Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?
Bohr's 1935 reply to Einstein–Podolsky–Rosen — Phys. Rev. 48, 696–702
Tradition: Copenhagen interpretation / philosophy of quantum mechanics
Bohr's 1935 reply to EPR — complementarity and the inseparability of system from measuring apparatus
Published in Physical Review 48 (1935), pp. 696-702 — same volume as Einstein, Boris Podolsky, and Nathan Rosen's 'Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?' (pp. 777-780, published five months earlier on 15 May 1935) — Bohr's reply takes the same title and replies in detail to the EPR thought experiment. The EPR paper had argued that quantum mechanics is incomplete: if two particles are prepared in an entangled state and then separated, measuring one allows prediction of the other with certainty; on the EPR 'criterion of reality' (an element of reality exists for any quantity that can be predicted with certainty without disturbing the system), the unmeasured particle must have had a definite position-and-momentum value all along — but quantum mechanics cannot represent this, hence quantum mechanics is incomplete. Bohr's reply argues that the EPR 'criterion of reality' rests on a tacit (and untenable) separation of the quantum system from the measuring apparatus. The famous central paragraph: 'The procedure of measurement has an essential influence on the conditions on which the very definition of the physical quantities in question rests. Since these conditions must be considered as an inherent element of any phenomenon to which the term physical reality can be unambiguously applied, we see that the argumentation of the mentioned authors does not justify their conclusion that quantum-mechanical description is essentially incomplete.' Bohr insists that 'unambiguous communication' about quantum phenomena requires reference to the whole experimental arrangement, and that the EPR argument's apparent demonstration of incompleteness collapses once that holism is accepted. The paper is the founding document of the modern philosophical literature on quantum non-locality and the principal Bohrian statement of the Copenhagen-interpretation response to EPR.
Author
Editions cited
- Phys. Rev. 48 (1935), 696-702
- Reprinted in J. A. Wheeler & W. H. Zurek (eds.), Quantum Theory and Measurement (Princeton, 1983), pp. 145-151
- EPR companion: A. Einstein, B. Podolsky, N. Rosen, 'Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?', Phys. Rev. 47 (1935), 777-780
- Critical context: Mara Beller, Quantum Dialogue (Chicago, 1999); Don Howard, 'Einstein on Locality and Separability', Studies in the History and Philosophy of Science 16 (1985)
School Embodiments
Canonical Bohrian reply to EPR — complementarity and contextual holism.
"The procedure of measurement has an essential influence on the conditions on which the very definition of the physical quantities in question rests." (Phys. Rev. 48, 1935, p. 700)
Operationalist criterion — physical reality is tied to experimentally definable concepts.
"The criterion of physical reality proposed by the authors contains an essential ambiguity when applied to quantum phenomena." (Phys. Rev. 48, 1935)
Foundational paper in the philosophy-of-physics canon.
"The whole experimental arrangement must be considered." (Phys. Rev. 48, 1935)
Phenomenological emphasis on the conditions of unambiguous observation.
"Unambiguous description requires reference to the experimental conditions." (Phys. Rev. 48, 1935)
Pragmatic-experimental orientation against the EPR realist criterion.
"Reality is what we can speak about unambiguously in experimental terms." (Phys. Rev. 48, 1935)
Analytic-philosophical tradition.
Internal Tensions
The canonical Bohrian reply to EPR; the origin of the modern philosophical literature on quantum non-locality. Bell's 1964 'On the Einstein-Podolsky-Rosen Paradox' (which proved that local hidden variables could not reproduce quantum predictions, opening the way to the 1972 Freedman-Clauser and 1982 Aspect experiments) emerged from continued reflection on the EPR-Bohr exchange; the contemporary literature on quantum foundations remains shaped by this 1935 dispute.
I. Time
Bohr's reply submitted 13 July 1935, published 15 October 1935 — five months after EPR's 15 May 1935 publication.
Attributes
II. Space
Copenhagen Institute — Bohr's institutional base. The geographical-political space is pre-war Europe; both Einstein (in Princeton) and Bohr (in Copenhagen) were responding to the philosophical implications of the new quantum mechanics.
Attributes
III. Matter
Single Physical Review paper (~7 pages). Form is technical-physical with substantial philosophical argument.
Attributes
IV. Observer
Bohr as defender of the Copenhagen interpretation. The observer-physicist is at the height of his interpretive-philosophical authority over the quantum-mechanical community.
Attributes
V. Energy
High-stakes polemical-philosophical energies of the EPR moment. The Bohr-Einstein dispute was the central philosophical controversy in twentieth-century physics.
Attributes
VI. Information
Seven-page paper of huge philosophical import. The 'whole experimental arrangement' argument is the central informational structure.
Attributes
Personas that cite this work
Personas with the nearest attribute fingerprint
Historical figures whose own classification on the same six-dimensional grid lands closest to this work's. Computed by attribute-agreement on coordinates both address.
Computed school proximity
The work's attribute fingerprint scored against all schools using the same quiz scorer. Useful as a sanity check on the hand-curated embodiments above.
How Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? resolves each dilemma
35 resolved positions across 4 dimensions, including 13 distinctive where the majority of schools go the other way · 22 unaligned.
Each dimension is sorted so minority positions come first. Mainstream positions are folded into an expandable list.
Time · 9 dilemmas, all mainstream
Matter · 7 dilemmas · 5 distinctive
What stuff is — fundamental, relational, or appearance.
Observer · 37 dilemmas · 5 distinctive
Mind, agency, and the knower's relation to the known.