In my eulogy for Stephen, at the interment of his ashes at Westminster Abbey, I memorialised that struggle with these words: “Newton gave us answers. Hawking gave us questions. And Hawking’s questions themselves keep on giving, generating breakthroughs decades later. When ultimately we master the quantum gravity laws, and comprehend fully the birth of our universe, it may largely be by standing on the shoulders of Hawking.”
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Just as our glorious 1974–5 year was only the beginning for my gravitational-wave quest, so it also was just the beginning for Stephen’s quest to understand in detail the laws of quantum gravity and what those laws say about the true nature of a black hole’s information and randomness, and also about the true nature of our universe’s singular birth, and the true nature of the singularities inside black holes—the true nature of the birth and death of time.
These are big questions. Very big.
I have shied away from big questions. I don’t have enough skills, wisdom or self-confidence to tackle them. Stephen, by contrast, was always attracted to big questions, whether they were deeply rooted in his science or not. He did have the necessary skills, wisdom and self-confidence.
This book is a compilation of his answers to the big questions, answers on which he was still working at the time of his death.
Stephen’s answers to six of the questions are deeply rooted in his science. (Is there a God? How did it all begin? Can we predict the future? What is inside a black hole? Is time travel possible? How do we shape the future?). Here you will find him discussing in depth the issues that I’ve described briefly in this Introduction, and also much, much more.
His answers to the other four big questions cannot possibly be rooted solidly in his science. (Will we survive on Earth? Is there other intelligent life in the universe? Should we colonise space? Will artificial intelligence outsmart us?) Nevertheless, his answers display deep wisdom and creativity, as we should expect.
I hope you find his answers as stimulating and insightful as do I. Enjoy!
Kip S. Thorne
July 2018
WHY WE MUST ASK THE BIG QUESTIONS
People have always wanted answers to the big questions. Where did we come from? How did the universe begin? What is the meaning and design behind it all? Is there anyone out there? The creation accounts of the past now seem less relevant and credible. They have been replaced by a variety of what can only be called superstitions, ranging from New Age to Star Trek. But real science can be far stranger than science fiction, and much more satisfying.
I am a scientist. And a scientist with a deep fascination with physics, cosmology, the universe and the future of humanity. I was brought up by my parents to have an unwavering curiosity and, like my father, to research and try to answer the many questions that science asks us. I have spent my life travelling across the universe, inside my mind. Through theoretical physics, I have sought to answer some of the great questions. At one point, I thought I would see the end of physics as we know it, but now I think the wonder of discovery will continue long after I am gone. We are close to some of these answers, but we are not there yet.
The problem is, most people believe that real science is too difficult and complicated for them to understand. But I don’t think this is the case. To do research on the fundamental laws that govern the universe would require a commitment of time that most people don’t have; the world would soon grind to a halt if we all tried to do theoretical physics. But most people can understand and appreciate the basic ideas if they are presented in a clear way without equations, which I believe is possible and which is something I have enjoyed trying to do throughout my life.
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 fifty years, and I’m happy if I have made a contribution. One of the great revelations of the space age has been the perspective it has given humanity on ourselves. When we see the Earth from space, we see ourselves as a whole. We see the unity, and not the divisions. It is such a simple image with a compelling message; one planet, one human race.
I want to add my voice to those who demand immediate action on the key challenges for our global community. I hope that going forward, even when I am no longer here, people with power can show creativity, courage and leadership. Let them rise to the challenge of the sustainable development goals, and act, not out of self-interest, but out of common interest. I am very aware of the preciousness of time. Seize the moment. Act now.
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I have written about my life before but some of my early experiences are worth repeating as I think about my lifelong fascination with the big questions.
I was born exactly 300 years after the death of Galileo, and I would like to think that this coincidence has had a bearing on how my scientific life has turned out. However, I estimate that about 200,000 other babies were also born that day; I don’t know whether any of them were later interested in astronomy.
I grew up in a tall, narrow Victorian house in Highgate, London, which my parents had bought very cheaply during the Second World War when everyone thought London was going to be bombed flat. In fact, a V2 rocket landed a few houses away from ours. I was away with my mother and sister at the time, and fortunately my father was not hurt. For years afterwards, there was a large bomb site down the road in which I used to play with my friend Howard. We investigated the results of the explosion with the same curiosity that drove me my whole life.
In 1950, my father’s place of work moved to the northern edge of London, to the newly constructed National Institute for Medical Research in Mill Hill, so my family relocated to the cathedral city of St Albans nearby. I was sent to the High School for Girls, which despite its name took boys up to the age of ten. Later I went to St Albans School. I was never more than about halfway up the class—it was a very bright class—but my classmates gave me the nickname Einstein, so presumably they saw signs of something better. When I was twelve, one of my friends bet another friend a bag of sweets that I would never come to anything.
