Tribute to Stephen Hawking： D.N. Page, J.B. Hartle, L. Parker, and K.Thorne

Hello, I'm Don Page from the University of Alberta and I was a postdoctoral research fellow with Stephen Hawking and collaborated with him on several papers. I'm highly honored to have this opportunity to give a tribute to my mentor Stephen Hawking. Stephen William Hawking was certainly the most famous scientist of the late 20th century and early 21st century. I regard him as the greatest expert on gravity since Einstein. He contributed enormously to classical general relativity with his singularity theorems and black hole area theorem to quantum effects in curved space-time with Hawking radiation and to quantum gravity and cosmology with his Euclidean path integral and the Hartle-Hawking no boundary proposal for the quantum state of the of the universe and for the implications that it has for the development of structure in our universe from initial fluctuations. Stephen was also an inspiration to millions by the enormous courage he showed in overcoming severe physical disabilities. Stephen was also a devoted father and a champion for the disabled and also for the National Health Health Service in England. For me personally, Stephen had much more influence than any other scientist as I was privileged to have my PhD co-supervisor by him and by Kip Thorne at Caltech and to be Stephen's postdoc at the University of Cambridge for three years while living in his home. We wrote eight papers together and 10 other papers of mine have Hawking in the title and with many more of the 48 papers I've written with black hole in the title along with other papers on similar subjects that are analyzing Stephen's remarkable ideas. During the time I lived with the Hawking's from 1976 to 79, my godson Timon was born to the Hawking's on Easter 1979 and before he was born I had the early Easter service of bringing Stephen and Jane to the hospital at 6 a.m and then having a long wait in the waiting room out front. With messages from Jane that nothing was happening, I did go off to the Easter morning service at the Round Church and then again for Evensong though when I returned from Evensong I found that Tim had been born. Jane later wrote the following about me and music to move the stars and I quote, then Don burst triumphantly into the delivery room. He was pleased to make his acquaintance with his godson and he was even more pleased with himself on account of a little ditty he had thought up under turning from church. To my embarrassment he would repeat it to everyone he met for several weeks after the event. It went like this, on Easter day the disciples went to the garden and found the empty tomb. I went to the hospital and found the empty womb. I'm sure you will share my bewilderment that no other poetry that I've written has ever been published. Stephen had a great sense of humor and often uttered wry one-line jokes. When we brought our 11-month-old son Andrew to Cambridge and strapped him into a chair attached to the table at the Hawking home, Stephen piped up, whatever happened to baby liberation? Stephen never avoided self-deprecating humor either. Once he and I were beginning to write a paper whose conclusions differed from those of a previous paper that he had co-authored and Stephen commented, this is one way to increase one's publication list. First write one paper, then write another paper showing that the first one was wrong. Once when I lived with them, Stephen and Jane offered to take me with them to a cottage above the Wye River in Wales owned by Stephen's parents. There was a sloping paved path from the road to the cottage, so I loaded Stephen's wheelchair with all the batteries I could fit on the bottom to avoid having to carry them up by hand. Stephen started ahead while I collected my backpack and other things to carry, but he did not realize how heavily laden he was. I looked up just as Stephen had turned the corner to a steeper section I'd never seen before and then slowly toppled backward into the bushes. The greatest expert on gravity being overcome by the Earth's weak gravitational field. After I rushed as fast as I could up the slope with my backpack on, Stephen was angrily trying to say something to me, but for once I was fortunate that his voice was so garbled I could not make out the words. We did extract him with no serious injuries. As many of you know, Stephen and I had different theological opinions, with Stephen generally accepting with his good-natured humor. For example, in the mornings before getting Stephen up, I would usually read the Bible and then at breakfast often tell Stephen a bit of what I'd read. One day I told Stephen about the Gospel of Matthew, chapter 8, verses 28 to 34, where Jesus cast out an evil spirit into swine who rushed down into the sea. Stephen responded, the Society for the Prevention of Cruelty to Animals wouldn't like that story, would they? Another morning I recounted to Stephen the parable of the worker in the vineyard in Matthew 20, verses 1 to 16, where it all got paid the same full day's wage, no matter how long they'd work, and Stephen retorted, the trade unions would not like that story, would they? During another breakfast when I was feeding him, I told Stephen about Matthew 24, 40 to 42, which says, quote, then there shall be two men in the field, one will be taken and one will be left. Two women will be grinding at the mill, one will be taken and one will be left. Therefore, be on the alert for you to not know which day your Lord is coming. Stephen piped up, or two at the breakfast table. Stephen Hawking was indeed an outstanding scientist with remarkable insights and innovative ideas, as well as an excellent mentor and communicator of science. His persistence in the face of his severe physical disabilities is an inspiration, not only to those of us who knew him personally and or appreciated his scientific ideas, but also to people around the world who are only barely familiar with his academic achievements. It has been a great honor for me to have known and to have worked with Stephen, to whom I owe a wonderful career that I've enjoyed in science. 