An Episode among the Many Contributions of Hans Bethe to Physics and Society
Wolfgang K.H. Panofsky
When President Eisenhower concluded that further development and spread of nuclear weapons had to be stopped, he was persuaded that an international ban on nuclear testing would be a major step toward this goal. Since the verifiability of such an agreement was in dispute, he embraced the idealistic concept that scientists from the states in an adversarial relationship should first meet to establish a technical basis for monitoring the cessation of nuclear weapons testing. This would lay the foundation for subsequent negotiations between politically instructed diplomats with the goal to attain a comprehensive nuclear test ban treaty. As a member of the President’s Science Advisory Committee (PSAC), Hans Bethe played a key role in developing this concept and its subsequent implementation. He chaired a subcommittee that reported on the diverse technical tools suitable to monitor nuclear test explosions conducted in the atmosphere, under water and underground. Methods analyzed were seismic detection, radio-nuclei sampling, underwater sound detection and the like. This committee became widely known as the “Bethe Panel.”
Following the completion of his report and other studies on the military significance of the test ban, PSAC advised the President that he should go forward with the proposal to convene a “Conference of Experts.” The Soviet Union agreed to the proposal; the resulting conference composed of scientists from the United States, Soviet Union, United Kingdom, France, Canada, Czechoslovakia, Poland and Romania convened in Geneva during the summer of 1958. The “Experts” were charged to assess the power of technical tools to detect and identify nuclear explosions. On the U.S. side, this scientific group was chaired by James Fisk, then president of the Bell Telephone Laboratory, an engineering physicist and experienced manager. The other U.S. delegates were E.O. Lawrence and Robert Bacher. They were supported by Bethe and a group of the most experienced U.S. scientists in the field independent of their political views on the test ban. The Soviet delegates were Federov (Chairman), Semenov, and Tsarapkin, who were also supported by prominent senior Soviet scientists, including Igor Tamm and others. (Tamm and Semenov were Nobel Laureates.)
It is noteworthy that, notwithstanding the vaunted objectivity of science, disagreements during negotiations tended to be in the same direction: the Soviet scientists always claimed that detection and identification were more powerful than the Americans maintained. Not accidentally, these disagreements matched the political interests of the parties: the Soviet Union opposed the necessity of extensive on-site inspections as interfering with their penchant for secrecy, while the U.S. was intent to strengthen verification. Nevertheless, in the face of these difficulties, the scientists crafted their joint report. Hans Bethe’s and President Eisenhower’s desire for cessation of nuclear weapons tests appeared closer to reality.
On the basis of the report of the Conference of Exerts, which concluded that verification of a ban was possible within specified limits, the negotiations on a comprehensive test ban began on a political level in the fall of 1958 between the U.S., Soviet Union and the U.K. Soon after these negotiations began, new seismic information was developed as a result of further U.S. underground testing which suggested to some that the threshold of detection of underground tests would be higher than previously believed. In addition, methods of avoiding the Expert’s monitoring system were proposed by the scientific opponents of impediments to nuclear testing, led by Edward Teller. They invented theoretically feasible means by which the Soviets could evade the proposed monitoring methods. Teller’s associates, notably a group of capable physicists from the Rand Corporation in Santa Monica, California, and at the Livermore Laboratory invented two methods for such evasion: First, “decoupling” nuclear explosions underground by detonating them in the center of a “big hole.” Such a cavity was to be large enough such that the pressure wave generated by the explosion would be sufficiently weak by the time it reached the cavity walls so that the elastic limit of the surrounding medium (rock or salt) would not be exceeded. Such decoupling would reduce the seismic signal by about 2 orders of magnitude, thereby severely degrading the detection and identification power of seismic instruments.
The second evasion method was nuclear weapons testing in outer space, possibly even behind the moon. One rocket would carry the nuclear device to be detonated to distances up to tens or even hundreds of thousands of kilometers; a second rocket would deploy the necessary test instruments in the vicinity of the detonation of the nuclear device carried by the first rocket, and then send the results to earth by telemetry. These evasion schemes were proposed under the implied assumption that the Soviets would do what they could do, a forerunner of the “capabilities based” approach promoted by the present Administration to justify weapons acquisition or even pre-emptive attack to counteract the perceived capability of an opponent.