I had six or seven close friends in St Albans, and I remember having long discussions and arguments about everything, from radio-controlled models to religion. One of the big questions we discussed was the origin of the universe, and whether it required a God to create it and set it going. I had heard that light from distant galaxies was shifted towards the red end of the spectrum and this was supposed to indicate that the universe was expanding. But I was sure there must be some other reason for the red shift. Maybe light got tired and more red on its way to us? An essentially unchanging and everlasting universe seemed so much more natural. (It was only years later, after the discovery of the cosmic microwave background about two years into my PhD research, that I realised I had been wrong.)
I was always very interested in how things operated, and I used to take them apart to see how they worked, but I was not so good at putting them back together again. My practical abilities never matched up to my theoretical qualities. My father encouraged my interest in science and was very keen that I should go to Oxford or Cambridge. He himself had gone to University College, Oxford, so he thought I should apply there. At that time, University College had no fellow in mathematics, so I had little option but to try for a scholarship in natural science. I surprised myself by being successful.
The prevailing attitude at Oxford at that time was very anti-work. You were supposed to be brilliant without effort, or to accept your limitations and get a fourth-class degree. I took this as an invitation to do very little. I’m not proud of this, I’m just describing my attitude at the time, shared by most of my fellow students. One result of my illness has been to change all that. When you are faced with the possibility of an early death, it makes you realise that there are lots of things you want to do before your life is over.
Because of my lack of work, I had planned to get through the final exam by avoiding questions
that required any factual knowledge and focus instead on problems in theoretical physics. But I didn’t sleep the night before the exam and so I didn’t do very well. I was on the borderline between a first-and second-class degree, and I had to be interviewed by the examiners to determine which I should get. In the interview they asked me about my future plans. I replied that I wanted to do research. If they gave me a first, I would go to Cambridge. If I only got a second, I would stay in Oxford. They gave me a first.
In the long vacation following my final exam, the college offered a number of small travel grants. I thought my chances of getting one would be greater the further I proposed to go, so I said I wanted to go to Iran. In the summer of 1962 I set out, taking a train to Istanbul, then on to Erzuerum in eastern Turkey, then to Tabriz, Tehran, Isfahan, Shiraz and Persepolis, the capital of the ancient Persian kings. On my way home, I and my travelling companion, Richard Chiin, were caught in the Bouin-Zahra earthquake, a massive 7.1 Richter quake that killed over 12,000 people. I must have been near the epicentre, but I was unaware of it because I was ill, and in a bus that was bouncing around on the Iranian roads that were then very uneven.
We spent the next several days in Tabriz, while I recovered from severe dysentery and from a broken rib sustained on the bus when I was thrown against the seat in front, still not knowing of the disaster because we didn’t speak Farsi. It was not until we reached Istanbul that we learned what had happened. I sent a postcard to my parents, who had been anxiously waiting for ten days, because the last they had heard I was leaving Tehran for the disaster region on the day of the quake. Despite the earthquake, I have many fond memories of my time in Iran. Intense curiosity about the world can put one in harm’s way, but for me this was probably the only time in my life that this was true.
I was twenty in October 1962, when I arrived in Cambridge at the department of applied mathematics and theoretical physics. I had applied to work with Fred Hoyle, the most famous British astronomer of the time. I say astronomer, because cosmology then was hardly recognised as a legitimate field. However, Hoyle had enough students already, so to my great disappointment I was assigned to Dennis Sciama, of whom I had not heard. But it was just as well I hadn’t been a student of Hoyle, because I would have been drawn into defending his steady-state theory, a task which would have been harder than negotiating Brexit. I began my work by reading old textbooks on general relativity—as ever, drawn to the biggest questions.
As some of you may have seen from the film in which Eddie Redmayne plays a particularly handsome version of me, in my third year at Oxford I noticed that I seemed to be getting clumsier. I fell over once or twice and couldn’t understand why, and I noticed that I could no longer row a sculling boat properly. It became clear something was not quite right, and I was somewhat disgruntled to be told by a doctor at the time to lay off the beer.
The winter after I arrived in Cambridge was very cold. I was home for the Christmas break when my mother persuaded me to go skating on the lake in St Albans, even though I knew I was not up to it. I fell over and had great difficulty getting up again. My mother realised something was wrong and took me to the doctor.
I spent weeks in St Bartholomew’s Hospital in London and had many tests. In 1962, the tests were somewhat more primitive than they are now. A muscle sample was taken from my arm, I had electrodes stuck into me and radio-opaque fluid was injected into my spine, which the doctors watched going up and down on X-rays, as the bed was tilted. They never actually told me what was wrong, but I guessed enough to know it was pretty bad, so I didn’t want to ask. I had gathered from the doctors’ conversations that it, whatever “it” was, would only get worse, and there was nothing they could do except give me vitamins. In fact, the doctor who performed the tests washed his hands of me and I never saw him again.
