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Ehrenfest theorem


The Ehrenfest theorem, named after Paul Ehrenfest, an Austrian theoretical physicist at Leiden University, relates the time derivative of the expectation values of the position and momentum operators x and p to the expectation value of the force F = −dV/dx on a massive particle moving in a scalar potential,

Loosely speaking, one can thus say that "quantum mechanical expectation values obey Newton’s classical equations of motion". (This loose statement needs some caveats, see.)

The Ehrenfest theorem is a special case of a more general relation between the expectation of any quantum mechanical operator and the expectation of the commutator of that operator with the Hamiltonian of the system


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