Wayne Myrvold

There seems to be a growing consensus that any interpretation of quantum mechanics other than an instrumentalist interpretation will have to abandon the requirement of Lorentz invariance, at least at the fundamental level, preserving at best Lorentz invariance of phenomena. In particular, it is often said that the collapse postulate is incompatible with the demands of relativity. It is the purpose of this paper to argue that such a conclusion is premature, and to defend the view that a covariant account of collapse can be given according to which the state histories yielded by different reference frames are the Lorentz transforms of each other. Objections that have been raised to such a view are considered.

The ambition of this book is a noble one: to provide a counter to the assumption, taken for granted made by many postmodernists, that quantum mechanics lends support to the view that scienti® c realism is nothing more than an outmoded fad. It is especially gratifying that this book comes from a literary theorist, author of a well-respected book on Derrida (Norris, 1987), who, by his own admission, has ª previously published several books on literary theory that might be construed ¼ as going along with the emergent trend towards anti-realism and cultural relativism in various quarters of `advanced’ theoretical debateº (Introduction, p. 1). One wishes, however, that Norris had taken more time to familiarize himself with issues that he writes about, and that he had taken more care in constructing his arguments. Although ª there will be more joy in heaven over one sinner who repents than over ninety-nine righteous persons who need no repentanceº (Luke 15: 7, RSV), we should not let jubilation blind us to the book’ s shortcomings. Among these is a lack of clarity in its central notion, that of realism. Early on, Norris quotes with approval William Alston’ s characterization of the alethic conception of realism, which is the conception advocated by Norris; the alethic conception ª implies that (almost always) what confers a truth-value on a statement is something independent of the cognitive-linguistic goings-on that issued in that statement, including any epistemic status of those goings-onº (p. 41). As the book progresses, however, additional conditions on what is to count as a realist interpretation of quantum mechanics emerge. Realism apparently becomes synonymous with ª causal-explanatoryº theories, and in one passage, Norris goes so far as to suggest that realism entails a commitment to synthetic a priori knowledge of the physical world: Bell’ s calculations and those applied in interpreting the Aspect results are themselves dependentÐ no less than EPRÐ on a range of distinctly ª classicalº assumptions, among them the existence of a physical object-domain which, however puzzling its details, permits such experiments to be carried out and conclusions to be drawn from them..

Once an experiment is done, the observations have been made and the data have been analyzed, what should scientists communicate to the world at large, and how should they do it? This, I will argue, is an intricate question, and one that philosophers can make a contribution to. I will illustrate these points by reference to the debate between Fisher and Neyman & Pearson in the 1950s, which I take to be, at heart, a debate about norms of scientific communication. I will argue that scientists need a richer set of tools for communicating epistemic states that may be very nuanced, and will point to way in which philosophers can contribute.

On April 1, 2016, at the Annual Meeting of the Pacific Division of the American Philosophical Association, a book symposium, organized by Alyssa Ney, was held in honor of David Albert’s After Physics. All participants agreed that it was a valuable and enlightening session. We have decided that it would be useful, for those who weren’t present, to make our remarks publicly available. Please bear in mind that what follows are remarks prepared for the session, and that on some points participants may have changed their minds in light of the ensuing discussion.

This paper addresses the question of how we should regard the probability distributions introduced into statistical mechanics. It will be argued that it is problematic to take them either as purely subjective credences, or as objective chances. I will propose a third alternative: they are "almost objective" probabilities, or "epistemic chances". The definition of such probabilities involves an interweaving of epistemic and physical considerations, and so cannot be classified as either purely subjective or purely objective. This conception, it will be argued, resolves some of the puzzles associated with statistical mechanical probabilities; it explains how probabilistic posits introduced on the basis of incomplete knowledge can yield testable predictions, and it also bypasses the problem of disastrous retrodictions, that is, the fact the standard equilibrium measures yield high probability of the system being in equilibrium in the recent past, even when we know otherwise. As the problem does not arise on the conception of probabilities considered here, there is no need to invoke a Past Hypothesis as a special posit to avoid it.