The theory of decoupling through use of the “big hole” is undeniably correct; the additional, but important, issue is how to construct undetected such a cavity of a diameter exceeding a hundred meters underground and how to assure its structural integrity. A nuclear testing program in space is an issue sufficiently complex that the President’s Science Advisor convened a special panel which I chaired and which included both Bethe and Teller among its members. That panel did not deny the scientific and technical feasibility of testing in outer space. However, it analyzed the effort in money and manpower such an undertaking would imply and the likelihood of success of such an enterprise. In consequence, the clear implication was that if the Soviets were to undertake such an evasion scheme, the effort diverted for that purpose from other military pursuits would be so large that U.S. security might be well served! The report was unanimously endorsed –including acceptance by both Bethe and Teller!
PSAC decided that the new information had to be presented in Geneva lest U.S. scientific credibility be degraded when that information inevitably became publicly known. In consequence, the United States government persuaded the Soviets to reopen the technical discussion to discuss “new data” that had become available since the Conference of Experts. The Soviets initially objected to reopening the technical discussions, maintaining that the Report of the Conference of Experts was the legal basis for the political discussion and therefore immutable. The U.S.’s position that the Report was a scientific-technical finding, and therefore subject to correction based on “new data,” eventually prevailed. Accordingly, two further technical negotiations were convened: one called Technical Working Group I (TWG- I); the U.S. delegation was again chaired by Fisk to update the assessment of seismic monitoring including the consideration of the implications of the ‘big hole.” The second group which I chaired (TWG-II) was to consider the monitoring of test explosions in outer space. The Soviet delegation was led by the geologist and explorer Federov.
The U.S. delegation to TWG-I agreed that Bethe should present the “big hole” idea, which he had concluded was theoretically sound, to the Soviets and he graciously agreed to take on that onerous task. The belief was that his distinguished reputation as a meticulous physicist who was known to favor a test ban would persuade the Soviets of the seriousness of the problem without suggesting to them that the U.S. was seeking to torpedo the negotiation by implicitly repudiating the Conference of Experts by showing the Soviets how to cheat! The Soviet delegation was stunned, but did not contradict the physical basis of the idea which appeared new to them. But they asked whether the U.S. delegation had political motives to bring this up. Still TWG-I reached agreement on the basic facts as to how a seismic signal would relate to the yield of a nuclear explosion, in essential agreement with the conclusions reached by the Conference of Experts.
TWG-II convened subsequently, also in Geneva and addressed the monitoring of explosions in outer space. We agreed on most of the detection methods for detecting soft x-ray and gamma ray fluxes from a nuclear explosion, and we estimated the intensity of such fluxes from weapons of various yields. In fact, during these negotiations some ideas were introduced by the U.S. delegation on the use of detection of single photons which apparently made it easier to detect such explosions than the Soviets had thought. However, the Soviet side balked at including in the list of detection approaches a method called ionospheric radar; this consisted of observing the disturbance in the ionosphere caused by the deposition of soft x-rays emitted by the exploding device which in turn would modify the reflection of radiowaves from the ground. The Soviets did not explain why they objected to this method, but it became clear that they were concerned that ionospheric radars could also detect missile traversals through the ionosphere. In a private session with Federov, I maintained that we were to assess the narrow issue of monitoring nuclear explosions while Federov replied, “I am to take all factors into account,” -- so much for the separation of scientifically relevant facts from political or strategic considerations. We then agreed to disagree on this point.
Notwithstanding some of these inherent tensions, the scientific delegation to the Conference of Experts, TWG-I and TWG-II, produced serious reports which broadly outlined the state of knowledge of detection and identification of nuclear weapons tests at that time. The rest is history. When the negotiations continued on the political level, disagreement persisted between the U.S. and Soviet sides on the number of on-site inspections which could be triggered by suspicious events. These disagreements frustrated the strongly expressed hopes of President Eisenhower and Hans Bethe to achieve a complete cessation of nuclear tests. On his departure from office President Eisenhower stated that failure to achieve such cessation was one of the great disappointments of his presidency.
