Von Neumann’s (1927 , 1932 ) measurement theory is based on an uncritical acceptance of the historical disturbance doctrine of measurements. It is an ineffectual attempt to relate empirical data to the partial Boolean structure of quantum mechanics. In this paper, I will argue that the measurement problem of quantum mechanics is soluble if it is reasonably posed. All difficulties stem from an indiscriminate conceptual approach and inadequate mathematical formulations.
Von Neumann’s (1927 , 1932 ) measurement theory is based on an uncritical acceptance of the historical disturbance doctrine of measurements. It is an ineffectual attempt to relate empirical data to the partial Boolean structure of quantum mechanics. In this paper, I will argue that the measurement problem of quantum mechanics is soluble if it is reasonably posed. All difficulties stem from an indiscriminate conceptual approach and inadequate mathematical formulations.
We provide an introduction to the theory of quantum measurements that is centered on the pivotal role played by John von Neumann's model. This introduction is accessible to students and researchers from outside the field of foundations of quantum mechanics and presented within a historical context. We first explain the origins and the meaning of the measurement problem in quantum theory, and why it is not present in classical physics. We perform a chronological review of the quantization of action and explain how this led to successive restrictions on what could be measured in atomic phenomena, until the consolidation of the orthodox interpretation of quantum mechanics. The clear separation between quantum system and classical apparatus that causes these restrictions is subverted in von Neumann's paradigmatic model of quantum measurements, a subject whose concepts we explain, while also providing the mathematical tools necessary to apply it to new problems. We show how this model was important in discussing the interpretations of quantum mechanics and how it is still relevant in modern applications. In particular, we explain in detail how it can be used to describe weak measurements and the surprising results they entail. We also discuss the limitations of von Neumann's model of measurements, and explain how they can be overcome with POVMs and Kraus operators. We provide the mathematical tools necessary to work with these generalized measurements and to derive master equations from them. Finally, we demonstrate how these can be applied in research problems by calculating the Quantum Zeno Effect.
Abstract The Bohr and von Neumann views on the measurement process in quantum mechanics have been interpreted for a long time in somewhat controversial terms, often leading to misconceptions. On the basis of some textual analysis, I would like to show that—contrary to a widespread opinion—their views should be taken less inconsistent, and much closer to each other, than usually thought. As a consequence, I claim that Bohr and von Neumann are conceptually on the same side on the issue of the universality of quantum mechanics: hopefully, this might contribute to a more accurate history of the measurement problem in quantum mechanics.
Abstract In this paper we provide a general account of the causal models which attempt to provide a solution to the famous measurement problem of Quantum Mechanics (QM). We will argue that—leaving aside instrumentalism which restricts the physical meaning of QM to the algorithmic prediction of measurement outcomes—the many interpretations which can be found in the literature can be distinguished through the way they model the measurement process, either in terms of theefficient causeor in terms of thefinal cause. We will discuss and analyze why both, ‘final cause’ and ‘efficient cause’ models, face severe difficulties to solve the measurement problem. In contradistinction to these schemes we will present a new model based on theimmanent causewhich, we will argue, provides an intuitive understanding of the measurement process in QM.
Recent years have seen increased interest towards quantum physics education research, and the topic has been studied from many perspectives both empirically and theoretically. The consensus of previous studies has been that the theory poses an exceptional challenge for learning and teaching, warranting more attention and further research. This dissertation aims to contribute to this discussion by asking what the underlying reasons for these challenges are and how they could potentially be alleviated. On one hand, the topic is approached from an interpretational point of view, considering the ontological foundations of the theory. It is argued that many of the fundamental difficulties in learning and teaching quantum mechanics stem from the ontological foundations of the theory. On the other hand, the historical development and the mathematical structure of the theory are discussed from an educational point of view. The dissertation consists of five articles that explore the above themes from different perspectives. The first study considers the development of one historical formulation of quantum mechanics, namely matrix mechanics. In general, the historical development of quantum theory has been complex and meandering, and its results may seem confusing to students. In our study, we discuss the use of matrix mechanics in quantum mechanics instruction to provide students with a clearer picture of the theory, its historical development, and the relations between its various formulations and used formalisms. The second and third studies add to the discussion on the roles of mathematics in physics and physics education. In quantum mechanics, the role of mathematics is especially pronounced, as the understanding of the theory heavily relies on its mathematical framework. Therefore, we argue that the focus of quantum mechanics instruction should be shifted away from calculational aspects to a more integrated approach that treats the conceptual and mathematical sides of the theory intertwined. In our studies, we provide an overview of the roles assigned to mathematics in previous physics education research literature and present our own layered characterisation of the roles, aiming at diversifying the discussion on the roles of mathematics within the physics education research community and in physics instruction. The fourth and fifth studies empirically examine the challenges of quantum mechanics instruction in the context of an introductory quantum mechanics course. In the fourth study, we explore the effect of initial mathematics knowledge and self-efficacy on student learning, while in the fifth study, we consider the effects of the instructional approach and different teaching strategies on student conceptual knowledge and self-efficacy. The specific focus is on the impact of implementing a new instructional approach, the so-called spin first approach, that emphasises the mathematical basis and conceptual understanding of the theory instead of repeated mathematical calculations. Our results show that the spin-first approach, combined with an active learning model, is able to foster a high level of student self-efficacy and conceptual learning. Quantum mechanics is one of the most successful theories in the history of physics. Nevertheless, learning and teaching its basic principles continue to pose significant challenges for both instructors and students. In this dissertation, we argue for an approach to teaching the theory that places greater emphasis on its mathematical foundations and treats physics and mathematics as intertwined disciplines.
Introduction As the decades of the twentieth century rolled on, quantum mechanics (QM) became more and more sophisticated and mathematical. Understanding what this theory means intuitively was confounded not only by nonclassical concepts such as wave–particle duality and quantum interference, but also by issues to do with observation. The Newtonian classical mechanics (CM) paradigm of reality, wherein reductionist laws of physics describe observer-independent dynamics of systems under observation (SUOs) with observer-independent properties, was found to be inadequate. Quantum theorists were confronted with the measurement problem , which attempts to understand, explain, and rationalize the laws of QM that underpin the processes of observation that go on in the laboratory. They are not the same as those of CM in several puzzling respects. Historically, the first sign of the measurement problem was Planck's quantization of energy (Planck, 1900b) and the second was Bohr's veto on radiation damping in hydrogen (Bohr, 1913). These occurred in the first quarter of the twentieth century, a period in physics often referred to as Old Quantum Mechanics . Another indicator that intuition was inadequate was Born's interpretation of the squared modulus of the Schrödinger wave function as a probability density (Born, 1926). That interpretation has everything to do with observers and observation, because probability without an observer is a vacuous concept. Eventually, the projection-valued measure (PVM) formalism emerged, championed by von Neumann in an influential book on the mathematical formulation of QM (von Neumann, 1955). Subsequently, pioneers such as Ludwig (Ludwig, 1983a,b) and Kraus (Kraus, 1974, 1983) refined the theory into the general positive operator-valued measure (POVM) formalism that we shall discuss and use. The quantized detector network (QDN) approach to quantum experiments is most naturally expressed in the PVM formalism, as QDN focuses on the individual detectors in the laboratory. However, the POVM formalism is more general than the PVM formalism, giving a description of multiple detector processes similar to QDN. This raises the question of how the two approaches, QDN and POVM, are related. The aim of this chapter is to explore this relationship. Before we review the PVM and POVM formalisms, we review some essential mathematical concepts.