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An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics Nahuel Sznajderhaus University of Leeds phns@leeds.ac.uk Whither Quantum Structures? Center Leo Apostel Brussels - Belgium 30 November 1 December
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 1/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Motivation for Modal Interpretations
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 3/21
Motivation for Modal Interpretations
◮ Interaction between the object-system and the measuring apparatus.
Both are described by quantum mechanics.
◮ The time evolution given by the Schr¨
cn |αn ⊗ |M0 − →
cn(t) |αn ⊗ |βn . (1)
◮ eigenvalue eigenstate association: the value of the observable is aj iff the
state of the system is |αn=j (the eigenvector associated to aj).
◮ Accordingly, the final state of the composed system given by right hand
side of eq. (1) cannot be interpreted to mean that the object-system possesses a determinate property associated with a determinate value {bn} on the apparatus.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 4/21
Motivation for Modal Interpretations
Ways out:
◮ von Neumann: Projection postulate. The final state is one of the
components |αn ⊗ |βn, associated with the measurement outcome. The probability of each outcome is given by Born rule, |cn|2. The principle of psychophysical parallelism assigns a role of consciousness in the measurement process.
◮ Common practise in physics, the “orthodox” view: takes the projection
postulate but ignores the role of the human consciousness. There is no need for interpretation.
◮ Bohmian mechanics. ◮ GRW. ◮ Everett. ◮ (The many different) Modal Interpretations.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 5/21
Niels Bohr
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 6/21
Niels Bohr
◮ Both Van Frassen and Dieks claim to be a continuation of Bohr. ◮ Van Fraassen does not thoroughly develop this idea. “From Bohr to
Feynman, physicists have expressed similar opinions: an observable might not have a specific value outside the context of measurement. That is part of the orthodox of Copenhagen interpretation” (1991, p. 109).
◮ Dieks favours a realist interpretation of Bohr.
Van Fraassen, 1991, Quantum Mechanics: an empiricist view. Oxford: OUP.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 7/21
Niels Bohr
◮ QM as an epistemological endeavour. ◮ Anti-metaphysics. ◮ Neo-Kantian flavour: The language of Newton and Maxwell
◮ Blockage in developing ‘new concepts’.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 8/21
Niels Bohr
Petersen, 1963, “The Philosophy of Niels Bohr”, Bulletin of the Atomic Scientists, Sep 1963, 8-14.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 9/21
Niels Bohr
◮ There is no room for a “measurement problem”. ◮ An empiricist interpretation on QM would seem to be more
◮ Instrumentalism seems a more straightforward continuation of
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 10/21
Modal Interpretations
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 11/21
Modal Interpretations
◮ Stay close to the standard formalism. ◮ Reject the projection postulate. Consider only unitarian
◮ Reject the eigenstate-eigenvalue ‘if and only if’ link. ◮ Intend to provide an objective reading of the mathematical
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 12/21
Van Fraassen’s ‘Copenhagen variant’
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 13/21
Van Fraassen’s ‘Copenhagen variant’
◮ Constructive Empiricism: “Science aims to give us theories
◮ Semantic approach: an uninterpreted theory is identified with
◮ Accepts the existence of macroscopical objects, but remains
◮ Whether his MI is properly accommodated within CE is a
Van Fraassen, 1980, The Scientific Image, Oxford: OUP.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 14/21
Van Fraassen’s ‘Copenhagen variant’
◮ Dynamical state and value state distinction. Denial of the
◮ Predictions coincide with the projection postulate: what the
◮ Measurement as a passage from the possible to the actual.
◮ Logical scheme for this passage.
Van Fraassen, 1991, Quantum Mechanics: an empiricist view. Oxford: OUP.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 15/21
Dieks’ Realist Attempt
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 16/21
Dieks’ Realist Attempt
◮ To be a realist is to hold that the structures postulated in a correct
scientific theory can be taken to really exist.
◮ There is an objective external world which exists independently of our
minds, our knowledge or our measurements. Science, plays the role of discovering the basic structure of this real world.
◮ The proposal is “to conceive of the mathematical structure of quantum
theory as a representation of the physical structure of the world” (Dieks 1989, p. 1416).
◮ The semantic approach to scientific theories.
Dieks, 1989, “Quantum Mechanics Without the Projection Postulate and Its Realistic Interpretation”, Foundations of Physics, 19, 1397-1423.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 17/21
Dieks’ Realist Attempt
If the ck are all different, then there is a unique bi-orthonormal decomposition
cn |αn ⊗ |βn , (2) “the partial system represented by the |αn, taken by itself, can be described as possessing one of the values of the physical quantity corresponding to the set {|αn}. The probabilities for the various possibilities to be realized are given by |cn|2” (1989, p. 1406). However this does not mean that the total state of eq. (2) can be considered as representing a situation in which there is only one term |αn ⊗ |βn present: “although the object system, taken by itself, may have the property related to [|αn] and the remainder of the system, taken by itself, the property related to [|βn], the conclusion does not follow that the total system is to be described by the conjunction of these two properties” (1988, p. 40). Dieks, 1988, “Quantum Mechanics and Realism”, Conceptus XXII, 57, 31-47.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 18/21
Conclusions and Perspectives
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 19/21
Conclusions and Perspectives
◮ Van Fraassen’s epistemic antirealism seems closer to Bohr than Dieks
Bohr.
◮ Dieks claims to be a structural realist! So, how would his MI relates to
current forms of structural realism? “[An] irreducibly statistical theory
predicts only probability distributions, and says nothing about the result which really will be realized in a single case. In brief, such a theory is not about what is real and actual, but only about what could be the case” (1988, p. 34).
◮ The notion of possibility and actuality still need to be fleshed out.
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 20/21
Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 21/21