HANS ALBRECHT BETHE: PHYSICIST EXTRAORDINAIRE (1906-2005)


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Hans Bethe, one of the true titans of twentieth century physics, and probably the greatest scientist who was alive, is dead at 98. A Nobel Laureate, he was Professor emeritus at Cornell University, where he had been ever since 1935. Among many outstanding discoveries, he was especially noted for his discovery of the nuclear processes that fuel the stars. With him, a remarkable and extraordinary age; the golden age of physics and the atomic age, finally passes into history.

When I heard this news, I got a sinking feeling in my heart, and immediately wanted to write about him to 'get it out of my system'. He was one of my favourite scientists. It is strange what impact unrelated people from past ages and faraway places make on you. Frankly, I was awaiting this news for some time now (you have to be realistic; he was in his nineties). Strangely, even though the news is quite saddening, it fills me with the kind of pensive peace that fills you upon hearing about an inevitability. I am not a physicist. But as a student of the history of physics, here's my humble two cents...my tribute to this great man.

It would be very difficult for me to write about Bethe in a short space. However, I will make an attempt to write a short biography on the spur of the moment, based on what I have read about him and the period which he lived in. Bethe was one of my most admired scientific figures, and I first encountered him many years ago, when I read Richard Feynman's delightful and well-known memoir, 'Surely you're joking Mr. Feynman!'. He was a scientist and humanitarian by the highest standards that could possibly be applied to anybody. He made pioneering contributions in almost every branch of modern physics. In many of these, he set the trends, and built the foundations upon which all future research was built. Most importantly, he was the last great survivor and one of the prime participants of an era which changed the face of our world and our existence forever; the nuclear age, preceded by the great age of the birth of modern physics. First, as head of the theoretical division of the Manhattan Project, and then as a member of many committees on nuclear disarmament, arms control, and nuclear power, Bethe in many ways represented the conscience of the scientist. He personally knew most of the outstanding physicists of the century. Even a partial list of his friends, teachers, and associates reads as a list of the greatest minds of our time; Niels Bohr, Arnold Sommerfeld, Robert Oppenheimer, Enrico Fermi, Richard Feynman, Freeman Dyson, Robert Wilson, Edward Teller, and John von Neumann, to name just a few. To many of these, his was a reassuring presence, and his strong personality was frequently a support to them in many ways.

EARLY YEARS:
Hans Albrecht Bethe was born in Strasbourg, Germany in 1906. His father was a medical physiologist. Ever since he was a child, Hans was fascinated by numbers and had an outstanding natural mathematical ability. The household was a quiet one; later, Hans's mother would have to be admitted to an asylum. Clumsiness with his hands decided Hans's destiny early on. Fortunately, he was born, and would live his life, in a time when our perception of the physical world was being changed completely; the dual edifices of quantum theory and relativity were demolishing earlier conceptions of space and time, and casting completely knew and astoundingly unintuitive light on our view of space and time, and matter. Mathematics was essential for understanding these abstract theories, and Bethe's talents could not have been better suited for the task.
Bethe attended the schools in Strasbourg, and for his PhD., decided to apprentice himself to Arnold Sommerfeld at Munich, who along with Niels Bohr, was probably the greatest teacher of theoretical physics in the world. Bethe was one of his favourite students, and during his tenure in Munich, he met and formed long-lasting associations with the great physicists of the time; at that time, students all over the world were flocking to Europe to immerse themselves in the study of the new quantum theory. At nearby Gottingen, a host of remarkable men of the likes of Max Born, Werner Heisenberg, Wolfgang Pauli and others were turning over the world of physics on its head. In Cambridge, men like Rutherford and Paul Dirac were creating and discovering fantastic facets of the atomic world. And in Copenhagen, Niels Bohr held court on the most intricate secrets of the quantum. It was a time such as no other, and Bethe benefited enormously.

