Angel "Java" Lopez en Blog

Publicado el 23 de Agosto, 2010, 0:19

En mi post de ayer (Física cuántica y variables ocultas, por de Broglie) mencioné algo de la relación entre David Bohm y el beato Mario Bunge. Una búsqueda rápida en Google me dió estos documentos:

The work of Argentinean physicist and philosopher Mario Bunge as an exemplary life for the
fruitful integration of philosophy and the sciences
Science and exile: David Bohm, the hot times of the Cold War, and his struggle for a
new interpretation of quantum mechanics

Del primero, una entrevista a Mario Bunge, destaco algunos fragmentos (disculpen que no traduzca):

Later, in 1955, I went to Chile to teach a physics seminar and a short course on the problems of causality, something that had concerned me for many years because it was understood at that time that causality had died—that the world was not causal but that it was indeterministic. First the psitivists and then the quantum physicists seemed to be determined. I wrote a book, Causality, which vindicated the role of causal laws. That book came out of the lectures I gave at the University of Chile. It was published by Harvard University Press, and later translated into eight languages.

Ese libro lo tengo en mi biblioteca, y es muy bueno. Discutiría algunos puntos, pero es un "debe ser leído".

No conocía este episodio, la problemática relación de Bunge con el peronismo de entonces:

The University of Buenos Aires had expelled me for not joining the Peronist party and for not contributing monthly to Eva Perón"s foundation—two very grave offenses. At the end of 1952, I was fired from the School of the Sciences, and in 1956, after the fall of Perón, I was reinstated as a professor there.

Aparece su relación con la física cuántica:

I taught quantum mechanics, and later I won a contest of philosophy of science in the Philosophy department. Going back to 1950, I was considered a physicist and an amateur philosopher, and spent most of my time earning a living and doing quantum physics. I was in favor of the official interpretation of quantum mechanics, called the Copenhagen school of interpretation, until I realized that it was false. I realized it with a very simple example: according to the Copenhagen interpretation, physical theories refer to observations and measurements, and not to reality. Then, all the variables that figure into a physics theory can be measured, and they all refer to objects that are being subject to observation and experimentation. But the simplest example is the free thing, which is not subject to any external action, and which in particular is not being subjected to operations of observation and experimentation: a free particle or the free photon, or an isolated thermodynamic system, etc.

Algo así lo relata el propio Bunge, ver mi post La epifanía de Mario Bunge.

Aparece Bohm, su acercamiento, y la crítica de sus ideas:

Then I realized that physics was becoming—real physics was turning out to be—the operationalist, positivist, semi-subjectivist Copenhagen interpretation.5 Now then, what do we put in its place? What do we replace it with? David Bohm believed that the theory had to be changed. I believed him at that time, and went to Sao Paulo on a post-doctorate for six months. But nothing came of that except my decision to write books about the problem of determinism in general, and in particular, about causality, problems of determination; these were ontological, metaphysical problems.

At first, I was very enthusiastic about Bohm's theory, and I taught it first in Buenos Aires and later in the United States—the idea of hidden variables—but suddenly I realized that it wasn't good for anything. Causal theory wasn't like Bohm thought it was, because he did not deduce the distribution of probabilities. Rather, he supposed it was the same as the Copenhagen theory, and I realized further that new solutions or experiments did not arise. Then I changed the focus of my work and decided to formulate standard quantum mechanics in purely objective terms, in terms of physical things regardless of observations. That took me a couple of years. I had the fortune of obtaining a Humboldt fellowship and spent a very productive year in Freiburg, in southern Germany, writing my book Foundations of Physics, in which I compose axioms, schematic sciences, and a lot of basic theories, among them the realist quantum mechanics. And earlier, in Buenos Aires, I had begun writing my book La investigación científica, su estrategia y su filosofía (Scientific Research), which was published in 1967, the same year that Foundations of Physics came out. When I wrote them, I had not found any manual of the philosophy of science that satisfied me. I found that the existing manuals had been written by philosophers that had never set foot in a laboratory, who were not interested in anything but physics theory, that were not interested in experiments because they had never done an experiment. Almost all of them were positivists, empiricists, but only verbally. Because an authentic empiricist has to be basically interested in scientific operations, such as observations of the earth.

