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Final Copy 2020 11 26 Thom This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Thomas Penney, Megan J Title: 1YQ5MEG General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Thomas Penney, Megan J Title: 1YQ5MEG General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Models, Interpretations, and Realism in Quantum Physics By MEGAN THOMAS PENNEY Department of Philosophy UNIVERSITY OF BRISTOL A dissertation submitted to the University of Bristol in ac- cordance with the requirements of the degree of DOCTOR OF PHILOSOPHY in the Faculty of Arts. JULY 2020 Word count: 58823 ABSTRACT rom the beginnings of quantum theory in the early 20th Century, physicists and philoso- phers of physics have been struggling to interpret it. The ongoing debate about the mea- Fsurement problem has lead to the creation of multiple different interpretations intended to solve it. Each interpretation presents quantum theory differently in an attempt to reconcile it with what we see in the world. The measurement problem, and alongside it the more general problem of the quantum to classical transition, are explored in the following chapters in a journey from the first interpre- tation of quantum mechanics to modern Quantum Field Theory. Chapter 1 examines the basic quantum formalism and the first quantum interpretations. In Chapter 2, a chronological review of influential quantum mechanical thought experiment highlights the central issue of measurement. Chapter 3 introduces the measurement problem and divides it in two; the unique outcomes problem and the preferred basis problem, and examines how each is addressed in different interpretations. Chapter 4 investigates the theory of decoherence. Chapter 5 re-examines the interpretations from Chapter 3 in the light of decoherence as a model for the emergence of classical macrostates from quantum microstates. Chapter 6 evaluates a possible analogy between using the idealisation of an infinite limit in the quantum to classical transition and in phase transitions in statistical mechanics. It argues that the analogy fails due to strange phenomena in the quantum to classical transition which are currently explained by semiclassical mechanics. Chapter 7 considers the issue of realism in interpretations of theories beyond ordinary quantum mechanics, such as Quantum Field Theory. This examination of quantum theory shows why interpreting it is so hard as to be ongoing after a hundred years of study, considers how we should choose between interpretations – and ultimately asks whether we should have to choose at all. i DEDICATION AND ACKNOWLEDGEMENTS y greatest thanks to my main supervisor James Ladyman for his guidance, sup- port, and encouragement throughout my degree. I am also very grateful to my M second supervisor Karim Thébault, who supported me both with my thesis and with opportunities in the wider academic world. I would like to express my deepest gratitude to the South West and Wales Doctoral Training Partnership for their funding and support during this project. Thank you to my fellow students in the SWWDTP, for your companionship and camaraderie, and particular thanks to Rebekah for all the wonderful chats over tea and cake. I am grateful to the community in the department of philosophy, and to Colette and Miriam for becoming my first friends in Bristol at the beginning of my degree. Alex and Greg, thank you for dedicating your precious free time to help me proof-read my thesis. Special thanks to Frazer for your continual presence, reassurance, and support through both the good and the bad times, and thank you for loving me enough to proof-read my whole thesis. A huge thank you to my family; to my father, Martin, for sending me coffee care packages, to my sisters for cheering me up and sending me pictures of the dog, and to my mother, Madeleine, who has been checking my work for me regardless of content since I first learnt how to write. I dedicate this thesis to my grandfather, Tony Crabb, whose great belief in me has always been an honour that I work hard to deserve. iii AUTHOR’S DECLARATION declare that the work in this dissertation was carried out in accordance with the requirements of the University’s Regulations and Code of Practice for Research IDegree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate’s own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED: MEGAN THOMAS PENNEY DATE: 06/07/2020 v TABLE OF CONTENTS Page List of Figures xi 1 Quantum Mechanics and the Copenhagen Interpretation1 1.1 Introduction .......................................... 1 1.2 Basic Quantum Formalism ................................. 4 1.3 The Original Copenhagen Interpretation......................... 13 1.4 The Orthodox Copenhagen Interpretation ........................ 15 1.5 Thesis Overview........................................ 16 2 Thought Experiments 21 2.1 Introduction .......................................... 21 2.2 The Development of Quantum Mechanics in Thought Experiments......... 22 2.2.1 EPR Paradox ..................................... 23 2.2.2 Schrödinger’s Cat................................... 24 2.2.3 Heisenberg’s Microscope .............................. 26 2.2.4 Renninger Negative-Result Experiment..................... 27 2.2.5 Wigner’s Friend.................................... 28 2.2.6 Bell’s Inequalities .................................. 30 2.2.7 Wheeler’s Delayed-Choice Experiment...................... 32 2.2.8 Leggett-Garg Inequality............................... 33 2.2.9 Hardy’s Paradox ................................... 35 2.2.10 Elitzur-Vaidman Bomb Tester........................... 36 vii TABLE OF CONTENTS 2.2.11 PR Boxes........................................ 38 2.2.12 Quantum Suicide and Immortality........................ 41 2.2.13 Quantum Games................................... 42 2.2.14 PBR Theorem..................................... 43 2.2.15 Brukner’s No-Go Theorem for Observer-Independent Facts ......... 45 2.2.16 Frauchiger and Renner’s Inconsistent Quantum Theory ........... 47 2.3 Thought Experiments in the Philosophy of Science................... 48 2.4 What do Quantum Mechanical Thought Experiments teach us about Thought Experiments in general?................................... 62 2.5 What do we learn about Quantum Mechanics from Thought Experiments? . 67 3 The Measurement Problem and Interpretations I 73 3.1 The Measurement Problem ................................. 73 3.2 The Problem of Unique Outcomes ............................. 74 3.3 The Preferred Basis Problem ................................ 75 3.4 Bohmian Mechanics...................................... 77 3.5 Collapse Theories....................................... 81 3.6 Modal Interpretations .................................... 85 3.7 Oxonian Everettianism (Many Worlds) .......................... 87 3.8 QBism.............................................
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