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Interview of Franco Selleri by Olival Freire on 2003 June 24, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/28003-1
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Selleri’s background includes undergraduate and graduate studies at the University of Bologna under G. Puppi. His idea of the one-pion-exchange model and his work at the Instituto Nazionale di Fisica Nucleare and CERN. His stay in the US at Cornell University. The conversion of scientific interest to foundations of quantum mechanics [FQM]. Reading of B. d’Espagnat’s Conceptions de la physique contemporaine. Suggestion to Italian Society of Physics to organize a Varenna’s summer school dedicated to FQM. Realism, social responsibility and science. His moving to the University of Ban, and his research and career there. The role of local realism in physics. His interaction with Louis de Brogue, Jean-Pierre Vigier, and Emilio Santos. His argument on the loopholes of Bell’s inequalities experiments. Proposal of experiments to test L. de Broglie’s wave and particle duality. Conference on FQM in Bari in the early 1980s, with Karl Popper and Leonard Mandel in attendance. Experiments held by L. Mandel. The role of journals like Nuovo Cimento, Foundations of Physics and Epistemological Letters as outlets for papers on FQM. Italian attitudes towards FQM, the role of Enrico Fermi. Students and collaborators like A. Garuccio and Rapisarda. Proposal of Bell’s tests in particle physics. His proposal of a new theory of relativity.
Okay. Testing, testing, testing. We are beginning an interview with Dr. Franco Selleri in Bari, June 24th, 2003. I think I don’t need to repeat all the questions, just the first. I would like to know if you came from a scientific family and would any of the ideas or attitudes of your family or early friends prove important for your later scientific or philosophic directions? And what was your education? Especially not only education but also scientific activities before 1969-1970, the time in which you began to work on foundations of quantum mechanics. So, you will talk about a kind of your prehistory?
Yes, I will. No, in my family there were no scientific interests. My father worked in the Italian railroad system. He checked tickets. And my mother was a housewife. I have a sister who is in Rome now. My mother is still alive. She is ninety-three now. So I cannot say that from my family I got an input. I think that I was very lucky from the point of view of school because I had an excellent teacher of mathematics and physics. The high school was called “Liceo Scientifico Augusto Righi” in Bologna, and the name of the teacher was Graffi. Excellent. He had really a robust personality and he could push people to be interested in mathematics and physics.
How do you spell his name?
Graffi, G-r-a-double f-i. Graffi.
I think that if I decided to be a physicist it was his merit. Not that he suggested to me in particular to study physics at the university, but just his type of personality was very strong and influential for me. Then I went to the university and there was a problem with my family who had not much money. Basically they said: you can go to university provided you have good grades and we don’t have to pay taxes, even though at the time the taxes were not very strong, but still they were a problem for us. This I succeeded in doing, but I inscribed at the university in engineering even though it was clear to me that physics was my interest. But I thought that as a physicist probably I could not get a job; as an engineer it looked much more promising, so that was the reason. During my studies I was lucky again.
There was in the local newspaper an interview with the new director of the Physics Institute in Bologna University. His name is Giampiero Puppi and in the interview he said, “We are opening now new activities in elementary particle physics and we are interested in young people to come,” so even though I was studying engineering — I was in the second year — I went to see him. And he said, “Show me your libretto with the grades, the records. I gave it to him and he said, “You can come even tomorrow.” So I switched from engineering to physics and then I was very happy because that was my real interest. Then I don’t know why, because I had very good grades, but I made a mistake. When came the moment for me to do the thesis I asked a lady, a very good theoretical physicist, to be my thesis advisor. And I think that was a mistake, because she gave me a book to read which I could really not understand. It was the highest level, okay, but very difficult. I later understood that it was a philosophical rejection on my side, but it was very difficult to understand anything. Then a new stroke of luck came. This lady left physics, went to the United States to get married. And she told me, “I cannot follow you. You will have to find somebody else for your thesis.” So I did not know what to do. I went to see the director, Puppi, and I told him the situation and he said, “Don’t worry. You will do the thesis with me.”
Now Puppi at the time was a wonderful personality. Everybody liked very much his teaching. He loved the physics and made people love it as well. His interests were then weak interactions.
There was a so-called Puppi triangle to express the universality of the weak interactions.
Puppi triangle, yes.
Then I also had other very good teachers at the university. Antonio Pignedoli was the teacher of mathematics, Dario Graffi (Graffi again, the brother of my high school teacher) was the teacher of rational mechanics and Giovanbattista Bonino was the teacher of chemistry — really very high class all three of them. I was very lucky from that point of view as well. So I started my career, and I entered the Instituto Nazionale di Fisica Nucleare as a fellow, but I was soon sent to CERN where I started doing research on my own. And then I had what I consider a very good idea. That was the one pion exchange model; that is to say, the idea that in some inelastic processes really what is going on is that one pion is exchanged. For example, if you have two protons colliding and producing one pion, let us say a positive pion, you have in the final state a proton, a neutron and a positive pion.
The idea was that the target proton (for example) emitted a virtual positive pion, becoming a neutron, and that the incoming proton scattered elastically on this virtual pion producing it as real in the final state. So this one-pion-exchange model was really my idea, my first idea, and it was immediately a remarkable success in fitting the experimental data. I became known in the whole of particle physics. And for example I could choose what to do, so I decided I wanted to go to the United States. I applied to five different universities and I got five positive answers so that in 1962 I decided to go to Cornell. I was attracted by the presence there of the famous physicist Hans Albrecht Bethe. But then, slowly, I started to develop a critical attitude towards contemporary physics. I mean I had a very strong drive. I liked physics very, very much and I was very active, but it was soon evident that there were problems, fundamental problems in physics. Already in 1965 I could see them. Perhaps I should say now that my doctorate degree in Bologna had been in 1958 when I was 22.
Oh. Very young.
Yes. And I started working at CERN in late 1959 and I remained as a fellow for more than two years. Then I decided to go to the United States. And I was in Cornell from 1961 to 1963. And during that time it became clear that there were great problems, because for example my model was, so to say, overcome by a different model that was called the one-pion-exchange model with absorption. Absorption means that instead of having plane waves in the initial state and in the final state you have to use distorted scattering waves. But that was very odd conceptually, because absorption of waves means that the initial nucleons and the final hadrons had strong interactions, and strong interactions go for example via pion exchanges and other similar ways.
So you had the one-pion-exchange model with absorption describing the inelastic process more or less as follows: a complicated interaction in the beginning, then a one-pion-exchange, then another complicated interaction in the final state. But then what is the sense of talking about one-pion-exchange? Perhaps today it does not seem so terrible, I know, but for me it was shocking. That was a frustrating development. I was very young and naive, so it was very difficult to take. So I slowly realized that if something like that was possible, that meant there were great problems in physics. And somehow I got very soon the conviction that the problems came from the foundations of quantum mechanics. That is to say, the problems in elementary particle physics are due to the fact that quantum mechanics is poorly understood and anyway is a very abstract idea. [Sound in background]. Could we interrupt? [recorder turned off, then turned back on ...]
We can resume, but I think very interesting the things you are talking, because I think that maybe your way to foundation of quantum mechanics was very singular in the sense that you face the problems in particles and fields and you went to foundations of quantum mechanics from these problems. Okay.
There were also other problems, yes. I mean not only my one-pion-exchange model. For example the Regge poles. You know about them?
