Subject Grouping: Praxis

It is sometimes said of someone that he or she was the right person in the right place at the right time. Never have I seen this more clearly than with Viki Weisskopf’s role as director-general at CERN. He was just the person needed, with his knowledge, his enthusiasm and his international network. With this and more, he had so much to give to CERN, but he probably also had in mind that this young, international institution that needed him might reward him with a very positive response to his special leadership.

The timing was important. In summer 1961, when Viki took over, CERN was perhaps not in a crisis but was nevertheless going through some very important transitions – a kind of puberty – with its uncertainties of direction.

Our founding fathers had done a wonderful job in creating this laboratory. They had selected a daring but very successful programme of accelerator construction. They had given us an unusually sound convention and had established a solid trust within the member states. CERN was considered, therefore, as a very successful organization in 1961, with one of the two best performing accelerators in the world. There were, however, a few aspects that the founding fathers had not foreseen or analysed in depth. Let us look at some issues that had surfaced by 1961.

One was the cost of operating such a laboratory. It became clear that the costs would be much higher than the member-state governments had anticipated, and a considerable amount of convincing was urgently needed. Viki and his collaborators succeeded in this.

Integration

Another aspect was how to integrate the high-energy physics groups in the universities and other laboratories in the member states into the experimental programme of CERN. Viki’s predecessors had arranged the formal framework for this, but the practice had to be established and much suspicion had to be overcome. Viki was superbly suited for this, being liked and trusted on all sides. In this connection I like to quote Viki’s own opening words in his last report to the Council in December 1965: “I would like to talk about the work of CERN. In fact, I will have to talk about the work of Europe. You cannot distinguish between the work in high-energy physics at CERN and in Europe. The work in Europe depends on CERN and the work of CERN depends on Europe.” This was Viki’s conviction and I feel that he must take much credit for the relative smoothness with which this integration process proceeded.

Let us then dwell for a while on, perhaps, the most important aspect of the situation that Viki faced at CERN in 1961, which occupied him during his whole reign, and which, in my subjective view, led to his greatest success, namely the long-term programme of CERN. First, I’ll give you a very short summary of the history of how the programme had developed.

A suitable starting point is the International Accelerator Conference in 1956, at which a number of new ideas on accelerators were presented, mainly from the US and the USSR. Soon afterwards, CERN set up an Accelerator Research Group within the proton synchrotron (PS) division to study (and catch up on) some of these ideas. After a few years of study, this group discarded most of the ideas, judging them to be unrealistic, at least within a reasonable timescale. From 1959 almost all of CERN’s accelerator research effort went into colliding proton beams. The study was first oriented towards a two-way fixed-field alternating gradient approach (an idea that was first developed by the Midwestern Universities Research Association). However, when the PS came into operation with the promise of much more intense beams than we had dared to hope for, attention moved to storage rings with beams injected from the PS. The feasibility study gave very promising results and at the end of 1960 four senior members of the Accelerator Research (AR) Division, as it was now called, wrote a report demonstrating the performance that one might expect from such a project, which was later named the Intersecting Storage Rings (ISR).

By early 1961, however, things started to go wrong. The enthusiasm of the AR Division became contagious and spread to the directorate, which issued a document (with much the same content as the report referred to above) to the Scientific Policy Committee (SPC) in the spring. This caused, more or less, an explosion among the particle physicists at CERN, who claimed that they had not been properly consulted and (rightly) insisted that their view should have been taken into account before such important matters went to the SPC. This criticism reached the ears of the SPC, which consequently gave the report a cold reception. The directorate had to make a temporary retreat.

This was an unfortunate start. Whether or not it negatively influenced the further process is guesswork. Let me remark that Viki had, if I remember correctly, little direct involvement in this early process because of his unfortunate car accident. However, we in the AR Division had had the pleasure of describing to him and discussing with him our results. There was no doubt that the possibility of reaching the very high centre-of-mass energy in this, in principle, simple and relatively cheap way, had caught his imagination.

Broadening the approach

During the early part of his tenure as director-general, Viki broadened the approach to the future programme in two important ways. He first asked us, as a parallel effort, to design a PS of considerably higher energy than the actual PS. This became the 300 GeV programme. Later, the improvement programme for the PS was also introduced, including, in particular, a higher-energy injector. All of this became an integrated programme where Viki carefully avoided giving one part precedence over another, although it was clear that he had a time priority in mind with the ISR first in line.

