# Why the Many-Worlds Interpretation?

^{1}

^{2}

## Abstract

**:**

## 1. Introduction

## 2. The MWI Is the Only Solution of the Measurement Problem without Action at a Distance

## 3. The MWI Is the Most Economical Quantum Theory Regarding the Theory’s Laws

## 4. The Paradoxes of the Quantum Theory Are Resolved in the Framework of the MWI Interpretation

## 5. Conceptual Changes in Our Approach to a Scientific Theory That Should Be Made When We Accept the World Splitting Structure of the Universe

## 6. What Is a “World” in the MWI?

A world is the totality of macroscopic objects: stars, cities, people, grains of sand, etc., in a definite classically described state.

## 7. Connection between Our Experience and the Universal Wave Function

## 8. The (Illusion of) Probability in the MWI

## 9. What Might Be the Reasons for the MWI Not Being in a Consensus?

## 10. Conclusions

- (a)
- The lack of action at a distance is a huge physical advantage which is not present in other interpretations;
- (b)
- Determinism is a huge philosophical advantage which is not considered as such due to an error in the evolution of science (apparently explained by not seeing a deterministic option for physics for too long);
- (c)
- The MWI allows us to view physics in three spatial dimensions within the particular world of the MWI we live in (however, we should not disregard nonlocality of entanglement which requires the configuration space for its description);
- (d)
- Our world defines our world wave function (the alleged preferred basis problem) and the difficult emergence program does not need a solution;
- (e)
- There is only an illusion of probability of outcomes of quantum measurements. It naturally leads to an effective Born Rule via measures of existence of worlds (and can be given an ignorance probability meaning as the probability of self-location in a particular world). Quantum worlds, contrary to classical worlds, might have measures of existence which are not just zero or one.