They are singularities in the complex angular momentum plane, and one can well wonder what they could have to do with the physical world. I soon disliked the idea because theoreticians did not only use poles, but very soon to fit the experimental data were forced to use the so-called Regge cuts. In the pole you have a coupling constant that is free, but in the cut you have a whole free function, the discontinuity across the cut, meaning that you can use this freedom to fit just about anything. You can for example fit the weather of the last month over Europe. The whole enterprise with Regge poles did not look like good physics to me.
So what kind of physics was that? I mean that Regge was not responsible for this, because his work had been done in potential scattering and was applied to high energy particle physics by other people in California who were trying to understand more. It was like a fashion that was followed by other fashions: dispersion relations as dynamical tools, Mandelstam representation, peratization, and so on. These were very abstract ideas, very different from reasonable conjectures about the objective reality to hope that they could possibly work. With such a start it is clear that I am not at all surprised of the great difficulties that particle physicists face today. These difficulties are the natural outcome that has been building up for a long time. So I —
If I could interrupt, about 1965. You came from the United States to Italy. Okay?
You published in 1969 a first paper about foundations of quantum mechanics, and one year later you went to Varenna school. I would like to know something about this period intermediary between your coming [and then] returning from United States and ‘69 and ‘70, if you could talk a little.
Well yes. When I came back to Italy I had important teaching to do. It was quantum field theory at the so-called “Scuola di perfezionamento” to people who had already a degree in physics. And I was teaching using the book by Bogolubov and I remember it was very hard. I was working very, very hard to prepare those lectures. And in research I was continuing to do what I had learned for more complicated versions of models for strong interaction. Also Bologna University was in trouble in physics at the time. There were struggles and problems. They had made mistakes in the choices of people to head the physics institute, that is my feeling anyway. So that was strongly reflected on the “climate”, I mean the political and cultural climate. In Ban there was this new university and I met with Ban people in a congress and they told me they would be happy if I came to their university, so I left Bologna and its problems and came here. And that was forever, I did not expect this at that time.
Okay. And what were the people you met, the first people from Bari?
They were experimentalists, because Bari at that time had no theoretical physicists yet. It so happened that I published the first paper in theoretical physics of Ban University. But it was a very good experimental group because there was a bubble chamber collaboration, called Saclay-Orsay-Bari-Bologna from the names of the participating institutions, that was well known internationally at those times. In Ban there were several good experimental physicists. The director was Michelangelo Merlin, other people included Aldo Romano, Nicola Armenise, Vittorio Picciarelli, Alberto Silvestri, Francesco Romano with whom I kept good relations. I think that for me it was a very good decision to come here, not only because the human relationships were much better, much more relaxed than in Bologna, but also because here I had space to do what I wanted and I had no great difficulties in doing foundations of quantum mechanics. In Bologna it would have been more difficult.
So when you came to Ban you were already thinking in foundation of quantum mechanics?
Yes. It was about the time when I switched from particle physics to foundations of quantum mechanics. In the beginning I thought that I would have made research both in particle physics and in quantum mechanics, but slowly I was completely attracted by the foundational problems.
Okay. One question I would like to put, that what were the most influential works you read at the time you were switching to quantum mechanics?
Yes, I was traveling a lot at those times. After my thesis I went for one year in Paris in Saclay. Then I went two years to the United States. Then I went to Brazil in 1970. Then perhaps in 1971 or ‘72 I was in Sweden. And it was in the library of the physics department of the University of Gothenbourg in Sweden that I found in French the book by Bernard d’Espagnat, Conceptions de la Physique Contemporaine.
It’s a book published in 1965.
Yes. I found it later.
It was a revelation. It was something fantastic to see how many problems were open in quantum mechanics.
Do you think Bernard d’Espagnat knows this?
Perhaps I told him, but I am not at all sure.
Oh, it would be interesting to let him know.
Given the philosophical disagreements he probably would not be very happy. But anyway, it was a revelation for me. Reading that book was a great discovery. There was a new field possible to create and a lot of research to do. In my opinion d’Espagnat at the time he wrote that book was still basically a realist. However this did not last long. After some years d’Espagnat switched to the opposite philosophical approach, idealism. I have a high respect for d’Espagnat as a working physicist, but philosophically I disagree with him. This happens very often to me with many authors. Let me tell you something more about his change of attitude. For example I heard d’Espagnat giving a talk at a conference, maybe twenty years ago, and he was saying that the idea of reality should be analyzed very carefully. Then he went on to imagine different types of reality. He made a list of possible realities in the beginning — the reality of physical objects, the reality of mathematical symbols and so on, the reality of God. And then in the talk and in the paper he analyzed one by one all of the possible forms of reality and discarded them, except one — which he did not talk about, the reality of God. It was very clear to me that his implicit conclusion was in favour only of the last type of reality.
That’s because you think he would be unhappy knowing the influence of his book, but I don’t think so because I think that this book was very important at the time, and it’s very interesting the information you are giving us about the role played by that book. And I remember that the first time I read that book, the book opened a spectrum of possibilities in the interpretation of the quantum mechanics. It’s not a book to support, or to present just one.
It was fascinating to see that so many possibilities were open. So it was clear that the Copenhagen approach was not unique, was not obligatory.
We had a philosophical freedom.
I don’t know if you know, but I am quoting in this paper, Leon Rosenfeld did not like at all that book, and at that time he wrote to d’Espagnat calling d’Espagnat to come to Copenhagen for to heal a kind of “wignerite” d’Espagnat was suffering in Rosenfeld’s words. But this is just a little curiosity.
I had Rosenfeld once as a teacher in the summer school of Les Houches, but he was very, very mathematically minded and I could not understand his physics. I really did not know him personally. He was just a teacher. But later I knew that he was considered to be a Marxist, and that is very difficult to understand. I mean how could he use the Marxist approach to justify the Bohr and Copenhagen philosophy which is basically in line, as told by Max Jammer, with the Kirkegaard and Hoffding philosophies. These people belonged to the right wing of Hegelianism, which is something very different from Marxism, which in principle should be the left wing. Kirkegaard basically says that there is the thesis and also the antithesis, but no synthesis is ever reached. According to him synthesis does not exist, it is impossible. So it’s difficult to understand the position of Rosenfeld given that Bohr’s complementarity is also a negation of syntheses, such as the one between space-time description and causality, or the one between wave and particle.
And do you remember the date of the Les Houches school you attended with Rosenfeld?
I am not sure about the year, but certainly it was in the sixties. Rosenfeld was teaching about the quantum addition of three angular momenta.
And the second question. At the time you met Rosenfeld you were not still concerned on the foundations of quantum mechanics, but did you know at the time that position of Rosenfeld trying to make a mixture of Marxism with complementarity.
At the time I did not know. I found out only later.
Later. Okay. One question I would like to put is that in your Varenna talk you put a strong emphasis at the beginning of the lecture on the role of realism as a philosophical conception in physics. From reading your text and from your interview one can understand that realism was a strong philosophical commandment in your point of view. Could you talk a little about the origins of this point of view in your biography? How did you become a realist?