Near the end of Viki’s mandate he got the CERN Council on his side with the miraculous result that it was persuaded to accept, more or less, Viki’s programme as a whole.

Meanwhile, he widened the consultations on the programme significantly. All groups of the community were pulled in. CERN physicists were encouraged to participate. To get all particle physicists in Europe involved, Viki created the European Committee for Future Accelerators, which still plays an important role. He even called in the founding fathers for consultation. And, of course, the SPC had regular and sometimes heated discussions on the subjects. One important aspect of all of these deliberations was that Viki never let the ISR get pushed off the agenda despite the active physics community pressing him to do so. I must admit that these discussions were vigorous and sometimes the hardest that I have ever participated in. Let us leave it at that and go to the well-known final outcome.

Near the end of Viki’s mandate he got the CERN Council on his side with the miraculous result that it was persuaded to accept, more or less, Viki’s programme as a whole. This meant that the PS improvement programme could start in 1966, ISR construction would start the same year, and the 300 GeV project was part of the programme, but time-shifted with respect to the ISR and with an undetermined schedule. In my opinion this was the greatest of Viki’s achievements as director-general.

Let us look a little at the consequences of his persistent efforts to make the ISR part of the laboratory’s future. First, the construction was a success and the performance went well beyond what had been foreseen, particularly in luminosity, but also in such things as clean beam conditions, operational flexibility and even energy.

Burning enthusiasm

Viki was, of course, the main speaker at the inauguration of the ISR in October 1971 (see figure 2). I take this opportunity to quote a few sentences from this speech because they are so typical of his general, visionary way of thinking. He summed up his enthusiasm for the ISR as follows: “My deep belief in the fundamental importance of our growing insight into the basic structure of matter. My deep conviction that the physicists of Europe can and should be not only on par with other scientific communities but that they should be ahead, at least in some aspects. My deep sentimental attachment to CERN. This unique social and political experiment, which brings together people from many different nations in a life full of intellectual creativity; moreover it happens to be located in one of the most beautiful spots on our planet.” This is Viki in a nutshell. Figure 3 shows him after the ceremony inspecting the ISR with friends and colleagues.

The significance of the ISR for the future of particle physics is also worth dwelling on. In doing so I prefer again to quote Viki’s own words rather than use my own. So we move on to the closure ceremony of the ISR in June 1984 at which again, naturally, Viki was a speaker. In figure 1, we see him on this occasion and I quote from his speech: “The really important thing about the ISR is its success as an instrument, because that fact did change the landscape of high-energy physics. First it was considered only as a window into the future. This was the historical significance of this first hadron collider. It showed the possibility of doing high-energy physics at much higher energies in the centre-of-mass system, where we can better observe what really happens because of the wider angular spread of the secondaries. After this was done, colliders became the fashion of the day. Today we have one more hadron collider at the SPS at a much higher energy. This again was a European first. But it was nothing other than a continuation of the ISR adventure. In a few years there will be a similar device at Fermilab, the Tevatron, with an even higher energy. The future plans of which we hear – in America the SSC, in Europe the plans for hadrons in the LEP tunnel – are further extensions of the ISR idea.”

Imagine that Viki had disappeared sometime between 1961 and 1964. The ISR would have died and the positive development described above would not have taken place.

This is definitely the direction that the development has taken: only colliders are in the picture for future hadron accelerator installations, some already operating, like the Tevatron at Fermilab, HERA at DESY and Brookhaven’s RHIC, with others under construction (CERN’s LHC). One can only guess how the development would have gone if CERN had not embarked on the ISR, but at best such speculations are pretty grim, when we remember that nobody else at that time was prepared to undertake such a venture.

Let us return to Viki’s role. Imagine that Viki had disappeared sometime between 1961 and 1964. The ISR would have died and the positive development described above would not have taken place. In short, his role was essential, and not only CERN but the whole particle-physics community has much to thank him for.

I had the privilege to work for Viki during his period at CERN. He was an unusually inspiring boss. His enthusiasm was contagious. When I joined CERN about 10 years before he became director-general, I was, of course, attracted by the scientific and technological challenges. However, 50% of the attraction was the opportunity to participate in this international collaboration. Viki, more than anybody, struck a resonance on this point with me and, I am sure, with most of our colleagues. CERN and Europe can be grateful to Viki for so successfully guiding this organization and the people involved through a very crucial period of its life.

