The purpose of this book is to explain Quantum Bayesianism ('QBism') to "people without easy access to mathematical formulas and equations" (4-5). Qbism is an interpretation of quantum mechanics that "doesn't meddle with the technical aspects of the theory [but instead] reinterprets the fundamental terms of the theory and gives them new meaning" (3). The most important motivation for QBism, enthusiastically stated on the book's cover, is that QBism provides "a way past quantum theory's paradoxes and puzzles" such that much of the weirdness associated with quantum theory "dissolves under the lens of QBism". Could a non-technical book that almost fits in your pocket really succeed in resolving the notorious paradoxes of quantum theory? I believe the answer is: not in this case. There are three primary reasons. Firstly, the argument that QBism solves quantum paradoxes is not convincing. Secondly, it proves difficult to pin down exactly what QBism says. Thirdly, as a scientific theory QBism seems explanatorily inert, which is maybe why the topic of scientific explanation is not broached. Sections 2-4 below discuss each of these problems in turn. However, there is still a wealth of insights that make this book a worthwhile read, and I shall begin with those.
The purpose of this book is to explain Quantum Bayesianism ('QBism') to "people without easy access to mathematical formulas and equations" (4-5). Qbism is an interpretation of quantum mechanics that "doesn't meddle with the technical aspects of the theory [but instead] reinterprets the fundamental terms of the theory and gives them new meaning" (3). The most important motivation for QBism, enthusiastically stated on the book's cover, is that QBism provides "a way past quantum theory's paradoxes and puzzles" such that much of the weirdness associated with quantum theory "dissolves under the lens of QBism". Could a non-technical book that almost fits in your pocket really succeed in resolving the notorious paradoxes of quantum theory? I believe the answer is: not in this case. There are three primary reasons. Firstly, the argument that QBism solves quantum paradoxes is not convincing. Secondly, it proves difficult to pin down exactly what QBism says. Thirdly, as a scientific theory QBism seems explanatorily inert, which is maybe why the topic of scientific explanation is not broached. Sections 2-4 below discuss each of these problems in turn. However, there is still a wealth of insights that make this book a worthwhile read, and I shall begin with those.
Measured by the accuracy of its predictions and the scope of its technological applications, quantum mechanics is one of the most successful theories in science--as well as one of the most misunderstood. The deeper meaning of quantum mechanics remains controversial almost a century after its invention. Providing a way past quantum theory's paradoxes and puzzles, QBism offers a strikingly new interpretation that opens up for the nonspecialist reader the profound implications of quantum mechanics for how we understand and interact with the world. Short for Quantum Bayesianism, QBism adapts many of the conventional features of quantum mechanics in light of a revised understanding of probability. Bayesian probability, unlike the standard "frequentist probability," is defined as a numerical measure of the degree of an observer's belief that a future event will occur or that a particular proposition is true. Bayesianism's advantages over frequentist probability are that it is applicable to singular events, its probability estimates can be updated based on acquisition of new information, and it can effortlessly include frequentist results. But perhaps most important, much of the weirdness associated with quantum theory--the idea that an atom can be in two places at once, or that signals can travel faster than the speed of light, or that Schrodinger's cat can be simultaneously dead and alive--dissolves under the lens of QBism. Using straightforward language without equations, Hans Christian von Baeyer clarifies the meaning of quantum mechanics in a commonsense way that suggests a new approach to physics in general.
Measured by the accuracy of its predictions and the scope of its technological applications, quantum mechanics is one of the most successful theories in science—as well as one of the most misunderstood. The deeper meaning of quantum mechanics remains controversial almost a century after its invention. Providing a way past quantum theory’s paradoxes and puzzles, QBism offers a strikingly new interpretation that opens up for the nonspecialist reader the profound implications of quantum mechanics for how we understand and interact with the world. Short for Quantum Bayesianism, QBism adapts many of the conventional features of quantum mechanics in light of a revised understanding of probability. Bayesian probability, unlike the standard “frequentist probability,” is defined as a numerical measure of the degree of an observer’s belief that a future event will occur or that a particular proposition is true. Bayesianism’s advantages over frequentist probability are that it is applicable to singular events, its probability estimates can be updated based on acquisition of new information, and it can effortlessly include frequentist results. But perhaps most important, much of the weirdness associated with quantum theory—the idea that an atom can be in two places at once, or that signals can travel faster than the speed of light, or that Schrödinger’s cat can be simultaneously dead and alive—dissolves under the lens of QBism. Using straightforward language without equations, Hans Christian von Baeyer clarifies the meaning of quantum mechanics in a commonsense way that suggests a new approach to physics in general.