Interesante su acercamiento y luego, su alejamiento de las ideas de Bohm. Hasta hace un tiempo, no conocía la postura de Bunge. Creo que el libro mencionado "La investigación científica", es el mismo que comencé a comentar en Principales características de la ciencia fáctica.

Del segundo documento que mencioné al principio, destaco que Bohm emigró a Brasil:

... Bohm developed an intense and large scientific activity in Brazil. He discussed his proposal with foreign visitors, like Richard Feynman, Isidor Rabi, Léon Rosenfeld, Mario Bunge, Carl Friedrich von Weizsäcker, Herbert Anderson, Donald Kerst, Marcos Moshinsky, A. Medina, and Guido Beck, and Brazilian physicists like Schönberg and Leite Lopes. And yet, most important of all, in Brazil his work led not only to some individual publications but also to papers in collaboration with foreign visitors, such as the Frenchman Jean-Pierre Vigier, who went to Brazil for three months especially to work with Bohm, the American Ralph Schiller, who had been a student of the cosmologist Peter Bergmann at Syracuse University and stayed in Brazil for two years as Bohm"s assistant, and the Brazilians Tiomno and Walther Schützer.

Interesante la relación de Bohm con Feynman, y el esfuerzo que hizo para acercarlo a sus ideas:

Bohm"s main hopes for getting an ally among foreign visitors in Brazil were directed towards Richard Feynman, who was spending his sabbatical year in 1951 at the CBPF in Rio de Janeiro.31 Bohm liked the way Feynman initially reacted to his talk: "At the scientific conference at Belo Horizonte, I gave a talk on the quantum theory, which was well received. Feynman was convinced that it is a logical possibility, and that it may lead to something new." His interaction with Feynman reinforced his conviction that he needed to talk with physicists in order to convince them, and that in Brazil, without a passport, everything became more difficult. How large was Bohm"s bet on Feynman can be inferred from this letter to Hanna Loewy, which is also evidence of Bohm"s distrust of the current trends of physics at the time:

Right now, I am in Rio giving a talk on the quantum theory. About the only person here who really understands is Feynman, and I am gradually winning him over. He already concedes that it is a logical possibility. Also, I am trying to get him out of his depressing trap down long and dreary calculations on a theory [procedures of renormalization in Quantum Field Theory] that is known to be of no use. Instead maybe he can be gotten interested in speculation about new ideas, as he used to do, before Bethe and the rest of the calculations got hold of him.

Bohm"s hopes were unfounded, since "in his physics Feynman always stayed close to experiments and showed little interest in theories that could not be tested experimentally." As we have discussed, at the time the hidden variable approach had no connections with experiments. Indeed, the only reference Feynman made to hidden variables approach was to include it as one of the possible avenues for the development of theoretical physics, in a general paper published in a Brazilian science journal. This minor
reference was too little for Bohm"s hopes.

Bohm encuentra un defensor (que no coincide con sus ideas), en un anterior asistente de Heisenberg:

Guido Beck, who was Heisenberg"s assistant, nd a refugee from the Nazi regime, was living in Brazil at the time Bohm stayed there. Bhm found Beck a supportive person for his scientific activities, even if Beck did not hare a belief in the causal interpretation. Beck defended Bohm against the acrimonious criticisms of Rosenfeld – especially the comparison between Bohm and a tourist - and maintained that one should wait to see what physical results Bohm would be able to get. He was also instrumental in Bohm"s relationship with the CNPq"s scientific director, Costa Ribeiro, concerning funding for Bohm"s research.

