The previous speakers have reviewed well the different facets of Viki's rich and full life; Viki the great physicist and Viki the director-general of CERN at a crucial time in the history of the organization. The title that has been given to me for this talk corresponds to that of one of Viki's popular books - Knowledge and Wonder: the Natural World As Man Knows It, to be more explicit - and I understood that to be an invitation to talk about Viki the humanist, namely a scientist with a very wide range of interests, a strong willingness to share his passion for science with others and much concern for present human problems. Knowledge and Wonder starts with a quote from Francis Bacon, which conveys Viki's great enthusiasm in talking to others about science, namely: "For all knowledge and wonder (which is the seed of knowledge) is an impression of pleasure in itself." When referring to his concern about society at large, I shall focus on his role as an indefatigable advocate for less tension and a better understanding among nations threatened by the danger of a nuclear war and I shall also partly cover his actions towards disarmament.

I have always had a great admiration for Viki. For me he first appeared as a monument, when I was a green physicist reading Blatt and Weisskopf and, when I had the chance to do it, listening to some of his brilliant talks at conferences. I later very much appreciated the friendship that we eventually developed. I consider this friendship as a great privilege and I cherish its memory.

Just after his death, I was asked to write a note for the CERN bulletin and a more extensive one for the CERN website. I was happy to collect some good appreciations expressed to me by several readers. One of the most moving ones came from a Large Hadron Collider engineer who said in his email: "Dear colleague, I had the fortune to read attentively your words caused by the passing of Dr V Weisskopf. I am sure that if he had read them, wherever he may be now he would have felt happy to know what impression he left. Thanks for letting me have the chance to read such nice words about a nice person I never met." Yet, I did not feel at all like I was overdoing anything when writing about Viki. I was simply speaking with my heart, as he had much earlier asked me to do when he had wished me to speak in Vesancy after the death of Ellen, his first wife. I can but hope that this address also carries well the emotion and feeling of admiration which I passed on in the note in the bulletin, though I shall focus on only some aspects of his life and great talents.

Viki the humanist

Speaking about Viki the humanist, I would actually like to start again with an anecdote that I mentioned in my note in the bulletin. This was more than 20 years ago, when Viki came to CERN and to Paris to give the first series of the Gregory lectures, which had been set up to honour the memory of Bernard Gregory, who had succeeded him as director-general of CERN. During this lecture series, he came to address a large audience at the Ecole Polytechnique but, as he was due to start, there was some trouble with the sound system that took a few minutes to fix. Viki had to wait but, spotting a grand piano that had been left in a corner of the stage, he went to it and started to play. The audience was overwhelmed. His love for music, his musical talents and his great musical culture are well known. As he once said: "When life is hard, there are two things which make it worth living: Mozart and quantum mechanics."

Viki was a great physicist and he had a passion for physics, which he so much wanted to pass on to others. But when he addressed a wide audience, it could be hard to dissociate his passion for physics from other passions as he often tried to convey his broad love for human scientific endeavour and human culture, physics being only one part of it. This he has done in many essays and in books written for a general audience. As he once said: "I owe much to the cultural tradition of Vienna, from Mozart and Beethoven to Freud and Boltzmann." He did so much to show that physics is not producing an alienated individual in a world dominated by science and technology and in which everything is reduced to impersonal scientific facts.

Science is great, but science is not everything. He once illustrated that through an analysis of the appreciation that one may have for a Beethoven sonata, describing it first in an interesting but limited way in the realm of present science alone but to conclude that there is nothing like the emotion that it triggers in ourselves when listening to it. He also often left the ivory tower of science to express his views on many crucial issues, willing to do as much as possible for the benefit of humankind and, in particular, using all his influence to temper the great threats of the Cold War. As he said on several occasions: "Human existence is based on two pillars: compassion and knowledge. Compassion without knowledge is ineffective; knowledge without compassion is inhuman." This emphatic sentence, a famous Viki quote, can be found in several instances in his writing with - sometimes - curiosity, interestingly, replacing knowledge.

Compassion is key

Viki told us that it is a privilege to be a physicist but also that it carries important duties: duties to inform on what science is all about; duties to warn against the dangers that could come from the irresponsible and even evil use of scientific knowledge; duties to feel concerned with the involvement of science in the events of the day; and duties to pass on to the new generation the spirit of research which we so much appreciate. As he once said: "We need basic science not only for the solution of practical problems but also to keep alive the spirit of this great human endeavour. If our students are no longer attracted by the sheer interest and excitement of the subject, we were delinquent in our duty as teachers." How bound should we feel today by all these duties, and in particular by the last one, when the number of physics majors entering university is on the decline in the whole industrialized world?

