Causation does not explain contextuality

Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-go theorems that show quantum correlations cannot be explained by non-contextual ontological models, where physical properties are assumed to exist prior to and independently of the act of measurement. However, all such contextuality proofs assume a traditional notion of causal structure, where causal influence flows from past to future according to ordinary dynamical laws. This leaves open the question of whether the apparent contextuality of quantum mechanics is simply the signature of some exotic causal structure, where the future might affect the past or distant systems might get correlated due to non-local constraints. Here we show that quantum predictions require a deeper form of contextuality: even allowing for arbitrary causal structure, no model can explain quantum correlations from non-contextual ontological properties of the world, be they initial states, dynamical laws, or global constraints.Comment: 18+8 pages, 3 figure

Updating the Born rule

Despite the tremendous empirical success of quantum theory there is still widespread disagreement about what it can tell us about the nature of the world. A central question is whether the theory is about our knowledge of reality, or a direct statement about reality itself. Regardless of their stance on this question, current interpretations of quantum theory regard the Born rule as fundamental and add an independent state-update (or "collapse") rule to describe how quantum states change upon measurement. In this paper we present an alternative perspective and derive a probability rule that subsumes both the Born rule and the collapse rule. We show that this more fundamental probability rule can provide a rigorous foundation for informational, or "knowledge-based", interpretations of quantum theory.Comment: 6+2 pages; 3 figure

Discovering Quantum Causal Models (final)

Costa and Shrapnel [2016] have recently proposed an interventionist theory of quantum causation. The formalism generalises the classical methods of Pearl [2000] and allows for the discovery of quantum causal structure via localised interventions. Classical causal structure is presented as a special case of this more general framework. I introduce the account and consider whether this formalism provides a causal explanation for the Bell correlations

The Two Sides of Interventionist Causation

Pearl and Woodward are both well-known advocates of interventionist causation. What is less well-known is the interesting relationship between their respective accounts. In this paper we discuss the different perspectives of causation these two accounts present and show that they are two sides of the same coin. Pearl’s focus is on leveraging global network constraints to correctly identify local causal relations. The rules by which global causal structures are composed from distinct causal relations are precisely defined by the global constraints. Woodward’s focus, however, is on the use of local manipulation to identify single causal relations that then compose into global causal structures. The rules by which this composition takes place emerge as a result of local interventionist constraints (or so the claim goes). We contend that the complete picture of causality to be found between these two perspectives from the interventionist tradition must recognise both the global constraints of the sort identified by Pearl and the local constraints of the sort identified by Woodward, and the interplay between them: Pearl requires the possibility of local interventions and Woodward requires a global statistical framework within which to build composite causal structures

The Two Sides of Interventionist Causation

Pearl and Woodward are both well-known advocates of interventionist causation. What is less well-known is the interesting relationship between their respective accounts. In this paper we discuss the different perspectives of causation these two accounts present and show that they are two sides of the same coin. Pearl’s focus is on leveraging global network constraints to correctly identify local causal relations. The rules by which global causal structures are composed from distinct causal relations are precisely defined by the global constraints. Woodward’s focus, however, is on the use of local manipulation to identify single causal relations that then compose into global causal structures. The rules by which this composition takes place emerge as a result of local interventionist constraints (or so the claim goes). We contend that the complete picture of causality to be found between these two perspectives from the interventionist tradition must recognise both the global constraints of the sort identified by Pearl and the local constraints of the sort identified by Woodward, and the interplay between them: Pearl requires the possibility of local interventions and Woodward requires a global statistical framework within which to build composite causal structures

Discovering quantum causal models

Costa and Shrapnel ([2016]) have recently proposed an interventionist theory of quantum causation. The formalism generalizes the classical methods of Pearl ([2000]) and allows for the discovery of quantum causal structure via localized interventions. Classical causal structure is presented as a special case of this more general framework. I introduce the account and consider whether this formalism provides a causal explanation for the Bell correlations. 1 Introduction 2 Classical Causal Models 3 What's the (Quantum) Problem? 4 Quantum Causal Models: Why Bother? 5 Markov Quantum Causal Models 6 The Bell Experiment 7 Bell's Objections

Causal asymmetry from the perspective of a causal agent

Agency accounts of causation are often criticised as being unacceptably subjective or anthropocentric. According to such criticisms, if there were no human agents then there would be no causal relations, or, at the very least, if humans had been different then so too would causal relations. Here we describe a model of a causal agent that is not human with a view to exploring this latter claim. This model obeys the known laws of physics, and we claim that it endows the causal agent with a "causal viewpoint: a distinctive mix of knowledge, ignorance and practical ability that a creature must apparently exemplify, if it is to be capable of employing causal concepts" (Price, 2007, p.255). We argue that this model of a causal agent provides a clear illustration of the epistemic constraints that define such a 'causal perspective', and we employ the model to demonstrate how shared constraints lead to a shared perspective. Furthermore, we use this model to scrutinise the alignment of three familiar asymmetries with the causal asymmetry: the thermodynamic arrow, the arrow of time, and the arrow of deliberation and action