I have the feeling that I always was a realist. I remember in high school the philosophy teacher — who was not very good anyway — arguing against realism and I remember I was scandalized. “How can you say that nonsense?” I asked myself. And then of course my choice to be a physicist was basically not because of prestige, but basically out of curiosity to understand the real world — atoms, stars and so on. And now when you arrive fully in the scientific activity you find that many people teach and say that the reality is not there. They make you feel that you are misplaced, yes, that you are not in the right place. So I had a very strong rejection of the antirealistic positions — very strong. And for example in one pion exchange model I believed that really there is a pion exchanged. It is visible, so to say, in the right variables. There is a typical maximum which is always there. You can see it. In 1970 I was already in Bari, but I went to the United States for one academic year. I was invited by an American physicist who had been here in Bari, David Golden, who came from the University of Nebraska. So I went to Nebraska for one year. They had a wonderful library and I can say I spent most of my time studying the books and articles in the foundation of quantum mechanics. And when I came back from that year in Nebraska I knew a lot about the history of quantum mechanics. Actually I decided I wanted to understand how it had been possible that the quantum mechanical antirealistic view was built.
So I started from the biographies of the physicists, twelve physicists, all the top big names — including Jordan, Pauli, Dirac. And I read books written by those people, especially autobiographical books or books exposing the main ideas like for example Physics and Philosophy, by Heisenberg. And then it was in that way I discovered how strong was the opposition to the Copenhagen approach, because soon I found out that Einstein was against, Planck was against, Schrodinger was against, de Broglie was against, Ehrenfest was against. It was not just one man, it was a lot of very important people. And then the problem, which is still open today (perhaps you know the answer, but I don’t) is: how is it possible that the existing scientific community was born from such a splitting in the group of the creators and founders? You can say basically that twelve of the most important people were split 50:50 against and in favor of the Copenhagen quantum mechanics. Now from a situation like this normally in any human activity you would find the later cultural community also split, but not in physics. In physics you have 99 to 1. Fifty-fifty for the founding fathers, but 99 to 1 for the people who are active in research. How was it possible, through repression and control of positions and publications? And then also a lot of dogma exists. People do not dare opposing important ideas. They feel that it is too dangerous, but they do not dare anyway.
Okay. So, still about your talk at the Varenna school, I remember that you spoke about the connection between philosophical realism and social responsibility. Would you talk a little about this relationship at that time as you thought and after that?
Yes. It has not changed. Basically I always thought that we get the money to do research (some people get lots, some people get little, but anyway it is public funding) and that it is our duty to build a science that can be communicated to everybody. And at those times I was thinking in terms of the working class, the working people. That is to say, if the only way to understand what I’m doing is to study differential equations or Hilbert space, it is obvious that there is no possibility to communicate because it takes too long to learn, there is too high a threshold. If instead I build physics in three-dimensional space and in time according to the rules of causality then I can communicate my results. Not the technical aspects, but I can tell what I found of how the world really works. I can explain the result I achieved. And I always thought that it is our duty to do just that as much as possible. Seeing that important ideas of the realist people like de Broglie and Einstein and so on were as much as possible forgotten, I understood that the scientific community does not work properly. Because you see, you can of course say Einstein is wrong, anybody can be wrong, but you have to show that he is wrong.
You cannot say he is wrong “because I say so.” And that proof was missing. Instead it was very clear that in physics fashion plays a great role. I saw so many fashions — Regge poles and Mandelstam representation and the peratization approach to weak interactions and then Regge cuts and dispersion relations used as dynamical tool and then the static model and so on and so on. And also that was impressive, because you could see a very large number of theoreticians all over the world working very hard for several years on a problem and then abandoning it without any result. For example I remember a lot of work went on pion nucleon elastic scattering, low-energy elastic scattering. Well, I can tell you that not even the sign of the small phase shifts was predicted when the problem was abandoned, not even the sign. It was a shocking activity to watch. You have a strong collaboration, everybody is doing research on the same problem, but after some years they abandon quickly the problem they were studying and pass to something else; then everybody is working on the new problem, until they abandon it too and pass to an entirely different matter, and so on and so on; without ever finding a firm result. That is the pattern of theoretical particle physics for the strong interactions.
They don’t know where they are now. So in my opinion the social responsibility is to do something different, to do something for which you can see the progress going on and which you can communicate especially to other people — to politicians, to interested people, to workers and to the taxpayer. So I am very much in favor of a social control. I know it sounds utopian because the reality is very, very different, the reality is a big science in which you can justify the need for big money in a very superficial way, as it is done in the United States and also in Europe. This produces distortions of the scientific culture and it is not good.
Okay. I would like to come back a little to get precise information about when did you convert your career as a physicist to the field of foundations of quantum mechanics. I believe that it was sometime in between 1965 and 1969, but could you say that in ‘69 and ‘70 your main research was already on the quantum mechanics, the foundation of quantum mechanics or the shift in career was later?
No, it was about at that time. In fact the 1969 paper you mentioned, a letter to Nuovo Cimento, was the first paper I ever wrote on the foundations of quantum mechanics. And then my interest for that activity started after reading d’Espagnat’s book. And I was then a member of the directive board of the Italian Physical Society so I suggested that a summer school be organized in Varenna by the Italian Physical Society on the foundations of quantum mechanics. The idea was accepted and d’Espagnat was named director of the school and many influential people were invited. Andrade Silva was there representing de Broglie.
A Portuguese physicist.
Yes. And then Bell was there, Jauch was there, it was a very interesting school. In 1969 for me conceiving the idea of that little paper was a revelation, because I had been educated in believing that the double slit experiment is something that cannot be explained by any intuitive approach. Instead I basically rediscovered something that of course was very well known to de Broglie, Bohm, and other people, I discovered that real waves associated with real particles in principle explain everything. That was the so called dual approach. Real waves and real particles propagating together. If you have that, you can understand the double slit experiment without any difficulty, even though many important books claim that it is a phenomenon going beyond the human reason. In that paper there was also an idea concerning neutrinos and the possibility of using them to discover the reality of the waves.
That was very unpractical. It was only for me it, was helpful to see that in principle something could result. When the paper was published a little time passed and then I received a nice letter from Louis de Brogue saying something like “I like very much your paper as I am working on this problem since a long time.” It was very nice to see that de Broglie had read my paper. Then later I went to Paris and eventually I met him. There was an exchange of letters, which I have kept. And then for some time Paris was looking as the most interesting place on earth for my type of research, because de Broglie was alive. There was the de Brogue Foundation, there was Vigier, there was d’Espagnat. There were young leftists like Paty, Levy-Leblond interested in fundamental questions, so it seemed like a paradise.
I have seen with time the paradise melting away completely, slowly, because eventually de Broglie died, the de Broglie Foundation after his death followed a path of low profile and it was not anymore a real defense of de Brogue’s ideas, d’Espagnat changed completely his philosophy, and Vigier was very difficult to agree with from the beginning, because he considered himself a nonlocal realist, a position whose motivation for me is still very difficult to understand. It is like realism with miracles, but then one can keep the Copenhagen approach, which is full of miracles. And then the young leftists converted to the orthodox line of thought as well, so with time nothing was left, and Paris disappeared from my horizon. And that was very strange to see, mostly because I had the feeling it was not a spontaneous, scientifically motivated shift. Instead there were forces at work, cultural forces working to undermine the plurality of ideas of French physics by repressing systematically all that was not in line with the orthodox approach. This in my opinion is a great mistake because the plurality of ideas is fundamental in producing real progress as it gives rise to real debate. And what else? What was the question?
It was about the date of your shift to that.
Yes. Basically 1970 with the Varenna School.
