Unifying Perspectives: All-encompassing Reality vs. All-inclusive Physics

Relational Quantum Mechanics (RQM) claims to be an interpretation of quantum theory \cite{Rovelli.21}. However, there are significant departures from quantum theory: (i) in RQM measurement outcomes arise from interactions which entangle a system S and an observer A without decoherence, and (ii) such an outcome is a "fact" relative to the observer A, but it is not a fact relative to another observer B who has not interacted with S or A during the foregoing measurement process. For B the system S⊗A remains entangled. We derive a GHZ-like contradiction showing that relative facts described by these statements are incompatible with quantum theory. Hence Relational Quantum Mechanics should not be considered an interpretation of quantum theory, according to a criterion for interpretations that we have introduced. The criterion states that whenever an interpretation introduces a notion of outcomes, these outcomes, whatever they are, must follow the probability distribution specified by the Born rule.

The STA is a mathematical system, rather than of itself containing new physics. However, when we employ it in the description of physical phenomena, we usually find that some fresh insight is obtained, often on old questions. The oldest question of 20th century physics is the interpretation of quantum mechanics, and in this lecture we aim to discuss some of the light that an STA approach can throw upon this issue. This will be undertaken in the context of specific examples, and so in the main these lecture notes contain the details of these, rather than the comments that will be made about issues of interpretation. We think these examples stand as interesting and important applications in their own right, irrespective of whether one thinks there is a problem to be solved in the interpretation of quantum theory. This is particularly true for the beginnings of a multiparticle STA approach which we describe here, since it seems undeniable that there is a need for a more coherent and justifiable rationale for the set of recipes and operational procedures that currently constitute relativistic multiparticle theory.KeywordsQuantum TheoryDirac EquationGeometric AlgebraSpin VectorPauli PrincipleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The aim of the article is to analyze the ontological foundations of quantum mechanics and the relationship of various interpretations of quantum mechanics with the question of truth in scientific knowledge. The theoretical material (various interpretations of quantum mechanics) was analyzed. The research methods were analysis, comparative-historical and institutional approaches. On the basis of the study, it can be concluded that physicists are only able to predict the probabilities of physical phenomena or processes, without any knowledge of the structure of entity in itself. The study helps to complement the theoretical picture of the ontology of quantum mechanics and to get an idea about the development prospects of the methodology of physical sciences. We should not ascribe properties that are unobservable in experience to the entity because science can truly interpret only the representation of entity in itself in experience and the ways of dealing with it, not future events or possible states of the entity. Otherwise, science “slides” down to the level of dialectical (rhetorical) exercises based not on true premises, but on generally accepted or “authoritative” biases, which gives room to extreme forms of relativism and takes natural scientists away from studying nature to inventing empirically unsupported hypotheses. When, in accordance with the Cartesian ontology, the scientist assumes that the entity is as the “subject” observes it (that is, the “reflection” of the entity in consciousness is identified with entity in itself), this assumption leads the scientist to attempts to “scientifically” describe the future events or the possible states of the entity. The criterion for the truth of a scientific theory put forward by Einstein in his dispute with Bohr remains a fundamentally unattainable ideal. Cognition of nature is probabilistically and fundamentally incomplete since a person can consciously comprehend natural phenomena only within the framework of their representation in the existing being. The probabilistic nature of quantum mechanics is due to the impossibility of knowing things as they exist by themselves, that is, as they exist outside of representation in the mind of the observer. This does not mean that physical entities did not exist before their knowledge: they existed potentially, but were not valid for the observer, that is, conscious. Quantum physics is as incomplete as any other physical theory when compared with an unattainable ideal, but this fact does not negate its truth for modern scientists since quantum theory is based on the results of verified experiments.

