Editorial

5 pages, 199 KiB

Open AccessEditorial

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

by Lev Vaidman

Quantum Rep. 2024, 6(2), 142-146; https://doi.org/10.3390/quantum6020011 - 18 Apr 2024

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This is a preface to a Special Issue of Quantum Reports devoted to the results of the workshop “The Many-Worlds Interpretation of Quantum Mechanics: Current Status and Relation to Other Interpretations” [...] Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

Research

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13 pages, 321 KiB

Open AccessArticle

Personal Identity and Uncertainty in the Everett Interpretation of Quantum Mechanics

by Zhonghao Lu

Quantum Rep. 2023, 5(3), 584-596; https://doi.org/10.3390/quantum5030038 - 11 Sep 2023

Viewed by 1298

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

16 pages, 430 KiB

Open AccessArticle

Teleportation Revealed

by Charles Alexandre Bédard

Quantum Rep. 2023, 5(2), 510-525; https://doi.org/10.3390/quantum5020034 - 13 Jun 2023

Viewed by 2079

Abstract

Quantum teleportation is the name of a problem: How can the real-valued parameters encoding the state at Alice’s location make their way to Bob’s location via shared entanglement and only two bits of classical communication? Without an explanation, teleportation appears to be a [...] Read more.

Quantum teleportation is the name of a problem: How can the real-valued parameters encoding the state at Alice’s location make their way to Bob’s location via shared entanglement and only two bits of classical communication? Without an explanation, teleportation appears to be a conjuring trick. Investigating the phenomenon with Schrödinger states and reduced density matrices shall always leave loose ends because they are not local and complete descriptions of quantum systems. Upon demonstrating that the Heisenberg picture admits a local and complete description, Deutsch and Hayden rendered its explanatory power manifest by revealing the trick behind teleportation, namely, by providing an entirely local account. Their analysis is re-exposed and further developed. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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14 pages, 561 KiB

Open AccessArticle

Quantum Probability from Temporal Structure

by Michael Ridley

Quantum Rep. 2023, 5(2), 496-509; https://doi.org/10.3390/quantum5020033 - 12 Jun 2023

Viewed by 2234

Abstract

The Born probability measure describes the statistics of measurements in which observers self-locate themselves in some region of reality. In

ψ

-ontic quantum theories, reality is directly represented by the wavefunction. We show that quantum probabilities may be identified using fractions of a [...] Read more.

The Born probability measure describes the statistics of measurements in which observers self-locate themselves in some region of reality. In

ψ

-ontic quantum theories, reality is directly represented by the wavefunction. We show that quantum probabilities may be identified using fractions of a universal multiple-time wavefunction containing both causal and retrocausal temporal parts. This wavefunction is defined in an appropriately generalized history space on the Keldysh time contour. Our deterministic formulation of quantum mechanics replaces the initial condition of standard Schrödinger dynamics, with a network of ‘fixed points’ defining quantum histories on the contour. The Born measure is derived by summing up the wavefunction along these histories. We then apply the same technique to the derivation of the statistics of measurements with pre- and postselection. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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8 pages, 276 KiB

Open AccessArticle

The Open Systems View and the Everett Interpretation

by Michael E. Cuffaro and Stephan Hartmann

Quantum Rep. 2023, 5(2), 418-425; https://doi.org/10.3390/quantum5020027 - 28 Apr 2023

Viewed by 2087

Abstract

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. [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

11 pages, 471 KiB

Open AccessArticle

How Everett Solved the Probability Problem in Everettian Quantum Mechanics

by Dustin Lazarovici

Quantum Rep. 2023, 5(2), 407-417; https://doi.org/10.3390/quantum5020026 - 26 Apr 2023

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Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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14 pages, 271 KiB

Open AccessArticle

Centering the Born Rule

by Isaac Wilhelm

Quantum Rep. 2023, 5(1), 311-324; https://doi.org/10.3390/quantum5010021 - 21 Mar 2023

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Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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15 pages, 335 KiB

Open AccessArticle

Everett’s Interpretation and Convivial Solipsism

by Hervé Zwirn

Quantum Rep. 2023, 5(1), 267-281; https://doi.org/10.3390/quantum5010018 - 10 Mar 2023

Cited by 2 | Viewed by 1458

Abstract

I show how the quantum paradoxes occurring when we adopt a standard realist framework (or a framework in which the collapse implies a physical change of the state of the system) vanish if we abandon the idea that a measurement is related (directly [...] Read more.

I show how the quantum paradoxes occurring when we adopt a standard realist framework (or a framework in which the collapse implies a physical change of the state of the system) vanish if we abandon the idea that a measurement is related (directly or indirectly) to a physical change of state. In Convivial Solipsism, similarly to Everett’s interpretation, there is no collapse of the wave function. However, contrary to Everett’s interpretation, there is only one world. This also allows us to get rid of any non-locality and to provide a solution to the Wigner’s friend problem and its more recent versions. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

16 pages, 300 KiB

Open AccessArticle

Set Theory and Many Worlds

by Paul Tappenden

Quantum Rep. 2023, 5(1), 237-252; https://doi.org/10.3390/quantum5010016 - 02 Mar 2023

Cited by 1 | Viewed by 1689

Abstract

The 2022 Tel Aviv conference on the many-worlds interpretation of quantum mechanics highlighted many differences between theorists. A very significant dichotomy is between Everettian fission (splitting) and Saunders–Wallace–Wilson divergence. For fission, an observer may have multiple futures, whereas for divergence they always [...] Read more.

