Double Stern-Gerlach experiment

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If I were to take some electrons and send them through a Stern-Gerlach experiment, then under normal conditions half of them would be deflected upward and half downward. If however, I were to make an hole in the machine where the spin up particles were detected after selection, and now instead of hitting a detector they go through another Stern-Gerlach experiment . Would those particles all still be spin up, even though they never hit a detector, or would they split into two groups again, spin up and spin down?

 

[The_Duck]

If however, I were to make an hole in the machine where the spin up particles were detected after selection, and now instead of hitting a detector they go through another Stern-Gerlach experiment . Would those particles all still be spin up

Yes.

The Feynman Lectures on Physics has a nice and detailed discussion of this scenario and many similar ones.