This post is a result of reading RKaster's links and I am wondering if there is some evidence that supports measurement being a two stage process. In the Stern Gerlach experiment the particles are in superposition until measured. But is the superposition ended once they enter the magnetic field? If we have a particle prepared in a spin up direction and then seek to determine its direction in a left right direction what is occurring? Is the left/right distinction made when the magnetic field is applied or when it it finally measured? Is there an experiment that can distinguish between the two situations?