A Phenomenological Approach to Quantum Mechanics by Steven French

Context

Steven French (born 1956) is an emeritus professor of the philosophy of science at Leeds University. His philosophical approach is that of ontic scientific realism.

Scientific realism has become dominant in the philosophy of science replacing anti-realism, an approach associated with logical positivism which arose in Vienna in the 1920s. It was characterised by the view that scientific knowledge is the only kind of factual knowledge and that all traditional metaphysical doctrines are to be rejected as meaningless. Antirealism became discredited through its reliance on positivist ideas about scientific language, for example that it can be divided into theoretical and observational parts, that much of it should not be taken literally, or that its empirical content is redundant. According to the Vienna Circle all true philosophy was held to be a critique of language, and its result is to show that all genuine knowledge about nature can be expressed in a single language common to all the sciences.

On the contrary, scientific realism requires belief in the unobservable entities hypothesised by the most successful scientific theories. It is widely held that the most powerful argument in favour of scientific realism is that of no-miracles. This was expressed by Hilary Putnam in 1975 as:

"The positive argument for realism is that it is the only philosophy that doesn't make the success of science a miracle."

However, the underdetermination argument is often cited as scepticism about theories of unobservable entities. The best-known of these arguments is pessimistic meta-induction, which supports the expectation that our best current scientific theories will themselves be abandoned, and hence that we ought not to assent to them.

How then are we to decide whether to believe in the full theoretical truth of scientific theories, including what they say about unobservable entities such as electrons and black holes, or whether to believe instead only that our best scientific theories are empirically adequate? John Worrall introduced the concept of structural realism in 1989 as a way to break the impasse that results from taking both arguments seriously, and have “the best of both worlds” in the debate about scientific realism. According to Worrall, we should not accept standard scientific realism, which asserts that the nature of the unobservable objects that cause the phenomena we observe is correctly described by our best theories. However, neither should we be antirealists about science. Rather, we should adopt structural realism and commit ourselves to the mathematical or structural content of our theories. Worrall sustains that there is structural retention across theory change. Structural realism both avoids the force of the pessimistic meta-induction (by not committing us to belief in the theory’s description of the world) and does not make the success of science seem miraculous (by committing us to the claim that the theory’s structure, over and above its empirical content, describes the world).

Ladyman (1998) questions whether Worrall’s structural realism should be understood as a metaphysical or epistemological modification of standard scientific realism. Worrall cites Poincaré who refers to redundant past theories which captured the true relations between the:

“real objects which Nature will hide forever from our eyes”

This suggests that Worrall is an epistemic structural realist committed only to the structure of the best scientific theories, but not to the rest of the content. This way of thinking about structural realism is that we only believe what scientific theories tell us about the relations entered into by unobservable objects, and suspend judgement as to their nature. This implies a new, more abstract approach to physicality than the previous standard model:

"On the structural realist view what Newton really discovered are the relationships between phenomena expressed in the mathematical equations of his theory."

Ontic structural realism was originally developed by Steven French and James Ladyman. It incorporates an explicit commitment to the claims that the world has an objective modal structure and that this structure is represented by the theoretical structure of the best scientific theories. The theory attributes a rich structure of natural necessity to the world, and this differentiates it from John Worrall’s epistemic structural realism, which rejects natural necessity. Ladyman and Ross extend their model from physics to the special sciences and invoke the notion of the objective modal structure of reality in their accounts of prediction, causation, and ontology.

Steven French's 2023 book A Phenomenological Approach to Quantum Mechanics has its philosophical origin in Edmund Husserl's phenomenology which focused on the structures of experience and consciousness, emphasising the first-person perspective and the ways in which individuals experience the world. It was later developed by philosophers such as Martin Heidegger, Maurice Merleau-Ponty and Jean-Paul Sartre.

The main background influence to French's book is London and Bauer’s La théorie de l’observation en mécanique quantique (1939), in which quantum mechanics is directly influenced by phenomenological considerations. Quantum observation theory involves studying observation processes using the tools of quantum physics. Both the observed system and the measuring apparatus are considered quantum systems. The measurement process is determined by their interaction and is described by a unitary evolution operator. This theoretical approach was initiated by John von Neumann (1932). It differed from current interpretations of quantum mechanics (Niels Bohr, Copenhagen interpretation), which require the measuring apparatus to be considered a classical system which does not obey quantum physics. This requirement is unjustified because quantum laws are universal. They apply to all material systems, microscopic and macroscopic. This universality is a direct consequence of the principles: if two quantum systems are brought together, they form a new quantum system. The number of components therefore changes nothing regarding the quantum nature of a system. The quantum theory of observation invites us to abandon the idea of the reduction of the wave function, because it is not necessary to explain the correlations between successive observations, and because it contradicts the Schrödinger equation.