Hans Bethe lived long enough to see a progression of agreements limiting nuclear test explosions: the 1963 Limited Test Ban Treaty which ruled out all nuclear explosions other than those underground; the 1974 Treaties limiting the yield of underground explosions to 150 kilotons and forbidding so-called peaceful nuclear test explosions. Finally, the Comprehensive Test Ban Treaty was signed by 160 countries. The United States was the first to sign in 1996, but has not as yet ratified the treaty. Therefore, the treaty is not yet in force because ratification of all states having potential capability to produce nuclear weapons is required. Nevertheless, all states have obeyed a nuclear test moratorium after 1998 when India and Pakistan conducted their tests. No predictions are possible today whether, after over 2,000 nuclear test explosions, such tests will ever resume. Even more important, no one can be sure today whether nuclear weapons will ever be used in hostilities again since 1945 when two American bombs extinguished the lives of a quarter of a million people in Hiroshima and Nagasaki.
WKH (Pief) Panofsky
Director Emeritus, SLAC
Hans Bethe and Societal Issues
Edwin E. Salpeter
A whole issue of Physics Today will be devoted to Hans Bethe, so here I will only touch on his Physics and Society impact. My reminiscences, although largely from Cornell, go back almost 60 years. I will mention some of his subtler but nevertheless very influential achievements.
Hans A. Bethe was born in 1906 in Strasbourg, when it was part of Germany, and then moved to Frankfurt with his parents. His father, a professor of Physiology, was Protestant and his mother was Jewish. Hans was a promising theoretical physicist already in his twenties and had already worked with Enrico Fermi in Rome before leaving Germany permanently in 1933 because of the Nazi Race Laws. After two years in England he came to Cornell, where he launched the Physics Department into the top rank. In 1936/37 he wrote (partly with co-authors) the "Bethe Bible" on essentially all that was known about nuclear physics then. In the following two years he worked out how stars generate energy by converting hydrogen into helium and the Nobel Prize came in 1967.During the war he became the Head of the Theoretical Division for the Los Alamos Manhattan Project, which built the first fission nuclear bomb. He was masterful not only in the work he did himself but in stimulating diverse brilliant physicists under him into a coherent output .
Soon after the war Bethe got involved in public policy issues, much of the time on the opposite side to Edward Teller, despite their similar European backgrounds. Although Bethe lost a few important battles, such as the building of the hydrogen bomb and the removal of J. R. Oppenheimer's security clearance, admiration for his unwavering strength of character and defense of life grew. His pronouncements against the hydrogen bomb helped to alert the general public against the utterly insane weapons build-up during the cold war and the eventual decrease of the nuclear weapons arsenal is to his credit. His enormous prestige on policy issues was partly explained by his statement, "I am a Dove--but I am a TOUGH Dove," as he continued to work on technical military matters. The Limited Test Ban Treaty in 1963, and the more comprehensive one in 1996 (the latter not yet ratified) were substantial achievements.
Bethe helped to debunk the Anti Ballistic Missile defense system in three different periods: First under Presidents Johnson and Nixon, then under President Reagan with his "Star Wars" initiative, and now under President Bush with the Boost Phase plans. For each of the three initiatives Hans encouraged his younger colleagues to undertake detailed investigations, which showed that these initiatives are doomed to failure.
On most public policy issues Hans Bethe is on the side of moderate liberal scientists, such as members of the Union of Concerned Scientists. However, his attitude in favor of further nuclear fission power plants, as the lesser of two evils, is the one exception. He has given detailed technical arguments that the safety issues for a working reactor are not so severe, but this is one of few cases where he has "shown his age" over the last few decades. The main fears and dilemmas have switched from in-use reactors (in spite of Chernobyl) to the decommissioning and then the disposal of nuclear waste. Bethe has not had much input into these worries.