Varenna School, yes. Still about Varenna School and as you spoke about Vigier and his nonlocal realism, I would like to remark that your talk at Varenna School, I think that it is very representative of your own line of approach to foundations of quantum mechanics. Because you maintained indeed your philosophical realistic approach in a very open sentence since the beginning. Second one, you explicitly denied the possibility of the standard quantum mechanics description for two systems. You denied that this kind of description could be a real phenomenon, so you did not accept non-locality. And a third one, you proposed experiments to decide, to see the questions. I think that these three different features are very proper of Selleri’s approach on foundations of quantum mechanics. I would like you speak a little and hear you about the third one, the role of experiments, because experiments were introduced in these fields from one side via Bell’s inequalities and the work of Clauser, Shimony and others. And the other via was the via you suggested independent of Bell’s inequalities. And since then you were still proposing experiments, analyzing experiments, so I think that suggesting and analyzing experiments you think that it is a very important part of your participation in this field. I spoke a lot, but I would like to hear you about the role the experiments have, what is the role of experiments in this field of research.
Of course for a physicist experiments should be everything essential. They should be the main way to learn, to make progress. From the very beginning I understood that Bell’s inequalities had a very strong generality that many people tried to deny. Still now from time to time I receive papers in which somebody tries to disprove the generality of Bell’s theorem. Psychologically this is due to the fact that many people like quantum mechanics and many people like local realism and they would be happy, such people, to keep both.
Unfortunately it is impossible. It is totally impossible. A part of quantum mechanics, the physics of a single particle, has been interpreted completely in terms of local realism. But there is not only that part. If you consider two correlated systems it becomes impossible to interpret quantum mechanics according to local realism. By the way, this I will come to explain in more detail, but there is a great epistemological lesson here, because we see that philosophical choices of a very important type can be tied to the mathematical apparatus of the theory to such an extent as to make it incompatible at the empirical level with a very natural philosophy, such as local realism. There are many interpretations of quantum mechanics, but all interpretations disagree with local realism because there is a perfectly definite empirical prediction of the mathematical apparatus of this theory saying that Bells inequality should be violated.
Therefore all those interpretations agree that there is incompatibility with local realism. It is a fantastic problem, as you can imagine. You do an experiment and you can choose the right philosophy of nature so to say, in the sense that a falsification of a wrong philosophy of nature can be obtained. No, the experiments were for me always very important; I always kept my eyes on experimental science because otherwise doing pure theory is nonsense. I mean you can create anything, you can invent a thousand theories but if you don’t have the control of experiments how do you know that what you are doing has a chance to be correct? So you are right to say that interest for experiments is a constant of my way of thinking. In the beginning I thought that it was a constant for everybody. Later I realized that it was not so. Basically in quantum mechanics I worked on two types of experiments. One type is the reality of quantum waves. The other type is Bell’s theorem. That is to say, I am convinced that quantum objects — photons, electrons, neutrons — have a double nature: they are a wave and they are a particle. In the same sense that you can have a boat on the water that is accompanied by a surface wave. So I published many papers suggesting experiments to detect the reality of quantum waves, especially in the ‘80s and also in the beginning of the ‘90s. And then I published papers to show that the experiments on Bell’s theorem that many people considered to be final really were not so. And for a very good reason, that Bell’s inequality has never been checked experimentally. They have checked something else. That is to say another inequality based on local realism plus additional assumptions. Are you clear on this?
Very good. You know a lot.
And then recently I published papers on particle physics for the EPR paradox. A system of two correlated neutral kaons can be very useful for checking the Einstein-Podolsky-Rosen paradox and Bell’s theorem, because high-energy detectors have a very high efficiency, so there is not the problem of two types of inequalities.
So if I understood your papers, you are suggesting to change the field of phenomena in which you can see the EPR paradox. So, not optical phenomena, but particle phenomena.
In particle physics you can really choose between local realism and quantum mechanics. In principle. In practice it is very difficult to convince people because there is a strong pressure coming from other more traditional problems. To convince those people to do an important experiment on the EPR particles is not easy. Also because they find some theoreticians telling them that the EPR paradox is already solved in favour of Bohr. So it is a waste of time they say, wrongly.
The first time you have suggested these experiments was —
With kaon pairs it was in ‘83.
Okay. 1983. Okay. But I would like to come back a little still about the initiative of the Varenna School. You told a very interesting thing about the origins of the idea of that school. Recently I tried to consult the records of the Italian Physical Society just to see the origins of the idea, but I was not able to consult with them. I did not get a good answer from them. But it is very important, the information that you suggested the idea, but I would like to know if you could remember if the idea was largely supported or there was any kind of doubts or any kind of opposition. So, could you talk about the origins of the idea of the Varenna Summer School? And second, about the realization of the conference, how that initiative was accepted among Italian physicists.
Well, as I told you, the idea was mine and I did make the proposal because I had been elected nationally as a member of the directive board of the Italian Physical Society. In principle I was elected for three years but I really remained only one year and after I resigned because I decided to go to the United States.
Yes, so I could not do those things. When I proposed to keep, to have this school, it was accepted. It was accepted, yes, by the other members, like Castagnoli, Ricci, Toraldo di Francia. I do not remember any real opposition to my proposal; only a certain cautiousness. And they invited the speakers, more speakers than I had thought, and I think they did a good job because Piron was included, for example, and other people as well, American experimentalists for example. The 1970 Varenna Summer School was accepted very well, especially by young physicists. That was a wonderful moment after the student unrest that had been very active in the physics departments. People were also very strong and motivated towards new ideas. So the Varenna School of 1970 on the foundations of quantum mechanics was held and the book of the proceedings was printed in which there is a picture of the participants. I don’t know if you saw it.
In the picture you can see many of those people. Several of them were active in the field of foundations of quantum mechanics.
If I could say one thing, my idea from historical studies of taking 1970 as a turning point, that idea came exactly when I saw the photo and the list of the names of people who talked and who attended Varenna Summer School.
Yeah, yeah, I was very impressed.
It was a very good choice, but you see, that was a moment in which so to say the foundations of quantum mechanics became, if I may use the expression, a mass activity. It’s not really true, but I mean compared with before.
Because the most important ideas came before 1970.1 mean Bell’s theorem and the very important demolition of von Neumann’s theorem done by Bohm and by Bell. Because that theorem had convinced many people, and when I went around to give talks I always found somebody saying, “Oh, but look this is nonsense, it is impossible because there is von Neumann’s theorem showing that you cannot have a causal completion of quantum mechanics.” And then there was a good answer: “that is not true because it has been shown by Bell and by Bohm that the hypotheses of this theorem are not general enough.” So there was very strong point in favour of the innovators. The idea — may I say something slightly different? You see the idea of real waves is difficult to imagine for many physicists because a wave in general is not a thing in itself, but a property of a medium. You can imagine a particle propagating and then I don’t know if you are aware of the phase part of the problem, that in every particle there is an internal oscillator. Every particle has an internal motion.
I have just a qualitative idea about this concept.
There is a vibration, and then the vibration, de Brogue teaches us, has the same phase as the wave in the point in which the particle is placed. So there is of course a connection between particle vibration and wave oscillation. So it strongly suggested the analogy with an oscillator going in the water and beating the water rhythmically, and then waves are generated and propagated with the same frequency of the oscillator, which are of course always exactly in phase with the motion of the mechanical oscillator in the point where the latter is placed. So the idea of real waves really requires a medium. And in recent years I switched to the foundations of relativity to see if a logical space existed for such a medium.
Okay. So this is a connection — there is a question I would like to introduce. The connection in your research between foundations of quantum mechanics and foundations of special relativity, a more recent subject.
