How should we characterise the observable aspects of quantum theory? This paper argues that philosophers and physicists should jettison a standard dogma: that observables must be represented by self-adjoint or Hermitian operators. Four classes of non-standard observables are identified: normal operators, symmetric operators, real-spectrum operators, and none of these. The philosophical and physical implications of each are explored.

In this paper I am concerned with analyzing in detail how ideas and expectations regarding the role of time in quantum theory arose and evolved in the early years of quantum mechanics. The general theme is that expectations which seemed reasonable from the point of view of matrix mechanics and Dirac's q-number formalism became implausible in light of Dirac-Jordan transformation theory, and were dashed by von Neumann's Hilbert space formalism which came to replace it. Nonetheless, I will identify two concerns (...) that remain relevant today, and which blunt the force of Hilgevoord's claim that the demand that time feature as an observable arose as the result of a simple conceptual error. (shrink)

How long does a quantum particle take to traverse a classically forbidden energy barrier? In other words, what is the correct expression for quantum tunnelling time? This seemingly simple question has inspired widespread debate in the physics literature. I argue that we should not expect the orthodox interpretation of quantum mechanics to provide a unique correct expression for quantum tunnelling time, because to do so it would have to provide a unique correct answer to a question whose assumptions are in (...) tension with its core interpretational commitments. I explain how this conclusion connects to time’s special status in quantum mechanics, the meaningfulness of classically inspired concepts in different interpretations of quantum mechanics, the prospect of constructing experimental tests to distinguish between different interpretations, and the status of weak measurement in resolving questions about the histories of subensembles. (shrink)

The idea that the quantum probabilities are best construed as the personal/subjective degrees of belief of Bayesian agents is an old one. In recent years the idea has been vigorously pursued by a group of physicists who fly the banner of quantum Bayesianism. The present paper aims to identify the prospects and problems of implementing QBism, and it critically assesses the claim that QBism provides a resolution of some of the long-standing foundations issues in quantum mechanics, including the measurement problem (...) and puzzles of nonlocality. (shrink)

This thesis is composed of three essays on the perdurantist approach to persistence and identity over time. In Chapter 1, I discuss how the following papers are to be understood as parts of a unified perdurantist account of persistence over time. This chapter also outlines some of my philosophical assumptions and provides some background information about the metaphysics of persistence. In Chapter 2, I respond to the objection that the worm theory is unable to account for our intuitions about ordinary (...) counting sentences. I do this by invoking the standard linguistic phenomenon of covert quantifier domain restriction and supplementing the worm theory with situation semantics. My version of the worm theory makes our intuitive judgements come out true, and it does so well enough that there is no need to adopt the stage theory or revisionary theories of counting. Furthermore, my version of the worm theory offers a unified account of event- and object-related counting. Chapter 3 focuses on a commonly neglected difference between different kinds of perdurantism, which are differences in mereological priority. I discuss three different views: parts-first perdurantism, no-priority perdurantism, and wholes-first perdurantism. I briefly outline all three views and some of the motivations for each of them. I fend off objections from and motivations for no-priority perdurantism. I also contend that intraperdurantist debates about phenomenology ought not to be framed with respect to these forms of perdurantism. Instead, I suggest that the relativity of simultaneity presents an interesting scenario for parts-first and wholes-first perdurantists. I respond to Thomas Pashby’s arguments against the doctrine of temporal parts in Chapter 3. Pashby argues that metaphysicians ought to give an account of how quantum systems persist over time and that nonrelativistic quantum mechanics is incompatible with perdurantism. I contend that his arguments rely on controversial, non-standard assumptions about the existence and importance of time observables. I demonstrate that perdurantists have no problem giving an account of how quantum systems persist over time in reference to an external time parameter. Finally, I conclude with a summary of my arguments and some thoughts about directions for future research. (shrink)

This paper provides a general method for defining a generalized quantum observable that supplies properly normalized conditional probabilities for the time of occurrence. This method treats the time of occurrence as a probabilistic variable whose value is to be determined by experiment and predicted by the Born rule. This avoids the problematic assumption that a question about the time at which an event occurs must be answered through instantaneous measurements of a projector by an observer, common to both Rovelli and (...) Oppenheim et al.. I also address the interpretation of experiments purporting to demonstrate the quantum Zeno effect, used by Oppenheim et al. to justify an inherent uncertainty for measurements of times. (shrink)