Relative State Research Articles

First Principles Numerical Demonstration of Emergent Decoherent Histories

Within the histories formalism the decoherence functional is a formal tool to investigate the emergence of classicality in isolated quantum systems, yet an explicit evaluation of it from first principles has not been reported. We provide such an evaluation for up to five-time histories based on exact numerical diagonalization of the Schrödinger equation. We find a robust emergence of decoherence for slow and coarse observables of a generic random matrix model and extract a finite-size scaling law by varying the Hilbert space dimension over 4 orders of magnitude. Specifically, we conjecture and observe an exponential suppression of coherent effects as a function of the particle number of the system. This suggests a solution to the preferred basis problem of the many-worlds interpretation (or the set selection problem of the histories formalism) within a minimal theoretical framework without relying on environmentally induced decoherence, quantum Darwinism, Markov approximations, low-entropy initial states, or ensemble averages. Published by the American Physical Society 2024

Freedom in the Many-Worlds Interpretation

I analyze the possibility of free-will in the many-worlds interpretation (MWI), arguing for their compatibility. I use as a starting point Nicolas Gisin’s “The Multiverse Pandemic” (preprint arXiv:2210.05377, 2022, after Gisin, N., “L’épidémie du multivers”, in “Le Plus Grand des Hasards”, Belin, Paris, 2010), in which he makes an interesting case that MWI is contradicted by our hard to deny free-will. The counts he raised are: (1) MWI is deterministic, forcing choices on us, (2) in MWI all our possible choices happen, and (3) MWI limits creativity, because everything is entangled with everything else. I argue that each of these features of MWI is in fact compatible with more freedom than it may seem. In particular, MWI allows compatibilist free-will, but also free-will very much like the libertarian free-will defined by Chisholm. I argue that the position that alternative choices exist as possibilities does not make sense from a physical point of view, but MWI offers a physical ground for alternatives.

Does fine-tuning support the existence of a multiverse?

Abstract In the context of the probabilistic fine-tuning argument for the existence of a divine designer, appeals to the existence of a multiverse have often seemed ad hoc. The situation is rather different though if there is independent evidence from physics for a multiverse. This paper argues that the fate of the fine-tuning argument depends on open questions in fundamental physics and cosmology. It also argues that the many-worlds interpretation of quantum mechanics opens up new routes to undercutting the force of the fine-tuning argument.

Alternate worlds

Two new science-fiction TV series – Constellation and Dark Matter – reveal the problem of using the many-worlds interpretation of quantum mechanics as a fictional device, say Robert P Crease and Jennifer Carter.

Many Worlds and Moral Responsibility

ABSTRACT Moral responsibility is integral to most forms of theism. Yet its coherence as a concept is contingent upon the fulfilment of certain metaphysical conditions. In this paper I argue that (1) the continued existence of the self, and (2) freedom of will and action, are necessary conditions for moral responsibility, particularly within a theistic context. I then argue that the Everett Interpretation of Quantum Mechanics (or, the Many Worlds Interpretation) throws these assumptions into question in new and interesting ways.

Non-separability, locality and criteria of reality: a reply to Waegell and McQueen

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.

The Many-Worlds Interpretation of Quantum Mechanics: Current Status and Relation to Other Interpretations

The Many-Worlds Interpretation of Quantum Mechanics: Current Status and Relation to Other Interpretations

Geometric phases, Everett’s many-worlds interpretation of quantum mechanics, and wormholes

Geometric phases, Everett’s many-worlds interpretation of quantum mechanics, and wormholes

Metaphysical indeterminacy in Everettian quantum mechanics

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.

Incoherent? No, Just Decoherent: How Quantum Many Worlds Emerge

AbstractThe modern Everett interpretation of quantum mechanics describes an emergent multiverse. The goal of this paper is to provide a perspicuous characterisation of how the multiverse emerges making use of a recent account of (weak) ontological emergence. This will be cashed out with a case study that identifies decoherence as the mechanism for emergence. The greater metaphysical clarity enables the rebuttal of critiques due to Baker (2007) and Dawid and Thébault (2015) that cast the emergent multiverse ontology as incoherent; responses are also offered to challenges to the Everettian approach from Maudlin (2010) and Monton (2013).

Существует ли связь между «many-worlds interpretation» и «many minds interpretation» в биокибернетике?

