Zenith Grant Awardee

Eric Cavalcanti

Griffith University

Co-Investigators

Howard Wiseman, Griffith University

Project Title

Events, agents and causation in ontological models of quantum theory

Project Summary

50 years ago, John Bell proved a theorem that has shaken the foundations of physics, and still causes widespread puzzlement. Bell’s theorem points to an apparent incompatibility between our two best physical theories. According to Bell, “a real synthesis of quantum and relativity theories requires not just technical developments but radical conceptual renewal”. This project starts from the premise that the incompatibility arises from the different roles that concepts of events, agency and causation play in the two theories. Implicit in Bell’s thought was Reichenbach’s principle of common cause (RPCC), which states that if two events are correlated, then either they are causally connected or share a common cause that explains the correlation. Bell’s theorem shows that this principle must be dropped to maintain relativistic causality. But RPCC is widely applicable; simply rejecting it leaves an explanatory vacuum. Some recent work has attempted to propose principles to substitute RPCC, but at the expense of introducing agent-centric notions such as measurement “settings’’ or “outcomes’’. In this project we will ask: are such notions necessary to make sense of causation in a quantum world? And if so, what does that say about the prospect of reconciling quantum theory and relativity?

Technical Abstract

This project starts from the premise that the apparent incompatibility between quantum theory and relativity raised by Bell’s theorem arises from the different roles that concepts of events, agency and causation play in the two theories. We show that Bell’s theorem can be seen as a clash between relativistic causality and a principle that we call causal completeness: “an event is ‘independent’ of any events not among its effects given its causes”. Pienaar and Brukner [arXiv:1406.0430] subsequently proposed a quantum causality condition: “an outcome is independent of all settings that are not its causes and all outcomes that do not share a common cause”. This condition comes at a price of requiring a distinction between two kinds of events: “outcomes” and “settings”. In other words, it seems to imply that causal concepts are fundamentally agential. As part of this project we aim to ask the question: is such a distinction necessary? If so, how can we better understand it? We will also analyse the concept of “explanation”, with reference to the philosophical literature. What does it mean to explain a correlation? Does every explanation of correlation require an explanation of individual events? Are all explanations causal?