The GRW dynamics propose a novel, relevantly “observer”-independent replacement for orthodox “measurement”-induced collapse. Yet the tails problem shows that this dynamical innovation is not enough: a principled alternative to the orthodox account demands some corresponding ontological advancement as well. In fact, there are three rival fundamental ontologies on offer for the GRW dynamics. Debate about the relative merits of these candidates is a microcosm of broader disagreement about the role of ontology in our physical theorizing. According to imprimitivists, the GRW (...) dynamics directly describe (only) some (element’s) undulation in an unfamiliar high-dimensional physical field. Primitivists resist this GRW0 proposal on the grounds that it fails to secure comprehensible contact with our data about macroscopic objects in ordinary lowdimensional space-time. They expect an adequate fundamental ontology to include at least some spatiotemporally localized entities—intuitively, concrete constituents of our familiar macroscopic landscape. The most compelling case goes by way of distributional basing: minimally, primitivists expect a theory’s predictions immediately about spatiotemporal distributions of fundamental entities to provide a supervenience base for data about configurations of macroscopic objects. But while the background intuition is familiar, the distributional model is surprisingly subtle. Lack of clarity about its details generates serious confusion for both sides of our debate. (shrink)

Scientific realism is the view that our best scientific theories can be regarded as (approximately) true. This is connected with the view that science, physics in particular, and metaphysics could (and should) inform one another: on the one hand, science tells us what the world is like, and on the other hand, metaphysical principles allow us to select between the various possible theories which are underdetermined by the data. Nonetheless, quantum mechanics has always been regarded as, at best, puzzling, if (...) not contradictory. As such, it has been considered for a long time at odds with scientific realism, and thus a naturalized quantum metaphysics was deemed impossible. Luckily, now we have many quantum theories compatible with a realist interpretation. However, scientific realists assumed that the wave-function, regarded as the principal ingredient of quantum theories, had to represent a physical entity, and because of this they struggled with quantum superpositions. In this paper I discuss a particular approach which makes quantum mechanics compatible with scientific realism without doing that. In this approach, the wave-function does not represent matter which is instead represented by some spatio-temporal entity dubbed the primitive ontology: point-particles, continuous matter fields, space-time events. I argue how within this framework one develops a distinctive theory-construction schema, which allows to perform a more informed theory evaluation by analyzing the various ingredients of the approach and their inter-relations. (shrink)

It has been argued that the transition from classical to quantum mechanics is an example of a Kuhnian scientific revolution, in which there is a shift from the simple, intuitive, straightforward classical paradigm, to the quantum, convoluted, counterintuitive, amazing new quantum paradigm. In this paper, after having clarified what these quantum paradigms are supposed to be, I analyze whether they constitute a radical departure from the classical paradigm. Contrary to what is commonly maintained, I argue that, in addition to radical (...) quantum paradigms, there are also legitimate ways of understanding the quantum world that do not require any substantial change to the classical paradigm. (shrink)

The primary quantum mechanical equation of motion entails that measurements typically do not have determinate outcomes, but result in superpositions of all possible outcomes. Dynamical collapse theories (e.g. GRW) supplement this equation with a stochastic Gaussian collapse function, intended to collapse the superposition of outcomes into one outcome. But the Gaussian collapses are imperfect in a way that leaves the superpositions intact. This is the tails problem. There are several ways of making this problem more precise. But many authors dismiss (...) the problem without considering the more severe formulations. Here I distinguish four distinct tails problems. The first (bare tails problem) and second (structured tails problem) exist in the literature. I argue that while the first is a pseudo-problem, the second has not been adequately addressed. The third (multiverse tails problem) reformulates the second to account for recently discovered dynamical consequences of collapse. Finally the fourth (tails problem dilemma) shows that solving the third by replacing the Gaussian with a non-Gaussian collapse function introduces new conflict with relativity theory. (shrink)

This paper defends the idea that there must be some joints in reality, some correct way to classify or categorize it. This may seem obvious, but we will see that there are at least three conventionalist arguments against this idea, as well as philosophers who have found them convincing. The thrust of these arguments is that the manner in which we structure, divide or carve up the world is not grounded in any natural, genuine boundaries in the world. Ultimately they (...) are supposed to pose a serious threat to realism. The first argument that will be examined concerns the claim that there are no natural boundaries in reality, the second one focuses on the basis of our classificatory schemes, which the conventionalist claims to be merely psychological, and the third considers the significance of our particular features in carving up the world, such as physical size and perceptual capabilities. The aim of this paper is to demonstrate that none of these objections succeed in undermining the existence of genuine joints in reality. (shrink)

