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The British Journal for the Philosophy of Science

Conspiracy Theories of Quantum Mechanics

Peter J. Lewis

Published Apr 12, 2006• 37 citations
Publisher

Abstract

It has long been recognized that a local hidden variable theory of quantum mechanics can in principle be constructed, provided one is willing to countenance pre-measurement correlations between the properties of measured systems and measuring devices. However, this ‘conspiratorial’ approach is typically dismissed out of hand. In this article I examine the justification for dismissing conspiracy theories of quantum mechanics. I consider the existing arguments against such theories, and find them to be less than conclusive. I suggest a more powerful argument against the leading strategy for constructing a conspiracy theory. Finally, I outline two alternative strategies for constructing conspiracy theories, both of which are immune to these arguments, but require one to either modify or reject the common cause principle. 1. Introduction 2. The incompleteness of quantum mechanics 3. Hidden variables 4. Hidden mechanism conspiracy theories 5. Existing arguments against hidden mechanisms 6. A new argument against hidden mechanisms 7. Backwards-causal conspiracy theories 8. Acausal conspiracy theories 9. Conclusion

DOI
10.1093/bjps/axl006

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It has long been recognized that a local hidden variable theory of quantum mechanics can in principle be constructed, provided one is willing to countenance pre-measurement correlations between the properties of measured systems and measuring devices. However, this ‘conspiratorial’ approach is typically dismissed out of hand. In this article I examine the justification for dismissing conspiracy theories of quantum mechanics. I consider the existing arguments against such theories, and find them to be less than conclusive. I suggest a more powerful argument against the leading strategy for constructing a conspiracy theory. Finally, I outline two alternative strategies for constructing conspiracy theories, both of which are immune to these arguments, but require one to either modify or reject the common cause principle. 1. Introduction 2. The incompleteness of quantum mechanics 3. Hidden variables 4. Hidden mechanism conspiracy theories 5. Existing arguments against hidden mechanisms 6. A new argument against hidden mechanisms 7. Backwards-causal conspiracy theories 8. Acausal conspiracy theories 9. Conclusion
We prove that superdeterministic models of quantum mechanics are conspiratorial in a mathematically well-defined sense, by further development of the ideas presented in a previous article A . We consider a Bell scenario where, in each run and at each wing, the experimenter chooses one of N devices to determine the local measurement setting. We prove, without assuming any features of quantum statistics, that superdeterministic models of this scenario must have a finely tuned distribution of hidden variables. Specifically, fine-tuning is required so that the measurement statistics depend on the measurement settings but not on the details of how the settings are chosen. We quantify this as the overhead fine-tuning F of the model, and show that F > 0 (corresponding to ‘fine-tuned’) for any N > 1. The notion of fine-tuning assumes that arbitrary (‘non-equilibrium’) hidden-variables distributions are possible in principle. We also show how to quantify superdeterministic conspiracy without using non-equilibrium. This second approach is based on the fact that superdeterministic correlations can mimic actual signalling. We argue that an analogous situation occurs in equilibrium where, for every run, the devices that the hidden variables are correlated with are coincidentally the same as the devices in fact used. This results in extremely large superdeterministic correlations, which we quantify as a drop of an appropriately defined formal entropy. Non-local and retrocausal models turn out to be non-conspiratorial according to both approaches.
Abstract What are the consequences of quantum mechanics for the structure of causal explanation? It depends on the interpretation you choose. According to a hidden variable theory like Bohm’s, a measurement on one particle can have instantaneous effects on another, no matter how distant. This nonlocality is in prima facie conflict with special relativity. The prospects for constructing a local hidden variable theory are assessed, in particular by invoking backward-in-time causation. Many-worlds theories do not invoke nonlocal causation. However, they do entail that microcausal explanations are in terms of waves, not particles, and they inject consideration of the observer’s location among the worlds into causal explanations. Spontaneous collapse theories like GRW do invoke nonlocal causation; the prospects for a local spontaneous collapse theory are investigated. All of the major interpretations of quantum mechanics modify the structure of causal explanation from the received classical ideal.
