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 2013 Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 1/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 2/21
Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Conclusions and Perspectives � 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 Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Conclusions and Perspectives � 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¨ odinger dynamics gives: � � c n | α n � ⊗ | M 0 � − → c n ( t ) | α n � ⊗ | β n � . (1) n n ◮ eigenvalue eigenstate association: the value of the observable is a j iff the state of the system is | α n = j � (the eigenvector associated to a j ). ◮ 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 { b n } 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 | α n � ⊗ | β n � , associated with the measurement outcome. The probability of each outcome is given by Born rule, | c n | 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 Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Conclusions and Perspectives � 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 will remain the language of physics for all time, as a new a priori . Focus on inter-subjectivity. ‘Reality’ is a word which we must learn to use correctly. ◮ 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 “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics con- cerns what we can say about nature” (quoted by Petersen, 1963, p. 12). 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 compatible to Bohr than a realist attempt. ◮ Instrumentalism seems a more straightforward continuation of Bohr than the ‘Copenhagen variant’. Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 10/21
Modal Interpretations Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Conclusions and Perspectives � Philosophy PG Seminar – 29 November – N. Sznajderhaus: An Historical and Philosophical Account of the Modal Interpretations of Quantum Mechanics 11/21
Modal Interpretations General common features: ◮ Stay close to the standard formalism. ◮ Reject the projection postulate. Consider only unitarian Schr¨ odinger-like time evolution. ◮ Reject the eigenstate-eigenvalue ‘if and only if’ link. ◮ Intend to provide an objective reading of the mathematical formalism in terms of properties possessed by physical systems, independently of consciousness and measurements. 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’ Outline Motivation for Modal Interpretations � The Measurement Problem Ways out Niels Bohr � Modal Interpretations � Van Fraassen’s ‘Copenhagen variant’ � Dieks’ Realist Attempt � Conclusions and Perspectives � 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 which are empirically adequate; and acceptance of a theory involves as belief only that it is empirically adequate” (1980, p. 12). Scientific theory is adequate when it ‘saves the phenomena’. ◮ Semantic approach: an uninterpreted theory is identified with the class of its abstract models. Theory is empirically successful when a structure in the empirical data is isomorphic to a substructure of one of the theoretical models. ◮ Accepts the existence of macroscopical objects, but remains sceptic about the unobservables (i.e. electrons, the world). ◮ Whether his MI is properly accommodated within CE is a matter of current debate. 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
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