MIDDLE YEARS AND SCIENTIFIC WORK:
After getting his PhD. Bethe spent a summer working with Enrico Fermi's famous group in Rome. This was a revelation to him. While Sommerfeld was a great physicist and teacher, his style was excessively mathematical and formal. From Fermi, Bethe learned how to do 'back of the envelope' calculations, and to not use complicated mathematics when the result could be obtained much more simply. These dual qualities that he picked up from Sommerfeld and Fermi would make Bethe a force to be reckoned with in the world of physics.
All seemed good for Bethe's future, and after teaching stints at Frankfurt and Munich, he accepted a post at the University of Tubingen. But as fate would have it, Hitler came to power in 1933 and issued the laws which decreed that anyone with a Jewish background could not occupy a respectable job in the country. One of Bethe's grandparents was a Jew; more than adequate a reason to warrant his dismissal from his job. When Bethe wrote to the well-known physicist Hans Geiger (of the Geiger counter fame), Geiger's reply was cold and completely unsympathetic. Bethe was fortunately offered a position at Cornell, and that would be his home away from home after that forever. Because of him, the University would become one of the finest centres of physics in the world. Bethe arrived in America in 1935, and almost immediately established himself as one of the leading physicists of his day. He wrote a famous article on the quantum mechanics of one and two electron systems during this time. Robert Bacher, who later became chief of the experimental division of the Manhattan Project, recalled how Bethe sat at a desk in a small room, and under a dim light there, wrote the entire article almost without a break. This event characterises two very important qualities in Bethe, stamina and and a quiet and indefatigable persistence, qualities that he would be quite famous for later.
While at Cornell, Bethe also met his future wife, Rose, who was the daughter of one of his Professors in Germany, the distinguished experimental physicist Paul Ewald. Throughout his life, Rose was to provide him with a quiet, strong and unwavering source of support and strength. They have two children, Henry and Monica, and three grandchildren.
It was during the 1930s that Bethe also wrote his famous articles on Nuclear Physics, that were published in the Reviews of Modern Physics. Together, these three massive review articles summarised almost everything that was known about the physics of nuclear systems until the time. They became known as 'Bethe's Bible' and served as a standard reference for the state of the science for many years.
Another important contribution that Bethe made during those years, which was crucial for chemistry, concrened the treatment of molecules and atoms in electric fields. This was the harbringer of 'crystal field theory' something that even I learnt about during my BSc.
The idea that finally got Bethe the Nobel Prize germinated at a conference in Ithaca, New York, that was organised to discuss nuclear reactions. The question turned to the origin of energy in the stars. A few years earlier, the physicists Rowan Atkinson and Fritz Houtermans had hypothesized that nuclear fusion could be responsible for the energy of the sun and stars. However, nobody knew the exact mechanism by which this took place. Bethe recounts how, on a train trip after the conference, he solved the problem in its essentiality. The 'carbon fusion cycle' which he discovered has now become part of astrophysical folklore. Bethe's work during that time marked the beginning of modern nuclear astrophysics, upon which almost all future developments are based. With these breakthroughs, Bethe put Cornell on the world-physics map.

THE WAR YEARS- LOS ALAMOS:
With 1939 came war. Bethe, who was not still a US citizen, could not technically work on classified war projects. By that time, many other brilliant scientists had emigrated from Europe to the United States to flee Nazism. These included John von Neumann, George Gamow, and the most famous of them all; Albert Einstein (who had taken up residence at the Institute for Advanced Study in Princeton). One scientist who was to become perhaps the most controversial post-war physicist in the United States had also left his native Hungary- Edward Teller. Teller, who was teaching at George Washington University, was Bethe's friend, and the two decided to see if they could possibly make a contribution to the war. They made a cross-country trip to California, where the distinguished aeronautical physicist from Hungary, Theodor von Karman was working at Caltech. Karman suggested that they work on the mechanism by which shock waves are propagated from a blast. This study would be very useful to the development of ballistics and missile launches. During the trip back home, Teller and Bethe came up with a treatment of the problem which became classified. Another important contribution that they made concerned the penetration of armor piercing shells and bullets.