With the passing of Viki we have lost one of the few surviving members on the list of distinguished scientists who founded modern quantum physics. Ever since I became Viki’s research associate at MIT 50 years ago he has been one of my major mentors and closest friends. The way he did physics, the way he enjoyed physics and the way he shared his pleasure at expanding his understanding of physics were all major ingredients in the early formation of my career. With his deep intuitive insights and his creative approach, Viki made pivotal contributions to opening new frontiers, and to enhancing those already opened by adding to a deeper understanding of their significance.

Viki considered himself an amateur, as opposed to an expert because, as he said, what he did was always “for the pleasure of it”. Never did he come even close to falling in the trap that Pauli cautioned against: “Don’t become an expert for two reasons: you become a virtuoso of formalism and forget real nature, and…risk that you are not working for anything interesting anymore.” Certainly no-one would ever accuse Viki of being a virtuoso of formalism.

The anti-Pauli

In an earlier tribute to Viki at CERN on the occasion of his 80th birthday, I recalled the wonderful experience of my first year with him in words that he wrote in describing his experience working with Pauli. In the American Journal of Physics Viki wrote: “It was absolutely marvellous working for Pauli. You could ask him anything, there was no worry that he would think a particular question was stupid since he thought all questions were stupid.” But as I remarked then, Viki was the anti-Pauli, because he accepted all questions not as stupid but as interesting. To him they were challenges to probe to deeper levels of understanding. The resulting discussions – with their insights and enthusiasm – were valuable experiences for those of us who had the good fortune to participate in them. We generally emerged with a deeper physical and intuitive understanding of what was going on. The great school of physics that Viki created at MIT starting in the 1950s can only be described as making physics exhilarating, exciting, demanding, and fun. It was a model for many of us for our own subsequent endeavours.

Viki also proved that even a theoretical physicist, with the right human qualities, can be an outstanding administrator and leader, as he was in his years as CERN’s director-general. I spent a year at CERN during his reign as director-general and the atmosphere was charged with progress, enthusiasm, and high expectations.

Throughout his life no-one was more committed than Viki to the value of international collaboration in science. This was much more than simple theoretical idealism on his part. He firmly believed in the importance of international collaboration for the advancement of science; all science, not just expensive big science. It was good for science. It also served to strengthen the bonds between communities in different countries working towards a more peaceful and co-operative world based on common principles of humanity and brotherhood. Viki’s commitment to this was total, both in the way he opened doors to welcome scientists from all parts of the globe and in his dedication to ensure the success of CERN as the outstanding international scientific institution we all recognize. His skills in achieving consensus among fellow scientists and in identifying the important directions of physics to focus on not only served CERN so well but were also of great value in helping mould the successful national physics programme in the US. Particularly valuable were his years as chair of the High-Energy Physics Advisory Panel working with the DOE and NSF to ensure that the US programme in high-energy physics flourished as a major participant in the broad, world community effort.

The bomb did end the cruel and destructive war with Japan, but since then it has developed into the greatest danger that humankind has ever faced.

Victor Weisskopf

All his life, to quote Hans Bethe, Viki has “sought and contributed to knowledge, and all his life he has shown compassion”; and I would add commitment. This is what made Viki the great man that we all loved so well. We all know Viki’s commitment to the cause of world peace. Having worked to develop the atomic bomb in Los Alamos during the Second World War he was fully aware of the awesome destructive potential of these terrible new weapons and the vital importance of seeing that they were never used again in combat. To this end Viki worked with unflagging dedication to help world leaders, from US presidents to European prime ministers and the Pope in Rome, to understand the physical realities of the nuclear threat. Repeatedly he called on them to lead in efforts to walk away from the brink of nuclear disaster and reduce that threat. As he said in a post-war speech at Los Alamos: “The bomb did end the cruel and destructive war with Japan, but since then it has developed into the greatest danger that humankind has ever faced. And it threatens more and more to destroy everything on Earth that we consider worth living for.”

