Losing Sight of the Forest for the ψ‎

Traditionally \1 is used to stand for both the mathematical wavefunction (the representation) and the quantum state (thing in the world). This elision has been elevated to a metaphysical thesis by advocates of wavefunction realism. The aim of Chapter 10 is to challenge the hegemony of the wavefunction by calling attention to a littleknown formulation of quantum theory that does not make use of the wavefunction in representing the quantum state. This approach, called Lagrangian quantum hydrodynamics (LQH), is a full alternative formulation, not an approximation scheme. A consideration of alternative formalisms is essential for any realist project that attempts to read the ontology of a theory off the mathematical formalism. The chapter shows that LQH falsifies the claim that one must represent the many-body quantum state as living in 3n-dimensional configuration space. When exploring quantum realism, regaining sight of the proverbial forest of quantum representations beyond the \1 is just the beginning.

Pragmatist Quantum Realism

Realism comes in many varieties, in science and elsewhere. Van Fraassen’s influential formulation took scientific realism to include the view that science aims to give us, in its theories, a literally true story of what the world is like. So understood, a quantum realist takes quantum theory to aim at correctly representing the world: many would add that its success justifies believing this representation is more or less correct. But quantum realism has been understood both more narrowly and more broadly. A pragmatist considers use prior to representation and this has prompted some to dub pragmatist views anti-realist, including the view of quantum theory that the author has been developing recently. But whether a pragmatist view of quantum theory should be labeled anti-realist depends not only on its ingredients but also on how that label should be applied. Pragmatism offers a healthy diet of quantum realism.

Can We Quarantine the Quantum Blight?

In the science fiction novel Quarantine, Greg Egan imagines a universe where interactions with human observers collapse quantum wavefunctions. Aliens, unable to collapse wavefunctions, tire of being slaughtered by these collapses. In response they erect an impenetrable shield around the solar system, protecting the rest of the universe from human interference and locking humanity into a starless Bubble. When confronting scientific realism and the quantum, many philosophers try to do the theoretical counterpart of this fictional practical strategy. Quantum mechanics is beset with many hard-to-resolve interpretational challenges. Philosophers—appealing to decoherence and coarse-graining—try to put these in a Bubble and hope that they can go about their philosophizing as before. Chapter 4 aims to burst this Bubble, and then explores ways of eliminating quantum underdetermination, showing that such attempts lead to philosophical gridlock.

Scientific Realism without the Wave Function

Scientific realism assumes that our best scientific theories can be regarded as (approximately) true. Quantum mechanics has long been regarded as at odds with scientific realism. It is now known that this is not true. However, scientific realists usually assume that the wave function represents physical entities. Chapter 11 discusses a particular approach which makes quantum mechanics compatible with scientific realism without assuming this: matter is instead represented by some spatio-temporal entity dubbed the primitive ontology. It argues how within this framework one developsa distinctive theory-construction schema, which allows us to perform a more informed theory evaluation by analyzing the various ingredients of the approach and their inter-relations.

Scientific Realism without the Quantum

Scientific realists often say that there should be belief in the approximate truth of ‘our best scientific theories.’ It is hard to hear the phrase ‘our best scientific theories’ without thinking of quantum mechanics and quantum field theories. But as numerous chapters in this collection make clear, it is unclear that some experts even know how to make sense of being a realist about quantum theories. They provide recipes for calculating incredibly precise predictions for observations, but beyond the recipes, they do not seem to offer a clear-cut or unambiguous picture of what physical reality is like at the fundamental level. After giving an overview of the problems that beset any attempt to believe in the truth or approximate truth of quantum theories, Chapter 2 turns to the question of how to protect scientific realism from the ills of the quantum. The aim is to show that it is possible to quarantine the worst of those ills, freeing us to adopt a robustly realistic attitude toward many other extremely successful areas of contemporary science, such as (parts of) geology, microbiology, and chemistry. The quarantine barrier may be imperfect and permeable in places, but is strong enough (the chapter argues) to help the cause of scientific realism.

Introduction

This chapter previews the contributions to this volume and lays out the broader context and motivations for engaging in the scientific realism debate specifically in relation to quantum physics.

Towards a Realist View of Quantum Field Theory

Quantum field theories (QFTs) pose their own distinctive challenges for the scientific realist. This chapter develops a strategy for articulating a realist view of QFT based on the renormalization group. It closes by considering some objections to this programme raised by Laura Ruetsche.

Perturbing Realism

Effective Realism marshals ideologies and technologies of our best current physics— the interacting quantum field theories making up the Standard Model—to articulate a selective realism resistant to skeptical affronts such as the Pessimistic Metainduction. Chapter 15 attempts an empiricist re-appropriation of the putatively realist commitments Effective Realists stake out. It also argues that resisting empiricist reappropriation entangles selective realists in something alarmingly similar to the very project of ‘Standard Interpretation’ they regard as misguided.

Naturalism and the Interpretation of Quantum Mechanics

Quantum mechanics is a paradigmatic example of a scientific theory seemingly demanding ‘an interpretation’. What is it to ‘interpret’ a physical theory? Bas van Fraassen has recently argued that the attitude towards the task of interpreting science can be used to demarcate two otherwise similar epistemic stances: empiricism and naturalism. He claims that while empiricists are committed to the task of interpretation, naturalists cannot make sense of interpretation from outside the scientific theory. Naturalists, it seems, would have to be quietists about interpretation. Chapter 6 investigates in what form, if any, naturalists can make sense of the task of interpretation in the case of quantum mechanics. Doing so will shed light on the question whether interpretation of physical theories is a distinctively philosophical task, and what its purpose might be. It suggests that the aim of interpreting theories is to enhance our understanding, and that this task is not exclusively philosophical.

The Non-Miraculous Success of Formal Analogies in Quantum Theories

The Higgs model was developed using purely formal analogies to models of superconductivity. This is in contrast to historical case studies such as the development of electromagnetism, which employed physical analogies. As a result, quantum case studies such as the development of the Higgs model carry new lessons for the scientific (anti-)realism debate. Chapter 13 argues that, by breaking the connection between success and approximate truth, the use of purely formal analogies is a counterexample to two prominent versions of the ‘No Miracles’ Argument (NMA) for scientific realism: Stathis Psillos’ Refined Explanationist Defense of Realism and the Argument from History of Science for structural realism. The NMA is undermined, but the success of the Higgs model is not miraculous because there is a naturalistically acceptable explanation for its success that does not invoke approximate truth. The chapter also suggests some possible strategies for adapting to the counterexample for scientific realists who wish to hold on to the NMA in some form.