The relationship between physics and phenomenology is a blind spot of current literature in a twofold sense. First, while many phenomenologists work on the interface to psychology, the cognitive sciences, biology, artificial intelligence, etc., only very few engage in phenomenological reflections on physics. This is puzzling since, as we shall see below, Husserl and other classical phenomenologists have been quite clear on the significance of such an undertaking, stressing the central role physics plays among the natural sciences. Secondly, while philosophy of physics has emerged as an important sub-discipline of philosophy in the twentieth century, there is hardly any work that addresses the role of phenomenology for the development of modern physics or the philosophical interpretation of physical theories (with notable exceptions that will be discussed below). This is puzzling since, as we shall see below, the father of modern field theory, Hermann Weyl, was inspired by phenomenological considerations when formulating his gauge principle, and there is a long (although usually unnoticed) history of phenomenological motifs in interpretations of quantum mechanics. Section 15.1 addresses the question of how to interpret physical theories and how to estimate the relationship between mathematical models and physical reality. In Sect. 15.2, we shed light on the perspectivist features of Husserl’s philosophy of science and discuss how it relates to current versions of scientific perspectivism. Section 15.3 addresses how phenomenological ideas have influenced the development and interpretation of early modern physics. In Sect. 15.4, we discuss observer-dependence in modern physics and highlight phenomenological motifs in Wheeler’s conception of “observer-participancy.” Finally, Sect. 15.5 sheds light on phenomenological motifs in a novel interpretation of quantum mechanics, namely QBism, and emphasizes similarities between phenomenology and the program of reconstructing quantum mechanics, a program that currently enjoys popularity in the field of quantum foundations. We shall see that the worldviews delivered by phenomenology and physics might be closer than is commonly assumed.

CONCEPTUAL FOUNDATIONS OF QUANTUM MECHANICS: THE ROLE OF EVIDENCE THEORY, QUANTUM SETS, AND MODAL LOGIC

The inadequacy of effective incoherence interpretations of quantum theory, as demonstrated by analysis of EPR measurements

I argue that philosophical reflection can contribute to a better understanding of physical theories by performing conceptual clarification, epistemological analysis and ontological exploration. I begin by reconstructing early ontological interpretations of quantum theory, i.e., by explaining Copenhagen instrumentalism and the shift toward a quantum realism. I turn to entanglement, whose chief philosophical challenge is to understand which deeper property of nature it reveals. The trouble is that the EPR-correlations it gives rise to are not produced by common causation. Conceptual analysis shows that this failure is due to the violation of separability in quantum theory. In entangled states, it is the composite state that is primary since it cannot be neatly divided into two states that unambiguously pertain to the partial systems. As a result, total states are not produced by an interaction among the parts. This feature can be interpreted in ontological terms as suggesting a holist picture of nature. Another question of philosophical import concerns the quantum measurement problem and the contribution decoherence makes to its solution. The conceptual point is what, precisely, this problem amounts to and what we require considering it settled. The issue that divides the philosophical factions is whether a solution needs to show that superpositions are actually destroyed or whether it suffices to demonstrate that superpositions become unobservable.

Interpretations of quantum theory have traditionally assumed a “Galilean” observer, a bare “point of view” implemented physically by a quantum system. This paper investigates the consequences of replacing such an informationally-impoverished observer with an observer that satisfies the requirements of classical automata theory, i.e., an observer that encodes sufficient prior information to identify the system being observed and recognize its acceptable states. It shows that with reasonable assumptions about the physical dynamics of information channels, the observations recorded by such an observer will display the typical characteristics predicted by quantum theory, without requiring any specific assumptions about the observer’s physical implementation.

In defence of Copenhagenism

In 1962, Eugene P. Wigner introduced a thought experiment that highlighted the incompatibility in quantum mechanics between unitary evolution and wave function reduction in a measurement. This work resulted in a class of thought experiments often called Wigner's Friend Scenarios, which have been providing insights over many frameworks and interpretations of quantum theory. Recently, a no-go theorem obtained by Daniela Frauchiger and Renato Renner brought attention back to the Wigner's Friend and its potential of putting theories to test. Many answers to this result pointed out how timing in the thought experiment could be yielding a paradox. In this work, we ask what would happen if the isolated friend in a Wigner's Friend Scenario did not share a time reference frame with the outer observer, and time should be tracked by a quantum clock. For this purpose, we recollect concepts provided by the theory of quantum reference frames and the quantum resource theory of asymmetry, to learn how to internalize time in this scenario, and introduce a model for a feasible quantum clock proposed by Mischa P. Woods, Ralph Silva and Jonathan Oppenheim, called the quasi-ideal clock. Our results have shown that no decoherent behavior comes from this approach, and the disagreement between the superobserver and its friend persists even for an imprecise clock, indicating that the source of paradox in a Wigner's Friend Scenario may be elsewhere.

