Gravitation and the noise needed in objective reduction models
  I briefly recall intersections of my research interests with those of John Bell. I then argue that the noise needed in theories of objective state vector reduction most likely comes from a fluctuating complex part in the classical spacetime metric, that is, state vector reduction is driven by {\it complex number valued} "spacetime foam". 
Stephen L. Adler
gr-qc hep-th math-ph math.MP quant-ph