Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? [Einstein, Podolsky, Rosen] WITH: Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? [BOHR]

Lancaster PA and New York NY: American Institue of Physics, 1935. 1st Edition. Original wrappers. Fine. FIRST EDITION of the famous "EPR" paper, one of the most discussed and debated papers of modern physics. WITH: Bohr's response. "In the May 15, 1935 issue of Physical Review Albert Einstein co-authored a paper with his two postdoctoral research associates at the Institute for Advanced Study, Boris Podolsky and Nathan Rosen. The article was entitled 'Can Quantum Mechanical Description of Physical Reality Be Considered Complete?' [...] Generally referred to as EPR, this paper quickly became a centerpiece in debates over the interpretation of quantum theory, debates that continue today. Ranked by impact, EPR is among the top ten of all papers ever published in Physical Review journals." (Stanford Encyclopedia of Philosophy).

Indeed, like the verification of Einstein's earlier prediction of the gravitational deflection of light, EPR even got attention in the popular press. Eleven days before the paper was published: "The New York Times carried an extensive report under the provocative headline 'Einstein Attacks Quantum Theory,' which was summarized by the sentences: 'Professor Einstein will attack science's important theory of quantum mechanics, a theory of which he was sort of grandfather. He concluded that while it [the quantum mechanics], is "correct" it is not "complete."'" (Mehra and Rechenberg, p. 724-25).

In essence, Einstein and his collaborators devised a thought-experiment involving two physical systems (say, A and B) with necessarily-correlated physical properties, that were widely separated in space. (For example, the two systems might have equal and opposite momenta and positions dictated by physical conservation laws.) From the perspective of quantum theory, the two systems could be described by a single wave function, or state vector. A measurement performed on A could precisely determine its position, which would also fix a precise position for B. The momenta of A and B could be determined in the same way. The central insight of EPR was that either the position and momentum of A and B were real, determinate and fixed prior to the measurement of A, or else B only took on a fixed and determinate value when A was measured. But the latter interpretation implied that the measurement event at A had somehow instantaneously fixed the (previously indeterminate) properties of B, despite the spatial separation between A and B, which could be made as great as one wished. Einstein argued that this implied one of two things: either that the quantum description of A and B was incomplete, in that each of them had a fixed, determinate position and momentum at all times; or that nature permitted actions such as measurement to have "nonlocal" influences on distant systems.

Leon Rosenfeld, who was in Copenhagen at the time, remembered the fallout of these developments vividly: "This onslaught came down upon as a bolt from the blue [...] As soon as Bohr heard my report of Einstein's argument, everything else was abandoned: we had to clear up such a misunderstanding at once." (Pais, 430). According to Rosenfeld, the next day Bohr was heard muttering "Podolski, Opodolski, Iopodolski," etc. By mocking Podolsky-who was, after all, only a postdoctoral student and the second-named author of EPR-Bohr presumably was, even in his anger, avoiding saying anything that might be interpreted as a direct attack on Einstein.

Bohr's argument proceeded with what some might describe as his characteristic lack of explanatory clarity. Indeed, in revisiting EPR fifteen years later, Bohr himself would admit, "[r]ereading these passages, I am deeply aware of the inefficiency of expression which must have made it very difficult to appreciate the trend of the argumentation" (Schilpp, p. 234; see also Lehner, p. 331, who describes Bohr's rebuttal of EPR as "obscure in content but confident in tone."). Generally speaking, however, Bohr's approach seems to boil down to a willingness to accept non-local or "contextual" theory of measurement interactions. In any event, it is clear that Bohr was more prepared than Einstein was to take quantum theory at face value as a complete theory, even if this meant abandoning notions of physical reality that are part of humanity's intuitive understanding of the world.

Later in a famous 1964 paper, John Bell, using an EPR-like thought experiment, proved that the situation was even worse than Einstein had imagined: even a hidden variable theory that reproduced the empirical predictions of quantum mechanics would necessarily violate Einstein's desideratum of local realism. As Christoph Lehner puts it, "this proof is of great importance because it shows the impossibility of Einstein's idea that quantum mechanics could be understood as an incomplete description of a reality that is objective and locally definite." (Lehner, p. 234).

Included are both papers - the original EPR paper and Bohr's response.

IN: The Physical Review,pp.777-780 Vol. 47, No. 10 (whole issue offered), May 15, 1935. Quarto, original green wrappers. WITH: Physical Review, vol. 48, no. 8 (whole issue), October, 1935. Quarto, complete issues in original wrappers; housed together in custom box. Stamp of P.E.O. Memorial Library, Iowa Wesleyan College (now defunct). Mild toning around edges (as often) otherwise crisp, clean copies.

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