Summary

Preface

Steven French recalls the influences which led him to a phenomenological approach to quantum mechanics. They happened through an introduction to London's thinking by way of his biography by Kostas Gavroglu which described his background in phenomenology and his work on the measurement problem in quantum mechanics. He focuses on the role of consciousness in the so-called ‘collapse’ of the wave-function. French says that now he has finished his book he is left with the feeling that philosophers of physics will look askance at the phenomenology, and philosophers of the latter inclination will recoil from all the physics.

Chapter 1 The Measurement Problem

In this introductory chapter, French presents the basics of the measurement problem. On the one hand, there are the continuous dynamics as embodied in Schrödinger’s Equation which describes the evolution of the wave-function. On the other, there is the discontinuous ‘collapse’ of that wave-function to give a definite outcome out of all the possible options. The usual interpretation presents this problem in the context of a standard history of the development of quantum theory that is entwined with philosophical reflections on its foundations. Both sets of histories are contested in the following chapters in the book.

Chapter 2 The Orthodox Solution, Its History and Multiplicity

The orthodox solution to the measurement problem is often presented in terms of ‘consciousness causes collapse’. It is widely understood to have been developed and presented by the mathematician von Neumann in his classic book, Mathematical Foundations of Quantum Mechanics (1932/1955) which lays down the core theoretical framework of quantum mechanics. However, the ‘problem’ was not even presented until the 1950s, which is when von Neumann’s book was finally translated into English, and there is barely any mention of consciousness in it. It is partly for this reason that London and Bauer are typically regarded as having clearly articulated what von Neumann only hinted at.

This chapter examines what von Neumann actually wrote about measurement in quantum mechanics in his 1932 book. It presents his ‘psychophysical parallelism’, which requires the existence of an interaction between subjective experiences and material systems. It also presents the famous ‘chain’ argument which concludes that something non-physical must induce the wave-function to collapse. Neumann argued that the mathematics of quantum mechanics allows the collapse of the wave function to be placed at any position in the causal chain from the measurement device to the "subjective perception" of the human observer. (In 1939, Fritz London and Edmond Bauer argued that the consciousness of the observer played an important role in measurement. However, London wrote about consciousness in terms of philosophical phenomenology and not necessarily as a physical process.)

Chapter 3 The Debate about Consciousness

It was Wigner who defended the role of consciousness in the context of the ‘measurement problem’ and this chapter presents his arguments. The Putnam and Shimony debate is analysed here. 

It was Wigner who introduced the consciousness of the observer as the cause of superposition collapse, largely based on a misreading of Fritz London and Edmond Bauer's book La théorie de l' observation en méchanique quantique (1939). This notably influenced the subsequent Wigner–Margenau–Putnam –Shimony debate that brought an end to the viability of the collapse accounts of quantum measurement due to consciousness.

The standard response to the measurement problem is that the observation of a system collapses the superposition into an unambiguous state. This view held the connection between the conscious observer and the system to be causal. (The observer either kills or spares Schrödinger’s cat, though they do not have a choice which.) French's phenomenological interpretation reveals that this account rested on sand. It is not a mysterious interaction between the apparatus and the object that produces a new wave form for the system during the measurement. It is only the consciousness of an ‘I’ who can separate himself from the former function and, by virtue of his observation, set up a new objectivity in attributing to the object a new function.

Chapter 4 Physical and Phenomenological Networks

This chapter situates London and Bauer’s ‘little book’ in its historical context, beginning with the co-authors’ scientific backgrounds. London in particular did important work in physics, using quantum theory to explain chemical bonding and superconductivity, for example. Working closely with Born, Sommerfeld, and, crucially, Schrödinger, London found himself at the heart of discussions over the foundations of the new theory. Notably he was part of the network of discussants used by Schrödinger to try out his ideas, which subsequently found expression in his famous ‘cat’ thought-experiment and in the notion of entanglement. However, London was also remarkable in having a strong background in philosophy, particularly phenomenology, and his student thesis on how we should conceive of scientific theories was actually published in the journal that Husserl founded. (London went on to establish phenomenology as a discipline in the USA.)

5 The Epoché and the Ego

The fundamentals of phenomenology are sketched in this chapter, focusing in particular on the nature of the ‘epoché’ and the role of the ego. The former is the central device in the phenomenologists’ toolkit whereby ‘the objective world’ is bracketed off, the better to hold up to the light the presuppositions underlying our ‘natural’ attitude towards it. Husserl’s view of the latter appears to have shifted over the years, but a consistent account can be given according to which the ego appears as the subject-pole standing in a certain relationship with the object-pole. This correlation between thinking and being is all that we have access to, Husserl maintained, and as Zahavi has emphasised, this represents a core feature of phenomenology according to which mind and world are bound constitutively together. It is this ‘correlationist’ understanding that is the key to the phenomenological reappraisal of London and Bauer’s work.

