For the fourth FraMEPhys meeting of 2020, Dr. Paul Näger (University of Münster) gave a talk entitled “How Quantum Mechanics Solves the Causal Problem of Entanglement” via Zoom to the University of Birmingham FraMEPhys group and guests.
ABSTRACT Recent works show that the statistics of typical experiments with entangled quantum objects (EPR/B experiments) contradict the usual principles of causal explanation, even if one disregards all spatio-temporal constraints (Wood & Spekkens 2015, Näger 2016). More precisely, this causal problem of entanglement consists in the fact that it is impossible that both central principles of the theory of causal Bayes nets (Glymour, Spirtes & Scheines 1993; Pearl 2000)—the causal Markov condition and the faithfulness condition—hold in such experiments. Any correct theory of the quantum realm must violate at least one of these conditions. This threatens the idea that the correlations in such experiments might be explained causally. In this talk I shall present a detailed analysis of the quantum mechanical formalism (in a GRW interpretation), revealing that quantum theory even violates both principles. Nevertheless, I shall argue for the claim that there are good reasons to regard the quantum mechanical explanation as a causal one. For the one, it is a well-known fact that the entangled quantum state does not screen off the correlations in such experiments. In other words, if quantum mechanics is complete, there is no screener-off for the correlations (van Fraassen 1982, Butterfield 1989, Cartwright 1989), implying that the theory violates the causal Markov condition (Spirtes, Glymour, Scheines 1993, Pearl 2000), which is a generalisation of Reichenbach’s principle of the common cause (Reichenbach 1956). Referring to the work of Cartwright (1988), however, I argue that in indeterministic worlds one should accept common causes that do not screen off. Further developing on Cartwright’s ideas, I present a generalisation of the Markov condition which is able to capture these new cases. This saves the central principle of causal explanation in the quantum realm, and makes explicit that underlying the quantum mechanical formalism is a causal structure that can explain the correlations. In a second step I show that the quantum mechanical formalism also violates the causal faithfulness condition. While being one of the central principles of the theory of causal Bayes nets, violating faithfulness does not seem to threaten a causal explanation per se: there are well-known counterexamples to the principle in perfectly causal situations. However, an unfaithfulness seems only acceptable in a causal explanation, when one indicates how it comes about (i.e. which type of unfaithfulness there is) given the causal connections in question; for not all types fit with all structures. Wood & Spekkens (2012) are tacit about which kind of unfaithfulness quantum mechanics involves; Näger (2015) claims that the theory involves an unfaithfulness of a supposedly new kind (unfaithfulness by internal cancelling paths), but only sketches its central features. In the present analysis I show explicitly how quantum mechanics explains the specific no-signalling independences by internal cancelling paths. I also provide an explanation for the unfaithfulness occurring between outcomes and local settings (for maximally entangled states), which reveals another so far unnoticed kind of unfaithfulness. In sum, my analysis shows that quantum mechanics solves the causal problem of entanglement in an astonishing and elegant way: though violating both central principles of causal explanation, the theory can still be considered as providing a causal explanation, if one moderately and reasonably modifies the original principles.
Some really excellent news for the FraMEPhys project team – our research fellow Katie Robertson has been awarded a three-year Early Career Fellowship by the Leverhulme Trust, to be hosted at the University of Birmingham and to start in 2021.
Katie’s project is called ‘Increasing entropy: from black holes to the direction of time’ and it links directly into her research with FraMEPhys. We’re all looking forward to continuing to work with Katie and excited to see the outcomes of her new project!
On Tuesday 18 February as part of the FraMEPhys Seminar series, Luke Fenton-Glynn (UCL) gave a talk entitled “Probabilistic Actual Causation” (Talk Slides, Full Paper) at the University of Birmingham. Luke presented an extension of recent theories of deterministic actual causation, formulated in terms of causal graphs, to irreucibly indeterministic cases.
ABSTRACT: Actual (token) causation – the sort of causal relation asserted to hold by claims like the Chicxulub impact caused the Cretaceous-Paleogene extinction event, Mr. Fairchild’s exposure to asbestos caused him to suffer mesothelioma, and the H7N9 virus outbreak was caused by poultry farmers becoming simultaneously infected by bird and human ’flu strains – is of significance to scientists, historians, and tort and criminal lawyers. Progress has been made in explicating the actual causal relation in the deterministic case by means of the use of structural equations models and causal graphs. I seek to make similar progress concerning the probabilistic case by using probabilistic causal models and associated causal graphs
Earlier on the same day, Luke took part in a reading group discussion of the above paper.
For the second FraMEPhys meeting of 2020, Prof. Dr. Andreas Hüttemann (University of Cologne) gave a talk on “Laws and their Modal Surface Structure” at the University of Birmingham (Muirhead Tower, 427).
ABSTRACT: Law statements or generalisations are involved in one way or another in explanation, confirmation, manipulation or prediction. I argue that these practices require a particular reading of the generalisations involved, namely as making claims about the behaviour of systems. These practices therefore presuppose the existence of systems or things (pace Ladyman, Ross etc.). Furthermore, I look at the metaphysical surface structure associated with laws. I use the term “surface structure” to indicate that this structure may or may not be reduced to non-modal facts – as the Humean has it. I will side-line the debate about whether Humeanism is a tenable philosophical position. The positive claim I advance is that the modal surface structure can be explicated in terms of invariance relations – where I take invariance to be a modal notion.
Earlier on the same day, from 1130-1230 in ERI 159, Prof. Dr. Hüttemann attended a reading group where we discussed his “Reduction and Monism“.
At the first FraMEPhys meeting of 2020 (21 January), Professor David Papineau (King’s College London) gave a talk on “The Seductions of Interventionism” at the University of Birmingham.
ABSTRACT: The philosophy of causation is changing. The new ‘interventionism’ promises to dissolve many longstanding problems. Based on the work of Judea Pearl, and transmitted to philosophy by Jim Woodward, this approach builds a bridge between the philosophical analysis of causation and techniques used in statistical causal modelling. It is certainly welcome that philosophers of causation are finally trying to make sense of these statistical techniques. But in the process of transmission a number of ungrounded ideas have been installed as philosophical orthodoxy. In this talk I shall expose two: first, the idea that we need to appeal to ‘interventions’ or actions to understand causation; second, the idea that correlational facts alone are insufficient to determine causal structure.