Richard Feynman famously declared, "I think that I can safely say that nobody really understands quantum mechanics." Sean Carroll lamented the persistence of this sentiment in a recent opinion piece entitled, "Even Physicists Don't Understand Quantum Mechanics. Worse, they don't seem to want to understand it." Quantum mechanics is arguably the greatest achievement of modern science and by and large we absolutely understand quantum theory. Rather, the "understanding" to which these two statements evidently refer concerns the ontological status of theoretical constructs. For example, "Do quantum wave functions accurately depict physical reality?" The quantum measurement problems represents a collection of such queries and the conundrums to which they lead. Most physicists are content with foregoing such metaphysical issues, falling back on Bohr's Copenhagen interpretation, and then get on with the business of doing physics. I suspect that Carroll would criticize these physicists as being too dismissive of the wonderful mysteries of quantum mechanics by relegating its role to that of an algorithm for making predictions. Quite to the contrary, I maintain that those who still pursue a resolution to the measurement problem are burdened with a classical view of reality and fail to truly embrace the fundamental quantum aspects of nature.
By means of the examples of classical and Bohmian quantum mechanics, we illustrate the well-known ideas of Boltzmann as to how one gets from laws defined for the universe as a whole to dynamical relations describing the evolution of subsystems. We explain how probabilities enter into this process, what quantum and classical probabilities have in common and where exactly their difference lies.
This is an extended essay review of Tanya and Jeffrey Bub's Totally Random: Why Nobody Understands Quantum Mechanics: A serious comic on entanglement. Princeton and Oxford: Princeton University Press (2018), ISBN: 9780691176956, 272 pp., 7x10 in., 254 b/w illus., £18.99 / $22.95 (paperback). We review the philosophical aspects of the book, provide suggestions for instructors on how to use the book in a class setting, and evaluate the authors' artistic choices in the context of comics theory.
In this study, I argue that the future is not open if quantum mechanics is complete. An open future means that the value observed when measuring a physical quantity in the future is not determined. At first glance, quantum mechanics seems to support the open future thesis, because it cannot always predict measurement value with certainty. However, many interpretations regard quantum mechanics as deterministic. These interpretations only suggest that the quantum mechanical world can be deterministic. I argue that, although quantum mechanics cannot predict the future with certainty, the quantum …
There are reasons to doubt that making sense of the wave function (other than as a probability algorithm) will help with the project of making sense of quantum mechanics. The consistency of the quantum-mechanical correlation laws with the existence of their correlata is demonstrated. The demonstration makes use of the fact (which is implied by the indeterminacy principle) that physical space is not partitioned "all the way down," and it requires that the eigenvalue-eigenstate link be replaced by a different interpretive principle, whose implications are explored.
If you have a restless intellect, it is very likely that you have played at some point with the idea of investigating the meaning and conceptual foundations of quantum mechanics. It is also probable (albeit not certain) that your intentions have been stopped on their tracks by an encounter with some version of the "Shut up and calculate" command. You may have heard that everything is already understood. That understanding is not your job. Or, if it is, it is either impossible or very difficult. Maybe somebody explained to you that physics is concerned with "hows" and not with "whys"; that whys…
What is Physics For? Why Classical Physics is not the Limit of Quantum Mechanics
University of Rochester（罗切斯特大学）；Universidade Federal do Rio de Janeiro（里约热内卢联邦大学）；École Normale Supérieure / CNRS（巴黎高等师范学院/法国国家科学研究中心）；Linköping University（林雪平大学）；Dartmouth College（达特茅斯学院）；University of Sydney（悉尼大学）
Christopher Fuchs and Rüdiger Schack have developed a way of understanding science, which, among other things, resolves many of the conceptual puzzles of quantum mechanics that have vexed people for the past nine decades. They call it QBism. I speculate on how John Bell might have reacted to QBism, and I explain the many ways in which QBism differs importantly from the orthodox ways of thinking about quantum mechanics associated with the term "Copenhagen interpretation."
We provide a novel perspective on "regularity" as a property of representations of the Weyl algebra. In Part I, we critiqued a proposal by Halvorson [2004, "Complementarity of representations in quantum mechanics", Studies in History and Philosophy of Modern Physics 35(1), pp. 45--56], who advocates for the use of the non-regular "position" and "momentum" representations of the Weyl algebra. Halvorson argues that the existence of these non-regular representations demonstrates that a quantum mechanical particle can have definite values for position or momentum, contrary to a widespread view. In…
We provide a novel perspective on "regularity" as a property of representations of the Weyl algebra. We first critique a proposal by Halvorson [2004, "Complementarity of representations in quantum mechanics", Studies in History and Philosophy of Modern Physics 35(1), pp. 45--56], who argues that the non-regular "position" and "momentum" representations of the Weyl algebra demonstrate that a quantum mechanical particle can have definite values for position or momentum, contrary to a widespread view. We show that there are obstacles to such an intepretation of non-regular representations. In Par…
A new quantum ontology of quantum mechanics has been proposed recently. This ontology is based on impossible to realize measurements which need to be performed repeatedly on the same single physical system or on the same pair of physical systems. We agree that quantum mechanics is a contextual theory and that the experimental contexts have to be a part of any description of quantum phenomena but in our opinion this new ontology is neither convincing nor useful. In particular the authors claim that their ontology explains the peaceful coexistence between quantum mechanics and relativity in spin…
We present a discussion of the extended Wigner's friend thought experiment proposed by Frauchiger and Renner in [1]. We show by using various arguments, including textbook quantum mechanics and the ontological approach of Contexts, Systems, Modalities (CSM), that no contradiction arises if one admits that agents must agree on what is considered as a system and what is not. In such a contextually objective approach of quantum mechanics, the apparent contradiction is automatically removed. We also discuss why this mutual agreement between agents is already implicit in the standard formulations o…
A recent Nature Physics editorial (Nat. Phys. (2022) 18, 961) falsely claims ``any theory that uses hidden variables still requires non-local physics.'' We correct this claim and explain why it is important to get this right.
