Using a 'reformulation of Bell's theorem', Waegell and McQueen, (2020) argue that any local theory which does not involve retro-causation or fine-tuning must be a many-worlds theory. Moreover they argue that non-separable many-worlds theories whose ontology is given by the wavefunction involve superluminal causation, as opposed to separable many-worlds theories (e.g. Waegell, 2021; Deutsch and Hayden 2000). I put forward three claims. (A) I challenge their argument for relying on a non-trivial, unquestioned assumption about elements of reality which allows Healey's approach (Healey, 2017b) to evade their claim. In an attempt to respond to (A), Waegell and McQueen may restrict their claim to theories which satisfy such an assumption, however, I also argue that (B) their argument fails to prove even the so weakened claim, as exemplified by theories that are both non-separable and local. Finally, (C) by arguing for the locality of the decoherence-based Everettian approach (Wallace, 2012) I refute Waegell and McQueen's claim that wavefunction-based ontologies, and more generally non-separable ontologies, involve superluminal causation. I close with some doubtful remarks about separable Everettian interpretations as compared to non-separable ones.
Using a 'reformulation of Bell's theorem', Waegell and McQueen, (2020) argue that any local theory which does not involve retro-causation or fine-tuning must be a many-worlds theory. Moreover they argue that non-separable many-worlds theories whose ontology is given by the wavefunction involve superluminal causation, as opposed to separable many-worlds theories (e.g. Waegell, 2021; Deutsch and Hayden 2000). I put forward three claims. (A) I challenge their argument for relying on a non-trivial, unquestioned assumption about elements of reality which allows Healey's approach (Healey, 2017b) to evade their claim. In an attempt to respond to (A), Waegell and McQueen may restrict their claim to theories which satisfy such an assumption, however, I also argue that (B) their argument fails to prove even the so weakened claim, as exemplified by theories that are both non-separable and local. Finally, (C) by arguing for the locality of the decoherence-based Everettian approach (Wallace, 2012) I refute Waegell and McQueen's claim that wavefunction-based ontologies, and more generally non-separable ontologies, involve superluminal causation. I close with some doubtful remarks about separable Everettian interpretations as compared to non-separable ones.
An apparently emerging consensus holds that Everettian Quantum Mechanics (EQM), in the Spacetime State Realism (SSR) version of Wallace and Timpson, involves ontological non-locality (i.e., non-separability) but is fully compatible with the dynamical notion of locality usually taken to be required by relativity. The claim of dynamical locality is based on the fact that the local beables postulated by the theory (namely, Reduced Density Matrices, RDMs, associated with localized regions) are not affected by interventions outside their past light cones. However, the theory's non-separability means that it posits non-local beables (namely RDMs for non-localized regions) in addition to the local ones. We argue here that the involvement of non-local beables introduces complications for extant formulations of dynamical locality and at least suggests, contrary to the emerging consensus, that SSR EQM should perhaps not be considered compatible with relativistic causality after all.
Bell's theorem establishes that a local and spatially separable physical theory with no superdeterminism or retrocausality must be a theory of many local worlds. The local many worlds formalism of quantum mechanics is a transparent separable physical theory in spacetime with a Lorentz covariant causal structure. Unlike the Everett many worlds interpretation, there is no nonseparable universal wavefunction in configuration space, but like Everett, there is only local unitary evolution which conserves probability (fluid) current, and no wavefunction collapse. Each event in spacetime has its own local wavefunction which is built up using only the local wavefunctions and local unitary evolution operators within its past light cone, and which is entirely disconnected from spacelike separated local wavefunctions. We call this the local Schrödinger picture. Local many worlds can also be described in the Heisenberg picture by ascribing Deutsch-Hayden (DH) descriptors to each individual system, each of which evolves under local unitary operations. Both the local wavefunctions and DH descriptors contain records of past interactions, and while the local wavefunctions provide a clear and intuitive physical narrative, the descriptors contain all of the same information in a much more compact form. Unfortunately, the compact form is also somewhat cryptic, which has made the local Heisenberg picture relatively inaccessible. The purpose of this article is to show that the local wavefunctions for any N-qubit system can always be constructed directly from the DH descriptors, allowing us to combine the benefits of both pictures.
n their contribution to this book, McQueen and Vaidman argue that common sense requires that explanations in physics be not only causal1 but also local. Their main claim is that the Many Worlds Interpretation (MWI) of quantum mechanics (originally due to Everett) provides local explanations of the outcomes of experiments that in other interpretations of quantum mechanics seem to require (some sort of) nonlocality. Particles in the MWI leave traces both in the world where they exist but also in other worlds in which they do not exist. So the explanation is said to be local because spacetime splits together with the particles so that there is no influence at space-like separation within a world, but the causal influence literally travels across ‘parallel’ worlds. This seems to stretch the concept of locality beyond common sense, if not beyond breaking point, even if one understands causation weakly in terms of counterfactual dependence rather than by straightforward physical interaction.
