Abstract

In this article we set out to understand the significance of the process matrix formalism and the quantum causal modelling programme for ongoing disputes about the role of causation in fundamental physics. We argue that the process matrix programme has correctly identified a notion of ‘causal order’ which plays an important role in fundamental physics, but this notion is weaker than the common-sense conception of causation because it does not involve asymmetry. We argue that causal order plays an important role in grounding more familiar causal phenomena. Then we apply these conclusions to the causal modelling programme within quantum foundations, arguing that since no-signalling quantum correlations cannot exhibit causal order, they should not be analysed using classical causal models. This resolves an open question about how to interpret fine-tuning in classical causal models of no-signalling correlations. Finally we observe that a quantum generalization of causal modelling can play a similar functional role to standard causal reasoning, but we emphasize that this functional characterisation does not entail that quantum causal models offer novel explanations of quantum processes.