Hans had a subtler but important influence on his younger colleagues and on University administrators, both by teaching them directly and by being a role-model for sensible attitudes. I found that out already as a young graduate student in England 58 years ago when Hans would visit and go from one student to the next (like a chess master playing multiple boards), giving advice not only on physics itself but on questions about their future. He had a strong influence on Cornell University presidents and their staff on the principle of not allowing any classified work to be carried out on campus. Hans, of course, continued to work on classified matters and it was of considerable inconvenience to him to not have classified facilities nearby and yet he insisted on this. His example was not lost on Cornell and this principle has been kept all these decades and has been quietly passed on to some other universities. Again, in the Joe McCarthy era Hans quietly strengthened Cornell's' resolve to shield local victims of the McCarthy witch hunts.
Hans Bethe was a thoroughly happy man both in science and life, but he told me that the slow drift towards fascism in the present U.S. administration left him very frustrated. Just when speaking-out against belligerent horrors and loss of civil liberties became particularly important, he felt that he was no longer listened to and so he did not speak. Worse, his younger colleagues were not speaking out as he had done at their age. Some of the Fascist parallels just cannot be appreciated fully by "youngsters" in their seventies and eighties, like myself. Unlike us, Hans was there in the Weimar Republic where citizens were not against democracy but just did not want to make waves. Unlike us, he was in Rome in the early Mussolini days during preparations for an attack on Abyssinia. The parallels between Iraq now and the occupation of Abyssinia then are particularly frightening: The occupation went quickly and easily but the understandable resentment of the Abyssinian populace led to troubles for Italian soldiers for many years and caused Mussolini to tell more lies.
We all revere the memory of Hans Bethe, and I hope that we will show it by clearly and forcefully speaking out now on the side of humanity.
Edwin E. Salpeter has been at Cornell University since 1949.
He is the J.G.White Distinguished Professor of Physical Sciences
Emeritus. He lived in Austria and in Australia and then first met
Hans Bethe in 1946 in England.
Hans Bethe - Last of the giants
Hans Bethe was the last of the giants of modern quantum and nuclear physics. He was present at its creation and for more than seven decades contributed enormously to deepening our understanding of the physical nature of the earth and the stars. Beyond his major contributions to advances in modern science and to the development of the atom bomb, he became an important and actively engaged leader among scientists who felt the responsibility of our community to help governments and societies understand the potential impact of these achievements on the human condition. To this end he contributed prodigiously throughout most of his life. As a government adviser at the highest levels and a participant in public forums he strove to ensure that consequences of scientific and technical advances – particularly in nuclear weapons and energy – were utilized toward peaceful and beneficial purposes.
I had the personal privilege of working with Hans for more than four decades on government committees concerned with nuclear weapons and arms control. Hans gave unstintingly of his enormous scientific talents to help the United States government make wise policy choices when it came to building a safe and reliable nuclear deterrent, to negotiating and verifying arms control treaties, and to understanding technical limits on complex systems. The batting average in activities of this type, measured by the ratio of successes in moving the policy decisions in the desired – and of course the correct – directions is not as high as one would hope. This, however, never discouraged Hans. He would just work harder the next time. I recall, in particular, our many sessions together in Washington and at the weapons labs trying to clarify the physical limits of potential ballistic missile defense systems, including exotic new concepts in the so-called Star Wars program during the 1980’s.
Hans always approached problems with an objective view based upon deep and sound scientific knowledge, which was the foundation of all his policy recommendations as well as his great scientific contributions. He was exemplary in shielding scientific facts from personal opinions or prejudices. This made his advice to governments and his public testimony uniquely valuable.
Perhaps Viki Weisskopf gave us the best description of Hans Bethe in 1995, during a celebration of Hans’s 60th anniversary as a professor at Cornell University, when he characterized him as a “dreadnaught” plowing straight ahead with irresistible force to achieve his scientific, technical, and policy goals. He was a giant in his time. We are all going to miss him.
Stanford Linear Accelerator Center