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After measuring a quantum state for a particular measurable, the state collapses to one of the eigenstate of that measurable. If we measure for momentum in an infinite square well, the system will collapse to a momentum eigenstate. But uncertainty in position is not arbitrary large (it's $2L$). So we are left with finite uncertainty in momentum and position at the same time. Does this mean that we aren't supposed to make such measurement? Or something else.


marked as duplicate by Qmechanic quantum-mechanics Oct 28 '16 at 13:28

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