The 2022 Tel Aviv conference on the many-worlds interpretation of quantum mechanics highlighted many differences between theorists. A very significant dichotomy is between Everettian fission (splitting) and Saunders–Wallace–Wilson divergence. For fission, an observer may have multiple futures, whereas for divergence they always have a single future. Divergence was explicitly introduced to resolve the problem of pre-measurement uncertainty for Everettian theory, which is universally believed to be absent for fission. Here I maintain that there is indeed pre-measurement uncertainty prior to fission, so long as objective probability is a property of Everettian branches. This is made possible if the universe is a set and branches are subsets with a probability measure. A universe that is a set of universes that are macroscopically isomorphic and span all possible configurations of local beäbles fulfills that role. If objective probability is a property of branches, then a successful Deutsch–Wallace decision-theoretic argument would justify the Principal Principle and be part of probability theory rather than specific to many-worlds theory. Any macroscopic object in our environment becomes a set of isomorphs with different microscopic configurations, each in an elemental universe (elemental in the set-theoretic sense). This is similar to the many-interacting-worlds theory, but the observer inhabits the set of worlds, not an individual world. An observer has many elemental bodies. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

9 pages, 385 KiB

Open AccessArticle

The Ontology of the Many-Worlds Theory

by Per Arve

Quantum Rep. 2023, 5(1), 228-236; https://doi.org/10.3390/quantum5010015 - 01 Mar 2023

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Abstract

It is shown that the wavefunction describes our observations using the postulate that relates position to the distribution

{| Ψ |}^{2}

. This finding implies that a primary ontology is unnecessary. However, what is real is not directly represented by the wavefunction [...] Read more.

It is shown that the wavefunction describes our observations using the postulate that relates position to the distribution

{| Ψ |}^{2}

. This finding implies that a primary ontology is unnecessary. However, what is real is not directly represented by the wavefunction but by the gauge invariants. In light of the presented ontology, Spacetime State Realism becomes not a fundamental ontology but derived. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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4 pages, 213 KiB

Open AccessArticle

The MWI and Distributive Justice

by David Papineau and Thomas Rowe

Quantum Rep. 2023, 5(1), 224-227; https://doi.org/10.3390/quantum5010014 - 28 Feb 2023

Viewed by 1129

Abstract

Everettians generally argue that their view recommends just the same rational choices as orthodoxy. In this note, however, we will show that Everettians should advocate non-standard choices in one specific kind of situation, namely situations where different people have unequal claims to an [...] Read more.

Everettians generally argue that their view recommends just the same rational choices as orthodoxy. In this note, however, we will show that Everettians should advocate non-standard choices in one specific kind of situation, namely situations where different people have unequal claims to an indivisible good. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

12 pages, 505 KiB

Open AccessArticle

Consistent Histories and Many Worlds

by Tomasz Bigaj

Quantum Rep. 2023, 5(1), 186-197; https://doi.org/10.3390/quantum5010012 - 23 Feb 2023

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Abstract

This paper discusses the fundamental assumptions and background of the consistent histories (CH) approach to quantum mechanics. The focus of the paper is on the concept of frameworks. It is proposed that frameworks should be interpreted objectively as observer-independent realities. Two further options [...] Read more.

This paper discusses the fundamental assumptions and background of the consistent histories (CH) approach to quantum mechanics. The focus of the paper is on the concept of frameworks. It is proposed that frameworks should be interpreted objectively as observer-independent realities. Two further options are considered: a hidden-variables variant of the CH approach, and a many-worlds version, which considers each individual history belonging to a given family as describing a separate world. The latter interpretation is subsequently compared and contrasted with the standard many-worlds interpretation. Finally, the solution to the measurement problem offered by the many-worlds variant of CH is analyzed and amended. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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30 pages, 2091 KiB

Open AccessArticle

Local Quantum Theory with Fluids in Space-Time

by Mordecai Waegell

Quantum Rep. 2023, 5(1), 156-185; https://doi.org/10.3390/quantum5010011 - 21 Feb 2023

Cited by 1 | Viewed by 1634

Abstract

In 1948, Schwinger developed a local Lorentz-covariant formulation of relativistic quantum electrodynamics in space-time which is fundamentally inconsistent with any delocalized interpretation of quantum mechanics. An interpretation compatible with Schwinger’s theory is presented, which reproduces all of the standard empirical predictions of conventional [...] Read more.