You see my research in the foundations of quantum mechanics has the following strong points, the way I see it. First, the proposal of experiments to detect the objective reality of the probability waves. Second, showing that the inequalities violated by experiments are very different from the original Bell’s inequalities in many ways, so that they do not constitute a violation of local realism. And third, proposing a set of new experiments with K mesons which could really allow one to discriminate between the Copenhagen approach and local realism. That is what I know. But this is not a new theory. It is only a set of ideas. But in relativity it is different. With relativity I could go much deeper and I have basically a new theory that can replace special relativity.
I would like you to speak a little. It’s a subject I am not familiarized with your research on foundations of relativity, your approach.
Yes. If you could speak, it will be interesting.
You see, in the foundations of relativity it becomes very clear that the theory of special relativity is based not only on experimental evidence but also on human conventions. There is a very important element of conventionality in the definition of simultaneity. That is to say, the time of special relativity should be seen as dialectical, that is contradictory in an Hegelian sense. On one side it is objective because moving clocks slow down. There is no doubt. That is an empirical fact. Moving clocks go —
Retaking, you can start.
Poincaré, Reichenbach and Jammer are the people who have stated most strongly that the choice of having the one way velocity of light equal to c is a convention. And eventually I found that also Einstein agreed on conventionality. For example in the 1905 paper there is just one statement, but very clear. He says, more or less “By assuming the universality of the velocity of light we are not making an assumption about the physics of light but we are establishing a convention.” So, you see, Reichenbach wrote a book entitled The Philosophy of Space and Time in which he introduced a parameter — called Reichenbach parameter — “epsilon”. When the Reichenbach parameter is one-half you have special relativity. But all the values between 0 and 1 are possible. You have in principle theories that work as well as special relativity but are different, philosophically different from the theory of special relativity. So what I did was to — I was influenced by Prokhovnik and his books and by John Bell who wrote an article on the foundations of special relativity.
By other people as well. And what I did is to check if that was possibly true, I mean that you could develop theories which are different from special relativity and still fit all the experimental data, for example the Michelson-Morley experiment. And yes, it is true. You have an infinite set of theories. Working always on the experimental side I could explain Romer, Fizeau, Doppler, Michelson-Morley, and so on. Many experiments can be explained by these theories. But then if you really wonder whether really it must be so, I mean that all possible experiments are fitted equally well by these theories or not, then you find that there are exceptions. Interesting exceptions are experiments with superluminal signals. There is considerable experimental evidence that they exist nowadays.
Other exceptions are phenomena with accelerations. Phenomena in which accelerations play a role, for example the Sagnac effect. Do you know what is the Sagnac effect?
Just a little.
Interference with an interferometer on a rotating disk.
The Sagnac Effect was never satisfactorily explained by special relativity. My latest paper is exactly on this.
I will make you a better copy.
Okay. I would like that very much.
And so if you really want to explain the Sagnac Effect you have to take a different theory. You have to take a value of the Reichenbach parameter different from that of relativity. You cannot use epsilon=l/2. You must take something else. In this way you find that the right theory is the one assuming absolute simultaneity. Meaning that simultaneity is the same for all inertial observers. In such a theory there is a privileged system and the privileged system is that one in which Lorentz’s ether is in rest. I must say from a logical point of view that this choice is not only possible, it is obligatory. Logically, strictly scientifically. Sociologically it is and will be very different, as the scientific community tends to be rather dogmatic on such matters. I expect my ideas to be accepted by very, very few. But, I repeat, from the scientific point of view it is obligatory to accept the Lorentz ether today. I have just published a book in Italian and now I am translating it in English.
In English. Very, very, very interesting.
In my book all this is said and the all the evidence is collected and so on. So you see by saying the Lorentz ether is unavoidable I am also saying that I have a way to create the quantum waves.
Okay, okay. I would like to come back again about some reminiscences on the ‘70s. In the ‘70s and the beginning of the ‘80s you had in Italy three or four important meetings about foundations of quantum mechanics. The first, Varenna School, the Erice meeting. I don’t know if the pronunciation is correct.
Erice [pronounced air’-ichih].
Erice, 1974. You had the other Varenna Summer School in 1976 if I am not wrong and you had a conference in Ban in 1982. So it was the time, the decade in which you have many experiments concerning Bell’s inequalities, but the main meetings about this subject happened in Italy. Could you talk about the role or the importance of that ensemble of meetings and about the Ban conference? I am interested in a more precise question. I think that Mandel came to the conference. As my colleague Joan Bromberg is focusing her studies on the role of Mandel, in quantum mechanics, could you speak a little bit about the Ban conference and about the Italian conferences of that time?
Yes. Well, when I started doing this activity I felt it was important to create contacts and have people give talks and try to spread the ideas as much as possible, so not only I organized conferences but I tried to push other people to organize conferences. Some conferences in Greece, Poland, Portugal were held after my suggestion. And so we had really a lot of activity and then we went in touch with a large number of physicists at those times. Our conferences were of course open also to those orthodox people who wanted a real confrontation of ideas. And the Ban conference was organized at the time to attract Karl Popper whom I understood then to be a very important philosopher for us, because Karl was very critical of the Copenhagen approach.
And by the way, he was also critical of special relativity and he was also critical of some developments of statistical thermodynamics and I think that every time he was critical he was right — which is not like saying that his philosophy was all correct, I don’t know, I’m not philosopher. Sometimes I find it complicated. Instead as a critic of the foundations of modern physics he is a genius in my opinion. He has done something fantastic - because he always could take the point and see exactly what was the difficulty. Eventually he told me, “Franco, what do you think of the theory of special relativity?” and I gave a vague answer because I did not have clear ideas (the episode was before I started doing research on the foundations of relativity) and he was very unhappy with me because of that. That was in the ‘80s, perhaps in 1985. In 1982 he had come to Ban. He arrived at the airport, and it so happens that the day before I had received the first copies of my first book. My first book was entitled “Die Debatte um die Quantentheorie” published by Vieweg in Germany after some lectures I had given in Vienna on the subject. There was Roman Sexl, who later died unfortunately, my good friend who followed my lectures in Vienna and invited me to write a book. That was the book. It after was translated into several languages, also Italian.
I read it in Spanish.
Probably it is the same book. And Popper came, I went to take him at the airport, and I gave him a copy of the book. The following morning there was the conference starting. He arrived at the conference with my book in his hand and started saying, “I have here a very nice book by Professor Selleri that I have read during the night and in my opinion it is basically right.” He was a very, very kind person. I had prepared for that conference a talk. You see I knew that Karl Popper had difficulties in understanding the philosophy of the Einstein-Podolsky-Rosen paradox.
So I prepared a talk to explain to him in the easiest possible way what was really the essence of the paradox. He did not like it at all. He said later, “You did not give a nice talk. That was an academic type of talk.” To me it did not look so because I had even prepared little dots, red and blue, to show the elements of reality and so on. But anyway after the Ban conference with Karl there were longer contacts also with exchanges of letters. I went to visit him in London at his house and we had discussions. And we agreed on quantum mechanics very much.
And even you have suggested experiments. You had published a paper by Popper, you and Garuccio.
That was by Garuccio, Popper and Vigier.
By the way, Garuccio is here across the corridor.
Yes. If he is still there, I would like very much to know him personally. Recently I read a paper by him on the history of the theoretical physics in Italy.