Landauer’s principle is, roughly, the principle that logically irreversible operations cannot be performed without dissipation of energy, with a specified lower bound on that dissipation. Although widely accepted in the literature on the thermodynamics of computation, it has been the subject of considerable dispute in the philosophical literature. Proofs of the principle have been questioned on the grounds of insufficient generality and on the grounds of the assumption, used in the proofs, of the availability of reversible processes at the microscale. The relevance of the principle, should it be true, has also been questioned, as it has been argued that microscale fluctuations entail dissipation that always greatly exceeds the Landauer bound. In this article Landauer’s principle is treated within statistical mechanics, and a proof of the principle is given that neither relies on neglect of fluctuations nor assumes the availability of thermodynamically reversible processes. In addition, it is argued that microscale fluctuations are no obstacle to approximating thermodynamic reversibility, in the appropriate sense, as closely as one would like.

In this chapter, I urge a fresh look at the problem of explaining equilibration. The process of equilibration, I argue, is best seen not as part of the subject matter of thermodynamics, but as a presupposition of thermodynamics. Further, the relevant tension between the macroscopic phenomena of equilibration and the underlying microdynamics lies not in a tension between time-reversal invariance of the microdynamics and the temporal asymmetry of equilibration, but in a tension between preservation of distinguishability of states at the level of microphysics and the continual effacing of the past at the macroscopic level. This suggests an open systems approach, where the puzzling question is not the erasure of the past, but the question of how reliable prediction, given only macroscopic data, is ever possible at all. I suggest that the answer lies in an approach that has not been afforded sufficient attention in the philosophical literature, namely, one based on the temporal asymmetry of causal explanation.

There is a significant body of literature, which includes Itamar Pitowksy’s “Betting on the outcomes of measurements,” that sheds light on the structure of quantum mechanics, and the ways in which it differs from classical mechanics, by casting the theory in terms of agents’ bets on the outcomes of experiments. Though this approach, by itself, is neutral as to the ontological status of quantum observables and quantum states, some, notably those who adopt the label “QBism” for their views, take this approach as providing incentive to conclude that quantum states represent nothing in physical reality, but, rather, merely encode an agent’s beliefs. In this chapter, I will argue that the arguments for realism about quantum states go through when the probabilities involved are taken to be subjective, if the conclusion is about the agent’s beliefs: an agent whose credences conform to quantum probabilities should believe that preparation procedures with which she associates distinct pure quantum states produce distinct states of reality. The conclusion can be avoided only by stipulation of limitations on the agent’s theorizing about the world, limitations that are not warranted by the empirical success of quantum mechanics or any other empirical considerations. Subjectivists about quantum probabilities should be realists about quantum states.

There is a long tradition, very much alive in the present day, of irrealism about quantum states—that is, of denying that quantum states represent anything in physical reality. In this chapter, I will argue that the grounds we have for taking quantum states to represent physical properties of the systems to which they are ascribed are as strong as the grounds we have for taking atoms or electromagnetic waves to be real and to have something like the properties we ascribe to them. I will take it for granted that we do, indeed, have sufficient grounds for belief in the reality of atoms and electromagnetic waves. It is not my intention to try to convince a committed scientific anti-realist to make an exception for quantum states. The issue at hand is orthogonal to the age-old struggle between scientific realists and anti-realists. My targets here are those who deny that quantum states represent anything in physical reality from a standpoint that holds that one can, indeed, under certain circumstances ascribe reality to entities that are not directly observable, but take it that there are reasons specific to the quantum context for denying ontological import to quantum states.

Much of the evidence for quantum mechanics is statistical in nature. The Everett interpretation, if it is to be a candidate for serious consideration, must be capable of doing justice to reasoning on which statistical evidence in which observed relative frequencies that closely match calculated probabilities counts as evidence in favour of a theory from which the probabilities are calculated. Since, on the Everett interpretation, all outcomes with nonzero amplitude are actualized on different branches, it is not obvious that sense can be made of ascribing probabilities to outcomes of experiments, and this poses a prima facie problem for statistical inference. It is incumbent on the Everettian either to make sense of ascribing probabilities to outcomes of experiments in the Everett interpretation, or to find a substitute on which the usual statistical analysis of experimental results continues to count as evidence for quantum mechanics, and, since it is the very evidence for quantum mechanics that is at stake, this must be done in a way that does not presuppose the correctness of Everettian quantum mechanics. This requires an account of theory confirmation that applies to branching-universe theories but does not presuppose the correctness of any such theory. In this paper, we supply and defend such an account. The account has the consequence that statistical evidence can confirm a branching-universe theory such as Everettian quantum mechanics in the same way in which it can confirm a probabilistic theory.

