Cause and effect in a quantum world

Speaker

Robert Spekkens, Perimeter Institute

Abstract

Scientific explanation often requires us to make inferences about what is unobservable from what is observable.  An important example of this pattern is to make inferences about causal mechanisms from observed correlations. In the context of quantum theory, the problem of figuring out what causes what is particularly vexing. One of the central results in the foundations of quantum theory, Bell's theorem, can be understood as demonstrating that it is impossible to provide a causal explanation of the correlations that arise for entangled quantum systems without resorting to fine-tuning. Impossible, that is, using the standard framework of causal models.  A new quantum notion of a causal model, however, holds promise for achieving such an explanation.  It also has practical applications, allowing one to infer causal relationships from observed correlations in scenarios where classically one could not.  Correlation does not imply causation… except in a quantum world, where for certain kinds of correlations it does.