R e a l is m , H ist o r y a n d t h e Q u a n t u m T h e o r y : PHILOSOPHICAL AND HISTORICAL ARGUMENTS FOR REALISM AS A METHODOLOGICAL THESIS Robin Findlay H endry London School of Economics and Political Science Thesis Submitted fo r the Degree of Doctor of Philosophy of The University of London N ovember 1995 l UMI Number: U093093 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U093093 Published by ProQuest LLC 2014. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 7h£5£S F 7SS2-. Skt+SZ'f ABSTRACT: REALISM, HISTORY AND THE QUANTUM THEORY: Philosophical and H istorical Argum ents fo r Realism as a Methodological T hesis Scientific realists and non-realists disagree over the reach of scientific knowledge: does it extend beyond the observational realm? Intuitions about abductive inferences are at the heart of many realist positions, but are brought into question by the non-realists’ contention that theories are underdetermined by data, and the alleged circularity of realist attempts to show that such inferencesare reliable. Some realists have tried to circumvent this problem by constructing methodological arguments for realism: if realism is embedded in scientific practice, the realist’s picture of science might provide the best explanation of scientific success. Some non-realists reply by again pointing to the circularity of this strategy, which relies, again, on an abductive inference. Others deny that scientists do adopt realist stances. A methodological realist position is constructed: realist constraints on the acceptance and pursuit of theories—for instance requirements of intertheoretic coherence, and the avoidance of ad hoc explanation —have often contributed to progress in science. The position is immune to non-realist worries about the circularity of realist arguments, for it is a thesis about how science is practised , not the kind of knowledge it provides. The argument is pursued within a diachronic account of theory appraisal: Imre Lakatos’ methodology o f scientific research programmes (MSRP) examines the principles that govern the construction of theories, and provides criteria—achievement of progress—for the appraisal of research programmes. Although Lakatos may have seen these selection criteria, when fulfilled, as symptoms of something else—the fulfilment in the theory’s development of some ideal of scientific honesty—achievement of Lakatosian progress can serve as an end in itself. The realist methods mentioned in the last paragraph are then appraised as means to this end. Since the position has a methodological formulation and background, it is applied as a historical thesis to case studies in line with Lakatos’ meftzmethodology. These comprise two explanatory forays into history: the consistency of Bohr’s 1913 model of the atom, and the construction by Heisenberg and Schrodinger of the two original formulations of quantum mechanics. There follows one contemporary application: the construction of explanations in quantum chemistry using approximate models of molecules. 2 CONTENTS Introduction 4 1. Pragmatic Progress: Scientific Realism and the Methodology of Scientific Research Programmes 6 1.1. Duhem, Quine and Research Programmes. 1.2. Heuristic and Appraisal. 1.3. Newton-Smith on Lakatos. 1.4. MSRP as Social Theory. 1.5. Papineau on Lakatos. 1.6. MSRP Naturalised. 1.7. Hacking on Lakatos. 2. Realism as a Methodological Thesis 51 2.1. Formulating Scientific Realism. 2.2. The Explanationist Argument. 2.3. The Vindicationist Argument. 2.4. Methodological Realism. 2.5. The Content of Methodological Realism. 2.6. Intended Interpretations: Methodological Realism and MSRP. Appendix 1. Models in Practice and in Logic. Appendix 2. Putnam on Skolemisation. 3. The Bohr Atom, Realism and Inconsistency 96 3.1. Background. 3.2. Bohr’s Thinking 1911-1913. 3.3. The Hydrogen Atom. 3.4. Success. 3.5. Was the Bohr Atom Inconsistent? 3.6. Was the Bohr Atom Ad Hoc? 4. Schrodinger vs. Heisenberg or The Importance of Intended Interpretations 123 4.1. Fine, Abductive Inferences and Twentieth-Century Physics. 4.2. Heisenberg’s Probabilistic Agnosticism. 4.3. Schrodinger’s Realistic Analogy. 4.4. The Two Were Not the Same. 5. Approximations in Quantum Chemistry 148 5.1. Quantum Chemistry in an Ideal World. 5.2. Critiques of Approximate Models. 5.3. Approximation and Explanation. 5.4. Approximation and Idealised Models. Conclusion 167 References 169 3 Introduction Among the arguments constructed, criticised and disagreed over by scientific realists and anti-realists are the methodological arguments for scientific realism. The common premise of these arguments is that scientific procedures presuppose the reality of the entities and processes invoked by theories. If science is a successful activity, scientific realism can be inferred as the best explanation, or inferred as a thesis that has been vindicated by the success that its assumption delivered. Although methodological theses may not be suitable as the premises of arguments that will convince the anti-realist of scientific realism, the central aim in what follows is to explore the common theme of these premises— methodological realism—and assess it as an historical claim about the construction of successful theories. Arguing in its favour, I propose an account of theory construction central to which is theintended interpretation of the equations that express a theory: the intended interpretation provides the theoretical background from which understanding (rather than calculating ability) is drawn. The realist’s approach to theories might be methodologically important in two ways. Firstly it might have heuristic value: for instance, where two theories are consistent according to their intended interpretations, realism provides the rationale for directing attention to models of the conjoined theories. On the other hand, there might be aregulative advantage to realism: in pursuit of realist aims (unification, explanation), scientists might expect more of their theories than if they regarded their theories as mere tools for prediction. Thus, for instance, if two theories are inconsistent when interpreted realistically, efforts to achieve consistency must be of prime importance to realists. Only observational inconsistency should concern the instrumentalist scientist. Methodological realism will be supported as an historical claim if realist aims and methods have been pursued and applied in successful episodes in the history of science. The text divides into two sections: the aims of the first—comprising chapters 1 and 2—are philosophical. In chapter 1, Lakatos’ methodology of scientific research programmes is defended as a historiographically illuminating account of theory construction. It is then set in a metamethodology that will ground a methodological conditional with a pragmatic consequent: the growth of knowledge. The antecedent of this conditional—the realistic attitude to theories—is set up in chapter 2. Put together, antecedent and consequent are linked either by the heuristic and regulative mechanisms outlined in the last paragraph. The resultant conditional grounds for a pragmatic rationale for realism: realistic interpretation might be a good means to pragmatic progress as an end. This is methodological realism, or realism as a methodological thesis. The second (shorter) section sets out to support methodological realism via specific historical counterfactuals, taking examples from quantum physics and chemistry. Chapter 4 INTRODUCTION 3, which centres on Bohr’s proposal of his 1913 atomic model, makes an existence claim for the intended interpretation in the case of the Bohr atom, and illustrates a regulative version of MR. The existence claim is based on Bohr’s re-interpretation of his equations, which allowed him to explain new sets of facts without altering those equations. What must have changed, it is argued, is his intended physical interpretation of his equations. The proposal by Schrodinger and Heisenberg of two curiously similar theories in 1925 and 1926 occupies chapter 4. It is argued that the continued presence of intended interpretations explains three sets of historical facts: (i) the authors’ heuristic routes to their respective formalisms; (ii) their taking positions in the debates over the correct interpretation of the joint formalism (and those positions themselves) even q/ferthe famous equivalence proofs; (iii) the continuity between (i) and (ii). The final chapter illustrates both heuristic and regulative versions of MR for molecular quantum chemistry. Quantum-chemical calculations start from models that are strictly false as descriptions of real molecules, for two sorts of reason: it is impossible in practice to enumerate (for instance) all the forces that act in and on a molecule; and even when one writes only as many of the initial conditions as are important, it is usually found that the resultant equations are insoluble. Instead, explanations are constructed with the help of idealised models. There are two realist