Viki’s commitment to science, international collaboration and the bonds joining the international community of science in the quest for peace are eloquently expressed in his tribute to Marie Curie at a ceremony in Warsaw in 1967:

Common value system

“The significance of scientific collaboration far exceeds the narrow aim of a more efficient prosecution of our scientific endeavours. It stresses a common bond among all human beings. Scientists, wherever they come from, adhere to a common way of thinking: they have a common system of values that guides their activities, at least within their own profession. New approaches in bringing nations together can perhaps be discussed with more ease within this community, some political misunderstandings can be cleared up, and dangerous tensions reduced. As an example, we recall that the agreement to stop the testing of nuclear bombs above ground stemmed, in part, from prior meetings among scientists.

“We must keep the doors of our laboratories wide open and foster the spirit of supranationality and human contact, of which the world is so much in need. It is our duty to stick together, in spite of mounting tension and threatening war in the world today. The present deterioration in the political world is a reason stronger than ever for closer scientific collaboration. The relationship among scientists must remain beyond the tensions and the conflicts of the day, even if these conflicts are as serious and frustrating as they are today. The world community of scientists must remain undivided, whatever actions are taken, or whatever views are expressed in the societies in which they live. We need this unity as an example for collaboration and understanding, as an intellectual bridge between the divided parts of mankind, and as a spearhead towards a better world.”

Thirty-five years later those words ring every bit as true as they did when he originally spoke them.

My most cherished recollections of Viki are the warm friendship that my wife and I enjoyed with him and Ellen, his wife for many years. With our families we had many wonderful occasions together that will always be a rich part of our lives. These included summer schools at Erice with Nino Zichichi, a spring together in Vienna in 1972, a year at CERN, summer visits to the Weisskopfs’ mountaintop home in Vesancy, France, and frequent visits to Cambridge and Stanford. Discussions ranged broadly over literature, politics, and especially music. Viki and I enjoyed a special bond of playing violin-piano sonatas together on many, many occasions. Indeed Viki often introduced me at seminars and colloquia, at CERN, MIT or wherever, by recalling that he first hired me as his research associate only after Felix Bloch said that even if I wasn’t all that great as a physicist, what a wonderful violinist I was for a sonata partner. I like to think that I can invoke a conservation law to balance those two evaluations, because I know the musical praise is excessive. But how we did enjoy our struggles with Brahms, Mozart, and Beethoven. That was a source of very special pleasure for us.

Viki was most fortunate to have enjoyed the loving, caring companionship of his wife, Duscha, for the last 13 years of his life. But as the 2nd Law assures us, all good things eventually come to an end. And so it has. We will sorely miss Viki, an irreplaceable friend, humanist, scientist and for me a musical colleague. He was surely one of the most beloved physics giants of our time.

In the spring of 1960, CERN’s new proton synchrotron was delivering its first beams. In the middle of this critical phase for European particle physics, the death of CERN’s director-general, Cornelis Bakker, in an aeroplane accident was a severe blow. Although CERN’s governing Council acted swiftly by appointing John Adams to the post of acting director-general, this step necessarily prolonged the period that, in retrospect, may be characterized by the dominance of brilliant accelerator scientists.

At the same Council meeting in June 1960 that confirmed the appointment of Adams, the “modern” structure of research committees with at least as many members from outside as inside the laboratory was also approved, and the search for a definite successor for Bakker was initiated.

In any case, Adams would have to leave CERN to take up an important position in Great Britain. The discussion centred around two eminent scientists – Hendrik B G Casimir and Victor F Weisskopf. The latter was already well known at CERN, having worked in the Theory Division for a year in 1957-1958. However, when first approached, he doubted his talents for such a position – with characteristic modesty – but he expressed his willingness to act as a director of research. Casimir, for his part, made it clear that his position with Philips would make it very difficult to free himself to take over the post of director-general of CERN.

In the course of the following months, a formal nomination procedure of candidates in the Scientific Policy Committee (where Weisskopf was formally proposed by Greece), extensive deliberations and successful persuasion led to Weisskopf’s election by the Council (8 December 1960). The period of his term was first envisaged to run from 1 August 1961 to 31 July 1963, which was later extended to 31 December 1965. It can be said, without exaggeration, that in that period and under Weisskopf’s guidance the future of CERN was shaped for many years to come.