1971-72, I made a long visit to Fred Hoyle's Institute of Theoretical Astronomy, as it was known then. Pulsars, quasars, and the cosmic background radiation had been discovered a little bit before. I went to Cambridge to retrain in the promising emerging field of relativistic astrophysics. There I had my first interactions with Stephen Hawking on a scientific basis. Right away, we seemed to be on the same wavelength, not in the sense of abilities or insights, of course, but in the sense of what was important and interesting. There we wrote a paper on how two black holes with equal charges and masses could be in an unstable equilibrium positions. This was to be the first of 11 papers on black holes and cosmology that we wrote over the years. For me, the high point of our joint efforts is the paper on the no boundary wave function of the universe. A quantum theory, if you like, of the Big Bang, a quantum cosmology. For me, the high point was that the singularity theorems of Penrose and others showed that the universe had a beginning in a hot Big Bang, but they did not show how our particular present universe emerged from that fiery start. The singularity theorem showed that the validity of the classic cosmology of Einstein ends near the Big Bang, but they did not specify the quantum cosmology that replaces it. Stephen realized that the breakdown of classical spacetime meant that the early universe did not have to have the three space and one time dimensions of classical physics. In earlier joint work, we had demonstrated the power of Euclidean geometry to help understand another quantum phenomenon, the Hawking radiation from black holes. If the universe couldn't begin classically with a Lorentzian geometry, perhaps it could begin quantum mechanically with the Euclidean one and later make a transition to a Lorentzian geometry. The result of this way of thinking was the no boundary proposal for the quantum state of the universe. The no boundary wave function does not just inform us about the beginning of the universe. It also predicts many of the large scale features of the universe that we observe today. The existence of its classical spacetime, the approximate homogeneity and isotropy, the fluctuations away from these symmetries that we see today in the cosmic background radiation and in large scale distribution of galaxies. I mentioned that this was the high point for me, but I think it was also the high point for Stephen. He said to me once that he thought that the no boundary wave function was the best thing that either of us had done. Well, he was at least right on one part of that statement. Now I want to address briefly the qualities that enabled Stephen to make his great discoveries. The first I think is the unity of his physics. Black holes in the beginning of the universe may seem very different kinds of phenomena, but they are unified in several different ways. For example, they're both accessible by the global techniques that Stephen and others pioneered. They both have issues with singularities and they're both very important for physics. Stephen made such connections very naturally in the course of his work. Stephen knew, always knew, what the right question to ask was whose answer would move this forward. But he also knew what the right thing was to give up to answer that question. How to give up on the idea that black holes were black with nothing coming out of them to get to the Hawking radiation, which did come out of them. How to give up on the steady state idea that the universe had no beginning to show that it had to have a beginning. How to give up on the idea that space-time always has three space dimensions and one time dimension to get to a theory of the Big Bang that had four space and no time directions. How to give up on the idea that the universe inevitably had a classically singular beginning to give it a quantum regular start. Stephen's scientific legacy lies not only in his papers and the achievements, only some of which I've described, but in the inspiration, the encouragement, and the opportunity that he provided those of us that followed him. This is most concretely illustrated by the very many graduate students he produced, but it's also illustrated by the way he was able to inspire interest and connect with a very large general public. A scientist, Stephen will be ever in our minds for the many contributions he made on which we build, but for those of us like me who had the privilege of knowing and working with him, he will also be always in our hearts. Thank you. My name is Leonard Parker. I first met Stephen Hawking at a luncheon at which Bryce DeWitt introduced me to Hawking in 1966 and we talked. I had completed my work on my Harvard PhD thesis on particle creation by the expansion of the universe. My thesis advisor, Sidney Coleman, was away for a couple of years at Trieste, so my thesis exam would take place when he returned to Harvard. Bryce offered me a position as an instructor at the University of North Carolina at Chapel Hill, which I accepted. After Coleman returned to Harvard, I returned there to take my thesis defense in the fall of 1966. I passed. On my thesis defense committee were Sidney Coleman, Sheldon Glashow, and Walter Gilbert. The latter two won Nobel Prizes in physics and chemistry respectively. I published papers on my thesis and physical review letters in 1968 and physical review in 1969. By the way, I hesitated to mention anything about black hole particle creation at the time because I was not entirely sure about it, but at the time that I passed my thesis defense in 1968, I suggested to Sidney Coleman that we look into particle creation by the formation of a black hole because the process was analogous to the expansion of the universe and would create particles. He suggested that I contact John A. Wheeler at Princeton for a position to work on that. When I contacted Wheeler about that, he said that he had nothing at the time but that I