Then that was Popper. Yes. It was very important to me meeting Popper, because he wrote whole books critical of quantum mechanics. Also he was a man of fantastic clarity. Surely you have read something by Popper. He obviously has a lifetime of exercising in being clear and he succeeds. I mean his ideas are presented in a fantastically clear way. Also orally when I talked to him he was very clear. He had a very, very attractive personality. In my opinion he was the best philosopher of the 20th century, the best philosopher of science, by far, without comparison. Okay, I will say something about Mandel. Of Mandel I had a very good idea because he had done so many interesting experiments. To mention just one, the Pfleegor-Mandel experiment, published on Physical Review, in which you have two lasers of very low intensity superimposing their beams and interfering. I will describe the experiment from the point of view of objectively real waves and particles. The intensity is so low that most of the time there are no photonic particles in the apparatus.
Then eventually you have one photon coming from one of the lasers and passing through the apparatus during the time Δt and then again no particles in the apparatus for a time much longer than Δt. Still, when one collects many arrivals it becomes evident that the two laser beams interfere, showing that the wave born in one laser can generate interference with the wave coming from a different laser and that a photonic particle feels the presence of both. Otherwise they would not show interference. In my opinion that experiment gives a strong confirmation of the objective reality of quantum waves. And so Mandel was the most attractive experimentalist we could see because of the nice experiments he had done and we invited him to participate in the Ban conference. Several years later Garuccio, who is a very good man, decided he would go to visit Mandel and went to see him in Rochester during some summers. You should really talk to Garuccio about this, also because I am not sure if he agrees with what I am about to say; but in my opinion the later Mandel was different from the earlier. There had been a switch in his scientific personality — especially in the latest part of his life. Probably — this is my conjecture — he was trying to get the Nobel Prize for his research and was putting this ahead of everything. As a consequence, sometimes the interactions with him were frustrating. I had suggested an experiment to be done and he decided to do it.
Then he sent me a reprint to see what I could say about his conclusion that my idea was wrong. Then I read it and then I said to myself, “Well, this is impossible. There is a conceptual mistake. It is not possible that Mandel has made such a trivial mistake.” I read it again and again. I wrote to him. And then he said, “Oh yes, yes, you are right. Then I must do it again, but nothing will change.” How could he know before doing an experiment correctly that nothing would change? That was just to keep me quiet. And then he did the experiment a second time with the same conclusions, he sent me the reprint, I again found an error. I told him. He said again, “Nothing will change,” and he repeated it for the third time and of course it came out the way he wanted, but I wonder how much I should trust that experiment having such a particular history. In the last part of his life Mandel often published papers on Physical Review Letters. Some of them are really strange because they contain very poor statistics where the form of the interference figure is crucially important. It is clear that it would have been possible to do it with much better statistics and the research is important enough to improve it, but he published that poor result and I wonder why. Basically interacting with Mandel I developed a critical attitude toward experimentalists. Before I had a rather “dogmatic” approach according to which an experimentalist is right by definition. And after this I understood that you must be very careful also with experimentalists because you never know what they cook up in their laboratories. I have a second story about a different group. I’ll tell you some experimental experience.
When I was advertising my experiments on empty waves I went in several laboratories — for example in a laboratory in Paris. I proposed my experiment and I had a well-known physicist who was very, very attentive and really interested, judging from the questions he asked. The conclusion of the long discussion was this: “Selleri, your ideas are very, very interesting, but unfortunately I cannot risk the scientific credibility of my laboratory by doing such an experiment)’ He was illuminating because you see, probably other people saw the matter in the same way but did not say it openly. He said it. If you do an experiment on the foundations of quantum mechanics by the very fact of doing it you are in trouble. You should not do experiments of a certain type because if you find that quantum mechanics is correct you have thrown away money and you are stupid because everybody knows that it would come out that way. If you find the quantum mechanics doesn’t work, if it’s a wrong experiment and one should be very careful before giving you some more money for research. So you see, experimentalists are also men and they are strongly influenced by philosophy. Third example: I had interacted with an experimental group in Europe who had performed an experiment on Bell’s theorem that I had suggested. It was a variant with three polarizers, not with two, and then when they started getting results I could not resist — I was young and very active, so I ran there and I talked to them and they told me they found a violation of quantum mechanics. Then the head of the group came. He denied that it was so, and the thing was covered up and later on they published something completely agreeing with quantum mechanics.
So I don’t know how the experimental world works. Certainly you don’t have to take literally many published experiments, but you must be very attentive to everything. It seems that you are interested in this side of the story. All what I tell you can be documented. At home I have two large libraries full of books and documents. Letters. I have many drawers full of correspondence. They are organized geographically. One drawer is for France, another one is for Germany and so on, so a large collection of letters. Anyway, I have the feeling that Italy is more tolerant than other countries for the foundations of quantum mechanics.
It is very interesting to hear this, because it is exactly one of the questions I would like to hear. How do you find the reactions in Italy and other countries about that subject?
For example in Italy I am here talking to you after many decades of activity in the foundations of quantum mechanics and of relativity. And Italian physicists have been basically fair with me on the average. Of course you can find unfair physicists here as well. On the average they have been fair. They pay for my publications, they pay for my travels to conferences and so on, and I am free to do my activity. Although basically I am I would not say isolated by it, but certainly I am not as strong as I would wish to be — as influential as I would wish to be. I am not. But I don’t know if that depends so much on repression as it does on the fact that anybody doing physics is less powerful than anybody doing something else. If you are interested mostly in organization, power and getting money you are more influential than somebody who spends all the time in research.
In my opinion the difference between Italy and other countries depends on Enrico Fermi, because Fermi had doubts about quantum mechanics. I definitely would like to give you a copy of this evidence.
Oh, it’s very, very interesting to hear this.
Yeah. He never published any critical paper on quantum mechanics, but his friends and biographers wrote about his unhappiness. For example he was unhappy when he went in Germany in 1926 and he said that Pauli and Heisenberg had done great work, but really had exaggerated in not trying to understand the physical reality correctly. He said this and several other interesting things as is reported by Pontecorvo, by Segre and by Persico, people who knew him very well and who wrote books about him. And I have collected all the pieces of evidence I could find of Fermi being critical of quantum theory.
And did you intend to publish something about this?
No, because it is only five or six sentences by Fermi. I will give them to you and if you want to use them in your publications please feel free to do so.
Oh, I would like, I would like very much, because from the historical point of view you are talking a very interesting and new thing to reflect.
So you see Fermi was a great man, was a great physicist with a fantastically powerful brain that never stopped to work. He was capable of creating physics in different fields. He was a theoretician, he was an experimentalist and he was a technologist, and in every field he produced top research. I had an experience myself once. I believe it was 1980, I’m not sure. I went to Paris for a conference on the history of elementary particle physics. All the top physicists — Feynman, Gell-Man, Yang, Lee, all the top men in particle physics were there. Well, that conference on the history of elementary particle physics practically became a celebration of Enrico Fermi. Everybody was talking about him, as if there was nothing else interesting to talk about. So I had the dimension of the man. Unfortunately as you know, he died when he was fifty-five. He died very early — and probably, in my opinion, he died because of exposure to radioactivity and not having protected himself enough. And that was a tragedy, because all the top people of elementary particle physics are pupils of Enrico Fermi. They are extremely brilliant people, very good, but they lack the good sense that Enrico had. His good sense and his directive role in elementary particle physics for another fifteen years or so could have changed the history of modern physics, if he had survived. Do you have in Portuguese an expression like “buon senso”?