Bell’s theorem is purported to demonstrate the impossibility of a local “hidden variable” theory underpinning quantum mechanics. It relies on the well-known assumption of ‘locality’, and also on a little-examined assumption called ‘statistical independence ’ (SI). Violations of this assumption have variously been thought to suggest “backward causation”, a “conspiracy ” on the part of nature, or the denial of “free will”. It will be shown here that these are spurious worries, and that denial of SI simply implies nonlocal correlation between spacelike degrees of freedom. Lorentz-invariant theories in which SI does not hold are easily constructed: two are exhibited here. It is conjectured, on this basis, that quantum-mechanical phenomena may be modeled by a local theory after all. 1
The primary criterion of adequacy of a probabilistic causal analysis is that the causal variable should render the simultaneous phenomenological data conditionally independent. The intuition back of this idea is that the common cause of the phenomena should factor out the observed correlations. So we label the principle the common cause criterion . If we find that the barometric pressure and temperature are both dropping at the same time, we do not think of one as the cause of the other but look for a common dynamical cause within the physical theory of meteorology. If we find fever and headaches positively correlated, we look for a common disease as the source and do not consider one the cause of the other. But we do not want to suggest that satisfaction of this criterion is the end of the search for causes or probabilistic explanations. It does represent a significant and important milestone in any particular investigation. Under another banner the search for common causes in quantum mechanics is the search for hidden variables. A hidden variable that satisfies the common cause criterion provides a satisfactory explanation “in classical terms” of the quantum phenomenon. Much of the earlier discussion of hidden variables in quantum mechanics has centered around the search for deterministic underlying processes, but for some time now the literature has also been concerned with the existence of probabilistic hidden variables. It is a striking and important fact that even probabilistic hidden variables do not always exist when certain intuitive criteria are imposed.
This preprint re-examines the widespread belief that “Einstein was wrong about quantum mechanics.” While Einstein is often portrayed as rejecting quantum theory due to his criticism of its probabilistic interpretation, this simplified narrative does not accurately reflect his actual position or the historical context. The paper organizes Einstein’s original arguments, clarifies common misunderstandings—such as the misattribution that he “advocated hidden variables”—and reviews the development of Bell’s inequalities and their experimental tests. These experiments ruled out simple local hidden-variable models but did not fully resolve Einstein’s deeper concern: the possible incompleteness of quantum mechanics as a physical theory. By revisiting historical documents and theoretical developments, this work argues that Einstein’s critique was not a fundamental mistake but has been misinterpreted over time. The goal is to provide a more accurate understanding of the Einstein–Bohr debates and the conceptual foundations of quantum mechanics.
It has been claimed that quantum mechanics is a non-local theory, i.e., that the predictions of quantum mechanics are at odds with a conception of the world where all the interactions are mediated by local mechanisms. The cited reason is the violation of the Bell inequality in cases where measurements are performed on quantum systems of particles that have interacted in the past. Quantum mechanics predicts that the state of the particles in such a system are correlated, a result obtained from considering a thought-experiment often known as EPR. In this thesis, I will argue that the violation of the Bell inequality in EPR forces us to either accept that causes sometimes act both backwards and forwards in time, or give up some widely-held assumptions about causal relations or the role of causal explanations. First, I will present three principles regarding causality that I take be widely accepted. I will then present the background for the claim the quantum mechanics is a non-local theory, and discuss the implications of non-local causal influences in light of the Special Theory of Relativity. One argument against a causal explanation of the EPR-correlations will be discussed, and different models for the causal structure of EPR will be assessed. I will argue that a retrocausal model – models that include instances of retrocausation, where the direction of causation is the opposite of the direction of time – is the only viable option if we want to uphold the three principles presented in chapter 1. I will discuss the plausibility of rejecting one of these principles, and argue that at least one of the can be restricted in a way that still accounts for our commitment to it. Finally, I will assess the non-local models against the retrocausal models, and argue that a retrocausal model offers interpretational advantages over the non-local alternatives.