Research

The question of whether Everettian quantum mechanics (EQM) justifies the existence of metaphysical indeterminacy has recently come to the fore. Metaphysical indeterminacy has been argued to emerge from three sources: coherent superpositions, the indefinite number of branches in the quantum multiverse and the nature of these branches. This paper reviews the evidence and concludes that those arguments don't rely on EQM alone and rest on metaphysical auxiliary assumptions that transcend the physics of EQM. We show how EQM can be ontologically interpreted without positing metaphysical indeterminacy by adopting a deflationary attitude towards branches. Two ways of developing the deflationary view are then proposed: one where branches are eliminated, and another where they are reduced to the universal quantum state.

The principle of least action (PLA) has often been cited as a counterexample to the dominant mode of causal explanation in physics. In particular, PLA seems to involve an appeal to final causes or some other teleological ideology. However, Ben-Menahem (2018) argues that such implications no longer apply given that PLA can be recovered as limiting case from quantum theory. In this paper, I argue that the metaphysical implications of PLA-based explanations are not undermined by its status as derivative. However, I contend that PLA functions as a diachronic constraint that licenses explanations by constraint (Lange, 2016). PLA-based explanations, on this account, are non-causal but also differ from familiar cases of teleological explanations in several respects.

Metaphysical indeterminacy in the context of quantum mechanics is often motivated by the eigenstate-eigenvalue link. However, the sparse view of Glick (2017) illustrates why it has no such implications. Other links connecting quantum states and property ascriptions—such as those associated with the GRW theory—may introduce indeterminacy, but such indeterminacy may be viewed as merely representational and is susceptible to familiar treatments of vagueness. Thus, I contend that such links fail to provide a compelling motivation for quantum metaphysical indeterminacy.

QBism is an agent-centered interpretation of quantum theory. It rejects the notion that quantum theory provides a God’s eye description of reality and claims instead that it imposes constraints on agents’ subjective degrees of belief. QBism’s emphasis on subjective belief has led critics to dismiss it as antirealism or instrumentalism, or even, idealism or solipsism. The aim of this paper is to consider the relation of QBism to scientific realism. I argue that while QBism is an unhappy fit with a standard way of thinking about scientific realism, an alternative conception I call ”perspectival normative realism” may allow for a reconciliation.

Tim Maudlin has claimed that EPR’s Reality Criterion is analytically true. We argue that it is not. Moreover, one may be a subjectivist about quantum probabilities without giving up on objective physical reality. Thus, would-be detractors must reject QBism and other epistemic approaches to quantum theory on other grounds.

John Worrall (1989) famously claimed that structural realism is the best of both worlds; it enables one to endorse the best arguments for scientific realism and antirealism. In this paper, I argue that structural realism also enables one to combine two other seemingly inconsistent positions: realism and pluralism. Indeed, the very features which form the basis of the structural realist's reply to the problem of theory change may be applied synchronically to allow for a pluralist structural realism. The resulting position incorporates a robust variety of scientific pluralism unavailable to the traditional realist and thereby allows the structural realist to take seriously the pluralism apparent in scientific practice.

Quantum entanglement has long been thought to be metaphysically exciting; for example, it is claimed that entanglement shows that Humean supervenience is false; or it inverts the usual dependence of wholes on parts. Some recent trends in the metaphysics of physics attempt to diffuse the puzzle of entanglement by eliminating problematic forms of nonlocality. In this paper we discuss two implementations of this strategy: (1) wavefunction realism and (2) the Humean version of Bohmian mechanics known as "Bohumeanism". In this paper we argue against this general strategy. Accepting the metaphysical consequences of entanglement is healthier and more natural than trying to evade them, for several reasons. First, by refusing to accept anything other than spatiotemporal (for the Bohumean) or quasi-spatiotemporal (for the wavefunction realist) relations as fundamental, both approaches leave hostages to fortune. Second, although they are offered as competing explanations of nonlocal phenomena, no genuine explanation is available in these approaches. By contrast, if one accepts the metaphysical novelty of entanglement, perhaps by interpreting it via an external relation in the fundamental ontology, or countenancing ontological dependence of entangled subsystems on compound entangled systems (dependence of parts on whole, rather than the usual whole-on-parts), then a genuine explanation is available. Thus, what we advocate instead is a genuine metaphysics of entanglement: instead of eliminating nonlocality, develop a metaphysics that accounts for and explains it.

