Xavier University Exhibit Conference on the Foundations of Quantum Journals, Publications, Conferences, and Mechanics (1962) Proceedings 2002 Conference Manuscript Boris Podolsky John B. Hart Xavier University - Cincinnati Frederick G. Werner Follow this and additional works at: http://www.exhibit.xavier.edu/conf_qm_1962 Recommended Citation Podolsky, Boris; Hart, John B.; and Werner, Frederick G., "Conference Manuscript" (2002). Conference on the Foundations of Quantum Mechanics (1962). Book 1. http://www.exhibit.xavier.edu/conf_qm_1962/1 This Book is brought to you for free and open access by the Journals, Publications, Conferences, and Proceedings at Exhibit. It has been accepted for inclusion in Conference on the Foundations of Quantum Mechanics (1962) by an authorized administrator of Exhibit. For more information, please contact [email protected]. CONFERENCE ON THE FOUNDATIONS OF QUANTUM MECHANICS Xavier University Cincinnati 7, Ohio October 1-5, 1962 Chairman Boris Podolsky Conference Manager John B. Hart Assistant Chairman Frederick G. Werner Sponsored jointly by the National Aeronautics and Space Administration, the Office of Naval Research, and the Judge Robert S. Marx Foundation. Copyright © , 1962, by Xavier University, Ohio This is a limited edition of the conference manuscript to be used for editing by the conferees. Roster of Limited-Attendance Portion of Conference Main Participants Professor Y. Aharonov Professor Boris Podolsky Yeshiva University Xavier University Professor P. A. M. Dirac Professor Nathan Rosen Cambridge University (England) Technion, Haifa, Israel Professor Wendell H. Furry Professor Eugene P. Wigner Harvard University Princeton University Limited-Attendance Group Dr. William Band Dr. Eugen Merzbacher Washington State University University of North Carolina Dr. Dieter R. Brill Dr. Jack Rivers Yale University University of Missouri Dr. Gideon Carmi Dr. O. von Roos Yeshiva University Jet Propulsion Laboratory California Institute of Dr. Harold Glaser Technology Office of Naval Research Dr. Solomon L. Schwebel Dr. Eugene Guth University of Cincinnati Oak Ridge National Laboratory Dr. Abner Shimony Dr. Arno Jaeger M. I. T. University of Cincinnati Dr. Jack A. Soules Dr. Kaiser S. Kunz Office of Naval Research New Mexico State University Dr. Frederick G. Werner Dr. Michael M. Yanase, S. J. Xavier University Institute for Advanced Studies, Princeton, N. J. Director of audio-visual recording: Mr. Thomas Fischer Assisted by: Robert Podolsky Austin Towle CONFERENCE ON THE FOUNDATIONS OF QUANTUM MECHANICS October 1-5, 1962 Public Relations Policy In order that each participant may feel free to express himself spontaneously in the spirit of the limited attendance portion of this conference, the chairman has adopted the following policy regarding references. It is understood that each person present, before referring in publication to remarks made by a participant during these sessions is expected to check such material with the participant or participants concerned. Reports of general conclusions are to be checked with the chairman. This policy applies as well to the published report of the proceedings, which is to be edited by the chairman. Dr. Podolsky: In the heat of an argument I can make a statement, and I probably will, which any freshman with a pencil and paper and five minutes can prove to be nonsense. Perhaps a few minutes later I might regret having made the statement. Now, we don't want such statements to get out. The principle reason for this is to make sure the participants won't stop to worry about whether or not what they're saying is really so, or whether it is nonsense. We want the participants to feel free to express themselves spontaneously, and afterwards, in more sober discussions, withdraw these statements without things getting out in the newspapers. MON-A.M. Conference - October 1-5, 1962 Part of Monday Morning Session after introductions: Podolsky: You probably have seen in the newspapers some reference to quantum-mechanical action at a distance. The idea of that occurred to me and probably has occurred to many other people. I would like sometime to have a discussion on this subject. Aharonov and Bohm suggested an experiment which was, as you know, performed by Mölllenstedt, and which can be interpreted in two ways. One is that the vector potential has physical significance. That was the way in which they presented it. But if you consider the fact that the observed phase shift in the wave function actually turns out to be proportional to the flux, which is gauge invariant, one might interpret the result of the experiment in a different way, namely, that the reason we have the shift is quantum-mechanical action at a distance. The fact that flux through a loop formed by the two electron beams actually affects the wave function of these two electron beams and