I had to have a tracheotomy operation. After this, I had to have 24 hour nursing care. This was made possible by grants from several foundations.

Before the operation, my speech had been getting more slurred, so that only a few people who knew me well, could understand me. But at least I could communicate. I wrote scientific papers by dictating to a secretary, and I gave seminars through an interpreter, who repeated my words more clearly. However, the tracheotomy operation removed my ability to speak altogether. For a time, the only way I could communicate was to spell out words letter by letter, by raising my eyebrows when someone pointed to the right letter on a spelling card. It is pretty difficult to carry on a conversation like that, let alone write a scientific paper. However, a computer expert in California, called Walt Woltosz, heard of my plight. He sent me a computer program he had written, called Equalizer. This allowed me to select words from a series of menus on the screen, by pressing a switch in my hand. The program could also be controlled by a switch, operated by head or eye movement. When I have built up what I want to say, I can send it to a speech synthesizer. At first, I just ran the Equalizer program on a desk top computer.
However David Mason, of Cambridge Adaptive Communication, fitted a small portable computer and a speech synthesizer to my wheel chair. This system allowed me to communicate much better than I could before. I can manage up to 15 words a minute. I can either speak what I have written, or save it to disk. I can then print it out, or call it back and speak it sentence by sentence. Using this system, I have written a book, and dozens of scientific papers. I have also given many scientific and popular talks. They have all been well received. I think that is in a large part due to the quality of the speech synthesiser, which is made by Speech Plus. One’s voice is very important. If you have a slurred voice, people are likely to treat you as mentally deficient: Does he take sugar? This synthesiser is by far the best I have heard, because it varies the intonation, and doesn’t speak like a Dalek. The only trouble is that it gives me an American accent.
I have had motor neurone disease for practically all my adult life. Yet it has not prevented me from having a very attractive family, and being successful in my work. This is thanks to the help I have received from Jane, my children, and a large number of other people and organisations. I have been lucky, that my condition has progressed more slowly than is often the case. But it shows that one need not lose hope.
                                                                                                           by Stephen Hawking