Why was CERN so fortunate to be led by precisely a personality like Weisskopf at precisely this time? The difficult situation for the laboratory, whose harmonious development had been interrupted at a critical point in its evolution, needed the special abilities of its director-general. Every fast-developing scientific organization must deal with the danger that its very size makes on its scientific aims. Scientists with little inclination towards administrative matters have to become subject to administrative and bureaucratic rules. This is even truer for an international organization.

The selection of collaborators and the future style of work is determined at the stage of most rapid initial growth, because the natural inertia of a structure made up of human beings makes it extremely difficult later on to rectify earlier mistakes. Just one number may serve as an illustration: at the end of 1960 the number of CERN staff and visiting scientists was 1166, rising to no fewer than 2530 at the time of Weisskopf’s departure in 1965.

Therefore, at this time in the history of CERN, even more than at any other, the director-general had to be a physicist who once and for all set the direction of the laboratory towards an absolute priority of science. To achieve this he had to rely on the authority of an acknowledged high reputation in his field, together with an ability to deal effectively with the administrative and organizational needs of a rapidly growing organization. In addition, CERN was placed in the delicate position of having to restore European research parity with that of the US, profiting as much as possible from the experience gained already in US, while retaining or creating at the same time the dominantly European character of the new organization.

Distinguished career

Born in Vienna in 1908, Weisskopf followed a truly cosmopolitan scientific career as a theoretical nuclear physicist, working with the most important founding fathers of modern quantum theory, contributing important results himself. Thus he was not only familiar with Germany (collaboration with Heisenberg), with Switzerland (collaboration with Pauli) and with the Nordic countries (collaboration with Niels Bohr in Copenhagen) from extended stays in the respective countries, but also with Russia (work with Landau in Kharkov), eventually accepting a position at Rochester, US, in 1937.

His qualities as a leader of a technological project in which theoretical physics only played an auxiliary role was exploited in the Manhattan Project (Los Alamos) towards the end of the Second World War. The dominantly European background of many of his collaborators was excellent preparation for the task of leading a European laboratory. Even pursuing the same scientific goal, the individual style of scientists differs greatly, the more so if those differences are amplified by distinct national backgrounds.

After the war, as professor at the Massachusetts Institute of Technology, Weisskopf soon resumed contact with Europe, which was slowly recovering from the dark years. Besides his outstanding qualifications as a theoretical physicist and as a leader of scientific enterprises, Weisskopf possessed a special quality as a physicist that physics in Europe is lacking to a large degree. Possibly because of the general structure of secondary education in Europe, mathematics plays an extremely important role in theoretical physics. Hence theoretical physics frequently becomes almost a mathematical discipline with the physical ideas submerged by an overemphasized mathematical formalism. Among experimentalists this very often causes a spectrum of emotions ranging from uncertainty to refusal, as far as the judgement of theoretical ideas is concerned.

In the US only a handful of gifted physicists knew how to bridge this gap. In my opinion Weisskopf was a master of this. Before coming to CERN, he had already taught a generation of nuclear physicists how to pick out the essential physical ideas that are always very transparent and simple (once they have been understood), but which may be hidden under many layers of mathematical formalism. Of course, the true masters of mathematical physics always knew how to isolate the physical content of complicated mathematical arguments, but the great majority of theoreticians in Europe, to this very day, unfortunately, are sometimes over-fascinated by the mathematical aspects of the physical description of nature.

The understanding of physical phenomena very often does not even require the use of precise formulae. Students at MIT had invented the notion of the “Weisskopfian”, which naturally takes care of numerical factors such ±1, i, 2π, etc. Moreover, in the book Theoretical Nuclear Physics by John M Blatt and Weisskopf, which remains a standard textbook to this day, the emphasis on simple, physically transparent arguments by Weisskopf and the more precise, but more formal presentation topics by his co-author are clearly discernible.

From MIT to CERN

To facilitate the transition from MIT to CERN, and to make optimal use of his whole period as director-general of CERN, Weisskopf became a part-time member of the CERN directorate in September 1960, dividing his time equally between MIT and CERN. Unfortunately during this transition period, in February 1961, he was involved in a traffic accident. His treatment required complicated hip surgery and a long stay in hospital. At the start of his term as director-general and less so during a large part of his stay in Geneva, Weisskopf was hampered in his freedom of movement. I vividly remember his tall figure walking with crutches through the corridors and obviously suffering pain, but never losing his friendly disposition.

