I address the question whether the wave function in quantum theory exists as a real (ontic) quantity or not. For this purpose, I discuss the essentials of the quantum formalism and emphasize the central role of the superposition principle. I then explain the measurement problem and discuss the process of decoherence. Finally, I address the special features that the quantization of gravity brings into the game. From all of this I conclude that the wave function really exists, that is, it is a real (ontic) feature of Nature.
I address the question whether the wave function in quantum theory exists as a real (ontic) quantity or not. For this purpose, I discuss the essentials of the quantum formalism and emphasize the central role of the superposition principle. I then explain the measurement problem and discuss the process of decoherence. Finally, I address the special features that the quantization of gravity brings into the game. From all of this I conclude that the wave function really exists, that is, it is a real (ontic) feature of Nature.
The wave function gives probabilities, but is it a real physical quantity, as in the ontic interpretation of quantum mechanics, or just a measure of human belief about a physical system, as in an epistemic interpretation? These questions are introduced by treating Schrödinger’s cat and Wigner’s friend. An important question is whether quantum mechanics applies to macroscopic objects, for example, cats. SQUID experiments have been performed that see quantum interference in very large objects, whereas with most macroscopic objects quantum interference disappears because of decoherence. Various views of the meaning of quantum mechanics are discussed: the Copenhagen interpretation, continuous spontaneous localization, Everett’s many-worlds interpretation, Bohm’s hidden-variable model, and quantum Bayesianism. The latter holds that the wave function represents one’s best belief about the state of a quantum system, rather than an actual physical property. This leads to discussions of recent theories and experiments explicitly designed to test wave function reality.
The meaning of the wave function has been a hot topic of debate since the early days of quantum mechanics. Recent years have witnessed a growing interest in this long-standing question. Is the wave function ontic, directly representing a state of reality, or epistemic, merely representing a state of (incomplete) knowledge, or something else? If the wave function is not ontic, then what, if any, is the underlying state of reality? If the wave function is indeed ontic, then exactly what physical state does it represent? In this book, I aim to make sense of the wave function in quantum mechanics and find the ontological content of the theory. The book can be divided into three parts. The first part addresses the question of the nature of the wave function (Chapters 1-5). After giving a comprehensive and critical review of the competing views of the wave function, I present a new argument for the ontic view in terms of protective measurements. In addition, I also analyze the origin of the wave function by deriving the free Schroedinger equation. The second part analyzes the ontological meaning of the wave function (Chapters 6, 7). I propose a new ontological interpretation of the wave function in terms of random discontinuous motion of particles, and give two main arguments supporting this interpretation. The third part investigates whether the suggested quantum ontology is complete in accounting for our definite experience and whether it needs to be revised in the relativistic domain (Chapters 8, 9).
The ontological status of the quantum wavefunction remains one of the most debated questions in quantum theory. While epistemic interpretations regard the wavefunction as a reflection of our knowledge or beliefs, ontic interpretations treat it as a real physical object. In this paper, we argue that epistemic approaches struggle to explain the universality and precision of the uncertainty principle, a core feature of quantum mechanics. By contrast, treating the wave-function as ontic allows a consistent and natural derivation of quantum uncertainty from the mathematical structure of Hilbert space. We examine key interpretations on both sides and highlight why the epistemic view falls short in addressing constraints that appear to be intrinsic to nature.
Two principle concerns prompt some theorists to link quantum mechanics and theories of mind or theories of consciousness. On the one hand, it is commonly thought that conscious minds play some important role in processes of quantum measurement and that any good theory of mind ought to explain how a mind can play such a role. On the other hand, a few people think that the framework of classical physics is not, by itself, sufficiently powerful to explain the myriad remarkable properties of minds and that a good explanation must rely on some special features of quantum mechanics. Usually, these features include either state vector reduction-the collapse of the wave function-or special capabilities, often computational or super-computational ones, allegedly displayed by physical substrates while existing in hypothesised coherent states of linear superposition. Two questions summarise the author's misgivings about both the above motivations for linking quantum mechanics and theories of mind. First, does the process of quantum measurement really require a conscious observer? Second, does quantum mechanics underwrite any special effects in, say, intraneuronal protein lattices, which could play a role in instantiating consciousness in biological systems? It turns out that the particular character of the negative answer suggested for the first question also prompts a negative answer for the second. He summarises these negative answers after describing briefly some popular attempts to forge quantum theories of mind.
The most puzzling issue in the foundations of quantum mechanics is perhaps that of the status of the wave function of a system in a quantum universe. Is the wave function objective or subjective? Does it represent the physical state of the system or merely our information about the system? If the former, does it provide a complete or partial description of the system ? We address these questions mainly from a Bohmian perspective and argue that part of the difficulty in ascertaining the status of the wave function arises from the fact that there are two different sorts of wave functions involved. The most fundamental wave function is that of the universe, which, we argue, has a law-like character. From the wave function of the universe together with its configuration one can define the wave function of a subsystem of the universe. This, although objective, has a strong informational/subjective aspect.
The measurement problem in quantum mechanics (QM) is related to the inability to include learning about the properties of a quantum system by an agent in the formalism of quantum theory. It includes questions about the physical processes behind the measurement, uniqueness, and randomness of obtained outcomes and an ontic or epistemic role of the state. These issues have triggered various interpretations of quantum theory. They vary from refusing any connection between physical reality and a measurement process to insisting that a collapse of the wave-function is real and possibly involves consciousness. On the other hand, the actual mechanism of a measurement is not extensively discussed in these interpretations. This essay attempts to investigate the quantum measurement problem from the position of the scientific consensus. We begin with a short overview of the development of sensing in living organisms. This is performed for the purpose of stressing the relation between reality and our experience. We then briefly present different approaches to the measurement problem in chosen interpretations. We then state three philosophical assumptions for further consideration and present a decomposition of the measurement act into four stages: transformation, conversion, amplification and broadcasting, and, finally, perception. Each of these stages provides an intuition about the physical processes contributing to it. These conclusions are then used in a discussion about, e.g., objectivity, the implausibility of reversing a measurement, or the epistemic status of the wave-function. Finally, we argue that those in favor of some of the most popular interpretations can find an overlap between their beliefs and the consequences of considerations presented here.