SciPost Submission Page
Causality and the Interpretation of Quantum Mechanics
by Kaixun Tu,Qing Wang
Submission summary
| Authors (as registered SciPost users): | Kaixun Tu |
| Submission information | |
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| Preprint Link: | scipost_202508_00002v3 (pdf) |
| Date submitted: | Feb. 7, 2026, 2:38 a.m. |
| Submitted by: | Kaixun Tu |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Theoretical |
Abstract
From the ancient Einstein-Podolsky-Rosen paradox to the recent Sorkin-type impossible measurements problem, the contradictions between relativistic causality, quantum non-locality, and quantum measurement have persisted. Unlike recent approaches that address causality by enlarging the Hilbert space to introduce the quantum states of the detectors, our perspective is that everything—including detectors, the environment, and even humans—is composed of the same fundamental fields. This implies that the Hilbert space of the entire system remains the same regardless of the number of detectors. We employ reduced density matrices to characterize the local information of quantum states and show that reduced density matrices cannot evolve superluminally, thereby establishing causality. We further analyze the constraint that causality imposes on physical operations. Based on this constraint and the inherent entanglement in quantum field theory, we clarify that the traditional derivation of the Schrödinger's cat paradox is problematic, and we show that the Reeh–Schlieder theorem makes it possible that the Schrödinger's cat paradox does not arise. We then point out that, if the Schrödinger's cat paradox is indeed absent from the outset, this opens the door to an interpretation of quantum mechanics that respects causality and preserves the completeness of quantum mechanics without invoking the many-worlds scenario.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
List of changes
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We have rewritten the abstract to avoid the misunderstanding raised by Referee 2 (namely, that we have already completed a quantitative construction of a new interpretation of quantum mechanics). The revised abstract is now aligned with the changes described below.
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We have removed the discussion of “pair production” from the first paragraph to avoid potential confusion for readers. Instead, we rewrote and streamlined the original first paragraph in accordance with Referee 2’s argument (“Since position measurements allow superluminal signalling, such measurements are not physical.”) and merged it with the second paragraph.
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We have included a concise introduction to the Schrödinger’s cat paradox in the latter part of the Introduction, clarified its central role in discussions of quantum interpretations, and explicitly indicated where in the paper the traditional derivation of the Schrödinger’s cat paradox is presented in detail.
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The technical mathematical material originally contained in Section 2.1 has been moved to Appendix B. In the revised version of Section 2.1, we added an explanatory paragraph at the end to clarify why this material is included in the paper.
5.In the second paragraph of Section 2.2, we now explicitly point out the connection between part of our discussion and the classic textbook Quantum Computation and Quantum Information by Michael A. Nielsen and Isaac L. Chuang.
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In the final paragraph of Section 2.2, we emphasize that the unitary operator $\hat U_a$ constructed formally in Eq. \eqref{U} has no direct physical significance; it merely serves as an intermediate mathematical tool used to prove causality.
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At the beginning of Section 3 (the first paragraph), we explicitly clarify the role of this section in the later discussion of measurement experiments and the Schrödinger’s cat paradox, in order to avoid the misunderstanding noted by Referee 2 that “Section 3 purports to model the measurement process in QFT.” Section 3 does not address the measurement process itself, but rather the preparation of the initial state for a measurement experiment. We also emphasize this point again in the final paragraph of the Introduction.
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We have reorganized the material on the traditional derivation of the Schrödinger’s cat paradox from the previous manuscript into a dedicated subsection, now presented as Section 4.1.
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We have added a new Section 4.3 to incorporate the preparation apparatus into the analysis of the Schrödinger’s cat paradox. This addition makes it even clearer why the Schrödinger’s cat paradox may not arise.
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We have added a new Section 4.5 to show that, according to the Reeh–Schlieder theorem, even if the final state of the measurement process is a superposition of macroscopically distinct classical configurations, the observed measurement outcome may still be a definite macroscopic state rather than a Schrödinger’s cat–like superposition.
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We have substantially rewritten Section 5 (Conclusion and Outlook), removing less essential material, expanding the discussion of the key points, and ensuring that it is fully consistent with the revisions described above.