The first progress report to CERN Council in December 1961 clearly reflects the situation of CERN at the beginning of the Weisskopf era. Two years after the first beam at the proton synchrotron, breakdowns and construction work on beams had prevented a completely satisfactory use of this machine, whereas the smaller synchrocyclotron was working very well. As research director, Gilberto Bernardini very aptly remarked that European researchers with a nuclear physics background had had little difficulty orienting their work towards the synchrocyclotron. The proton synchrotron, on the other hand, was a novelty for physicists, so certain mistakes had been made, particularly owing to insufficient time for the preparation of experiments.

Nevertheless, 1961 was the first year with a vigorous research programme at CERN. Not surprisingly, organizational problems and difficulties in the management of relations with universities in the member states became acute. It was recognized that at least track chamber experiments required the collaboration with institutes outside CERN for the scanning, measuring and evaluation of data. For electronic experiments, such a need was not yet seen.

The construction of the 2 m bubble chamber was continuing well, but experimental work was still done on the basis of data from the tiny 30 cm chamber and with the 81 cm Saclay chamber. The heavy-liquid chamber had looked in vain for fast neutrinos in the neutrino beam. Simon van der Meer’s neutrino horn, intended to improve this situation, had just finished its design stage.

Addressing CERN Council for the first time on the problem of the long-range future of CERN, the new director-general strongly emphasized two directions of development that, as subsequent history has shown, were decisive for CERN’s future success. One project, based on design work by Kjell Johnson and collaborators, foresaw the construction of storage rings, the other was aimed at a much larger “300 GeV accelerator”.

The financial implications of such proposals and the necessity to formalize budget preparations for more than one year in advance led to the creation of a working group headed by the Dutch delegate Jan Bannier. From this group emerged the remarkable “Bannier procedure”, under which firm and provisional estimates of budget figures for the coming years are fixed annually. It was decided that the cost-variation index should not be provided automatically, and that Council should make a decision on this index each year.

First research successes

The discovery that different neutrinos came from electrons and from muons was made in 1962 not at CERN, but at Brookhaven. In retrospect it became clear that CERN’s attempt was bound to fail for technical reasons. The disappointment, however, did not overshadow some remarkable successes in the first full year of CERN under Weisskopf’s leadership. The shrinking of the diffraction peak in elastic proton collisions was first seen at CERN – in agreement with the new ideas of Regge pole theory, which had also originated in Europe. The cascade antihyperon was found simultaneously with Brookhaven, but the beta decay of the pi meson and the anomalous magnetic moment of the muon were “pure” CERN discoveries. For the first time, development of a novel type of scanning device for bubble-chamber pictures (the Hough-Powell device), which started at CERN, was taken over by US institutions. Still, Weisskopf had to complain to Council about the “equipment gap” at the proton synchrotron, caused by the lack of increase in real value of the budgets in 1960 and 1961.

In some sense, the most important experimental result of 1963 was the determination of the positive relative parity between the lambda and the sigma-hyperon, obtained at CERN in the evaluation of data from the 80 cm bubble chamber. This result was in disagreement with predictions from a much-publicized idea of Heisenberg, and gave further support to the growing confidence in internal symmetries. Despite a long shutdown, needed at the proton synchrotron to install the fast ejection mechanism giving extracted beam energies of up to 25 GeV, the proton synchrotron now began its reliable and faithful operation, which, to this day, is the basis of all accelerator physics at CERN. Thanks to a neutrino beam that was 50 times as intense as that at Brookhaven, the first bubble chamber pictures of neutrino events were made.

The year 1963 saw the creation of a new body of European physicists under the chairmanship of Edoardo Amaldi. Taking into account future plans outside Europe, this body strongly recommended the storage-ring project, as well as the plans for a 300 GeV accelerator. CERN Council authorized a “supplementary programme” for 1964 to study the technical implications of these two projects. This Amaldi Committee, set up as a working group of CERN’s Scientific Policy Committee, was the forerunner of ECFA, the European Committee for Future Accelerators, founded three years later, again under the chairmanship of Amaldi. ECFA has remained ever since the independent “parliament” of European particle physicists.