Si, si. Yes, yes. Yes, bom senso.
Bom senso. Because you see, in Latin languages we have such expressions, while in English they say “common sense,” which becomes a little different.
And so the “bom senso” of Fermi was fundamental. How did I arrive there?
The peculiarity of the Italian physics concerning foundations of quantum mechanics.
Enrico Fermi was the father of Italian physics, he was the top man who teached to people such as Amaldi, Pontecorvo, Segre and many others who were recognized as leaders in atomic physics. So if he had doubts perhaps you can imagine that his followers were not so dogmatic about those quantum things.
You see for example I became a full professor in 1980 and my career was delayed about ten years. I could have become full professor in 1970, so ten years before. My career was delayed because I switched to quantum mechanics. I have no doubts that if I had stopped to do research in 1970, considering the success of the one-pion-exchange model I would have got a chair in 1970. The fact is that doing something so dangerous like foundations of quantum mechanics made people also here more careful, but they did not really stop me. Actually, later, they gave me a chair. I had no doubt, knowing the situation in countries like the Soviet Union, United States and France, that I would have been destroyed there as a scientist. There was no tolerance for the foundations of quantum mechanics.
Okay. Okay. It’s very interesting because we are looking for — we, me, Joan Bromberg and from a historical point of view to identify national peculiarities of the physicist community. It is a very important thing. And but you are talking about your position you became full professor in 1980. And there are two related things I would like to know a little, about the kind of funds you could get to your research. You told that you would get funds to publish, to travel, but I would like to know a little more about this and about your collaborators and students related to that subject.
Yes. About my collaborators, it is not a very easy story to tell because they had to change activity to find jobs. It was not possible to keep them. For a long time I thought this was pure repression. Then I came to realize better that it was not only that, but it was also the fact that I was not powerful enough. Everybody tries to grab as much as possible for himself. If your hands are not long enough you get nothing. So my pupils had to find different jobs. The best placed of my pupils is Augusto Garuccio who is associate professor here. Another pupil is Giancarlo Scalera, who is a geologist in Rome, in the Instituto Nazionale di Geologia. Another one is Dino Fortunato, who became mathematician and has a chair in mathematics here in Bari. Other people, Sandro Graffi, Grecchi and Turchetti have chairs in rational mechanics in the North of Italy. Schiavulli and Augelli…
We can resume, but if you could repeat the last names for us.
Yes, Schiavulli and Augelli, who are doing solid state physics here in this physics department. That was a condition for survival, because doing foundations of quantum mechanics did not allow them to get a job. So it is difficult to say that I made a school. There are a lot of disconnected people doing different activities. We are still in contact, we are friends, we talk and so on, but everybody is doing his thing.
I would like you to talk a little about funds, but as you told about the kind of physics some of your students, ex-students, are doing here in Ban. I would like to know a little what kind of physics is done in Ban besides you and Garuccio’s works.
In Bari we have experimental particle physics. We have important experiments connected with CERN.
Then we have now a good theoretical group with several people, mostly doing elementary particle physics with some statistical physics. And then we have laser physics, but mostly applied, upstairs. And then some solid state physics, and nuclear physics. We have a good group of nuclear physicists.
Okay. The problem of funds in Italy, you have told that since the 70s you didn’t have any difficulty, a big difficulty to get funds to your activities, and theoretical activities, it’s sure.
Yes, it is so. I have been treated fairly. I have not been discriminated for the activity I did even though I can find, if I really think, I can find episodes, single episodes of discrimination but nothing really systematic. For example now I asked the INFN to get money to go to London and I got it. Today I have been told that it has been made available to me the money needed to go to London for a conference on the foundations of relativity next September, for example.
And when I publish a paper there is no problem in spending the money. For example we have a subscription in the library to Foundations of Physics and Foundations of Physics Letters. But of course it is not the big money that is coming in this way. It is the survival money.
Okay. I think that we could now talk about more precise points. It is interesting you spoke about the Foundations of Physics the journal and Foundations of Physics Letters. I would like to know what in your opinion the role it played, this journal, in the field of foundations of quantum mechanics. It is very interesting because it was created in the same year of the Varenna Summer School Conference, 1970.
That was a coincidence. The founder was Yourgrau, I believe.
Margenau. Yourgrau came to Ban. And it must have been 1970 or 1971, I don’t remember exactly how long ago. Yourgrau came, gave a seminar on the history of physics centered on Schrodinger whom he had known very well. He told me that coming here to meet me he was expecting to find an old man with a long beard.
And he was surprised, completely surprised.
Yes, but not long after, as you know, Yourgrau died. Alwyn van der Merwe replaced him, and later I went to visit him. I went to see van der Merwe in Denver.
Denver, Colorado, yes.
And later, in 1988, I suggested that also Foundations of Physics Letters be made. Alwyn liked the idea and he proposed it to Plenum and eventually this publisher accepted. So that the publication of Foundations of Physics Letters was after suggestion. And I think FP and FPL have had a very important role. Later other journals had been opening their pages to the foundations of quantum mechanics, and now sometimes I can publish on Physical Review. I have some papers published in it.
But for a long time it was not so; it was impossible to publish in most of those journals. And so it was very important the existence of Foundations of Physics that was culturally open. From the first issue it was evident that it was open to different approaches, and so it was very much on the line of the 1970 Varenna school. Many different ideas could be presented from all the different groups.
Okay. Still about the journals, if you look at Nuovo Cimento, one could say that even in the ‘70s Nuovo Cimento was an outlet for, a good place to publish some papers concerning foundations of quantum mechanics. And even before 1970. I am thinking for instance in papers by David Bohm, by Wigner, by — they were published in.
Janossy. Janossy, the Hungarian.
So do you think that this inclination of Nuovo Cimento is rather a reflection of the Italian physics, the openness of the Italian physics too?
It could be. There was — the most open journal was Lettere al Nuovo Cimento. That was very helpful for some years and after it was closed up and given to the European Physical Society and now it has become the European Physics Letters or something like that.
Its completely different now. It has become very conservative and one sided.
Instead Lettere al Nuovo Cimento was really open, very much open, and I know that this was worrying for the directive board of the Italian Physical Society. They were worried of having something they could not really understand and direct. Too open for them. Probably somebody was criticizing them about this journal, so they were happy to give it up to make it become an European journal But it is true that good papers were published not only on Lettere al Nuovo Cimento. For example, the famous paper by Philippidis, Dewdney, and Hiley was published in Nuovo Cimento.
Oh yes, yes, yes.
And Clauser did a very interesting experiment on the EPR paradox with some unexpected results and published it on Nuovo Cimento. Even before, in the ‘50s, there was the paper by Janossy, which is a fundamental paper on quantum mechanics because it shows that photons undergo self interference. It was a very large interferometer that was built, the experiment done in Budapest 30 meters underground to stop all disturbances. At that early time they had a huge interferometer with arms of 15 meters. The stability, the termal stability was such that if a man entered the laboratory it disrupted the interference figure for more than one day.
Okay. I know this. Okay. Still about journals, there was a journal Epistemological Letters. It is not longer published. I think that it was published under the auspices of the Ferdinand Gonseth Foundation. In some interviews, and consulting some lists of publications, it seems that this journal was very important at that time to publish in the firsthand some new ideas concerning the foundations of quantum mechanics. What do you remember, what kind of reminiscences do you have about this journal Epistemological Letters?