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

- Vaidman, L. On Schizophrenic Experiences of the Neutron or Why We Should Believe in the Many-Worlds Interpretation of Quantum Theory; University of South Carolina: Columbia, SC, USA, 1990; Available online: https://www.tau.ac.il/~vaidman/lvhp/r3.pdf (accessed on 4 August 2022).
- Vaidman, L. On the paradoxical aspects of new quantum experiments. In PSA 1994; Hull, D.M.F., Burian, R., Eds.; Philosophy of Science Association: Baltimore County, MD, USA, 1994; pp. 211–217. [Google Scholar]
- Vaidman, L. On schizophrenic experiences of the neutron or why we should believe in the many-worlds interpretation of quantum theory. Int. Stud. Philos. Sci.
**1998**, 12, 245–261. [Google Scholar] [CrossRef][Green Version] - Vaidman, L. Many-Worlds Interpretation of Quantum Mechanics. In The Stanford Encyclopedia of Philosophy; Zalta, E.N., Ed.; Metaphysics Research Lab, Stanford University: Stanford, CA, USA, 2021. [Google Scholar]
- Vaidman, L. Time Symmetry and the Many-Worlds Interpretation. In Many Worlds?: Everett, Quantum Theory, & Reality; Saunders, S., Barrett, J., Kent, A., Wallace, D., Eds.; Oxford University Press: Oxford, UK, 2010; pp. 582–596. [Google Scholar]
- Vaidman, L. Probability in the many-worlds interpretation of quantum mechanics. In Probability in Physics; Springer: Berlin, Germany, 2012; pp. 299–311. [Google Scholar]
- Groisman, B.; Hallakoun, N.; Vaidman, L. The measure of existence of a quantum world and the Sleeping Beauty Problem. Analysis
**2013**, 73, 695–706. [Google Scholar] [CrossRef][Green Version] - Vaidman, L. Quantum theory and determinism. Quantum Stud. Math. Found.
**2014**, 1, 5–38. [Google Scholar] [CrossRef][Green Version] - Vaidman, L. Bell inequality and many-worlds interpretation. In Quantum Nonlocality and Reality: 50 Years of Bell’s Theorem; Gao, M.B.S., Ed.; Cambridge University Press: Cambridge, UK, 2015; pp. 195–203. [Google Scholar]
- Vaidman, L. All is Ψ. J. Phys. Conf. Ser.
**2016**, 701, 012020. [Google Scholar] [CrossRef][Green Version] - McQueen, K.J.; Vaidman, L. In defence of the self-location uncertainty account of probability in the many-worlds interpretation. Stud. Hist. Philos. Sci. Part B Stud. Hist. Philos. Mod. Phys.
**2018**, 66, 14–23. [Google Scholar] [CrossRef][Green Version] - Vaidman, L. Ontology of the wave function and the many-worlds interpretation. In Quantum Worlds: Perspectives on the Ontology of Quantum Mechanics; Lombardi, O., Fortin, S., López, C., Holik, F., Eds.; Cambridge University Press: Cambridge, UK, 2019. [Google Scholar]
- Vaidman, L. Derivations of the Born rule. In Quantum, Probability, Logic: The Work and Influence of Itamar Pitowsky; Hemmo, M., Shenker, O., Eds.; Springer Nature: Berlin, Germany, 2020; pp. 567–584. [Google Scholar]
- McQueen, K.J.; Vaidman, L. How the Many Worlds Interpretation brings Common Sense to Paradoxical Quantum Experiments. In Scientific Challenges to Common Sense Philosophy; Routledge: London, UK, 2020; pp. 40–60. [Google Scholar]
- Vaidman, L. Wave function realism and three dimensions. In Quantum Mechanics and Fundamentality: Naturalizing Quantum Theory between Scientific Realism and Ontological Indeterminacy; Allori, V., Ed.; Springer: Berlin, Germany, 2022; Volume 460, pp. 195–209. [Google Scholar]
- Everett, H., III. “Relative state” formulation of quantum mechanics. Rev. Mod. Phys.
**1957**, 29, 454–462. [Google Scholar] [CrossRef][Green Version] - Everett, H., III. The Theory of the Universal Wave Function. In The Many-Worlds Interpretation of Quantum Mechanics; DeWitt, B.S., Graham, N., Eds.; Princeton University Press: Princeton, NJ, USA, 1973. [Google Scholar]
- Aharonov, Y.; Albert, D.Z. Is the usual notion of time evolution adequate for quantum-mechanical systems? Phys. Rev. D
**1984**, 29, 223. [Google Scholar] [CrossRef] - Elitzur, A.C.; Vaidman, L. Quantum mechanical interaction-free measurements. Found. Phys.
**1993**, 23, 987–997. [Google Scholar] [CrossRef][Green Version] - Aharonov, Y.; Vaidman, L. Complete description of a quantum system at a given time. J. Phys. A: Math. Gen.
**1991**, 24, 2315. [Google Scholar] [CrossRef] - Hardy, L. Quantum mechanics, local realistic theories, and Lorentz-invariant realistic theories. Phys. Rev. Lett.
**1992**, 68, 2981. [Google Scholar] [CrossRef] [PubMed] - Aharonov, Y.; Colombo, F.; Popescu, S.; Sabadini, I.; Struppa, D.; Tollaksen, J. Quantum violation of the pigeonhole principle and the nature of quantum correlations. Proc. Natl. Acad. Sci. USA
**2016**, 113, 532. [Google Scholar] [CrossRef] [PubMed][Green Version] - Vaidman, L. Past of a quantum particle. Phys. Rev. A
**2013**, 87, 052104. [Google Scholar] [CrossRef][Green Version] - Saunders, S.; Barrett, J.; Kent, A.; Wallace, D. Many Worlds? Everett, Quantum Theory, & Reality; OUP Oxford: Oxford, UK, 2010. [Google Scholar]
- Wallace, D. The Emergent Multiverse: Quantum Theory according to the Everett Interpretation; Oxford University Press: Oxford, UK, 2012. [Google Scholar]
- Deutsch, D.; Jozsa, R. Rapid solution of problems by quantum computation. Proc. R. Soc. London. Ser. A Math. Phys. Sci.
**1992**, 439, 553–558. [Google Scholar] - Albert, D.Z. Wave function realism. In The Wave Function: Essays on The Metaphysics of Quantum Mechanics; Ney, A., Albert, D.Z., Eds.; University Press Oxford: Oxford, UK, 2013; pp. 52–57. [Google Scholar]
- Maudlin, T. Can the world be only wavefunction? In Many Worlds? Everett, Quantum Theory, & Reality; Saunders, S., Barrett, J., Kent, A., Wallace, D., Eds.; Oxford University Press: Oxford, UK, 2010; pp. 121–143. [Google Scholar]
- Allori, V.; Goldstein, S.; Tumulka, R.; Zanghì, N. Predictions and primitive ontology in quantum foundations: A study of examples. Br. J. Philos. Sci.
**2014**, 65, 323–352. [Google Scholar] [CrossRef][Green Version] - Deutsch, D. Quantum theory of probability and decisions. Proc. R. Soc. London. Ser. A Math. Phys. Eng. Sci.
**1999**, 455, 3129–3137. [Google Scholar] [CrossRef][Green Version] - Ney, A. The World in the Wave Function: A Metaphysics for Quantum Physics; Oxford University Press: Oxford, UK, 2021. [Google Scholar]
- Deutsch, D.; Hayden, P. Information flow in entangled quantum systems. Proc. R. Soc. London. Ser. A Math. Phys. Eng. Sci.
**2000**, 456, 1759–1774. [Google Scholar] [CrossRef][Green Version] - Bédard, C.A. The cost of quantum locality. Proc. R. Soc. A
**2021**, 477, 20200602. [Google Scholar] [CrossRef] [PubMed]

**Figure 1.**

**Measurement problem.**(

**a**) The detection of a single photon is fully understood by the creation of a particular quantum wave of parts of the single-photon detector. (

**b**) In the experiment with a single-photon source, beamsplitter, and two detectors, the quantum mechanical equations show a similar (although reduced) change in two detectors. Nevertheless, we never observe simultaneous clicks of the two detectors.

**Figure 2.**

**Action at a distance in a single-world universe.**If we do nothing at A, then at a particular moment, there will be probability $p=0.5$ of finding a photon at a spacelike separated region B. Introducing a detector just before A will lead to a superluminal change in B to $p=0$ or $p=1$. The change will not be known immediately at B, but it does not change the fact that something in B changed, e.g., the readiness of an agent in A to bet about the result of an experiment in B.

**Figure 3.**

**The world structure in the MWI and a single-world universe.**(

**a**) The whole tree of many worlds in the MWI. (

**b**) One world of the MWI until present together with the tree of future worlds splitting out of it in the future. (

**c**) One of the corresponding worlds of the theory with collapse.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |

© 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Vaidman, L. Why the Many-Worlds Interpretation? *Quantum Rep.* **2022**, *4*, 264-271.
https://doi.org/10.3390/quantum4030018

**AMA Style**

Vaidman L. Why the Many-Worlds Interpretation? *Quantum Reports*. 2022; 4(3):264-271.
https://doi.org/10.3390/quantum4030018

**Chicago/Turabian Style**

Vaidman, Lev. 2022. "Why the Many-Worlds Interpretation?" *Quantum Reports* 4, no. 3: 264-271.
https://doi.org/10.3390/quantum4030018