Aparece de nuevo Bunge (yo no conocía su relación con Beck):

The Argentine Mario Bunge, who had been a doctoral student of Guido Beck in Buenos Aires, is a lesser-known case of adhesion to the causal interpretation. He read Bohm"s papers and became motivated to work in such a direction. Bohm replied to the letter in which he asked questions about the hidden variable models with an invitation to come to São Paulo. Bunge spent one year working with Bohm, but in spite of the good conversation, nothing came out. Indeed, Bunge attacked a problem which was more difficult than he had thought before, that is, the "Bohmization" of relativistic quantum mechanics and elimination of infinitudes in quantum electrodynamics. Besides Bunge, other causal interpretation supporters unsuccessfully tackled the same problem. In the middle of the 1960s, disenchanted with the hidden variable interpretation, he would give it up, as we will see later [así se lo comunicó Bunge al autor de este documento] Bohm enjoyed conversation with Feynman, Beck, and Bunge, in addition to the cooperative work with Vigier and Schiller; however, his feelings were different with other visitors such as Isidor Rabi, Léon Rosenfeld, and von Weizsäcker.

We had an international Congress of Physics. […] 8 physicists from the States (including Wigner, Rabi, Herb, Kerst, and others), 10 from Mexico, Argentina, and Bolivia, aside few from Europe, were brought here by the UNESCO and by the Brazilian National Res. Council. […] The Americans are clearly very competent in their own fields, but very naïve and reactionary in other fields. […] I gave a talk on my hidden variables, but ran into much opposition, especially from Rabi. Most of it made no real sense.

Bohm complemented his description of the meeting by formulating Rabi"s view thus: "As yet, your theory is just based on hopes, so why bother us with it until it produces results. The hidden variables are at present analogous to the "angels" which people introduced in the Middle Ages to explain things." We can be sure that Bohm produced a faithful description of the content of Rabi"s intervention, even if the proceedings of the meeting do not include the reference to the medieval angels. Indeed, according to Rabi, "I do not see how the causal interpretation gives us any line to work on other than the use of the concepts of quantum theory. Every time a concept of quantum theory comes along, you can say yes, it would do the same thing as this in the causal interpretation. But I would like to see a situation where the thing turns around, when you predict something and we say, yes, the quantum theory can do it too."

Interesante la defensa que adoptó Bohm, recurriendo a la historia del atomismo:

Bohm"s main answer was to compare the current context with the debates on atomism in the 19th century: "[E]xactly the same criticism that you are making was made against the atomic theory – that nobody had seen the atoms, nobody knew what they were like, and the deduction about them was gotten from the perfect gas law, which was already known."

Yo conocía algo de la física en Brasil de aquel entonces, pero ahora tengo más información (no ví que Argentina pasara por una etapa así):

The support that Bohm found in Brazil for his research can also be evidenced by the funds he raised. Bohm arrived at a moment when Brazilian physics was flourishing, after Cesare Lattes"s discovery, in 1947, with Cecil F. Powell and Giuseppe Occhialini, in England, of the pion in cosmic rays, and the detection by Lattes and Eugene Gardner, in the United States, of artificially produced pions. These scientific achievements resonated in Brazil, and led to an alliance between scientists, the military, businessmen, and politicians that was aimed at developing nuclear physics, and physics in general, in Brazil.

De ahí, pudo Bunge financiar su estadía en Brasil:

In 1952, the Department of Physics of USP was granted Cr$1,246.000.00 by the CNPq, and a supplement of Cr$528,000.00 was assured in December 1953. About 18% and 24% of those amounts, respectively, went to grants for students and visiting professors related to Bohm"s activities at USP. Those funds permitted Bunge to stay in São Paulo for one year..

Encuentro la nota 96, una declaración de Bunge:

"However, as time went by and no new predictions came out of the new formulation, I started to have doubts. Then, in 1964, when I started working on the axiomatization of NRQM for my Foundations of physics (Springer, 1967), I realized that Bohm's was not a valuable addition to standard QM and that the solution to his (and de Broglie's and Einstein's) problems lay elsewhere, namely in a realistic einterpretation of standard QM."" Mario Bunge to the author, 1 Nov 1996

Habría mucho para comentar. Les recomiendo la lectura de los dos documentos. Sería interesante leer también The Early History of David Bohm"s Quantum Mechanics Through the Perspective of Ludwik Fleck"s Thought-Collectives , Mario Bunge on Causality.

Nos leemos!

Angel "Java" Lopez

Por ajlopez, en: Ciencia