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Quantum Theory and Causation

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Quantum Information".

Deadline for manuscript submissions: closed (18 May 2021) | Viewed by 27457

Special Issue Editor


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Guest Editor
Physics & Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192, USA
Interests: quantum foundations; entanglement; retrocausality

Special Issue Information

Dear Colleagues,

Despite agreement that quantum phenomena are counter-intuitive, it remains unclear which of our intuitions are most at fault. This Special Issue concerns the relationship between quantum theory and our causal intuitions. Recent decades have seen significant progress in formalizing our concepts of causality, both logically and mathematically. In particular, both Judea Pearl's causal models and the "interventionist" accounts of causation promoted by James Woodward can now formally analyze causation without explicit reference to temporal order. However, despite the growing adoption of such "modern" accounts of causation, these concepts are only occasionally being applied to quantum theory (see, for example, arXiv:1208.4119). A large number of issues remain to be explored, including the following: how exactly do various ideas in quantum mechanics and quantum field theory map to causal models, and what explanations do these models imply? Are there natural modifications of the causal model framework that lead to unconventional causal models that could be useful in a quantum context? If so, how and why would conventional causation be recovered in the classical limit? Zooming out, does causal inference imply some special role for cosmological boundary conditions? Zooming in, what are the causal restrictions on hidden variable models? It is hoped that framing this discussion in the context of interventionist causation will help address open questions in quantum foundations.

Prof. Dr. Ken Wharton
Guest Editor

Manuscript Submission Information

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Keywords

  • quantum foundations
  • causal models
  • retrocausation
  • hidden variables
  • quantum cosmology

Published Papers (9 papers)

