On Multi-Time Correlations in Stochastic Mechanics

We address a long-standing criticism of the stochastic mechanics approach to quantum theory by one of its pioneers, Edward Nelson: multi-time correlations in stochastic mechanics differ from those in textbook quantum theory. We elaborate upon an answer to this criticism by Blanchard et al. (1986), who showed that if the (derived) wave function in stochastic mechanics is assumed to collapse to a delta function in a position measurement, the collapse will change the stochastic process for the particles (because the stochastic process depends on derivatives of the wave function), and the resulting multi-time correlations will agree with those in textbook quantum theory. We show that this assumption can be made rigorous through the tool of `effective collapse' familiar from pilot-wave theories, and we illustrate this with an example involving the double-slit experiment. We also show that in the case of multi-time correlations between multiple particles, effective collapse implies nonlocal influences between particles. Hence one of the major lingering objections to stochastic mechanics is dissolved.