Abstract A common understanding of both the many-worlds theory and the original version of the GRW theory holds that they are ontologically monistic, postulating only the existence of the wavefunction and nothing else. Sometimes an appeal to Occam's razor is used to promote this as a boon for these theories. But without more detailed argumentation, it is hard to see how such an austere ontology can make comprehensible contact with the experimental facts that inspired the development of quantum theory in the first place, or indeed with our whole pre-theoretical picture of the physical world.
Abstract A common understanding of both the many-worlds theory and the original version of the GRW theory holds that they are ontologically monistic, postulating only the existence of the wavefunction and nothing else. Sometimes an appeal to Occam's razor is used to promote this as a boon for these theories. But without more detailed argumentation, it is hard to see how such an austere ontology can make comprehensible contact with the experimental facts that inspired the development of quantum theory in the first place, or indeed with our whole pre-theoretical picture of the physical world.
Is wave function monism, the view that the wave function completely \ndescribes physical objects, a sensible view? GRW, one candidate \nto solve the measurement problem, might be taken to be an \nexample of such view. I argue in this paper that it not so obviously \nso. I first show that a bare version of wave function monism is impossible, \nand even if one can construct monistic theories with additional \nrules (but no additional ontologies), they are not to be taken seriously. \nInstead, a preferable choice is that of a quantum theory in which physical \nobjects are represented by entities in three–dimensional space or \nin four-dimensional space-time.
Abstract The three major interpretations of quantum mechanics—Bohm, GRW, and many worlds—all treat the wave function as a physical entity. But this entity apparently resides in a high-dimensional configuration space, with three coordinates for each particle in the universe. Some conclude on this basis that the three-dimensionality of the world of experience is an illusion. Others respond by adding three-dimensional ontology to the theory or by reinterpreting the wave function either as a law or as an indirect representation of properties in three-dimensional space. It is argued that the latter possibility makes it unnecessary to postulate either additional ontology or a fundamentally high-dimensional world.
Abstract What does realism about the quantum state imply? What follows when quantum theory is applied without restriction, if need be, to the whole universe? These are the questions which are debated in this book. All the chapters start from the point of realism, and based on the need, or the aspiration, for a theory that unites micro- and macroworlds, at least in principle. But the further claim argued by some is that if you allow the Schrödinger equation unrestricted application, supposing the quantum state to be something physically real, then this universe is one of countlessly many others, constantly branching in time, all of which are real. The result is the many worlds theory, also known as the Everett interpretation of quantum mechanics. The contrary claim sees this picture of many worlds as in no sense inherent in quantum mechanics, even when the latter is allowed unrestricted scope and even given that the quantum state itself is something physically real. For this picture of branching worlds fails to make physical sense, let alone common sense, even on its own terms. The status of these worlds, what they are made of, is never adequately explained. Ordinary ideas about time and identity over time become hopelessly compromised. The concept of probability itself is brought into question. This picture of many branching worlds is inchoate, it is a vision, an error. There are realist alternatives to many worlds, some even that preserve the Schrödinger equation unchanged. Twenty chapters, accompanied by commentaries and discussions, examine these claims and counterclaims in depth. They focus first on the question of ontology, the existence of worlds, second on the interpretation of probability, and third on alternatives or additions to many worlds. The introduction offers a helpful guide to the arguments for the Everett interpretation, particularly as they have been formulated in the last two decades.
Abstract This article provides an overview of the philosophical literature on the GRW theory of quantum mechanics, and argues for a particular position regarding that literature. Much of the literature is ontological; it attempts to defend a conception of what the world is like according to the GRW theory against perceived competitors. I argue that there is no real debate here, since these supposedly conflicting positions are better regarded as alternative and compatible ways of describing the world of the GRW theory.
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).
Abstract Although the basic approach of the many-worlds interpretation is that the ontology of our universe is a unitarily evolving highly entangled wavefunction, we live in a world in which we only perceive a tiny part of the global wavefunction, and the quantum state corresponding to our world does not evolve unitarily, making our world an effectively open system. Recently, the common approach that within a world conservation laws hold only for an ensemble of measurements was questioned. This chapter analyses how this can affect viewing worlds as open systems and proposes a possible resolution of the unitarity puzzle.