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## Main Question or Discussion Point

I have been under the impression that application of a magnetic field will quantise the z component of an electrons spin in that direction. I see this as a physical process, but Is this incorrect as it is often described as a measurement of a random variable/ wavefunction collapse? I am familiar with the arguments of the Bell Inequality and appreciate how they would apply if the application of a magnetic field altered nothing, but am struggling to see how an application of a field would be assumed to have no effect on the initial state. Any insights would be greatly appreciated.