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Causality and the Interpretation of Quantum Mechanics

by Kaixun Tu,Qing Wang

This is not the latest submitted version.

Submission summary

Authors (as registered SciPost users): Kaixun Tu
Submission information
Preprint Link: scipost_202508_00002v1  (pdf)
Date submitted: Aug. 1, 2025, 4:18 a.m.
Submitted by: Kaixun Tu
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
Specialties:
  • High-Energy Physics - Theory
  • Quantum Physics
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. Based on quantum field theory, our work provides a framework that harmoniously integrates these three aspects. This framework consists of causality expressed by reduced density matrices and an interpretation of quantum mechanics that considers quantum mechanics to be complete. Specifically, we use reduced density matrices to represent the local information of the quantum state and show that the reduced density matrices cannot evolve superluminally. Unlike recent approaches that address causality by introducing new operators to represent detectors, our perspective is that everything—including detectors, the environment, and even humans—is made up of the same fundamental fields. This viewpoint leads us to question the validity of the Schrodinger's cat paradox and motivates us to propose an interpretation of quantum mechanics that requires no extra assumptions and remains fully compatible with relativity.

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
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Comments

Anonymous on 2025-09-05  [id 5784]

Category:
remark

Here’s a very simple, plain-language intro to the paper:

We don’t need the many-worlds hypothesis

In nonrelativistic quantum mechanics, the Schrödinger’s cat paradox pushes us toward the many-worlds idea. But we show that in relativistic quantum field theory, the Schrödinger’s cat paradox does not arise. Therefore, we do not need the many-worlds hypothesis to uphold the spirit of the many-worlds interpretation — namely, that quantum mechanics is complete.

Measurement respects causality

If quantum mechanics is complete, then measurement processes can be fully described by the Schrödinger equation. Since relativistic quantum field theory respects causality, all measurement processes also remain causal.

Bell’s inequality

Quantum measurement outcomes depend on the initial state of the whole experiment. Roughly speaking, the apparent randomness of quantum measurements comes from thermal fluctuations of the apparatus. In this sense, the “hidden variables” are simply the experiment’s initial states. Because quantum mechanics is nonlocal, this sort of hidden-variable picture does not conflict with Bell-type experiments — and, somewhat surprisingly, the whole picture can still be causal.

In summary, quantum mechanics is complete and does not require the many-worlds hypothesis. We may figuratively refer to this as the one-world interpretation of quantum mechanics.