Viki was much concerned about science and society issues. As he said: "The human problems caused by the ever increasing development of a science-based technology are too threatening and they overshadow the significance of fundamental science as a provider of deeper insight into nature." And he added: "This puts the scientist in the midst of social and political life and strife and he has the obligation to be the guardian, the contributor and the advocate of scientific knowledge and insight." Continuing with his own words, I may add: "Science cannot develop unless it is pursued for the sake of pure knowledge and insight. It will not survive unless it is used intensely and wisely for the betterment of humanity and not as an instrument of domination by one group over another."

Viki magnificently conveyed his passion for research as a great human endeavour. In his essay "The significance of science", he quotes Ecclesiastes: "And I gave my heart to seek and search out by wisdom concerning all things that are done under heaven. This sore task hath God given to the sons of man to be exercised herewith." But, much aware of the dangers that could be brought by an evil use of knowledge, he also summarized his worries quoting again Ecclesiastes: "For in much wisdom is much grief and he that increaseth knowledge increaseth sorrow." No wonder he did so much to emphasize the positive aspects of knowledge and insight and warn against evil uses, while stressing that compassion should keep a key role. As Hans Bethe put it in his preface to Physics in the 20th Century: "Having devoted so much of his life to compassionate endeavour, Weisskopf is most qualified to raise his voice for knowledge now, when so many people call for compassion alone, ignoring or even regarding knowledge as dangerous." This is an important task, which he left us to continue with continuous effort at "catching the chance of achieving a better world".

This longing for a better world was already clear in his youth and in particular in the way he conducted some militant actions through well applauded pantomimes that he performed with socialist friends in post First World War Austria. Even though music and eventually physics became his primary passions, his concern about society always remained on his mind, often reinforced by Bohr's own attitude and actions about human problems. His work on the bomb, which had represented an extremely exciting period in his life, left him with a bitter aftertaste. "We were proud of our achievements, yet we were hindered with the realization that we were responsible for creating the most destructive weapon ever devised," he said. "The consequence of my work on the atomic bomb and its impact on the world of the future weighed on my conscience."

The arms race

In 1944 Viki became one of the founders of the Federation of Atomic Scientists, whose aim was to warn the public of the dreadful consequences of a nuclear war and to support the peaceful use of atomic energy. He soon also became a member of the Emergency Committee of Scientists initiated by Leo Szilard, which, under the chairmanship of Einstein, had a similar goal. It eventually led, in the late 1950s, to the highly valuable Pugwash meetings, which allowed Western and Eastern scientists to maintain an extremely useful dialogue at the time of the Cold War and in which he played an active role. He helped to create the Bulletin of Atomic Scientists with its unique coverage of questions associated with nuclear policies, arms controls and disarmaments. Bohr's dream of the internationalization of nuclear matters was blown away by the widespread but short-lasting belief that Western supremacy was here to stay; by the Russian bomb, coming already in 1949; and by the H-bomb developed and exploded on both sides in 1951. Yet Viki kept an unfailing commitment to telling governments and citizens about the great danger of an arms race that had started and kept amplifying.

It was only by the late 1970s and early 1980s that the idea of the absolute impossibility of "winning" a nuclear war was recognized, not only by the public but also by governments. By the 1990s Viki could at long last say: "I am grateful to have lived to see our efforts to make this a more peaceful world seem to bear fruit...Perhaps a time is coming when the nuclear arms race of the past decades will be regarded as a serious case of collective mental disease that was cured just in time." By that time, tests in the atmosphere had been banned, the ABM treaty had been brought in and the East-West thaw was paving the way to mutual disarmament.

Viki's own and latter important actions towards that lofty goal had strongly used his membership in the Pontifical Academy. He had been elected to it in 1976, the same year that he was elected to the Soviet Academy of Sciences, something that he considered as keeping a proper balance. He used the latter position to support Sakharov and the former one was instrumental in his helping to shape the attitude that the Pope soon took, publicly underlining the great threat to mankind that resulted from the on-going nuclear arms race. I still remember listening to the Pope's New Year address in 1980. I had seen much of Viki just before in connection with his Gregory lectures, and when the Pope came to mention the nuclear threat I could not refrain from exclaiming: "But these are Viki's words!" If I may say that now it is because the Pope himself said that he had come to his stand on that matter by "listening to what his scientists had told him". Viki was of course teased by journalists about his particular role in all that but he would respond: "The Pope is inspired by God and not by a Viennese Jew." His actions were well recognized and he was awarded the Public Welfare Medal of the US National Academy of Sciences in 1991.

