Abstract

The most serious candidates for common causes that fail to screen off (‘interactive common causes’, ICCs) and thus violate the causal Markov condition (CMC) refer to quantum phenomena. In her seminal debate with Hausman and Woodward, Cartwright early on focussed on unfortunate non-quantum examples. Especially, Hausman and Woodward’s redescriptions of quantum cases saving the CMC remain unchallenged. This paper takes up this lose end of the discussion and aims to resolve the debate in favour of Cartwright’s position. It systematically considers redescriptions of ICC structures, including those by Hausman and Woodward, and explains why these are inappropriate, when quantum mechanics (in an objective collapse interpretation) is true. It first shows that all cases of purported quantum ICCs are cases of entanglement and then, using the tools of causal modelling, it provides an analysis of the quantum mechanical formalism for the case that the collapse of entangled systems is best described as a causal model with an ICC.

Highlights

  • The common wisdom is that common causes screen off their effects: If two variables a and b have a common cause c and are not directly causally related, a and b are marginally correlated but statistically independent given knowledge about c

  • Upholding independent fixability would save the causal Markov condition (CMC) because the problematic correlation between the outcomes is hidden in the joint variable

  • It would be desirable to uphold all usual principles of causal modelling, I think that there are at least three good reasons to describe the immediate outcomes after collapse of the entangled state as two variables and to accept a violation of independent fixability and modularity, and, to acknowledge an anomaly for interventionist theories of causation requiring the principles

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Summary

Introduction

The common wisdom is that common causes screen off their effects: If two variables a and b have a common cause c and are not directly causally related (neither is a a cause of b nor vice versa), a and b are marginally correlated but statistically independent given knowledge about c.

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Cartwright’s paradigmatic case and a decaying molecule
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Quantum ICCs are the most serious candidates for genuine ICCs
Prima facie classification of proposed quantum ICCs
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Causal analysis of the quantum mechanical formalism
Modelling the entangled state prior to collapse as a single variable
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There are no further relevant variables prior to collapse
The product state after collapse is not a unit
Against unity by identity
Against unity by composition
Against unity by dependent fixability
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Discussion
The entangled state is a common cause of the collapsed states
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There is no connection between the collapsed states
Hausman’s view
Making the models more explicit
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Interactions
Non-separability
Collapse
Conservation laws
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Result
Generalization to continuous collapse theories
Discussion of other interpretations
Conclusion
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