Western University Scholarship@Western Electronic Thesis and Dissertation Repository 4-23-2012 12:00 AM The Case for Quantum State Realism Morgan C. Tait The University of Western Ontario Supervisor Wayne Myrvold The University of Western Ontario Graduate Program in Philosophy A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Morgan C. Tait 2012 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Philosophy Commons Recommended Citation Tait, Morgan C., "The Case for Quantum State Realism" (2012). Electronic Thesis and Dissertation Repository. 499. https://ir.lib.uwo.ca/etd/499 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. THE CASE FOR QUANTUM STATE REALISM Thesis format: Monograph by Morgan Tait Department of Philosophy A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy The School of Graduate and Postdoctoral Studies The University of Western Ontario London, Ontario, Canada © Morgan Tait 2012 THE UNIVERSITY OF WESTERN ONTARIO School of Graduate and Postdoctoral Studies CERTIFICATE OF EXAMINATION Supervisor Examiners ______________________________ ______________________________ Dr. Wayne Myrvold Dr. Dan Christensen Supervisory Committee ______________________________ Dr. Robert Spekkens ______________________________ Dr. Robert DiSalle ______________________________ Dr. Chris Smeenk The thesis by Morgan Christopher Tait entitled: The Case for Quantum State Realism is accepted in partial fulfillment of the requirements for the degree of « Doctor of Philosophy» ______________________ _______________________________ Date Chair of the Thesis Examination Board ii Abstract I argue for a realist interpretation of the quantum state. I begin by reviewing and critically evaluating two arguments for an antirealist interpretation of the quantum state, the first derived from the so-called ‘measurement problem’, and the second from the concept of local causality. I argue that existing antirealist interpretations do not solve the measurement problem. Furthermore, I argue that it is possible to construct a local, realist interpretation of quantum mechanics, using methods borrowed from quantum field theory and based on John S. Bell’s concept of ‘local beables’. If the quantum state is interpreted subjectively, then the probabilities it associates with experimental outcomes are themselves subjective. I address the prospects for developing a subjective Bayesian interpretation of quantum mechanical probabilities based on the Quantum de Finetti Representation Theorem. Epistemic interpretations of the quantum state can be divided into those that are epistemic with respect to underlying ontic states, and those that are epistemic with respect to measurement outcomes. The Pusey Barrett and Rudolph (PBR) theorem places serious constraints on the former family of interpretations. I identify an important explanatory gap in the latter sort of interpretation. In particular, if the quantum state is a subjective representation of beliefs about future experimental outcomes, then it is not clear why those experimenters who use quantum mechanics should be better able to negotiate the world than those who do not. iii I then turn to the task of articulating a positive argument for the thesis of quantum state realism. I begin by articulating a minimal set of conditions that any realist interpretation must meet. One assumption built into the PBR result is that systems prepared in a given quantum state have a well-defined set of physical properties, which may be completely or incompletely described by the quantum state. Antirealist interpretations that reject this assumption are therefore compatible with the PBR result. A compelling case for quantum state realism must therefore be made on more general grounds. I consider two concrete examples of phenomena described by quantum mechanics that strongly suggest that the quantum state is genuinely representational in character. Keywords: Philosophy of physics, foundations of quantum mechanics, the measurement problem, philosophy of science, quantum state, realism, confirmation theory, philosophy of probability iv For Rick Tait and Meaghan Eastwood v Acknowledgements I would like to extend a very special thank you to Wayne Myrvold. This project would not have been possible without Wayne’s constant intellectual support and encouragement. Special thanks to Robert DiSalle, Chris Smeenk, William Demopoulos and Erik Curiel for valuable discussion and comments along the way. Thank you also to Ryan Samaroo, Mike Cuffaro, Molly Kao, Robert Batterman, William Harper, and Doreen Fraser. I would also like to thank my external examiners Robert Spekkens and Dan Christensen. I owe a special debt of gratitude to Chris Fuchs, whose work in the foundations of quantum mechanics was an inspiration for this project, and who very graciously invited me to participate in discussions at the Perimeter Institute for Theoretical Physics in the fall of 2009. Finally, I would like to gratefully acknowledge financial support from the Social Sciences and Humanities Research Council and the Foundational Questions Institute. vi Table of Contents Certificate of Examination ................................................................................................................... ii Abstract ......................................................................................................................................................iii Acknowledgements ............................................................................................................................... vi Table of Contents ................................................................................................................................. vii Introduction .............................................................................................................................................. 1 Why Does Quantum Mechanics Need an Interpretation? .................................................. 1 Motivations for Quantum State Antirealism ............................................................................ 4 Outline of Thesis Structure ............................................................................................................. 9 Chapter 2: Critical Examination of Two Arguments for Quantum State Antirealism 14 Introduction ...................................................................................................................................... 14 2.1 The Measurement Problem as Motivation for Quantum State Antirealism ...... 21 Bub on the ‘Two Dogmas of Quantum Mechanics’ ........................................................ 24 Fuchs on Quantum Measurement as Bayesian Updating............................................ 35 2.2 Is Locality Incompatible with Quantum State Realism? ...................................... 47 Einstein’s Incompleteness argument and Quantum State Antirealism ................. 47 The Bell Factorizability Condition and Locality ............................................................. 52 Local Beables and the Prospects for a Local, Realist Quantum Theory ................ 62 Conclusion .......................................................................................................................................... 72 Chapter 3: Evidence, Explanation and the Quantum State .................................................. 74 Introduction: The Nature of Probabilities, Classical and Quantum ............................. 74 The Dualistic Conception of Probability ............................................................................ 74 The Subjectivist Interpretation of Probability and Quantum State Tomography ........................................................................................................................................................... 79 vii 3.1 The Subjectivist Interpretation of Probability and Quantum Bayesianism ...... 83 Quantum Bayesianism and the Space of Epistemic Interpretations of the Quantum State ............................................................................................................................. 84 The de Finetti Representation Theorem ........................................................................... 89 The Quantum de Finetti Representation Theorem and Quantum State Tomography ................................................................................................................................. 96 3.2 The Means/Ends Objection and the Role of the Preparation Device ................. 101 The Born Rule as an Empirical Addition to Bayesian Coherence .......................... 115 Conclusion ........................................................................................................................................ 128 Chapter 4: The Case for Quantum State Realism ................................................................... 130 Introduction .................................................................................................................................... 130 4.1 Yes, but… .............................................................................................................................