I would like to close this section with a lighter anecdote. Viki's militant actions in the late 1940s, his past socialist stand in Vienna and his two long visits to the Soviet Union in the 1930s could have raised serious suspicions during the McCarthy era. This was apparently not the case, perhaps because he had always denounced vigorously the Stalinist excesses that he had witnessed first-hand at a time when André Gide was writing in the same spirit his Return from the USSR. Viki came to Paris in 1950 to spend a semester at the Sorbonne. As an American professor he had come in September but to discover that, in those days, nothing started seriously before November. He then decided to leave with his family for a wandering vacation through Europe leaving no specific address. Learning through the newspapers of the disappearance of Bruno Pontecorvo, who resurfaced soon after in the Soviet Union, he was afraid that people might think he was following a similar track and he telegraphed immediately to Paris to say that he would certainly be there for the beginning of his course.

Art and science

When preparing for this talk I read, or in most cases read once again, some of Viki's popular books, two of which are actually collections of essays. I read in particular The Joy of Insight, his autobiography, out of which come many of the previous quotes. I also read The Privilege of Being a Physicist, Physics in the 20th Century and, of course, Knowledge and Wonder. I enjoyed very much that reading and re-reading. In my career, I have had to give many talks and write several essays about science in a general context, though lacking much of Viki's insight, knowledge and experience. I realize now, however, that many things that I have chosen to emphasize in my talks were actually from his writings. This showed me how influential Viki had been on my thinking about science and society and the value of research, and this made me realize my debt for all that I had learned from him and taken as my own.

"Art and science", which I took here as an intermediate title, is probably the first of his wide audience essays I read, more than 20 years ago. It is very typical of his style when discussing science in a general context and, in that instance, opposing art and science in a Bohrian way to show that, if there are great differences, there are also important similarities in the two intellectual approaches and that one should rather stress their complementarity. He starts by writing: "What could be more different than science and art? Science is considered a rational, objective, cool study of nature; art is often regarded as a subjective, irrational expression of feelings and emotions." But he adds: "One can just as well consider scientific discoveries as the products of imagination, of sparks of sudden insight, whereas art could be viewed as the product of painstaking work, carefully adding one part to the other by rational thinking." He goes on to discuss points of convergence and divergence, with many poetic and scientific quotes on the way, to conclude on complementarity, a complementarity between reason and passion, mystery being another form of reality and adding: "No wonder scientists are attracted by the fugues of Bach."

He makes the point that science and art both respond to our urge for sense, meaning and hope, quoting Goethe who said: "He who has art and science also has a religion, but those who do not have them better have religion." He concludes with the words: "There may come a day when scientific and artistic meanings will combine and help to bring forth that ground swell of meaning and value for which there is so great a need. The growing awareness of this need is in itself an important element that brings people together and creates common values and even elation." Viki always acknowledged how much he learned from Bohr and his complementarity approach, which he liked to apply to walks of life other than quantum mechanics. A complementarity between precision and truth - Klarheit und Wahreit - often shows up in his essays.

I remember enjoying reading "Art and science", which he also used in one of his Gregory lectures and in several other talks, and when, some years later, I was asked for a contribution to a book presented to him on his 80th birthday, I wrote a similar essay with Bohrian complementarity on "Myth and science" with illustrations from Dürer. Great was my pleasure when I learned that he had appreciated it. Viki should probably have been happy to hear of the success of a recent venture, masterminded by Ken McMullen of the London Institute, which brought to CERN several well-known artists coming for a while to collect inspiration for pieces of art which they then conceived and produced, and which have been shown together in much appreciated exhibitions in London, Rome, Geneva and soon to be shown in Lisbon.

Knowledge and wonder

With Knowledge and Wonder we meet a different, but also typical, facet of Viki's writing for a wide audience. In this case, the book is about science alone. Yet it has a very broad coverage since, after presenting our place in space and in time, the forces met in nature, atomic structure and quantum physics, it turns to chemistry and life sciences, illustrating magnificently the great unifying view provided by quantum mechanics. Viki has the same enthusiasm and the same eloquence at all levels of what he refers to as the "quantum ladder", going from the very low energies of metabolism and genetics to the very high ones of particle physics. Different structures occur at rather sharply different steps, thus eliminating the Boltzmann paradox of equipartition of energy when considering finer and finer constituents. He shows equally well how it was a great discovery to find that uncharged matter actually does consist of a combination of positive and negative electricity and an impressive moment in the scientific endeavour when proof was found, here on Earth, that the Earth had not existed forever.