Yes, it is as you say. It was a good place to compare ideas, to discuss with other people and so on. To me it is mostly tied to an unpleasant scientific experience. There was a paper in which I thought we could show there was a problem in quantum mechanics; that is to say, I thought that I could show that action at a distance was implied by the orthodox quantum mechanics. Action at a distance is an expression really strongly charged philosophically. It is something very different for a positivist or for a realist. For a realist like me action at a distance is two electrons interact at a distance, but a positivist will never accept this. He will say that action at a distance is the possibility to transmit a signal from a human being to a different human being. To him only that possibility is action at a distance. Well, I thought I could show that, even in this positivistic sense, there was action at a distance in quantum mechanics. And the reasoning we made in that paper is in my opinion completely correct, except that at the time I had not understood that the quantum mechanics is not unique but there is a multiplicity of quantum mechanics and that people switch from one to another according to the needs. I was referring to the Bohr’s ideas, thinking that Bohr’s was quantum mechanics.
True, Bohr’s is one of the quantum mechanics. If you assume angular momentum conservation and you assume a classical apparatus, following Bohr’s ideas, then you can show that you have action at a distance. But instead, if you adopt von Neumann’s point of view, you can describe the apparatus with quantum mechanics with ket and bra vectors and so on. Action at a distance is not there anymore for complex reasons. So now I understand that in order to find an inconsistency in the theory it is not enough to find it in one branch, you have to find it in all of them. Really quantum mechanics from the epistemological point of view is not a well defined theory. It is rather a set of more or less parallel theories. In practice this situation is not a weakness of the theory, it is a strength. Of course it is a disaster scientifically to have such ambiguities in a fundamental theory, but people do not care so that the ambiguity becomes practically a strength, as it is very difficult to kill all the interpretations together. Only the EPR paradox can do that. It’s a decision that could be made with a suitable experiment. But then people don’t do the experiment and that’s the end of the story.
Okay. But you were speaking about a specific paper in Epistemological Letters or in general?
Yes, it is a specific paper that was first published in Epistemological Letters and then was submitted to Comptes Rendus de l’Academie des Sciences, and there was a very long debate between the authors on this last paper. I was not alone then but also Petroni and Garuccio and perhaps Vigier were also involved, and the referee. We knew that the referee was d’Espagnat. And eventually the referee won after a long struggle in the sense that we could not publish the paper the way we wanted.
But it started in Epistemological Letters.
Okay, okay. I would like to change to other specific questions. I would like to hear your view about the role played by David Bohm in this field. I know that Bohm’s first approach was a nonlocal model and I know that Bohm in the ‘60s gave up even this first model, but I think that he played a very important role in the beginning of this field. And I would like to hear your view about David Bohm, the role he played, a little about his ideas, and eventually your personal view about his contribution.
I have a very high opinion of David Bohm, because he was a sort of a hero as he was alone in defending the causal outlook in the early fifties. In the late ‘40s and the early ‘50s (the hardest times) there was only David Bohm and nobody else — not even Louis de Broglie, because you know that de Broglie was basically converted to the orthodox way of thinking from 1928 to 1952.
So he had abandoned his early physical position and it was David Bohm who pushed de Broglie to come back to a critical attitude.
So I think he was a very courageous and very honest and a great physicist. His papers in Physical Review are very nice. The turning point in my opinion for David Bohm was a paper in 1957 if I remember well in collaboration with Aharonov, but not the paper on the Bohm-Aharonov effect, not that one.
It’s a paper in which it is discussed what kind of experiments could give information about the EPR paradox.
Yeah, yeah, yeah, exactly, exactly.
They analyzed the experimental data maybe obtained by Madame Wu.
Yes, yes. Exactly that. Exactly that. Because in that moment he understood that the experiments were not compatible with what we now call the factorable quantum mechanics. You know, there are three different approaches: (1) there is orthodox quantum mechanics, (2) there is a mutilated quantum mechanics in which all state vectors of correlated systems become factorable, (3) there is the causal approach.
Some people call point (2) above Furry theorem or Bohm-Aharonov theorem. And then with (3) you have of course a completely different approach in which quantum mechanics is reinterpreted as much as possible according to causality. Now the second line was the one that obviously Bohm was hoping to develop, and when he found that it was not possible because it was not compatible with experiments, he gave up basically and accepted non locality - which was a little bit of a tragedy. Of course he had the right to do what he wanted. He had done so much in the field that I am very ready to forgive him, if it means anything. But it is a pity, because nobody else really defended local realism to the very end. In my opinion Louis de Broglie did not understand very well the problem, so he did nothing on this. And Bohm gave up. d’Espagnat was against, so really there was a time before 1970 in which research favorable to local realism was not at all carried out.
And Emilio Santos, what is the position of Emilio Santos, isn’t that?
That was later. Emilio Santos and I became active on the issue of nonlocality only with the 1970 Varenna school. Emilio Santos disagreed with almost all other physicists because he shared with me the critical attitude towards nonlocal quantum mechanics. Presently he does not accept the violations of Bell’s theorem.
So we can say that Santos is a local realist. I think he would probably accept this definition. He is my good friend. But we disagree on something very important, because we can be very similar philosophically and then disagree about physics. It is possible. The physics that you can do with local realism is not unique. That would be too easy. We disagree on Brownian motion.
There is no disagreement philosophically speaking. Philosophically his ideas are all right. Santos likes stochastic electrodynamics, Brownian motion, and I don’t like it. I will tell you the reason why I don’t like them. Let us take a very simple example to make the case clear, the photodisintegration of the deuteron. A gamma ray hits a deuteron, the gamma ray disappears and you have a proton and a neutron coming out. Now, the gamma ray has well defined energy-momentum so the proton and the neutron also come out correlated, very strongly correlated. In other words, if this room is the laboratory and if you could put there the detector of the proton you know that you must put in a well defined position the detector of the neutron. Otherwise you don’t find it. There is a very strong correlation in that case. Now the earliest formulation on the idea by Nelson — or even by Bohm and Vigier — was that Brownian motion makes the particle jump at random in all points in which you have the wave function. Now in the case of a scattering process like the photodisintegration of the deuteron, the wave function is a spherical wave outgoing from the target and filling the whole laboratory. So you should imagine that the proton and the neutron are dancing like hell all through the room before being detected eventually in some place. But then, if you detect the proton there you must detect a neutron exactly in another well defined position, no matter how much later. So you must imagine that when you detect a proton, the neutron stops dancing because it must be found in agreement with the energy momentum conservation. This stop of the random dance is nonsense. I told this objection to all of them many times, and the best answer I could get from Santos is that Brownian motion exists but only for little jumps around the trajectory. So, according to them, energy and momentum are not conserved but until now it has not been possible to refine the experiment to such an extent to find a little violation, because the neutron is not really jumping all through space but it is making little jumps around the trajectory.
It seems an ad hoc explanation.
Yes, very much so. Therefore, even though we agree philosophically we disagree physically. I don’t believe that Brownian motion has any role. I believe energy and momentum are conserved. The real waves guide the real particles, and that’s it.
This is the end of Tape 2, Side B
Philippidis, & Dewdney, &S Hiley, B. J. “Quantum Interference and the Quantum Potential”, IL NUOVO CIMENTO, 52 B, 15-23, 1979
Bohm & Aharonov, Physical Review, 108(4), 1070-1076 (1957).