Tuesday, February 23, 2016

quantum mechanics - Can two electrons have the same momentum and spin directions?


I am trying to understand the Pauli exclusion principle. Here is an except from Feynman Lectures on Physics



It just isn’t possible at all for two Fermi particles—such as two electrons—to get into exactly the same state. You will never find two electrons in the same position with their two spins in the same direction. It is not possible for two electrons to have the same momentum and the same spin directions. If they are at the same location or with the same state of motion, the only possibility is that they must be spinning opposite to each other.



http://www.feynmanlectures.caltech.edu/III_04.html [emphasis added]



I don't understand about "It is not possible for two electrons to have the same momentum and the same spin directions." Is it not possible for two electrons, even if they are at different locations, to have the same momentum and the same spin directions?




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