In 1942, Bethe's life witnessed an important change, when Robert Oppenheimer invited him to participate in a top-secret Government project to produce a practical weapon in the form of a bomb. Initially Bethe did not believe that a chain reaction could be sustained in a practical manner in Uranium. In fact, before the war began and before fission was discovered, interestingly, he had strenuously argued against fission. But when he saw the first self-sustaining chain reacting pile that Enrico Fermi had constructed under the football stands of the University of Chicago, Bethe became convinced of the feasibility of the project. Before embarking on anything, he had a discussion with his wife, and decided that he must play his role before the Nazis could possibly get their hands on such a weapon. By this time, Bethe was a citizen, and in the summer of 1942, he took part in a secret discussion at Berkeley that discussed the theory behind a potential atomic weapon. The discussion was presided over by Oppenheimer, and Bethe called the time one of the most intellectually exciting times that he had participated in. During this time, an ominous possibility was raised by Teller; that the atomic bomb could potentially ignite the atmosphere of the earth. While Oppenheimer thought the possibility serious enough to go to Michigan and discuss it with Nobel Laureate Arthur Compton (one of the administrative heads of the project), Bethe, with his usual cool and calm attitude, did an all-night calculation and ruled out the possibility.

The culmination of this and many other events finally led to the establishment of the famous bomb laboratory at Los Alamos, New Mexico. Bethe found the time he spent here the most challenging time of his life. He enjoyed hiking in the mountains and developed a lifelong love of the outdoors. For the project, Oppenheimer made Bethe the head of the important theoretical division, probably the most dominant division in the laboratory. This was a move that highly irked the volatile Teller. However, Oppenheimer had good reason to take this step. After the war, Bethe himself testified that his slow, prodding, and persistent approach to problems was seen more as an asset than Teller's rash and brilliant attitude. To placate Teller, Oppenheimer let him pursue his own ominous ideas; the precursors to the development of a hydrogen bomb. However, sadly after this, relations between Teller and Bethe were always strained. During this time, Klaus Fuchs, who committed espionage for the Russians, was also in Bethe's division. Like everyone else, Bethe had no idea that Fuchs was a spy.

The rest of the Manhattan Project is history. During the development of the bomb, many moral and ethical dilemmas came up. Bethe was not really involved with facing these dilemmas. Not because he did not care; in fact far from it, as became clear after the war, but because at the time, as head of an important division, his job was to ensure that the project was led to fruition. Although he did participate in many discussions related to choice of targets, strategy of dropping the bomb etc., his first priority was to make sure the weapon would work. Finally, after three years of tremendous hard work and creativity, the first atomic bomb was exploded in the New Mexico desert on July 16, 1945. An anecdote during this time demonstrates Bethe's essential qualities. Just before the test, in a dummy explosion, doubt was cast about whether the bomb would work or not. The situation became very tense, especially for Oppenheimer, and the resolution of the problem depended on understanding the working of an important instrument designed to validate the test results. Bethe again stayed up all night and did calculations that indicated, that the machine had a flaw which would not have let it distinguish between a successful and unsuccessful test. The problem was solved and everybody breathed easy. Characteristic Bethe.
Of course, the bombs were finally used then, and it marked the beginning of a new age. Again, we don't know if Bethe had anything profound to say about the implications of the terrible weapon he had helped to create. Throughout his life, he used to say, 'I am not a philosopher'.

LATER YEARS: ARMS CONTROL:
After the war, Bethe wanted to immediately return to his life's pursuit- pure physics. He himself said that 'just like the soldiers, we had done our job, and now just like them, we wanted to go back to our universities to do what we liked best'.
By this time, because of the war work, Bethe had also become a superb applied scientist, in addition to being an extraordinary pure physicist. His persistent approach to problems earned him the nickname 'The Battleship', except that this equally formidable vessel usually boomed with laughter. In the words of Richard Feynman, who by now was his close friend and colleague, he was 'absolutely top-notch at calculation'. He knew literally hundreds of mathematical tricks that could simplify complex mathematical problems. However, when the situation demanded, he had tremendous energy and could also do extensive and tedious numerical work to get the solution. On rare occasions, his candor could be jarring. When asked by the physicist Victor Weiskopf about the complexity of a problem, he replied, 'For me, it would take three days, for you it would take three weeks'. This was not supposed to be a put-off in any way; it was a true fact that Weiskopf acknowledged. At Cornell, Bethe shared a close relationship with Feynman. During his time at Los Alamos, Feynman had used Bethe as his sounding board. This trend continued at Cornell, where Bethe was a reassuring presence for Feynman; he had lost his wife to tuberculosis during the war. People could hear the two arguing volubly many times; they called Feynman 'The Mosquito Boat'. At Cornell, Bethe trained many outstanding physicists, most notably the English physicist Freeman Dyson, who he called his most brilliant student. He was the centre of Cornell's scientific universe.

