Abstract The most common metaphysical consequence claimed of quantum mechanics is indeterminism. But while the GRW theory is indeterministic, Bohm’s theory is fully deterministic. The many-worlds theory is more interesting. What place could there be for probability in a theory in which every possible outcome of a measurement actually occurs? The options for locating uncertainty within a many-worlds ontology are surveyed, and the arguments that probabilities can be assigned to the worlds are critically assessed. The argument that all of us are immortal according to the many-worlds theory is considered and shown to be mistaken. The consequences of quantum mechanics for free will are shown to be minimal.
Abstract The most common metaphysical consequence claimed of quantum mechanics is indeterminism. But while the GRW theory is indeterministic, Bohm’s theory is fully deterministic. The many-worlds theory is more interesting. What place could there be for probability in a theory in which every possible outcome of a measurement actually occurs? The options for locating uncertainty within a many-worlds ontology are surveyed, and the arguments that probabilities can be assigned to the worlds are critically assessed. The argument that all of us are immortal according to the many-worlds theory is considered and shown to be mistaken. The consequences of quantum mechanics for free will are shown to be minimal.
Abstract Is the world deterministic and can we ever know whether it is or is not so? This chapter critically evaluates recent results that bear on these issues, and points out the relation to probabilities. While results from classical physics are neither fully relevant nor conclusive, quantum mechanics is often assumed to establish indeterminism beyond doubt. However, whether the quantum world is indeterministic crucially depends on how the measurement problem is solved. There are both deterministic and indeterministic contenders in this field, some of them empirically equivalent to another one. This is shown using the deterministic Bohm theory and Nelsonsion mechanics, which is indeterministic. Two arguments that purport to establish indeterminism and that rely on Gleason's theorem and on Conway and Kochen's recent Free Will Theorem are shown to be wanting.
Abstract The foundations of quantum mechanics are so contested that it yields few definitive answers to metaphysical questions. So the best we can do is to lay out the various possibilities. The six possibilities considered are as follows: Bohm’s hidden variable theory, particle-only hidden variable theories, the GRW spontaneous collapse theory, spontaneous collapse theories with added three-dimensional ontology, the “flashy” spontaneous collapse theory, and the many-worlds theory. The metaphysical consequences of each of these theories are summarized. Even if quantum mechanics does not settle many ontological questions, it shifts the debate in interesting and fruitful ways. Furthermore, the metaphysical consequences may in some cases reflect back on the tenability of the theories themselves.
The main problem with the many-worlds theory is that it is not clear how the notion of probability should be understood in a theory in which every possible outcome of a measurement actually occurs. In this paper, I argue for the following theses concerning the many-worlds theory: (1) If probability can be applied at all to measurement outcomes, it must function as a measure of an agent's self-location uncertainty. (2) Such probabilities typically violate reflection. (3) Many-worlds branching does not have sufficient structure to admit self-location probabilities. (4) Decision-theoretic arguments do not solve this problem.
Abstract Metaphysicians should pay attention to quantum mechanics, but not because it provides definitive answers to many metaphysical questions. The theory itself is remarkably silent on the nature of the physical world, and the various interpretations of the theory on offer present conflicting ontological pictures. Rather, quantum mechanics is essential to the metaphysician because it reshapes standard metaphysical debates and opens up unforeseen new metaphysical possibilities. Even if quantum mechanics provides few clear answers, there are good reasons to think that any adequate understanding of the quantum world will result in a radical reshaping of our classical worldview in some way or other. Whatever the world is like at the atomic scale, it is almost certainly not the swarm of particles pushed around by forces that is often presupposed. This book guides readers through the theory of quantum mechanics and its implications for metaphysics in a clear and accessible way. The theory and its various interpretations are presented with a minimum of technicality. The consequences of these interpretations for metaphysical debates concerning realism, indeterminacy, causation, determinism, holism, and individuality (among other topics) are explored in detail, stressing the novel form that the debates take given the empirical facts in the quantum domain. While quantum mechanics may not deliver unconditional pronouncements on these issues, the range of possibilities consistent with our knowledge of the empirical world is relatively small—and each possibility is metaphysically revisionary in some way.
A non-relativistic quantum mechanical theory is proposed that describes the universe as a continuum of worlds whose mutual interference gives rise to quantum phenomena. A logical framework is introduced to properly deal with propositions about objects in a multiplicity of worlds. In this logical framework, the continuum of worlds is treated in analogy to the continuum of time points; both “time” and “world” are considered as mutually independent modes of existence. The theory combines elements of Bohmian mechanics and of Everett’s many-worlds interpretation; it has a clear ontology and a set of precisely defined postulates from where the predictions of standard quantum mechanics can be derived. Probability as given by the Born rule emerges as a consequence of insufficient knowledge of observers about which world it is that they live in. The theory describes a continuum of worlds rather than a single world or a discrete set of worlds, so it is similar in spirit to many-worlds interpretations based on Everett’s approach, without being actually reducible to these. In particular, there is no splitting of worlds, which is a typical feature of Everett-type theories. Altogether, the theory explains (1) the subjective occurrence of probabilities, (2) their quantitative value as given by the Born rule, and (3) the apparently random “collapse of the wavefunction” caused by the measurement, while still being an objectively deterministic theory.
Classical physics is generally regarded as deterministic, as opposed to quantum mechanics that is considered the first theory to have introduced genuine indeterminism into physics. We challenge this view by arguing that the alleged determinism of classical physics relies on the tacit, metaphysical assumption that there exists an actual value of every physical quantity, with its infinite predetermined digits (which we name principle of infinite precision). Building on recent information-theoretic arguments showing that the principle of infinite precision (which translates into the attribution of a physical meaning to mathematical real numbers) leads to unphysical consequences, we consider possible alternative indeterministic interpretations of classical physics. We also link those to well-known interpretations of quantum mechanics. In particular, we propose a model of classical indeterminism based on finite information quantities (FIQs). Moreover, we discuss the perspectives that an indeterministic physics could open (such as strong emergence), as well as some potential problematic issues. Finally, we make evident that any indeterministic interpretation of physics would have to deal with the problem of explaining how the indeterminate values become determinate, a problem known in the context of quantum mechanics as (part of) the ``quantum measurement problem.'' We discuss some similarities between the classical and the quantum measurement problems, and propose ideas for possible solutions (e.g., ``collapse models'' and ``top-down causation'').