June 1997, “Painting My Stripes” I am just returning from the library, where – completely by accident – I ran into and read an entertaining little article: A Peres, “Einstein, Gödel, Bohr,” Foundations of Physics 15 (2), 1985, 201–205. I was especially entertained by your closing line, “Any attempt to inject realism in physical theory is bound to lead to inconsistencies.” Do you have any other writings (beside the AJP paper with Zurek) where you expand upon the ideas presented in this? In connection to this, I have another question. If I recall correctly, you once told me that you finally came to grips (“interpretationally,” that is) with quantum mechanics in 1986. (Perhaps I have the year wrong, but that's part of the question.) Would you be willing to expand upon that point? In particular, was your arrived-at comfort founded upon the line I quote above? I suppose I ask these questions for several reasons, perhaps the strongest of which is a renewed dilettante interest in the foundations of quantum theory. Among other things, I am trying to plan (or dream up!) a talk for the Hull conference in September to be titled something like: “Quantum Information Theory's Implications for the Foundations of the Quantum as a Whole.” My own pet “idea for an idea” (as Wheeler would say) is that the quantum theoretical description – along with its Hilbert-space structure – is forced upon us when the information we have about a physical situation/system is of a certain variety.
June 1997, “Painting My Stripes” I am just returning from the library, where – completely by accident – I ran into and read an entertaining little article: A Peres, “Einstein, Gödel, Bohr,” Foundations of Physics 15 (2), 1985, 201–205. I was especially entertained by your closing line, “Any attempt to inject realism in physical theory is bound to lead to inconsistencies.” Do you have any other writings (beside the AJP paper with Zurek) where you expand upon the ideas presented in this? In connection to this, I have another question. If I recall correctly, you once told me that you finally came to grips (“interpretationally,” that is) with quantum mechanics in 1986. (Perhaps I have the year wrong, but that's part of the question.) Would you be willing to expand upon that point? In particular, was your arrived-at comfort founded upon the line I quote above? I suppose I ask these questions for several reasons, perhaps the strongest of which is a renewed dilettante interest in the foundations of quantum theory. Among other things, I am trying to plan (or dream up!) a talk for the Hull conference in September to be titled something like: “Quantum Information Theory's Implications for the Foundations of the Quantum as a Whole.” My own pet “idea for an idea” (as Wheeler would say) is that the quantum theoretical description – along with its Hilbert-space structure – is forced upon us when the information we have about a physical situation/system is of a certain variety.
22 August 1999, “Your Article” I am writing to let you know that I enjoyed your article quant-ph/9812050, “Why Quantum Mechanics is Hard to Understand,” very much. I was in particular very pleased with your Section IV “Dynamics vs. History.” It may interest you to know that Markus Fierz expressed a similar point of view in his article: “Does a physical theory comprehend an ‘objective, real, single process’?” in Observation and Interpretation in the Philosophy of Physics , edited by S. Körner (Dover, NY, 1957), pp. 93–96. I will append the full text below for your enjoyment. [See note to Rüdiger Schack, dated 29 August 1999.] Most importantly, I would like to ask you for the final coordinates of your paper. Was it published somewhere? I would like to cite it in an upcoming paper. 28 August 1999, “Not Much” I don't have a good idea about where to send your paper. I think chances are that AJP will be tougher than FP . In any case, it had an impact on me. My old advisor used to say of our joint papers, “If three people read this paper, we'll be doing OK!” If you know of two others with yours, you're probably doing OK. I like this focus on the concept of “object.” I look forward to anything you might have to say about it. I have some slides that I use as a rallying cry to the idea that quantum information theory may have some impact on quantum foundations. The first is a list of axioms for quantum mechanics.
February 2000, “The Quantum View” What a really nice article! I read it once this evening with dinner (at a place that served grilled chicken – not so easy to scroll through a computer screen under those conditions!). Now, with my jetlag in distinct control – its 3:30 AM for me – let me read it again and make a few comments here and there. (I just arrived in Haifa yesterday for a visit with Asher Peres; I'll be here a little over a week.) Why don't you write the following for your requested reference: C. A. Fuchs, “The Structure of Quantum Information,” available at […] [Of course, it is no longer available. Instead, see note to Carl Caves, dated 21 December 1997.] I like this view of physics as being like a jig-saw puzzle. Note a typo in this paragraph: you misspelled de Broglie. Ruskai-ism 1: As far as I am aware, there is no evidence that either Heisenberg or Schrödinger was motivated by political or social factors . Actually there is a pretty strong case that these two guys were indeed quite motivated by cultural factors to find an indeterministic element in physics. And that was long before quantum mechanics took a final form. Two important articles to read in this regard are: P. Forman, “Weimar Culture, Causality, and Quantum Theory, 1918–1927: Adaptation by German Physicists and Mathematicians to a Hostile Intellectual Environment,” in Historical Studies in the Physical Sciences, Vol. 3 , edited by R. McCormmach (U. Pennsylvania Press, Philadelphia, 1971), pp. 1–115. […]
“Partners in crime again?” CAF to AP 29 September 1999 Introduction Irving John Good once titled a paper, “46,656 Varieties of Bayesians.” With little stretch of the imagination, one can believe that a similar paper on the interpretations of quantum mechanics exists somewhere out there too. And that may be true even though 46,656 is greater than the whole membership of the American Physical Society! It is no wonder that taking a stand on quantum foundations is treacherous business. Nevertheless, in the March 2000 issue of Physics Today , Asher Peres and I flouted the usual rewards of a calm life and did just that. Our article was titled, “Quantum Theory Needs No ‘Interpretation’.” This chapter is about the evolution of that article and a later “reply to critics.” When I was an undergraduate at the University of Texas, Bryce DeWitt made a great impression on me by saying something I have not forgotten: “We learn mathematics so that we don't have to think when we do physics.” My paper with Asher contained no mathematics. We had to think, and think very hard. The fruits of that labor, for my part, were in a greatly enhanced keenness for seeing through various foundational issues. How I wanted to share that newfound keenness with the reader! But it was difficult, if not impossible, to convey such an aspect of the paper-writing process in the very paper itself.
