Quantum mechanics has always presented a problem for scientific realists. For it does not seem to offer a coherent picture of the world. I think it does, and that there is a viable quantum mechanical model of reality. But it cannot be constructed, given the continuity constraints that we usually place on realistic models. To be a quantum mechanical realist, one has to be willing to accept that there are two fundamentally different kinds of processes occurring in nature: continuous, but quantum mechanically indeterminate, energy transfer processes and discontinuous, but spatially extended, changes of state. The unwillingness of philosophers to accept that there is such a distinction has caused many of them to doubt the reality of Schrödinger waves, and the processes of their generation and collapse. I am fully aware that I am treading on well-trodden territory, and that the technical difficulties that must be faced by anyone who is not a specialist in the field are immense. Nevertheless, I think there is a fairly clear metaphysical position on these issues derivable from the kind of essentialist realism outlined in the previous chapter, and I ask readers to bear with me.

First, realism about Schrödinger waves requires the belief that particles are always transmitted as quantum mechanically indeterminate waves, but always act as classically determinate particles on whatever absorbs them. The probability of absorption by a given absorbing object (e.g. measuring instrument) at a given location is determined by the value of the Ψ-function at this point.