SG results and Realism

[Alan Grayson]

Since spin is determined by the axis of an SG apparatus, and different axis orientations give difference spin orientations, is this sufficient to deny Realism since the spin is determined by the measuring device, and has no preexisting orientation? TY, AG

[Brent Meeker]

I don't think you can conclude that the particle did not a have a spin state before measurement.  We certainly know that when it does have a spin state that we know, the SG result still depends on the SG orientation.  So it is not true that "the spin is determined by the measuring device"; it is determined by both the particle spin state and the apparatus.

Also note that I used the phrase "spin state" not spin "axis" or "orientation".  That's because the spin state can include superpositions of different axes with different phases.  States that are superpositions of the measurable eigenstates are still real states even though we don't have an instrument that detects them, e.g. a circularly polarized electron wave.

Brent

On 11/24/2024 7:40 PM, Alan Grayson wrote:

Since spin is determined by the axis of an SG apparatus, and different axis orientations give difference spin orientations, is this sufficient to deny Realism since the spin is determined by the measuring device, and has no preexisting orientation? TY, AG --

[scerir]

AG wrote: Since spin is determined by the axis of an SG apparatus, and different axis orientations give difference spin orientations, is this sufficient to deny Realism since the spin is determined by the measuring device, and has no preexisting orientation?

scerir: The Aharonov-Bergmann-Lebowitz rule (ABL) assigns *probabilities* to outcomes of quantum measurement results, at time t, on the condition that the system is prepared (preselected) in a given way at t1 < t and found (postselected) in a given state at t2 > t

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