10 February 1997, “Sunday Afternoons and Consistent Histories” I've finally completed to my satisfaction your challenge of taking a plunge into “consistent histories.” And I've had great fun! In particular, I read all or most of each of the following: “Consistent Histories and the Interpretation of Quantum Mechanics,” “Quantum Interpretation Using Consistent Histories,” “Correlations in separated quantum systems: A consistent history analysis of the EPR problem,” “The Consistency of Consistent Histories: A Reply to d'Espagnat,” “A Consistent History Approach to the Logic of Quantum Mechanics,” “Consistent Histories and Quantum Reasoning.” I don't think I've read everything, but I'll trust that I haven't missed anything too significant – at least for a novice education in the subject. I say I had great fun because, before this, my only introduction to consistent histories had been through various talks by Gell-Mann, Hartle, and Zurek. And, I can't say I ever found any of those satisfactory – they all made it a very confusing muddle to me. I never could figure out the point, i.e., what actually was being proposed as a “solution” to the quantum interpretation problem. Consequently, I often just fell asleep or thought about other things or both. In contrast, I found all your papers logically crisp.
The Copenhagen Interpretation of quantum mechanics has become the standard way of explaining the physical philosophical meaning of the mathematics of microscopic behavior. It developed from the thought of people who attended the Institute for Theoretical Physics of the University of Copenhagen during the 40 years that Niels Bohr directed it, from 1920 to 1962. Bohr took a large part in developing the Copenhagen Interpretation, he didn't escape all controversy over it (although the quote above is a bit of an exaggeration). Bohr did die before the experimental theoretical developments that have transposed the debate over the appropriateness adequacy of the Copenhagen Interpretation into a new key, he may well have been lucky to have escaped when he did. There is no authoritative codification of CI [the Copenhagen Interpretation], write T Gornitz C. E von Weizsacker of the Max Planck Institute in Starnberg, West Germany in' their formal presentation to the recent Loyola Conference on Mathematical Interpretational Problems in Relativistic Quantum Theory, and under the conditions of its origin there probably could not be one.... All prominent authors of the time who wrote on these questions, like Bohr, [Werner] Heisenberg, [Wolfgang] Pauli, J[ohn] v[on] Neumann on one side, [Albert] Einstein [Erwin] Schrodinger on the other, fell, so we feel, into some stammering when they tried to express their own positions. Nevertheless there is what might be called a Copenhagen attitude. It concentrates on observable phenomena, makes statistics probability central to its understanding, considers quantum mechanics primarily a theory of knowledge or information becomes a kind of physica negativa (analogous to a theologia negativa) in trying not to say too much about things that can't be seen or felt. For example, it doesn't much care whether the orbits of electrons in atoms are real or not and, in fact, tends to regard them as unreal. It appears in most textbooks as the standard way of looking at things.
This commentator format is quite unfamiliar to me, and somewhat uncomfortable. I don't know whether I'm supposed to flatter the speakers, criticize them, grade them, or merely parrot them. Or should I go off on my own? This latter is tempting. If unleashed I could provide you with true answers to all the questions before us, philosophical, historical, physical, mathematical, physical-mathematical, and so on. But I'll bite my tongue and try to stick to the commentator role. First, a few words on the topic of the opening session this afternoon - why are philosophers interested in quantum field theory? Quantum mechanics undoubtedly abounds in genuine, deep and still unresolved philosophical questions. These are usually posed, at least in popular accounts, in the context of finite systems of nonrelativistic point particles. In preparation for the conference, I asked myself: does relativistic QFT introduce any really distinctive philosophical problems? There are several possibilities, which I can only express in low-brow form. For one thing, a field is really a collection of infinitely many degrees of freedom, one for each point in space. I can well suppose that infinity raises interesting questions for philosophers. Certainly for physicists, especially in the field theory context, it has been a great preoccupation. As we'll hear later from Jackiw, infinity has its useful aspects. Next, for systems of relativistic particles in interaction, it is no longer so easily possible to speak of measurements of position and momentum of individual particles, except perhaps in asymptotic regions.