could come if I had the funds. In 1969, after joining the University of Wisconsin at Milwaukee, I was awarded an NSF grant that included my proposal to work on particle creation by the collapse of matter to form a black hole. In 1970, I went to Princeton University as a visiting associate professor in the group of John A. Wheeler. Soon after I arrived at Princeton, Professor Arthur Whiteman asked me to become second reader for the PhD thesis of one of his students, Stephen Fuling, which I was pleased to do. Fuling became my first postdoc at UWM, later supported by my NSF grant. While at Princeton, I freely discussed that I was working on particle creation by a black hole and I even mentioned it in a colloquium I gave. Professor John A. Wheeler took an active interest in this work and we had several meetings on it. Hawking's genius was evident in his 1974 publication in Nature on the creation of particles in the collapse of matter to form a black hole, as well as in his many other insightful papers written under very difficult conditions. He basically developed the fundamental theory of black holes greatly. He went on as far as was possible at the time. I was honored to have him as a friend. Stephen Hawking and I were close personal friends. Our friendship was much more important to me than our shared science interests. I'd like to give you a few personal glimpses of Stephen that arise from that friendship. Stephen's zest for life was legendary. Here are three little examples that are burned into my visual and auditory memory. In spring 1997, at the inaugural ball for Caltech's new president, David Baltimore, Stephen drove his wheelchair onto the dance floor and executed whirl after whirl after whirl with Baltimore's daughter Teak flying around beside him, her hand tightly gripping one of the wheelchair's back supports. Later that year, in the depths of the Antarctic winter, Claudio Bunster arranged for the Chilean Air Force to fly Stephen and me and a few others to the tip of the Antarctic Peninsula in a Hercules C-134 cargo plane. Upon landing, when the cargo hatch was lowered, Stephen was the first out of the plane, driving his wheelchair as fast as he could into the blindingly white snow, a broad grin on his face as the chair slowed to a halt with wheels spinning in the snow. In February 2011, my wife and I took Stephen to see the play 33 Variations with the actress Jane Fonda as a musicologist afflicted with ALS, an ALS that evolved through the play in much the same way as Stephen's ALS evolved through his adult life. At Jane's request, after the play, we went backstage to meet her. Stephen greeted her with a broad grin on his face in the pre-programmed sentence, you were my idol. Not missing a beat, Jane responded, and what am I now, chopped liver? Stephen's grin broadened and they moved into about 20 minutes of slow repartee, visibly energized by each other. Stephen was the most stubborn person I ever knew. He refused, of course, to let his physical disability get in the way of his science. He also refused to let it get in the way of living a full and vigorous personal and social life. Whenever he visited me at Cal Tech, the intensity of my own social life tripled due to him. The only person I have ever known who could begin to match Stephen in stubbornness was his daughter Lucy, and when they were at loggerheads, the flying sparks were amazing to see. But their concern for each other, their love for each other, was also marvelous to behold. In his later years, when his computer generated speech was slowed to two or three words per minute or even less, he persisted seemingly endlessly in producing each word and then each sentence over a period of tens of minutes or hours, never showing anger and almost never giving up when a word failed to come out right, time after time after time after time. And if I tried to guess what that word was, so to speed up the conversation, he pushed doggedly forward, not letting me guess, but instead putting his own precise spin on all the words. The only exception was when a taxi was waiting to take me to the train or airport, and we absolutely had to complete our conversation. Only then would he let me guess and move onward from my guess, if I was more or less right. Stephen had a fabulous sense of humor. It infused his public lectures and his private conversations. As I watched him assemble a sentence laboriously, word by word, I often didn't know till nearly the end whether he was producing a pearl of great wisdom or an off-the-wall joke. I'll conclude with my own brief appraisal of Stephen's science, adapted from a eulogy that I gave after his death. Stephen, like Isaac Newton, guided the course of science through great discoveries, such as Hawking radiation, Stephen's laws of black hole thermodynamics, and with Jim Hartle, his no-boundary proposal for the creation of the universe. But Stephen's greatest impacts, I think, were the questions with which he challenged us, especially what is the origin of black hole entropy, and is information lost down black holes, or more precisely, is the evolution from a black hole's formation through its evaporation into Hawking radiation, is that evolution unitary, or is it non-unitary, thereby violating the tenets of quantum theory? And if unitary, how is that achieved? And if non-unitary, what's the correct formulation of quantum theory? Is it a Feynman sum over histories, which can accommodate non-unitary evolution? For more than 40 years, we physicists have struggled with Stephen's questions. They seem to be keys to help unlock the most difficult mystery we have ever tackled, the quest to discover and comprehend the laws that governed our universe's birth, the laws of quantum gravity. We remember Newton for answers. We remember Hawking for questions. And Hawking's questions themselves keep on giving, generating breakthroughs decades later. When ultimately we master the quantum gravity laws and fully comprehend the birth of the universe, we'll be at least in part by standing on the shoulders of Stephen Hawking.