At some point I must have learned that the diagnosis was amyotrophic lateral sclerosis (ALS), a type of motor neurone disease, in which the nerve cells of the brain and spinal cord atrophy and then scar or harden. I also learned that people with this disease gradually lose the ability to control their movements, to speak, to eat and eventually to breathe.
My illness seemed to progress rapidly. Understandably, I became depressed and couldn’t see the point of continuing to research my PhD, because I didn’t know if I would live long enough to finish it. But then the progression slowed down and I had a renewed enthusiasm for my work. After my expectations had been reduced to zero, every new day became a bonus, and I began to appreciate everything I did have. While there’s life, there is hope.
And, of course, there was also a young woman called Jane, whom I had met at a party. She was very determined that together we could fight my condition. Her confidence gave me hope. Getting engaged lifted my spirits, and I realised, if we were going to get married, I had to get a job and finish my PhD. And as always, those big questions were driving me. I began to work hard and I enjoyed it.
To support myself during my studies, I applied for a research fellowship at Gonvillle and Cauis College. To my great surprise, I was elected and have been a fellow of Caius ever since. The fellowship was a turning point in my life. It meant that I could continue my research despite my increasing disability. It also meant that Jane and I could get married, which we did in July 1965. Our first child, Robert, was born after we had been married about two years. Our second child, Lucy, was born about three years later. Our third child, Timothy, would be born in 1979.
As a father, I would try to instill the importance of asking questions, always. My son Tim once told a story in an interview about asking a question which I think at the time he worried was a bit silly. He wanted to know if there were lots of tiny universes dotted around. I told him never to be afraid to come up with an idea or a hypothesis no matter how daft (his words not mine) it might seem.
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The big question in cosmology in the early 1960s 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. This was clearly a fundamental question, and it was just what I needed to complete my PhD thesis.
Roger Penrose had shown that once a dying star had contracted to a certain radius, there would inevitably be a singularity, that is a point where space and time came to an end. Surely, I thought, we already knew that nothing could prevent a massive cold star from collapsing under its own gravity until it reached a singularity of infinite density. I realised that similar arguments could be applied to the expansion of the universe. In this case, I could prove there were singularities where space–time had a beginning.
A eureka moment came in 1970, a few days after the birth of my daughter, Lucy. While getting into bed one evening, which my disability made a slow process, I realised that I could apply to black holes the casual structure theory I had developed for singularity theorems. If general relativity is correct and the energy density is positive, the surface area of the event horizon—the boundary of a black hole—has the property that it always increases when additional matter or radiation falls into it. Moreover, if two black holes collide and merge to form a single black hole, the area of the event horizon around the resulting black hole is greater than the sum of the areas of the event horizons around the original black holes.
This was a golden age, in which we solved most of the major problems in black hole theory even before there was any observational evidence for black holes. In fact, 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 our book The Large Scale Structure of Space–Time. 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. In particular, I wondered, can one
have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe? My investigations revealed a deep and previously unsuspected relationship between gravity and thermodynamics, the science of heat, and resolved a paradox that had been argued over for thirty years without much progress: how could the radiation left over from a shrinking black hole carry all of the information about what made the black hole? I discovered that information is not lost, but it is not returned in a useful way—like burning an encyclopedia but retaining the smoke and ashes.
To answer this, I studied how quantum fields or particles 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 itself. 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. This entropy, a measure of the disorder of a system, is summed up in this simple formula
which expresses the entropy in terms of the area of the horizon, and the three fundamental constants of nature, c, the speed of light, G, Newton’s constant of gravitation, and ħ, Planck’s constant. The emission of this thermal radiation from the black hole is now called Hawking radiation and I’m proud to have discovered it.
In 1974, I was elected a fellow of the Royal Society. This election came as a surprise to members of my department because I was young and only a lowly research assistant. But within three years I had been promoted to professor. My work on black holes had given me hope that we would discover a theory of everything, and that quest for an answer drove me on.
In the same year, my friend Kip Thorne invited me and my young family and a number of others working in general relativity to the California Institute of Technology (Caltech). For the previous four years, I had been using a manual wheelchair as well as a blue electric three-wheeled car, which went at a slow cycling speed, and in which I sometimes illegally carried passengers. When we went to California, we stayed in a Caltech-owned colonial-style house near campus and there I was able to enjoy full-time use of an electric wheelchair for the first time. It gave me a considerable degree of independence, especially as in the United States buildings and sidewalks are much more accessible for the disabled than they are in Britain.
Brief Answers to the Big Questions Page 2
