2017 Annual Lecture in Memory of Prof. Itamar Pitowsky

19.4.2017,Â 20:00,Â At the Edelstein Center

Robert Spekkens,Â Perimeter Institute for Theoretical Physics

Cause and effect in a quantum world

Scientific explanation often involves makingÂ inferences about what is unobservable from what is observable.Â Â An important example is the problem of makingÂ inferences aboutÂ causal mechanisms from observed correlations. In the context of quantumÂ theory, the problem of inferring causal mechanisms is particularlyÂ vexing. OneÂ of the central results in the foundations of quantum theory, Bell’sÂ theorem, can be understood as demonstrating that it is impossible to provideÂ a causalÂ explanation of the correlations that arise for entangled quantumÂ systems without resorting to fine-tuning. Impossible, that is, using theÂ standard framework of causalÂ models.Â An intrinsically quantumÂ notion of a causal model, however, holds promise for achieving suchÂ an explanation. Critically, this notion makes sense only if theÂ correct theoryÂ of Bayesian inference is assumed to be determined empirically, and classicalÂ probability theory is understood to be merely a special case of a moreÂ generalÂ theory.Â The notion also has practical applications, allowing one to inferÂ causal relationships from observed correlations in scenarios whereÂ classically oneÂ could not.Â Contrary to the statistician’s slogan, inÂ a quantum world, certain kinds of correlationsÂ *do*Â imply causation.