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Research

16 pages, 915 KiB  
Article
Implications of Local Friendliness Violation for Quantum Causality
by Eric G. Cavalcanti and Howard M. Wiseman
Entropy 2021, 23(8), 925; https://doi.org/10.3390/e23080925 - 21 Jul 2021
Cited by 12 | Viewed by 3417
Abstract
We provide a new formulation of the Local Friendliness no-go theorem of Bong et al. [Nat. Phys. 16, 1199 (2020)] from fundamental causal principles, providing another perspective on how it puts strictly stronger bounds on quantum reality than Bell’s theorem. In particular, quantum [...] Read more.
We provide a new formulation of the Local Friendliness no-go theorem of Bong et al. [Nat. Phys. 16, 1199 (2020)] from fundamental causal principles, providing another perspective on how it puts strictly stronger bounds on quantum reality than Bell’s theorem. In particular, quantum causal models have been proposed as a way to maintain a peaceful coexistence between quantum mechanics and relativistic causality while respecting Leibniz’s methodological principle. This works for Bell’s theorem but does not work for the Local Friendliness no-go theorem, which considers an extended Wigner’s Friend scenario. More radical conceptual renewal is required; we suggest that cleaving to Leibniz’s principle requires extending relativity to events themselves. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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12 pages, 316 KiB  
Article
Objective Quantum Fields, Retrocausality and Ontology
by Peter D. Drummond and Margaret D. Reid
Entropy 2021, 23(6), 749; https://doi.org/10.3390/e23060749 - 14 Jun 2021
Cited by 8 | Viewed by 2432
Abstract
We compare different approaches to quantum ontology. In particular, we discuss an interpretation of quantum mechanics that we call objective quantum field theory (OQFT), which involves retrocausal fields. Here, objective implies the existence of fields independent of an observer, but not that the [...] Read more.
We compare different approaches to quantum ontology. In particular, we discuss an interpretation of quantum mechanics that we call objective quantum field theory (OQFT), which involves retrocausal fields. Here, objective implies the existence of fields independent of an observer, but not that the results of conjugate measurements are predetermined: the theory is contextual. The ideas and analyses of Einstein and Bohr through to more recent approaches to objective realism are discussed. We briefly describe measurement induced projections, the guided wave interpretation, many-universes, consistent histories and modal theories. These earlier interpretations are compared with OQFT. We argue that this approach is compatible both with Bohr’s quantum complementarity and Einstein’s objective realism. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
8 pages, 357 KiB  
Article
Causality Is an Effect, II
by Lawrence S. Schulman
Entropy 2021, 23(6), 682; https://doi.org/10.3390/e23060682 - 28 May 2021
Viewed by 1772
Abstract
Causality follows the thermodynamic arrow of time, where the latter is defined by the direction of entropy increase. After a brief review of an earlier version of this article, rooted in classical mechanics, we give a quantum generalization of the results. The quantum [...] Read more.
Causality follows the thermodynamic arrow of time, where the latter is defined by the direction of entropy increase. After a brief review of an earlier version of this article, rooted in classical mechanics, we give a quantum generalization of the results. The quantum proofs are limited to a gas of Gaussian wave packets. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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30 pages, 628 KiB  
Article
Lapsing Quickly into Fatalism: Bell on Backward Causation
by Travis Norsen and Huw Price
Entropy 2021, 23(2), 251; https://doi.org/10.3390/e23020251 - 22 Feb 2021
Cited by 1 | Viewed by 3642
Abstract
This is a dialogue between Huw Price and Travis Norsen, loosely inspired by a letter that Price received from J. S. Bell in 1988. The main topic of discussion is Bell’s views about retrocausal approaches to quantum theory and their relevance to contemporary [...] Read more.
This is a dialogue between Huw Price and Travis Norsen, loosely inspired by a letter that Price received from J. S. Bell in 1988. The main topic of discussion is Bell’s views about retrocausal approaches to quantum theory and their relevance to contemporary issues. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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29 pages, 693 KiB  
Article
Beyond Causal Explanation: Einstein’s Principle Not Reichenbach’s
by Michael Silberstein, William Mark Stuckey and Timothy McDevitt
Entropy 2021, 23(1), 114; https://doi.org/10.3390/e23010114 - 16 Jan 2021
Cited by 3 | Viewed by 4709
Abstract
Our account provides a local, realist and fully non-causal principle explanation for EPR correlations, contextuality, no-signalling, and the Tsirelson bound. Indeed, the account herein is fully consistent with the causal structure of Minkowski spacetime. We argue that retrocausal accounts of quantum mechanics are [...] Read more.
Our account provides a local, realist and fully non-causal principle explanation for EPR correlations, contextuality, no-signalling, and the Tsirelson bound. Indeed, the account herein is fully consistent with the causal structure of Minkowski spacetime. We argue that retrocausal accounts of quantum mechanics are problematic precisely because they do not fully transcend the assumption that causal or constructive explanation must always be fundamental. Unlike retrocausal accounts, our principle explanation is a complete rejection of Reichenbach’s Principle. Furthermore, we will argue that the basis for our principle account of quantum mechanics is the physical principle sought by quantum information theorists for their reconstructions of quantum mechanics. Finally, we explain why our account is both fully realist and psi-epistemic. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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8 pages, 223 KiB  
Article
Quantum Computation and Arrows of Time
by Nathan Argaman
Entropy 2021, 23(1), 49; https://doi.org/10.3390/e23010049 - 30 Dec 2020
Cited by 1 | Viewed by 1815