Abstract The approach to quantum mechanics that we present in this book aligns fairly well with the QBist position in quantum foundations, which takes quantum mechanics as describing the interaction of an agent with the world: A theory mainly offers a way for the agent to manage her expectations about the outcomes of her interactions, not a picture of what nature is really like. We introduce QBism briefly and situate the framework within a range of options for integrating agency and quantum mechanics. We agree with QBism on many fundamental issues, but we do not subscribe to QBism wholesale. We agree with QBism’s pragmatic outlook that takes scientific theories to be tools for agents to use, and with the QBist goal of developing a participatory realism. But we are critical of the particular idealisations that QBism in its present form subscribes to. Most importantly, we are critical of the structural choice not to resolve the agent nor the world in any detail. In our view, scientific agents learn by modelling. Models are tools that agents can use and develop in dealing with the world. Guided by concrete examples, we describe a scientific modelling framework that allows for loops of three different degrees of difficulty and complexity. These range from quantum state updating, which neatly fits the QBist approach of working within a fixed probability space, via a broader class of updates including so-called Hamiltonian learning, up to the most difficult cases in which true scientific creativity is at play. All three levels of difficulty need to be acknowledged for a full picture of real scientific agency. At the end of the chapter, we describe the project of modelling scientific agency itself, which leads to the topics of Chaps. 5 and 6 .
Fuchs and Peres (2000) claimed that standard Quantum Mechanics needs no interpretation. In this essay, I show the flaws of the arguments presented in support to this thesis. Specifically, it will be claimed that the authors conflate QM with Quantum Bayesianism (QBism) - the most prominent subjective formulation of quantum theory; thus, they endorse a specific interpretation of the quantum formalism. Secondly, I will explain the main reasons for which QBism should not be considered a physical theory, being it concerned exclusively with agents' beliefs and silent about the physics of the quantum regime. Consequently, the solutions to the quantum puzzles provided by this approach cannot be satisfactory from a physical perspective. In the third place, I evaluate Fuchs and Peres arguments contra the non-standard interpretations of QM, showing again the fragility of their claims. Finally, it will be stressed the importance of the interpretational work in the context of quantum theory.
The interpretation of quantum mechanics known as QBism developed out of efforts to understand the probabilities arising in quantum physics as Bayesian in character. But this development was neither easy nor without casualties. Many ideas voiced, and even committed to print, during earlier stages of Quantum Bayesianism turn out to be quite fallacious when seen from the vantage point of QBism. I trace the history of what we might call “proto-QBism” becoming QBism proper, showing that the process was one of becoming consistently Jamesian. But William James and phenomenology are evolutionary cousins, and so guided by QBism's history, I will sketch ways in which phenomenological turns may be inspirational for future developments in the QBist project. The prize, I will argue, would be if phenomenology can evoke a new technical development in the reconstruction of quantum theory or the understanding of the classical limit.
QBism may be the most significant contribution to the search for meaning in quantum mechanics since Bohr, even as Bohr's philosophy remains the most significant revision of Kant's theory of science. There are two ironies here. Bohr failed to realize the full extent of the affinity of his way of thinking with Kant's, and QBists fail to realize the full extent of their agreement with Bohr. While Bohr's discovery of contextuality updates Kant's transcendental philosophy in a way that leaves the central elements of the latter intact, Kant's insight into the roles that our cognitive faculties play in constructing physical theories can considerably alleviate the difficulties that Bohr's writings present to his readers. And while throwing a QBist searchlight on Bohr's writings can further alleviate these difficulties (as well as reveal the presence in them of the salient elements of QBist thought), Bohr's writings can in turn provide answers to important questions that QBism leaves unanswered (and also allay some of QBism's excesses). In the final sections I confront the two most impenetrable mysteries yet unearthed: making sense of quantum mechanics, and the dual mystery of making sense of (i) the existence of consciousness in a seemingly material world and (ii) the existence in consciousness of a seemingly material world. Here the relevant arguments are framed in the context of the philosophy of the Upanishads, according to which we (as Schrödinger put it) "are all really only various aspects of the One." There is no world that exists out of relation to consciousness, but there are different poises of consciousness. In particular, there is a poise of consciousness peculiar to the human species at this point in time, and there are poises of consciousness that are yet to evolve (and that may be essential to averting the calamities towards which humanity appears to be heading).