  Nondifferentiable fluctuations in space-time on a Planck scale introduce
stochastic terms into the equations for quantum states, resulting in a proposed
new foundation for an existing alternative quantum theory, primary state
diffusion (PSD). Planck-scale stochastic space-time structure results in
quantum fluctuations, whilst larger-scale curvature is responsible for
gravitational forces. The gravitational field and the quantum fluctuation field
are the same, differing only in scale. The quantum mechanics of small systems,
classical mechanics of large systems and the physics of quantum experiments are
all derived dynamically, without any prior division into classical and quantum
domains, and without any measurement hypothesis. Unlike the earlier derivation
of PSD, the new derivation, based on a stochastic space-time differential
geometry, has essentially no free parameters. However many features of this
structure remain to be determined. The theory is falsifiable in the laboratory,
and critical matter interferometry experiments to distinguish it from ordinary
quantum mechanics may be feasible within the next decade.