Bell's Theorem demonstrates that factorizable theories for the EPR experiment (EPR) cannot reproduce the quantum correlations. Factorizability is motivated by various locality conditions. So to understand the nature of nonlocality in EPR, we first need to understand the conceptual relations between factorizability, these various locality conditions and the nature of the quantum correlations. That is the main focus of my thesis. My main conclusion is that these conceptual relations are more subtle than the literature has usually suggested. Chapter 1 is a general introduction. In Chapter 2, I review the general framework of factorizable stochastic theories for EPR. I argue that factorizability can be motivated by various locality conditions, even in theories that admit time-dependent states and take the measurement interactions to be neither instantaneous, nor simultaneous. In Chapter 3, I focus on Cartwright' s (1989) and Humphreys' (1989) theories of probabilistic causation for singular events, which are based on modifications of traditional causal linear modelling. I argue (against Cartwright) that local models for EPR in the framework of these theories are committed to factorizability; and so they cannot reproduce the EPR correlations. In Chapter 4, I turn to Stochastic-Einstein Locality (SEL). Hellman (1982) proposed that SEL with some provisos characterizes the No-Superluminal-Action (NSA) of the Special Theory of Relativity (STR), and he argued that SEL is not violated in EPR. Butterfield (1994) proposed that SEL (without Hellman's provisos) characterizes the lack of superluminal Lewisian causation, and he argued that SEL is violated in EPR. I argue that SEL (without Hellman's provisos) is motivated by NSA and spatiotemporal separability. Thus, the violation of SEL might arise from the failure of spatiotemporal separability. And this failure is compatible with NSA and superluminal Lewisian causation. Accordingly, Hellman's and Butterfield's views need not be in tension. In Chapter 5, I focus on the implications for nonlocality of Jarrett's (1984) analysis of factorizability into "locality" and "completeness". I argue that although this analysis cannot distinguish between failures of factorizability which are compatible with STR and those which are not, it is significant for clarifying the implications of Bell's theorem for nonlocality. In Chapter 6, I qmsider three arguments that are intended to deny superluminal causal propagation in EPR, and a fourth argument that is intended to establish the opposite conclusion. I argue that in various ways these arguments have gone wrong. Three of these argument rely on implicit assumptions that have been overlooked. Accordingly, two of them reached a reasonable conclusion, i.e. the failure of separability, for the wrong reasons; whereas the third reached a wrong conclusion, i.e. that the failure of the contiguity of causal processes explains the failure of factorizability in EPR. The fourth relies on a wrong assumption, and thus it reaches a too strong conclusion, that the EPR correlations require superluminal action. My main conclusion is that the quantum correlations require nonseparability . In Chapter 7, I focus on decision theory in the context of EPR. In both EPR and the famous Newcomb's problem (NewProb), there are unscreenable-off correlations. I argue that NewProb can be related to EPR, in the sense that a NewProb can be realized by that experiment.
Bell's theorem is commonly understood as showing that no theory satisfying the relevant locality and separability assumptions can reproduce all quantum correlations. The result is often interpreted as forcing a choice among nonlocality, rejection of hidden variables, denial of measurement independence, or revision of the ontology of quantum systems. This paper develops a philosophy-facing interpretation of Bell correlations within the Geometric Monism (GM) framework. GM models quantum entities as continuous torsional standing-wave structures embedded in a 5-dimensional geometric manifold governed by a universal Planck Stiffness \(\kT=c^4/G\). The central proposal is that Bell-type correlations are best understood, within GM, not as superluminal influences between independent particles, but as boundary projections of a single non-separable geometric entity. The paper does not dispute Bell's theorem, nor does it propose a controllable signaling mechanism. Instead, it examines which ontological assumption fails if entangled systems are not fundamentally composed of separable particle-like subsystems. In GM, an entangled pair is represented as a globally constrained torsional structure whose localized detection events occur at 4-dimensional measurement boundaries. On this view, Bell factorizability fails because the joint system is not decomposable into two independent local beables connected only by a shared hidden variable. The relevant ontology is one continuous non-separable entity with multiple boundary-accessible nodes. The analysis compares GM with standard interpretations of Bell's theorem, including local hidden-variable theories, Bohmian mechanics, Everettian approaches, and operational no-signaling views. It argues that GM occupies a distinct philosophical position: it accepts Bell's mathematical result, preserves no-signaling, rejects point-particle separability, and interprets quantum correlations as arising from continuous geometric non-separability. The paper is intended as a philosophy of physics proposal, not as a replacement for the quantum formalism or a completed physical derivation of Bell correlations.
Abstract This chapter defends the idea that the Everett (many-worlds) interpretation is, given Hamiltonians with only local interactions, dynamically local at both the level of fundamental and emergent ontology. At the level of fundamental ontology because the complete state of a given spacetime region will be fixed by the complete state on a spacelike hypersurface that obstructs the past light cone of that first region. At the level of emergent ontology because the dynamics of the emergent ontology will be grounded in the dynamics of the fundamental ontology. If the world-notion in the many-worlds interpretation is understood in terms of emergent ontology, then it will follow that the dynamical locality holds also at the level of worlds. Our picture pairs dynamical locality with kinematical nonlocality (non-separability). The chapter articulates how the demands of Lorentz covariance are fully satisfied in this picture. In our view, failure of kinematical locality is a harmless, indeed beneficial (if nonclassical), feature and it coexists with dynamical locality and Lorentz covariance. It has sometimes been suggested that—along the lines indicated by Deutsch and Hayden—seeking a kinematically local theory is nonetheless to be preferred or is, perhaps, required. The chapter revisits and restates some of our previous arguments to the effect that reintroducing kinematical locality in this way is both unnecessary and undesirable: the benefits of the move, such as they are, are not worth the costs.