In 1948, Schwinger developed a local Lorentz-covariant formulation of relativistic quantum electrodynamics in space-time which is fundamentally inconsistent with any delocalized interpretation of quantum mechanics. An interpretation compatible with Schwinger’s theory is presented, which reproduces all of the standard empirical predictions of conventional delocalized quantum theory in configuration space. This is an explicit, unambiguous, and Lorentz-covariant “local hidden variable theory” in space-time, whose existence proves definitively that such theories are possible. This does not conflict with Bell’s theorem because it is a local many-worlds theory. Each physical system is characterized by a wave-field, which is a set of indexed piece-wise single-particle wavefunctions in space-time, each with its own coefficient, along with a memory which contains the separate local Hilbert-space quantum state at each event in space-time. Each single-particle wavefunction of a fundamental system describes the motion of a portion of a conserved fluid in space-time, with the fluid decomposing into many classical point particles, each following a world-line and recording a local memory. Local interactions between two systems take the form of local boundary conditions between the differently indexed pieces of those systems’ wave-fields, with new indexes encoding each orthogonal outcome of the interaction. The general machinery is introduced, including the local mechanisms for entanglement and interference. The experience of collapse, Born rule probability, and environmental decoherence are discussed, and a number of illustrative examples are given. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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14 pages, 374 KiB

Open AccessArticle

The Relation between Wavefunction and 3D Space Implies Many Worlds with Local Beables and Probabilities

by Ovidiu Cristinel Stoica

Quantum Rep. 2023, 5(1), 102-115; https://doi.org/10.3390/quantum5010008 - 08 Feb 2023

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Abstract

We show that the quantum wavefunctional can be seen as a set of classical fields on the 3D space aggregated by a measure. We obtain a complete description of the wavefunctional in terms of classical local beables. With this correspondence, classical explanations of [...] Read more.

We show that the quantum wavefunctional can be seen as a set of classical fields on the 3D space aggregated by a measure. We obtain a complete description of the wavefunctional in terms of classical local beables. With this correspondence, classical explanations of the macro level and of probabilities transfer almost directly to the quantum. A key difference is that, in quantum theory, the classical states coexist in parallel, so the probabilities come from self-location uncertainty. We show that these states are distributed according to the Born rule. The coexistence of classical states implies that there are many worlds, even if we assume the collapse postulate. This leads automatically to a new version of the many-worlds interpretation in which the major objections are addressed naturally. We show that background-free quantum gravity provides additional support for this proposal and suggests why branching happens toward the future. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

22 pages, 346 KiB

Open AccessArticle

Many-Worlds: Why Is It Not the Consensus?

by Valia Allori

Quantum Rep. 2023, 5(1), 80-101; https://doi.org/10.3390/quantum5010007 - 06 Feb 2023

Viewed by 2787

Abstract

In this paper, I argue that the many-worlds theory, even if it is arguably the mathematically most straightforward realist reading of quantum formalism, even if it is arguably local and deterministic, is not universally regarded as the best realist quantum theory because it [...] Read more.

In this paper, I argue that the many-worlds theory, even if it is arguably the mathematically most straightforward realist reading of quantum formalism, even if it is arguably local and deterministic, is not universally regarded as the best realist quantum theory because it provides a type of explanation that is not universally accepted. Since people disagree about what desiderata a satisfactory physical theory should possess, they also disagree about which explanatory schema one should look for in a theory, and this leads different people to different options. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

8 pages, 663 KiB

Open AccessFeature PaperArticle

Why the Many-Worlds Interpretation?

by Lev Vaidman

Quantum Rep. 2022, 4(3), 264-271; https://doi.org/10.3390/quantum4030018 - 04 Aug 2022

Cited by 6 | Viewed by 4054

Abstract

A brief (subjective) description of the state of the art of the many-worlds interpretation of quantum mechanics (MWI) is presented. It is argued that the MWI is the only interpretation which removes action at a distance and randomness from quantum theory. Limitations of [...] Read more.

A brief (subjective) description of the state of the art of the many-worlds interpretation of quantum mechanics (MWI) is presented. It is argued that the MWI is the only interpretation which removes action at a distance and randomness from quantum theory. Limitations of the MWI regarding questions of probability which can be legitimately asked are specified. The ontological picture of the MWI as a theory of the universal wave function decomposed into a superposition of world wave functions, the important parts of which are defined in three-dimensional space, is presented from the point of view of our particular branch. Some speculations about misconceptions, which apparently prevent the MWI from being in the consensus, are mentioned. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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Review

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25 pages, 396 KiB

Open AccessReview

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

by Michael Huber

Quantum Rep. 2023, 5(2), 345-369; https://doi.org/10.3390/quantum5020023 - 18 Apr 2023

Cited by 1 | Viewed by 1563

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

Other

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6 pages, 235 KiB

Open AccessOpinion

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

by Vlatko Vedral

Quantum Rep. 2023, 5(2), 475-480; https://doi.org/10.3390/quantum5020031 - 06 Jun 2023

Viewed by 2951

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Many-Worlds Interpretation of Quantum Mechanics)

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