Weisskopf’s clear vision of the importance of education resulted in his legendary theoretical seminars for experimentalists at CERN. I had the privilege of being allowed to collaborate with him at that time on some aspects of the preparation of these seminars, and my view of theoretical physics has been decisively influenced by Weisskopf’s insistence on stressing the physical basis of new theoretical methods.

From 1964, CERN’s synchrocyclotron started to concentrate on nuclear physics alone, whereas the proton synchrotron was now the most intensive and most reliable accelerator in the world. Another world premiere was the first radiofrequency separator, allowing K-meson beams of unprecedented energy. At CERN, also for the first time, small online computers were employed in electronic experiments. A flurry of fluctuating excitement was caused by the analysis of muon and muon-electron pairs in the neutrino events seen in the spark chamber. When it turned out that they could not have been produced by the intermediate W-boson (to be discovered at CERN exactly 20 years later, at much higher energies), these events were more or less disregarded. Only 10 years later, after the charmed quark was found in the US, was it realized that these events were examples of charm decay – admittedly very difficult to understand on the basis of the knowledge of 1964. The unsuccessful hunt for free quarks also started in 1964, together with the acceptance of the concept of quarks as the fundamental building blocks of matter.

Relentless prodding

Thanks to Weisskopf’s relentless prodding in 1964, CERN member states were convinced that the time was ripe for a decision on the future programme of CERN. Rather than rush into an easier, but one-sided decision, Weisskopf was careful to emphasize the need for a comprehensive step involving three elements:

• further improvements of existing CERN facilities, comprising, among other things, two very large bubble chambers containing respectively 25 cubic metres of hydrogen and 10 cubic metres of heavy liquid;

• the construction of intersecting storage rings (ISR) on a new site offered by France, adjacent to the existing laboratory;

• and the construction of a 300 GeV proton accelerator “somewhere in Europe”.

Although a decision had to be postponed in 1964 – due to the difficult procedure to be set up for the site selection of the new 300 GeV laboratory – optimism prevailed that such a decision would be possible in 1965. After recommending the ISR supplementary programme in June 1965, the formal decision by Council was finally taken in December 1965.

The novel ISR project had no counterpart elsewhere in the world. Although experience had been gained at the CESR test ring for stacking electrons and for ultrahigh vacuum, this bold decision reflected the increasing self-confidence of European physics. Thus, the foundation stone was laid for the dominating role of European collider physics, which eventually led to the antiproton-proton collider, the LEP electron-positron collider and the LHC proton collider.

At the same time as the ISR project was authorized, a supplementary programme for the preparation of the 300 GeV project was also approved.

When Weisskopf’s mandate ended at the end of 1965, particle physics had passed through, perhaps, its most important stage of development. From an appendix to nuclear physics and cosmic-ray experiments, it had become a field with genuine new methods and results. The many new particle states disentangled by CERN and other laboratories gradually found a place in a framework determined by a new substructure, the quarks. In addition, many new discoveries in weak interactions, and especially at the unique neutrino beam of CERN, showed close similarities between weak and electromagnetic interactions and paved the way for unified field theory.

An important part of the enthusiasm that enabled CERN experimentalists to participate so successfully was certainly due to Weisskopf. It is still remembered at CERN how Weisskopf made a point of regularly visiting and talking to the experimentalists at their experiments. More than once he visited experiments during the night. These frequent contacts on the experimental floor with physicists at all levels gave CERN a new atmosphere and even created contacts between different groups – something that was lacking before. Weisskopf himself was aware of this. When asked on his departure from CERN what he thought his main contribution had been, he replied that administration, committees etc. would have functioned perfectly well without him. But he thought that he had just given CERN “atmosphere”.

During the Weisskopf era, directions were set for the distant future. Almost 40 years later, the basis of the CERN programme is still determined by those decisions taken in 1965. How could Weisskopf have been so successful in his promotion of CERN in Europe, dealing with member states among which at any given time there always was at least one with special problems regarding the support of particle physics and CERN?

Politicians have to trust valued experts. Weisskopf could achieve so much for the laboratory because he was deeply trusted by the representatives of the member states. Although enthusiastic in the support of new ideas in scientific projects, he never lost his self-critical attitude, quick to try to understand opposing points of view in science, and in scientific policy. The enthusiasm, honesty and modesty of Victor Weisskopf left a rich inheritance and have determined the future of CERN.