At Cornell, Bethe was interested in the new fields of particle physics and quantum electrodynamics; the interaction of light with matter. In order to map out future developments in physics, a series of distinguished conferences was organised, with Oppenheimer as presiding chair. To these conferences came the most brilliant breed of the young masters, in addition to the old school of experts. These included John Wheeler, Richard Feynman, Julian Schwinger, and Freeman Dyson, all of whom were going to play key roles in the development of physics in post-war America. Memorable during these conferences was Schwinger's marathon lecture, lasting for several hours. Purportedly, only Fermi and Bethe, who were known for their tremendous stamina, were alert (and awake) at the end of the lecture. At the conference, the most interesting and baffling problem that was discussed was of the so called Lamb Shift, concerning the difference in the energy levels of electrons. While nobody was making any headaway with the problem, Bethe provided the first calculation that indicated the way out of the difficulty. Again, he worked out the essential steps of the problem on a train journey. This gave an impetus to researchers like Feynman, who became the pioneers of modern quantum electrodynamics.

In the early 1950s, the Cold War started raging, and the paranoia of McCarthysm gripped the country. After the Soviets exploded their A-bomb, and the leakage of information through espionage became known, President Truman ordered a crash program to develop the H-bomb. At the helm of the effort was Bethe's old friend, Edward Teller. In 1950, Bethe wrote an article arguing against H-bomb development. But Teller tried to persuade Bethe to help him on the project. After a lot of deliberation, Bethe agreed to be a consultant on the project at Los Alamos, mainly because of the very interesting physics that it involved, and because at first he thought the project so unlikely, that he wanted to work on it merely to prove it impossible. After the H-bomb was developed however, Bethe became an outspoken critic of nuclear development. He served on the scientific advisory committee to Presidents Kennedy and Johnson. He began to make a case for discontinuation of nuclear testing. In 1963, Bethe was one of the driving forces behind the Limited Test Ban Treaty.
In 1954, Oppenheimer was put on trial and lost his security clearance during a much publicised hearing. Bethe unequivocally testified in favour of Oppenheimer; throughout his life he held him in great regard, and tried in vain to persuade Teller against testifying against the brilliant and committed scientist. Teller's testimony was particularly damning, and this event further and permanently widened the rift between him and Bethe. When Oppenheimer died in 1967, Bethe remarked that he felt almost as if he had lost an older brother.

In 1967, Bethe won the Nobel Prize for his work in deducing the source of energy in the stars. Freeman Dyson says that the Nobel Committe could have considered awarding the prize for many other contributions that he made. However, this discovery is particularly important; it is a deep and fundamental discovery related to our cosmic origins.