produces the observed phase shift at the place where the flux is not, will be an example of an action at a distance. N ow if this experiment was alone it would not convince me that there is such an action at a distance, because then it would be simplest to say that a vector potential has a direct effect. But there is this old question, sometimes referred to as the Einstein-Podolsky-Rosen paradox, where also we have a kind of action at a distance. You are all probably familiar with that. I have discussed this question of quantum-mechanical action at a distance with several people and one of them said "Well, of course, in all the quantum-mechanical effects there is action at a distance." For example: when you take the so-called reduction of a wave packet and the wave function suddenly changes from one thing to something quite different, there is again a kind of action at a distance, I would like expressions of opinion about this question of action at a distance. MON-A.M. -2- Aharonov: It is clear that this action at a distance is never observable in the usual sense. The usual statement about observation involves probabilistic statements, and it is clearly the case that in all the other examples that you mention about action at a distance there will be a change in a particular case, but not a probabilistic change in an ensemble of cases. Podolsky: But what about the Aharonov-Bohm experiment? Aharonov: Well, in that case there is a change in probabilities too, of course, because that is what we observe in the experiment. But one can in that particular case discuss a local action which involves an interaction with potentials. You wanted to strengthen the idea of action at a distance by discussing other examples, but I am not aware of any other example of action at a distance that will involve change in probabilities and not only in information. In one particular case, namely, in the case of ensembles, there is no change in probabilities after so-called action at a distance. Podolsky: What about the experiment of Wu and Shaknov? Aharonov: Well, this case is exactly similar to any other example of the Einstein-Podolsky-Rosen paradox. That is to say: in any individual case, when you make an experiment on one of the particles that are involved in the setup of the paradox, you learn something about the state of the other particle. In that sense, you have made a change in the wave function of the total system, and also of the particle that is far away. So you can predict something about the probabilities of an experiment that will be made on the other particle. But if you consider an ensemble of similar experiments, you ask whether your measurements of the first particle in each pair of particles that appear in his ensemble will cause changes in probability of the second particle in the ensemble. This means -3- MON-A.M. that the observer that makes experiments on the second particle (all the members that are called second particle in the ensemble of Einstein-Podolsky-Rosen pairs) will never be able to discover that the experiment was done on the first particle. On the other hand, this action at a distance cannot send any information, or any change of probabilities to the faraway members. In other words, there is a transformation of knowledge but not of probabilities from one side to the other. Podolsky: That makes the wave function purely a subjective entity. That this isn't a subjective thing is shown by the fact that in a measurement when there is a transformation of knowledge, the wave function changes completely, while no other change occurs. (A brief discussion here continues about the question whether the change is complete or if only a partial change occurs in the wave function). Wigner: Well, it is true that under certain conditions the change in the wave function is complete. Anyway, it does not matter whether it is a knowledge? Wigner: No. Furry: By introduction of means of measurement, one could introduce a statistical situation which, from the point of view of the coordinates of the particle to be measured, is a mixed state. This mixed state is just the same thing as the classical Gibbs ensemble. I did not say it difficulty, as in the case of Einstein-Podolsky-Rosen, that the ensemble MON-A.M. -4- can be interpreted from many points of view. When I said the Gibbs ensemble, it implies a realistic interpretation. This realistic interpretation is valid only in the usual laboratory set-up, when one is interested in measuring something that has non-uniform distribution over the possible to interpret it in many different ways. This is, in a sense, an artificial situation, but the theory has to deal also with artificial situations. Well, it just seems to me that the problem is perhaps the wholeness of the quantum state, and the quantum state may have this character as a whole extending over a very large distance.