Abstract
Quantum physics is surprising in many ways. One surprise is the threat to locality implied by Bell’s Theorem. Another surprise is the capacity of quantum computation, which poses a threat to the complexity-theoretic Church-Turing thesis. In both cases, the surprise may be due [...] Read more.
Quantum physics is surprising in many ways. One surprise is the threat to locality implied by Bell’s Theorem. Another surprise is the capacity of quantum computation, which poses a threat to the complexity-theoretic Church-Turing thesis. In both cases, the surprise may be due to taking for granted a strict arrow-of-time assumption whose applicability may be limited to the classical domain. This possibility has been noted repeatedly in the context of Bell’s Theorem. The argument concerning quantum computation is described here. Further development of models which violate this strong arrow-of-time assumption, replacing it by a weaker arrow which is yet to be identified, is called for. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
12 pages, 6111 KiB  
Article
Causal Intuition and Delayed-Choice Experiments
by Michael B. Heaney
Entropy 2021, 23(1), 23; https://doi.org/10.3390/e23010023 - 26 Dec 2020
Cited by 1 | Viewed by 1803
Abstract
The conventional explanation of delayed-choice experiments appears to violate our causal intuition at the quantum level. I reanalyze these experiments using time-reversed and time-symmetric formulations of quantum mechanics. The time-reversed formulation does not give the same experimental predictions. The time-symmetric formulation gives the [...] Read more.
The conventional explanation of delayed-choice experiments appears to violate our causal intuition at the quantum level. I reanalyze these experiments using time-reversed and time-symmetric formulations of quantum mechanics. The time-reversed formulation does not give the same experimental predictions. The time-symmetric formulation gives the same experimental predictions but actually violates our causal intuition at the quantum level. I explore the reasons why our causal intuition may be wrong at the quantum level, suggest how conventional causation might be recovered in the classical limit, propose a quantum analog to the classical block universe viewpoint, and speculate on implications of the time-symmetric formulation for cosmological boundary conditions. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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18 pages, 281 KiB  
Article
The End of a Classical Ontology for Quantum Mechanics?
by Peter W. Evans
Entropy 2021, 23(1), 12; https://doi.org/10.3390/e23010012 - 24 Dec 2020
Cited by 1 | Viewed by 2310
Abstract
In this paper, I argue that the Shrapnel–Costa no-go theorem undermines the last remaining viability of the view that the fundamental ontology of quantum mechanics is essentially classical: that is, the view that physical reality is underpinned by objectively real, counterfactually definite, uniquely [...] Read more.
In this paper, I argue that the Shrapnel–Costa no-go theorem undermines the last remaining viability of the view that the fundamental ontology of quantum mechanics is essentially classical: that is, the view that physical reality is underpinned by objectively real, counterfactually definite, uniquely spatiotemporally defined, local, dynamical entities with determinate valued properties, and where typically ‘quantum’ behaviour emerges as a function of our own in-principle ignorance of such entities. Call this view Einstein–Bell realism. One can show that the causally symmetric local hidden variable approach to interpreting quantum theory is the most natural interpretation that follows from Einstein–Bell realism, where causal symmetry plays a significant role in circumventing the nonclassical consequences of the traditional no-go theorems. However, Shrapnel and Costa argue that exotic causal structures, such as causal symmetry, are incapable of explaining quantum behaviour as arising as a result of noncontextual ontological properties of the world. This is particularly worrying for Einstein–Bell realism and classical ontology. In the first instance, the obvious consequence of the theorem is a straightforward rejection of Einstein–Bell realism. However, more than this, I argue that, even where there looks to be a possibility of accounting for contextual ontic variables within a causally symmetric framework, the cost of such an account undermines a key advantage of causal symmetry: that accepting causal symmetry is more economical than rejecting a classical ontology. Either way, it looks like we should give up on classical ontology. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
23 pages, 308 KiB  
Article
The Operational Choi–Jamiołkowski Isomorphism
by Emily Adlam
Entropy 2020, 22(9), 1063; https://doi.org/10.3390/e22091063 - 22 Sep 2020
Cited by 4 | Viewed by 4742
Abstract
In this article, I use an operational formulation of the Choi–Jamiołkowski isomorphism to explore an approach to quantum mechanics in which the state is not the fundamental object. I first situate this project in the context of generalized probabilistic theories and argue that [...] Read more.
In this article, I use an operational formulation of the Choi–Jamiołkowski isomorphism to explore an approach to quantum mechanics in which the state is not the fundamental object. I first situate this project in the context of generalized probabilistic theories and argue that this framework may be understood as a means of drawing conclusions about the intratheoretic causal structure of quantum mechanics which are independent of any specific ontological picture. I then give an operational formulation of the Choi–Jamiołkowski isomorphism and show that, in an operational theory which exhibits this isomorphism, several features of the theory which are usually regarded as properties of the quantum state can be derived from constraints on non-local correlations. This demonstrates that there is no need to postulate states to be the bearers of these properties, since they can be understood as consequences of a fundamental equivalence between multipartite and temporal correlations. Full article
(This article belongs to the Special Issue Quantum Theory and Causation)
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