6 London and Bauer Revisited 

French presents a detailed account of London and Bauer’s ‘little book’, beginning with their central claim that quantum mechanics should itself be understood as a theory of knowledge, because it sets at its core the relationship between mind and the world. This is revealed through a careful analysis of the measurement situation, presented in detail by London and Bauer. In particular, they insist that the observer is able to know her own state because she has with herself a relationship of a special character, as manifested through the faculty of introspection. By virtue of this immanent knowledge she is then able to separate herself from the quantum superposition and establish her own objectivity. However, this is not to be equated with her consciousness mysteriously ‘causing’ the wave-function to collapse; rather, her ego thereby emerges as one pole of the relationship, with the system, now also in a definite state, as the ‘object-pole’. The terms used in the text are redolent of phenomenological language and with that understanding. It is then suggested that this ‘little book’ may serve as the basis for a novel phenomenological understanding of quantum physics. 

7 Completing the Crisis

A phenomenological understanding of quantum theory offers an entirely new perspective on scientific objectivity and our relationship with the world more generally. However, it is important to recognise that it sits contrary to the usual realist and empiricist stances that are debated within the philosophy of science. This becomes apparent when we consider Husserl’s great unfinished work, The Crisis of the European Sciences. In this chapter, following Trizio’s recent analysis, Husserl’s account of the nature of science and its relationship to the everyday ‘life-world’ is described. In particular, the ‘crisis’ is understood as arising from the mathematization of science, with its inherent idealisation, which has produced a kind of ‘psychophysical’ splitting of material nature. London and Bauer’s account is then presented as offering a way to overcome this ‘split’ through the correlation between mind and world and thereby complete Husserl’s final project.

8 QBism and the Subjective Stance 

Phenomenology has also been brought to bear on quantum mechanics in the context of recent discussions over the approach known as ‘QBism’. This takes the theoretical formalism to be simply a device for predicting an agent’s future experiences, rather than as representing the world. Such a first-person perspective has been widely taken to mesh with the phenomenological stance, as usually understood. However, although advocates of QBism maintain that any slide into solipsism can be resisted, they struggle to accommodate reactions from the world. Here it is argued that in order to do so while remaining within a phenomenological framework, the interaction between the subject and object of knowledge identified by London and Bauer should be incorporated. This can be summarised as:

"...what we observe is not nature in itself, but nature exposed to our method of questioning."

Interestingly, one of the phenomenologist philosophers who is often cited in this specific context, Merleau-Ponty, took classes with Gurwitsch and drew on London and Bauer’s ‘little book’ in his own analysis of quantum physics.

9. Many Worlds, Many Minds, and Many Relations

Accounts of quantum theory that bring to the fore the relationship between the system and the observer, or measuring device, include Everett’s ‘Many Worlds’ interpretation and Rovelli’s ‘Relational Quantum Mechanics’. The former understands the state of a system as relative to that of the observer and in Everett’s original formulation, the definite outcomes obtained through measurement were manifested via the observer’s memory sequences. The subjectivist aspect of this interpretation is made even more explicit in the so-called ‘Many Minds’ variant. Relational Quantum Mechanics adopts a relational or perspectival approach to the states of the system under observation. In this chapter both approaches are considered as offering a way of aligning quantum theory with the correlationist feature of phenomenology. Both are then compared with QBism and the pros and cons of all three are considered in terms of possible avenues for developing a phenomenological form of quantum theory.

10 Interpretation or Reconstruction? 

Both the ‘Many Worlds’ interpretation and Relational Quantum Mechanics are typically presented as interpretations of quantum theory, whereas QBism is understood as a reconstruction of it. The latter has been suggested as the appropriate approach for phenomenologists to adopt, particularly since this account adopts a first-person perspective. However, in Chapter 10 French argues that such a dramatic move is not necessary as London and Bauer have already laid down the groundwork for an appropriately phenomenological understanding of the theory. This can then be supplemented with the relationist features emphasised by ‘Many Worlds’ and Relational Quantum Mechanics. Husserl himself insisted that phenomenology does not require any such reshaping of scientific practice itself, theoretical or otherwise; rather it and its foundations need to be understood from the perspective afforded by the epoché. It is precisely this understanding that London and Bauer’s ‘little book’ presents, with the theory taken as not just a piece of physics but a theory of knowledge in itself. The book concludes with the suggestion that as a result, London and Bauer’s account sits somewhere between an interpretation and a reconstruction of the theory and so represents an advance in considerations of how we should conceive of our relationship to the world.