As sketched in the previous chapter, Niels Bohr’s engagement in the development of quantum theory, especially in its crucial phase around the mid-1920s, proceeded with a critical examination of basic concepts such as continuity/discontinuity, space-time and causality, which underlie not only atomic physics, but the modern-scientific view of nature in general. This led to his introduction in 1927 of the idea of complementarity as an interpretation of quantum theory, newly established as quantum mechanics. While closely linked with Heisenberg’s uncertainty relations, Bohr’s complementarity is marked by its own distinctive philosophical notions and implications. Here and throughout this study (as noted in the Introduction), I use the term ‘complementarity’ to refer not only to Bohr’s concept of complementarity, but – following his own and many commentators’ usage – also to his overall philosophical thought revolving around this concept.

Until recently most of the discussion concerning the interpretation of quantum theory has been carried out in the context of phenomena that can be adequately treated using the non-relativistic Schrödinger equation. In this context the interpretations of quantum mechanics proposed by de Broglie (1926; 1927) and by Bohm (1952a,b; Bohm and Vigier 1954) formally overlap in the one-particle case in what de Broglie called the “pilot-wave” theory and Bell called the de Broglie—Bohm interpretation.1 Both Bohm’s and de Broglie’s approach yield the same guidance condition for the “particle”, but they differ in what the particle is. For Bohm the particles are point-like whilst their guiding ψ-field exists in configuration space, whereas in de Broglie’s theory the particle is considered to be a solitonlike structure in its own ψ-field, consequently the field of each particle must exist in real space (and not the abstract configuration-space of the many-particle non-relativistic Schrödinger equation). The latter idea presented grave difficulties for de Broglie, which were never satisfactorily solved and we do not consider the soliton solutions in this paper.

As always, Albert Einstein was ahead of his time. Quantum theory was still in its infancy, its formalism a mere sketch, and its implications only beginning to be realized. Yet Einstein, in 1917, already spotted what would trouble him throughout his lifetime. He concluded that the nascent theory, which he had helped initiate, seemed to leave “time and direction of elementary processes,” such as the spontaneous emission of radiation from a molecule, “to chance” [1]. Einstein’s conclusion was visionary. It was also incredibly bold, for it suggested a radical departure from the powerful, centuries-old deterministic and causal worldview of classical physics. But Einstein also immediately expressed his discomfort with the idea of fundamental chance. In fact, his worries were just the seed of what would turn into one of the longest and most heated debates in the history of physics. What does quantum theory mean, and what does it tell us about the nature of reality? Some of the brightest minds in physics locked horns over these issues. Besides Einstein, there were Niels Bohr, Erwin Schrodinger, Werner Heisenberg, Pascual Jordan, Carl Friedrich von Weizsacker, Wolfgang Pauli, and Richard Feynman, just to name a few. Ask anyone today working on foundational questions in quantum theory and you are likely to hear that there is still no consensus on many of these questions—all the while, of course, everybody seems to be in perfect agreement on how to apply the quantum formalism when it comes to making experimental predictions. Remarkably, there has never been any serious attempt to find out what the current opinions of the community really are and how

For more than eighty years, quantum theory (QT) has dominated physical science. This domination remains unchallenged to this day. Some physicists celebrate this remarkable stability. Others lament this fact and argue that QT inhibits our understanding of physical reality. They feel that numerous problems that have accumulated in physical science require stepping beyond the horizon outlined by QT. The article offers a critical examination of the foundational assumptions of QT that shape its practice. It uses two interpretations of QT as case studies—Copenhagen interpretation and the theoretical perspective advanced by American physicist David Bohm—to explain one major problem that continues to plague our study of physics. The article sketches a path to a possible solution and outlines a new science practice that this solution will require.

Klein-Weyl's program and the ontology of gauge and quantum systems