Quantum Bayesianism, or QBism, is a recent development of the epistemic view of quantum states, according to which the state vector represents knowledge about a quantum system, rather than the true state of the system. QBism explicitly adopts the subjective view of probability, wherein probability assignments express an agent's personal degrees of belief about an event. QBists claim that most if not all conceptual problems of quantum mechanics vanish if we simply take a proper epistemic and probabilistic perspective. Although this judgement is largely subjective and logically consistent, I exp…
Using a very simple Gedankenexperiment, I remind the reader that (contrary to what happens in classical mechanics) the energy of a quantum system is inevitably increased just by performing (some) textbook measurements on it. As a direct conclusion, this means that some measurements require the expenditure of a finite amount of energy to be carried out. I also argue that this makes it very difficult to regard measurements as disembodied, immaterial, informational operations, and it forces us to look at them as physical processes just like any other one.
In-principle restrictions on the amount of information that can be gathered about a system have been proposed as a foundational principle in several recent reconstructions of the formalism of quantum mechanics. However, it seems unclear precisely why one should be thus restricted. We investigate the notion of paradoxical self-reference as a possible origin of such epistemic horizons by means of a fixed-point theorem in Cartesian closed categories due to F. W. Lawvere that illuminates and unifies the different perspectives on self-reference.
I analyze the meaning of mass in Newtonian mechanics. First, I explain the notion of primitive ontology, which was originally introduced in the philosophy of quantum mechanics. Then I examine the two common interpretations of mass: mass as a measure of the quantity of matter and mass as a dynamical property. I claim that the former is ill-defined, and the latter is only plausible with respect to a metaphysical interpretation of laws of nature. I explore the following options for the status of laws: Humeanism, primitivism about laws, dispositionalism, and ontic structural realism.
In this brief note I address the question not frequently asked, namely, why did it take two decades between Einstein's first proposal of photons and derivation of the full Planck formula from first principles of Statistical Mechanics, albeit with a fundamental new approach to counting of states. Secondly, why did it fall to an independent inquirer, S. N. Bose, in far away Dacca to arrive at the correct derivation of this formula, arguably a most crucial one of the first half of the twentieth century? Reasonable hypotheses are proposed for answers to both. I also argue that the timing of Bose's…
A brief (subjective) description of the state of the art of the many-worlds interpretation of quantum mechanics (MWI) is presented. It is argued that the MWI is the only interpretation which removes action at a distance and randomness from quantum theory. Limitations of the MWI regarding questions of probability which can be legitimately asked are specified. The ontological picture of the MWI as a theory of the universal wave function decomposed into a superposition of world wave functions, the important parts of which are defined in three-dimensional space, is presented from the point of view…
We still lack any consensus about what one is actually talking about as one uses quantum mechanics. There is a gap between the abstract terms in which the theory is couched and the phenomena the theory enables each of us to account for so well. Because it has no practical consequences for how we each use quantum mechanics to deal with physical problems, this cognitive dissonance has managed to coexist with the quantum theory from the very beginning. The absence of conceptual clarity for almost a century suggests that the problem might lie in some implicit misconceptions about the nature of sci…
Symmetries have a crucial role in today's physics. In this thesis, we are mostly concerned with time reversal invariance (T-symmetry). A physical system is time reversal invariant if its underlying laws are not sensitive to the direction of time. There are various accounts of time reversal transformation resulting in different views on whether or not a given theory in physics is time reversal invariant. With a focus on quantum mechanics, I describe the standard account of time reversal and compare it with my alternative account, arguing why it deserves serious attention. Then, I review three k…
The wave function in quantum mechanics presents an interesting challenge to our understanding of the physical world. In this paper, I show that the wave function can be understood as four intrinsic relations on physical space. My account has three desirable features that the standard account lacks: (1) it does not refer to any abstract mathematical objects, (2) it is free from the usual arbitrary conventions, and (3) it explains why the wave function has its gauge degrees of freedom, something that are usually put into the theory by hand. Hence, this account has implications for debates in phi…
This paper develops a number of quantum mechanical characterisations of Stern-Gerlach. It discusses areas of vagueness in their formulation. Philosophers criticise quantum mechanics for unacceptable vagueness in connection with the measurement problem. The quantum formulation problems identified by this paper go beyond the locus of philosophical criticism. It concludes with an open question, are some areas of vagueness in quantum mechanics more acceptable philosophically than others and, if so, why?
We address the issue of the interpretation of quantum mechanics by asking why the issue never arises in the description of high-energy interactions. We argue that several tenets of quantum mechanics, specifically the collapse of the wave function, follow directly once one accepts the essential randomness of fundamental interaction events. We then show that scale separation of fundamental interactions ensures that decoherent measurement can be unambiguously separated from the random quantum events. Finally, we argue that the fundamental symmetries of space and time guarantee the existence of a …
Albert Einstein made fundamental contributions to the development of quantum mechanics. However, he was never satisfied with the quantum worldview. In fact, during most of his life he attempted to find inconsistencies and paradoxes within quantum mechanics. His famous quote "God does not play dice" shows how disturbing was to Einstein one of the most important aspects of quantum mechanics: non-determinism. In this paper we will present the basic concepts of quantum mechanics, we will describe Einstein's attempts to destroy it and we will discuss why we can nowadays state that, in this regard, …