In a recent essay, Oisín Deery and Eddy Nahmias (2017) utilize interventionism about causation to develop an account of causal sourcehood in order to defend compatibilism about free will and moral responsibility from manipulation arguments. In this paper, we criticize Deery and Nahmias’ analysis of sourcehood by drawing a distinction between two forms of causal invariance that can come into conflict on their account. We conclude that any attempt to resolve this conflict will either result in counterintuitive attributions of moral responsibility or will undermine their response to manipulation arguments.

Ontic structural realism (OSR) claims that all there is to the world is structure. But how can this slogan be turned into a worked-out metaphysics? Here I consider one potential answer: a metaphysical framework known as generalism (Dasgupta, 2009, 2016). According to the generalist, the most fundamental description of the world is not given in terms of individuals bearing properties, but rather, general facts about which states of affairs obtain. However, I contend that despite several apparent similarities between the positions, generalism is unable to capture the two main motivations for OSR. I suggest instead that OSR should be construed as a meta-metaphysical position.

Experiments involving delayed-choice entanglement swapping seem to suggest that particles can become entangled after they've already been detected. This astonishing result is taken by some to undermine realism about entanglement. In this paper, I argue that one can offer a fully realist explanation of delayed-choice entanglement swapping by countenancing timelike entanglement relations. I argue that such an explanation—radical though it may be—isn't incoherent and doesn't invite paradox. I compare this approach to the antirealist alternative and a more deflationary realist strategy defended by Egg (2013), each of which face certain challenges. The upshot is that we should take seriously the possibility of timelike entanglement and seek to develop a framework for quantum theory which allows for it.

A growing literature is premised on the claim that quantum mechanics provides evidence for metaphysical indeterminacy. But does it? None of the currently fashionable realist interpretations involve fundamental indeterminacy and the "standard interpretation,"  to the extent that it can be made out, doesn't require indeterminacy either.

In this paper I elicit a prediction from structural realism and compare it, not to a historical case, but to a contemporary scientific theory. If structural realism is correct, then we should expect physics to develop theories that fail to provide an ontology of the sort sought by traditional realists. If structure alone is responsible for instrumental success, we should expect surplus ontology to be eliminated. Quantum field theory (QFT) provides the framework for some of the best confirmed theories in science, but debates over its ontology are vexed. Rather than taking a stand on these matters, the structural realist can embrace QFT as an example of just the kind of theory their view should lead us to expect. Yet, it is not clear that QFT meets the structuralist's positive expectation by providing a structure for the world. In particular, the problem of unitarily inequivalent representations threatens to undermine the possibility of QFT providing a unique structure for the world. In response to this problem, I suggest that the structuralist should endorse pluralism about structure.

John Stachel proposed that quantum mechanics and general relativity share a curious feature: both fail to distinguish "which is which" when it comes to how they represent objects and their properties. This paper is concerned with the metaphysical implications of this feature, which Stachel calls "general permutability" (GP). It has been argued that GP provides support for scientific structuralism, but extant proposal fall short of providing a metaphysical grounding for GP. My own view, "Minimal Structural Essentialism" aims to provide a clear structuralist metaphysics motivated by GP. Roughly, my view is that points and particles have their structural properties essentially. This compels us to view representations related by permutation as equivalent, thus supporting GP. It also serves as an explication of the structuralist image of fundamental objects as principally elements of structure. One surprising consequence of my view is that objects in physics are individuals insofar as they can be individuated by their position in structure.