Title: Deterministic and Stochastic Counterfactuals, Interference Between Treatments, Causal Interactions, Bell's Inequality in Quantum Mechanics, and The Nature of Reality
James M. Robins
Departments of Epidemiology and Biostatistics, Harvard School of Public Health (based on joint work with Tyler Vanderweele and Richard Gill)
Neyman introduced a formal mathematical theory of counterfactual causation that now has become standard language in many quantitative disciplines, but not in physics. We use results on causal interaction and interference between treatments (derived under the Neyman theory) to give a simple new proof of a well-known result in quantum physics, namely, Bell's inequality.
Now the predictions of quantum mechanics and the results of experiment both violate Bell's inequality. In the remainder of the talk, we review the implications for a counterfactual theory of causation. Assuming with Einstein that faster than light (supraluminal) communication is not possible, one can view the Neyman theory of counterfactuals as falsified by experiment. The last sentence remains true, even when we extend the Neyman theory to allow for stochastic counterfactuals.
By the end of the talk we will have answered the following. How is it possible that empirical data can be used to reject the existence of counterfactuals outcomes? Is it safe for a quantitative discipline to rely on a counterfactual approach to causation, when our best confrimed physical theory falsifies their existence?