Themes

Background

With the invention of mathematical logic, it became possible to think of scientific theories as objects in their own right. The logical positivists said that theories are sets of axioms in a formal language. Nobody thought of this claim as controversial until the 1970s, when a second-wave of philosophers of science argued that the syntactic view is a patently inadequate account of the nature of theories. These philosophers proposed, instead, that theories are collections of models and thus, the semantic view of theories was born. Even so, nobody was thinking much about the fact that if theories are mathematical objects, then if theories exist, so do mathematical objects, which implies that platonism is true.

Two philosophical approaches

One kind of philosophical vision thinks that there is a preferred, fundamental ontological language and that a sentence in any other language is true if it corresponds to something true in the fundamental language.

Another kind of philosopher denies the existence of the notion of a fundamental language. This kind of philosopher might think that some modes of speech are less object-oriented than others. 

For example, if an analytical philosopher asked me to give the number of reasons for saying I had reasons to feel happy and what underlying reasons I was referring to, I would think these questions were laughable. Nor would the situation be improved if I think that 'there are reasons' is made true by facts that do not involve reasons. 

'Theories' occupy a similar location in logical space as 'reasons'. If you insist on treating theories as things, then it is going to be hard to make sense of science. 

Theories

In a previous book There Are No Such Things As Theories (2020), French asks 

"What is a scientific theory? Is it a set of propositions? Or a family of models? Or is it some kind of abstract artefact?" 

He examines these options in the context of a comparison between theories and artworks. On the one hand, theories are said to be like certain kinds of paintings, in that they play a representational role; on the other, they are compared to musical works, insofar as they can be multiply presented. The author argues that such comparisons should be treated with care and that all of those options face problems. 

Instead, he suggests, we should adopt a form of eliminativism towards theories, in the sense that a theory should not be regarded as a thing. Nevertheless, we can still talk about them and attribute certain qualities to them, where that talk is understood to be made true by certain practices. This shift to practices as truth-makers for theory talk then has certain implications for how we regard theories in the realism debate and in the context of the nature and role of representation in science.

French applies an eliminativist view of theories which maintains that theories (and models) should not be reified as abstract entities in some sense and that presentations of these theories help to establish the ‘truth makers’ for certain claims that we take to be ‘about’ such theories. Such claims may refer to certain aesthetic qualities attributed to theories that by situating these qualities within the actual practices of science — in particular, the presentations and publications by which results are shared — we can better grasp their nature and function.

Objections to Structural Realism

- Structural realism collapses into standard realism

Psillos (1995) argues that any form of structural realism presupposes a distinction between the form and content of a theory, and/or a distinction between our ability to know the structure and our ability to know the nature of the world. According to Psillos both are illusory because the scientific revolution banished mysterious forms and substances that might not be fully describable in structural terms. For Psillos, properties in mature science are defined by the laws in which they feature, and:

 “the nature and the structure of a physical entity form a continuum." 

For Psillos, structural realism is either false or collapses into traditional realism. Similarly, David Papineau in 1996 argued that:

 “restriction of belief to structural claims is in fact no restriction at all”

Structural realism gains no advantage over traditional realism with the problem of theory change because it fails to make any distinction between parts of theories that should and should not enjoy our ontological commitment. Kyle Stanford (2003) also argues that we cannot distinguish the structural claims of theories from their claims about content or natures. Structural realism must be a form of scientific realism.

- When theory changes not all structure is retained

If structural realism is understood as a form of selective realism seeking to identify what will be retained in advance then this makes it hopeless. However, the structural realist is not claiming that all structure is retained on theory-change, just that the relations or structure and in scientific revolutions the empirical content of the old theory is recovered as a limiting case of the new theory. Post claimed there are no successor theories losing all or part of the well-confirmed empirical structures of their predecessors. Well-confirmed relations among phenomena must be retained by future theories. This goes beyond belief in the empirical adequacy of our theories if we suppose that the relations in question are genuine modal relations rather than generalisations about actual phenomena. However, Newman (2010) argues that structuralism cannot deal with the pessimistic meta-induction. McArthur (2011) argues that structural realism eliminates both theory change in science and scientific discovery. 

- Structural realism is too revisionary of metaphysics

There is no general agreement among philosophers that any of the metaphysical theories of universals, for example, is adequate. It is also arguable that metaphysical categories inherited from the ancient Greeks, the scholastics and the early moderns are not appropriate for contemporary science. Naturalists argue that we should reject metaphysical doctrines if they are not supported by science. Michael Esfeld (2004) argues against any gap between epistemology and metaphysics. Similarly, Ladyman and Ross (2007) argue for a kind of verificationism in metaphysics.

A key motivation for Ontic Structural Realism is summed up by Ernan McMullin: 

[I]maginability must not be made the test for ontology. The realist claim is that the scientist is discovering the structures of the world; it is not required in addition that these structures be imaginable in the categories of the macroworld. (1984)