Preface xll

Part I Introduction and Background

1 Introduction 3

1.1 Quantum foundations 3

1.2 The Idea of a therapeutic approach 6

1.3 Outline of this work 8

2 Sketch of the Formalism 13

2.1 The Hilbert space formalism 13

2.2 Measurement and collapse 18

2.3 Many-component systems and entanglement 21

3 Interpretations as Solutions to the Measurement Problem 26

3.1 Exposition of the problem 26

3.1.1 Maudlin's formulation 26

3.1.2 A fallacious solution 29

3.2 Additional parameters 31

3.2.1 Pilot wave theory 31

3.2.2 Alternatives: modal interpretations 37

3.3 SchrOdinger time-evolution not universal? 38

3.3.1 From Wigner to Penrose 39

3.3.2 The GRYV model 40

3.4 No determinate outcomes 41

3.4.1 Defining branches 42

3.4.2 How do probabilities fit into the picture? 44

Part II The Rule Perspective

4 Motivating a Therapeutic Approach 49

4.1 Absence of the foundational problems In practice 49

4.2 Philosophy as therapy 50

4.3 Quantum states as non-descriptive 53

4.3.1 Dissolving the measurement problem 54

4.3.2 Collapse as update 55

4.3.3 Types of epistemic accounts 56

4.4 Space-time structure and collapse 58

5 In Search of a Viable Epistemic Account 61

5.1 Knowledge of probabilities versus probabilities as degrees of belief 61

5.2 Quantum Bayeslanism 62

5.2.1 Probabilities as subjective 62

5.2.2 Values of observables as subjective? 64

5.3 Objectivity of observables measured in an epistemic account of states 68

5.4 Constitutive rules 71

6 Quantum Probabilities: What Are They? 75

6.1 Probabilities of what? 75

6.2 Probabilities of what kind? 79

6.2.1 Relative frequencies? 80

6.2.2 Propensities? 82

6.2.3 Objective probabilities as constraints on rational credences 84

6.3 Objections to this interpretation of probabilities 85

6.3.1 The means/ends objection 85

6.3.2 The quantum Bayesian Moore's paradox 87

Part III Objections

7 Copenhagen Reloaded? 95

7.1 Bohr and 'classical language' 96

7.2 Heisenberg and the epistemic conception of quantum states 99

7.2.1 Heisenberg on pure versus mixed states 99

7.2.2 Heisenberg on quantum probabilities as 'objective tendencies' 102

8 The Charge of Anthropocentrism 105

8.1 Bell's criticism 105

8.2 Anthropocentric notions and value determinateness 108

9 Reduction and Explanation 113

9.1 The micro/macro divide 113

9.2 Explanation without ontic quantum states 115

Part IV Non-locality, Quantum Field Theory, and Reality

10 Non-locality Reconsidered 125

10.1 Quantum theory and special relativity - again 125

10.2 Formulating local causality 127

10.2.1 Causation and counterfactuals 129

10.2.2 Local causality probabilistically 132

10.3 The Principal Principle and admissible evidence 136

10.4 Intuitive probabilistic local causality in the language of the Principal Principle 139

10.5 Quantum theory, local causality, and the Principal Principle 141

10.6 But how does nature perform the trick? 143

11 A Look at Quantum Field Theory 146

11.1 Lagranglan versus algebraic quantum field theory 146

11.2 Basics of the algebraic approach 147

11.3 'Pristine' interpretations 148

11.4 The Rule Perspective and unpristlne interpretations 150

11.5 The case for an unpristlne interpretation 152

12 Quantum Theory and 'Reality' 157

12.1 Instrumentalism? 158

12.2 Sharp values for all observables? 161

12.3 Conclusion 166

Appendices

Appendix A Sketch of Bell's Theorem 168

Appendix B The Kochen-Specker Theorem in a Nutshell 172

Appendix C The Pusey-Barrett-Rudolph (PBR) Theorem - A Short Introduction 175

Notes 178

Bibliography 187

Index 197