в 1957 году Х. Эверетт представил гипотезу «многомировой динамики» или «мультивселенной». Последние 20 лет появились работы в области «many minds interpretation». При этом делаются попытки соединить эти два научных направления в нечто целое. Фактически речь идет об объединении нейронаук (наук о мозге) с квантовой теорией. Это выполнено на базе эффекта Еськова–Зинченко, т. е. на основе доказательства потери эргодичности биосистем. Именно этот эффект раскрывает сильные и слабые стороны квантовой теории сознания М. Б. Менского. Подчеркнем, что эта теория последние 15 лет никем не обсуждается, хотя она заслуживает особого внимания со стороны нейронаук. in 1957, H. Everett presented the hypothesis of “multi-world dynamics” or “multiverse”. Over the past 20 years, the “many minds interpretation” approach evolved. Also, there are attempts to combine these two scientific paradigms. It is about combining neurosciences (sciences about the brain) with quantum theory. This was done on the basis of the Eskov-Zinchenko effect, i.e. evidence of the loss of ergodicity of biosystems. It is this effect that reveals the strengths and weaknesses of Mensky’s quantum theory of consciousness. We emphasize that this theory was not discussed for the last 15 years, although it deserves special attention from neuroscientists.

Personal Identity and Uncertainty in the Everett Interpretation of Quantum Mechanics

The deterministic nature of EQM (the Everett Interpretation of Quantum Mechanics) seems to be inconsistent with the use of probability in EQM, giving rise to what is known as the “incoherence problem”. In this paper, I explore approaches to solve the incoherence problem of EQM via pre-measurement uncertainty. Previous discussions on the validity of pre-measurement uncertainty have leaned heavily on intricate aspects of the theory of semantics and reference, the embrace of either four-dimensionalism or three-dimensionalism of personhood, or the ontology of EQM. In this paper, I argue that, regardless of the adoption of three-dimensionalism or four-dimensionalism of personhood, the overlapping view or the divergence view of the ontology of EQM, the pre-measurement uncertainty approach to the incoherence problem of EQM can only achive success while contradicting fundamental principles of physicalism. I also use the divergence view of EQM as an example to illustrate my analyses.

An Elementary Proof That Everett’s Quantum Multiverse Is Nonlocal: Bell-Locality and Branch-Symmetry in the Many-Worlds Interpretation

Everett’s many-worlds or multiverse theory is an attempt to find an alternative to the standard Copenhagen interpretation of quantum mechanics. Everett’s theory is often claimed to be local in the Bell sense. Here, we show that this is not the case and debunk the contradictions by analyzing in detail the Greenberger–Horne–Zeilinger (GHZ) nonlocality theorem. We discuss and compare different notions of locality often mixed in the Everettian literature and try to explain the nature of the confusion. We conclude with a discussion of probability and statistics in the many-worlds theory and stress that the strong symmetry existing between branches in the theory prohibits the definition of probability and that the theory cannot recover statistics. The only way out from this contradiction is to modify the theory by adding hidden variables à la Bohm and, as a consequence, the new theory is explicitly Bell-nonlocal.

The Everything-Is-a-Quantum-Wave Interpretation of Quantum Physics

In this paper, I would like to outline what I think is the most natural interpretation of quantum mechanics. By natural, I simply mean that it requires the least amount of excess baggage and that it is universal in the sense that it can be consistently applied to all the observed phenomena, including the universe as a whole. I call it the “Everything is a Quantum Wave” Interpretation (EQWI) because I think this is a more appropriate name than the Many Worlds Interpretation (MWI). The paper explains why this is so.

