When an atoms/electron spin is measured, why do the measurements of spin always align with the direction of the magnets used while measuring it ? (based on my reading of Chris Bernhardt, Quantum Computing For Everyone).

Isn't the reason that when we measure spin using a magnetic field the atom/electron aligns itself parallel to this field. If so why is this behavior observed when measuring spin considered very peculiar?

  • $\begingroup$ Is this about the peculiarity of the spin aligning compared to classical magnetic moments? $\endgroup$
    – Mauricio
    Commented Aug 29, 2022 at 16:17

1 Answer 1


Attempting to answer the first question, the measurements always align with the direction of the magnets used due to the projective nature of the measurement. Since the measurements are projective they must be measured to one axis or the other.

As for why this is considered peculiar, I would suggest this is due to the probabilistic nature of that measurement. You may set up your experiment identically every time, but the results of that experiment will still be be probabilistic. (You can know the likelihood of each outcome, but not which outcome will be measured at any point.)


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