The priority monist holds that the cosmos is the only fundamental object, of which every other concrete object is a dependent part. One major argument against monism goes back to Russell, who claimed that pluralism is favoured by common sense. However, Jonathan Schaffer turns this argument on its head and uses it to defend priority monism. He suggests that common sense holds that the cosmos is a whole, of which ordinary physical objects are arbitrary portions, and that arbitrary portions depend (...) for their existence on the existence of the whole. In this paper, we challenge Schaffer’s claim that the parts of the cosmos are all arbitrary portions. We suggest that there is a way of carving up the universe such that at least some of its parts are not arbitrary. We offer two arguments in support of this claim. First, we shall outline semantic reasons in its favour: in order to accept that empirical judgements are made true or false by the way the world is, one must accept that the cosmos includes parts whose existence is not arbitrary. Second, we offer an ontological argument: in order for macro-physical phenomena to exist, there must be some micro-physical order which they depend upon, and this order must itself be non-arbitrary. We conclude that Schaffer’s common sense argument for monism cannot be made to work. (shrink)

There is a recurring line of argument in the literature to the effect that Bohm's theory fails to solve the measurement problem. I show that this argument fails in all its variants. Hence Bohm's theory, whatever its drawbacks, at least succeeds in solving the measurement problem. I briefly discuss a similar argument that has been raised against the GRW theory.

In collapse theories of quantum mechanics such as the GRW theory, the measurement result is represented by the post-measurement state which is still a superposition of different result branches, although the modulus squared of the amplitude of one result branch is close to one. This leads to the tails problem. In this paper, I present a new analysis of the tails problem of collapse theories, and suggest a more complete solution to the problem. First, I argue that the tails problem (...) exists not only in collapse theories, but also in Everett's theory and even in Bohm's theory. Moreover, I point out that the tails problem has two levels: the physical and mental levels, which may be called the objective and subjective tails problems, respectively. One needs to analyze not only the connection between high modulus-squared values and macro-existence, but also the connection between these values and our experience of macro-existence. Second, I briefly review the existing solutions to the objective and subjective tails problems. I argue that although the objective tails problem may be solved more directly, one needs to further investigate the psychophysical connection in order to solve the subjective tails problem. Third, I analyze how the mental state of an observer is determined by her wave function in collapse theories. It is argued that the mental content of an observer is related to the amplitude of each result branch of the superposition she is physically in, and it may be composed of all possible results. Moreover, it is conjectured that the modulus squared of the amplitude of each result branch may determine the vividness of the part of the mental content containing the result. Finally, I argue that this vividness conjecture may help solve the subjective tails problem of collapse theories. (shrink)

The pairing argument aims to demonstrate the impossibility of non-spatial objects (including minds) standing in causal relations. Its chief premises are (roughly) that causation requires pairing relations between causes and effects and that pairing relations require spatial relations. Critics have argued that the first claim suffers from counterexamples involving indeterministic causation. After briefly rehearsing the pairing argument and the objection from indeterministic causation, I offer two ways of revising the pairing argument to meet the objection from indeterministic causation.

In this paper I wish to connect the recent debate in the philosophy of quantum mechanics concerning the nature of the wave function to the historical debate in the philosophy of science regarding the tenability of scientific realism. Being realist about quantum mechanics is particularly challenging when focusing on the wave function. According to the wave function ontology approach, the wave function is a concrete physical entity. In contrast, according to an alternative viewpoint, namely the primitive ontology approach, the wave (...) function does not represent physical entities. In this paper, I argue that the primitive ontology approach can naturally be interpreted as an instance of the so-called ‘explanationism’ realism, which has been proposed as a response to the pessimistic-meta induction argument against scientific realism. If my arguments are sound, then one could conclude that: (1) contrarily to what is commonly though, if explanationism realism is a good response to the pessimistic-meta induction argument, it can be straightforwardly extended also to the quantum domain; (2) the primitive ontology approach is in better shape than the wave function ontology approach in resisting the pessimistic-meta induction argument against scientific realism. (shrink)

The Mass Density approach to GRW (GRWm for short) has been widely discussed in the quantum foundations literature. A crucial feature of GRWm is the introduction of a Criterion of Accessibility for mass, which allows to explain the determinacy of experimental outcomes thus also addressing the tails problem of GRW. However, the Criterion of Accessibility leaves the ontological meaning of the non-accessible portion of mass utterly unexplained. In this paper I discuss two viable approaches to non-accessible mass, which I call (...) anti-realist and realist, and will defend the latter. First, I show that the anti-realist approach suffers from various objections. Second, I develop an account of non-accessible mass density states as objectively indeterminate states of affairs. (shrink)