Delayed-Choice Quantum Erasers and the Einstein-Podolsky-Rosen Paradox

Considering the delayed-choice quantum eraser using a Mach-Zehnder interferometer with a nonsymmetric beam splitter, we explicitly demonstrate that it shares exactly the same formal structure with the Einstein-Podolsky-Rosen-Bohm (EPR-Bohm) experiment. Therefore, the effect of quantum erasure can be understood in terms of the standard EPR correlation. Nevertheless, the quantum eraser still raises a conceptual issue beyond the standard EPR paradox, if counterfactual reasoning is taken into account. Furthermore, the quantum eraser experiments can be classified into two major categories: the entanglement quantum eraser and the Scully-Dr\"uhl-type quantum eraser. These two types are formally equivalent to each other, but conceptually the latter presents a "mystery" more prominent than the former. In the Scully-Dr\"uhl-type quantum eraser, the statement that the which-way information can be influenced by the delayed-choice measurement is not purely a consequence of counterfactual reasoning but bears some factual significance. Accordingly, it makes good sense to say that the "record" of the which-way information is "erased" if the potentiality to yield a conclusive outcome that discriminates the record is eliminated by the delayed-choice measurement. We also reconsider the quantum eraser in the many-worlds interpretation (MWI), making clear the conceptual merits and demerits of the MWI.

On the Cardinality of Future Worldlines in Discrete Spacetime Structures

We give an analysis over a variation of causal sets where the light cone of an event is represented by finitely branching trees with respect to any given arbitrary dynamics. We argue through basic topological properties of Cantor space that under certain assumptions about the universe, spacetime structure and causation, given any event x, the number of all possible future worldlines of x within the many-worlds interpretation is uncountable. However, if all worldlines extending the event x are ‘eventually deterministic’, then the cardinality of the set of future worldlines with respect to x is exactly $$\aleph _0$$ , i.e., countably infinite. We also observe that if there are countably many future worldlines with respect to x, then at least one of them must be necessarily ‘decidable’ in the sense that there is an algorithm which determines whether or not any given event belongs to that worldline. We then show that if there are only finitely many worldlines in the future of an event x, then they are all decidable. We finally point out the fact that there can be only countably many terminating worldlines.

The Open Systems View and the Everett Interpretation

It is argued that those who defend the Everett, or ‘many-worlds’, interpretation of quantum mechanics should embrace what we call the general quantum theory of open systems (GT) as the proper framework in which to conduct foundational and philosophical investigations in quantum physics. GT is a wider dynamical framework than its alternative, standard quantum theory (ST). This is true even though GT makes no modifications to the quantum formalism. GT rather takes a different view, what we call the open systems view, of the formalism; i.e., in GT, the dynamics of systems whose physical states are fundamentally represented by density operators are represented as fundamentally open as specified by an in general non-unitary dynamical map. This includes, in principle, the dynamics of the universe as a whole. We argue that the more general dynamics describable in GT can be physically motivated, that there is as much prima facie empirical support for GT as there is for ST, and that GT could be fully in the spirit of the Everett interpretation—that there might, in short, be little reason for an Everettian not to embrace the more general theoretical landscape that GT allows one to explore.

How Everett Solved the Probability Problem in Everettian Quantum Mechanics

A longstanding issue in the Everettian (Many-Worlds) interpretation is to justify and make sense of the Born rule that underlies the statistical predictions of standard quantum mechanics. The paper offers a reappraisal of Everett’s original account in light of the recent literature on the concept of typicality. It argues that Everett’s derivation of the Born rule is sound and, in a certain sense, even an optimal result, and defends it against the charge of circularity. The conclusion is that Everett’s typicality argument can successfully ground post-factum explanations of Born statistics, while questions remain about the predictive power of the Many-Worlds interpretation.

Defending Many Worlds via Case Discrimination: An Attempt to Showcase the Conceptual Incoherence of Anti-Realist Interpretations and Relational Quantum Mechanics

In this work, an alternative attempt to motivate the Many-Worlds Interpretation (MWI) is undertaken. The usual way of arguing for MWI mostly revolves around how it might solve the measurement problem in a more straightforward and concise manner than rival interpretations. However, here an effort is made to defend MWI in an indirect manner, namely via repeated case discrimination and a process of ‘conceptual elimination’. That is, it will be argued that its major rivals, with QBism and Relational Quantum-Mechanics being among the most noteworthy ones, either face conceptual incoherence or conceptually collapse into a variant of MWI. Finally, it is argued that hidden-variable theories face severe challenges when being applied to Quantum Field Theory such that appropriate modifications may lead back to MWI, thereby purportedly leaving MWI as the only viable option.

Centering the Born Rule

The centered Everett interpretation solves a problem that various approaches to quantum theory face. In this paper, I continue developing the theory underlying that solution. In particular, I defend the centered Everett interpretation against a few objections, and I provide additional motivation for some of its key features.