His presentation of quantum mechanics is a masterpiece. It is clear that quantum mechanics cannot be understood in terms of so-called classical concepts, and calls for a new way of thinking. But, whereas so many popular texts choose to emphasize the lack of certitude that quantum mechanics seems to bring to our description of the world, with its uncertainty relations and predictions in terms of probabilities only, he beautifully stresses the fact that, at long last, one has an understanding for the stability of the atom, the identical nature of all atoms of the same species and the automatic regeneration of the initial atomic structure after any perturbation. Such fundamental properties, on which all observed structures actually depend, could not be understood in classical terms, following a planetary analogy, which is often wrongly emphasized. The world as a whole is actually governed by quantum theory acting at different levels of the quantum ladder. So, rather than making our world more "uncertain", quantum mechanics makes it more definite. It is the cause of the dependability of the world to which we are accustomed.

In his brilliant coverage of the different structures in the universe, Viki exhibits his typical way of clarifying complicated matters relying on the proper orders of magnitude. One reads between the lines the frequent use of Weisskopf's units, whereby numerical factors of order one, and even 2π, can be set equal to unity and that to a decent approximation. His unique mastering of such an approach made him once recognized as "the Los Alamos oracle".

Knowledge and Wonder is, as Hans Bethe put it: "a delightful book in which Viki appears as an exquisite interpreter of science". He added: "Viki is most eloquent on the intrinsic value of science. Science is truly universal, the same questions are asked by all those involved in science, the same joy of insight is experienced when a new aspect of deeper coherence is found in the fabric of nature."

Viki was the eloquent advocate of the role that science can take in bringing people together, and this brings me to the last topic that I would like to cover.

A prominent citizen of the world

As Hans Bethe also wrote in his introduction to Physics in the 20th Century, one of Viki's main tasks of compassion was his fostering of international collaboration: "It is at CERN that he accomplished his most important goal, namely to make scientists from the many nations of Western Europe work together in a common task and, more difficult, to satisfy the governments of all of these nations that this co-operation was worthwhile both scientifically and politically. He also encouraged collaboration with Eastern scientists as much as possible." Louis Leprince-Ringuet said: "The spirit of CERN is his creation." Viki's actions have beautifully demonstrated that scientific endeavour has so many co-operative aspects that it makes the scientific community supranational, because it transcends national and political differences. We benefit so much today from that spirit of co-operation.

Viki was always optimistic about the role and virtue of scientific collaboration. He referred to physicists as: "This happy breed of men, having a common task and believing - let me say religiously - in the explicability of nature." In the late 1940s and early 1950s he had been instrumental in helping the first East-West contacts and in particular in obtaining visas for Soviet physicists coming to conferences in the US.

He wrote in his essay on Madame Curie - prepared for her centennial - soon after he left CERN and when the Cold War was still raging: "We must keep the doors of our laboratories wide open and foster the spirit of supranationality and human contact, of which the world is much in need. It is our duty to stick together in spite of mounting tensions and threatening wars in the world today. The present deterioration in the political world is a stronger-than-ever reason for closer scientific collaboration. The relationship between 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."

He lived to see this emphatic vision bear fruit. Extensive scientific collaboration certainly contributed to the thaw between East and West, as illustrated in great detail by the CERN-Dubna joint exhibition, "Science bringing nations together", which started its travels in Oslo six years ago.

Influencing society

There is, however, a long way between the laws of physics and those of human behaviour. In one of his essays Viki quoted Max Born, saying: "Intellect distinguishes between the possible and the impossible, but reason distinguishes between the sensible and the senseless. Even the possible can be senseless." Science is great but it is not enough when dealing with human behaviour. In another essay, he quoted Niels Bohr, who said: "The steady and incessant growth of our understanding of material structures may have helped to steady the minds of the scientists who live in this century of turmoil and upheaval. It did not have that influence on society as such."

There is certainly room for pessimism even for an enthusiastic physicist much concerned about the situation of the world. As Viki said himself: "There is a great temptation to transfer the methods that were so successful in natural science directly to social and political problems. But this is not possible for the most important problems." Yet, we should still be inspired by his drive for international collaboration, his concern about the future of humankind and achieving a better understanding among nations, and we should remain courageous. We should try to follow the example that he has set for us, in particular through his courageous and unfailing actions to temper the arms race. We should not be discouraged and I would like to conclude with yet another famous Weisskopf quote: "There is always hope for hope."