Andrew Wayne discusses some recent attempts to account, within a Bayesian framework, for the "common methodological adage" that "diverse evidence better confirms a hypothesis than does the same amount of similar evidence". One of the approaches considered by Wayne is that suggested by Howson and Urbach and dubbed the "correlation approach" by Wayne. This approach is, indeed, incomplete, in that it neglects the role of the hypothesis under consideration in determining what diversity in a body of evidence is relevant diversity. In this paper, it is shown how this gap can be filled, resulting in a more satisfactory account of the evidential role of diversity of evidence. In addition, it is argued that Wayne's criticism of the correlation approach does not indicate a serious flaw in the approach

A comparison is made of the traditional Loschmidt and Zermelo objections to Boltzmann's H-theorem, and its simplified variant in the Ehrenfests' 1912 wind-tree model. The little-cited 1896 objection of Zermelo is also analysed. Significant differences between the objections are highlighted, and several old and modern misconceptions concerning both them and the H-theorem are clarified. We give particular emphasis to the radical nature of Poincare's and Zermelo's attack, and the importance of the shift in Boltzmann's thinking in response to the objections as a whole.

There is a long tradition of thinking of thermodynamics, not as a theory of fundamental physics, but as a theory of how manipulations of a physical system may be used to obtain desired effects, such as mechanical work. On this view, the basic concepts of thermodynamics, heat and work, and with them, the concept of entropy, are relative to a class of envisaged manipulations. This article is a sketch and defense of a science of manipulations and their effects on physical systems. I call this science thermo-dynamics, or ΘΔcs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Theta \Delta }^{\text{cs}}$$\end{document}, for short, to highlight that it may be different from the science of thermodynamics, as the reader conceives it. An upshot of the discussion is a clarification of the roles of the Gibbs and von Neumann entropies. Light is also shed on the use of coarse-grained entropies.

Richard Pettigrew has recently advanced a justification of the Principle of Indifference on the basis of a principle that he calls “cognitive conservatism,” or “extreme epistemic conservatism.” However, the credences based on the Principle of Indifference, as Pettigrew formulates it, violate another desideratum, namely, that learning from experience be possible. If it is accepted that learning from experience should be possible, this provides grounds for rejecting cognitive conservatism. Another set of criteria considered by Pettigrew, which involves a weighted mean of worst-case and best-case accuracy, affords some learning, but not the sort that one would expect. This raises the question of whether accuracy-based considerations can be adapted to justify credence functions that permit induction.

The impossibility of an indeterministic evolution for standard relativistic quantum field theories, that is, theories in which all fields satisfy the condition that the generators of space-time translation have spectra in the forward light-cone, is demonstrated. The demonstration proceeds by arguing that a relativistically invariant theory must have a stable vacuum and then showing that stability of the vacuum, together with the requirements imposed by relativistic causality, entails deterministic evolution, if all degrees of freedom are standard degrees of freedom.

In this chapter, I will discuss what it takes for a dynamical collapse theory to provide a reasonable description of the actual world. I will start with discussions of what is required, in general, of the ontology of a physical theory, and then apply it to the quantum case. One issue of interest is whether a collapse theory can be a quantum state monist theory, adding nothing to the quantum state and changing only its dynamics. Although this was one of the motivations for advancing such theories, its viability has been questioned, and it has been argued that, in order to provide an account of the world, a collapse theory must supplement the quantum state with additional ontology, making such theories more like hidden-variables theories than would first appear. I will make a case for quantum state monism as an adequate ontology, and, indeed, the only sensible ontology for collapse theories. This will involve taking dynamical variables to possess, not sharp values, as in classical physics, but distributions of values.

A shift in focus, of the sort recently advocated by David Wallace, towards consideration of work in nonequilibrium statistical mechanics has the potential for far-reaching consequences in the way we think about the foundations of statistical mechanics. In particular, consideration of the approach to equilibrium helps to pick out appropriate equilibrium measures, measures that are picked out by the dynamics as "natural' measures for systems in equilibrium. Consideration of the rationale for using such measures reveals that the scope of their legitimate employment is much more limited than an appeal to a Principle of Indifference would suggest. These points are illustrated by use of a toy model that I call the parabola gadget.