In 1968, Bethe essentially broke off with the Government. In a courageous article in Scientific American with the IBM physicist Richard Garwin, he laid down points that argued against the deployment of an anti ballistic missile system that the US Government was developing, ostensibly against Chinese ballistic missile attacks. In the article, the two authors argued how ANY system that the US could develop could not possibly contain such an attack; in fact if anything, it would lead to bitter conflict between the two sides. I have read this article and it is a remarkable model of clarity and candor. This event demonstrates Bethe's conviction and integrity as a humanitarian, assets that he continued to exemplify.
In 1983, at President Reagan's initiative, the Strategic Defense Initiative (SDI) or 'Star Wars' system was conceived, that was designed to act as a 'missile shield' for a possible Soviet attack. (Teller, again, was one of the chief architects). Bethe and Garwin, along with Cornell physicist Kurt Gottfried, wrote another aticle akin to the earlier one, arguing against the futility of the system and the enormous sums of money that were being spent on its development.
In 1985, after the Chernobyl disaster, Bethe put together a committee of experts that analysed the accident. They cited human error and a fundamentally faulty design as the cause, and so ruled out the accident happening in any reasonably good US reactor. Bethe was always an outspoken advocate of electricity from nuclear power, and believed that it represented the best hope of the world for the future energy crisis. He served on many committees that investigated reactor technology and its development. His assesments will surely be borne out by time.

All through the 1970s, 80s and 90s, Bethe kept working on cutting edge problems in physics, mainly astrophysics, and 'political physics', as he called arms disarmament. He still carried his old slide-rule with him, and had no problem digesting reams of supercomputer printouts. Even after retiring and facing a debilitating condition that affects muscles and which limited the use of his left arm, he kept coming to his department everyday. He loved to lie in his bathtub for 45 minutes everyday; he said it got his thoughts in order. His hobbies included mountain climbing (his lifelong love) and stamp collecting; about the latter, he said that it is the only situation which enables all the countries in the world to live together in peace...
In the 1980s, well in his own eighties, Bethe started a collaboration with Gerald Brown of SUNY Stony Brook. Together, they published many articles about nuclear processes, especially in supernovae. In the mid 1980s, Bethe wrote an important article discussing the famous solar neutrino problem. Distinguished colleagues of his attest that they don't know of any scientist in the history of physics who has done such important work in his eighties. A couple of years ago, he gave a set of lectures on quantum physics to his neighbours to tell them of that wondrous age in which he had participated. We are lucky to have them online on the Cornell website.

In 1999, at the ripe old age of 93, this grand old man of science wrote a petition opposing the United States senate's decision to reject the Comprehensive Test Ban Treaty (CTBT). In it, Bethe outlined how this act is, if anything, going to lessen the US's advantage in maintaining a nuclear initiative. In the petition, as someone who was more worthy to comment on this than anybody else, he made an appeal to all scientists to desist working on nuclear weapons development.

BETHE'S CHARACTER AND LEGACY:
During my earlier readings, whenever I used to read about the atomic pioneers, Bethe always stood out as the quiet, brilliant, morally strong and unwavering, and concerned scientist that he was. Hans Bethe's life is an extraordinary example of achievement, concern and humanitarianism. He was a true giant of science. His colleague, the distinguished physicist Robert Wilson, said that his quintessential quality was 'responsibility'. Bethe shared his responsibility for his personal life, his personal and professional advancement, for physics in America, and for world physics. He participated in one of the most exciting ages in scientific history, and his stewardship in that age contributed a paradigm shift in our perception of science, politics and humanity.
He is the perfect example of the scientist-citizen. In his research he was indefatigable, and demonstrated extraordinary brilliance and perseverance. He was one of the last 'universalists' who contributed to virtually every branch of modern physics. In his public life, he was a quiet worker who went along doing his job and executing his responsibilities with characteristic fervor. When the time arose though, he was not one to shirk from being an outspoken advocate or opponent.
His colleagues always spoke fondly of him and with great reverence; I do not remember having read a single bad opinion about him uttered by anyone, including the sharp-tongued Oppenheimer.
Hans Bethe's life, in my opinion teaches us many things. It teaches us love for science and a basic love for our fellowmen. It demonstrates the responsibility that scientists have towards the public and the world. And it teaches us never to lose our wonder for the universe, and never to lose our conviction towards humanity and most importantly, oneself. It is truly an extraordinary life.
He will be sorely missed.

References:
1. Hans Bethe: Prophet of Energy- Jeremy Bernstein
2. Brighter than a Thousand Suns- Robert Jungk
3. The Making of the Atomic Bomb- Richard Rhodes
4. Enrico Fermi: Physicist- Emilio Segre
5. Cornell University website