When an electron goes thru a Stern-Gerlach appliance it changes its spin projection. Then there must be a change of energy content of the electron due to this event. But it is also known that magnetic field carries no energy. So I wonder where the energy (if any) can come from?
After realizing that the electron energy does not depend on the projection of the spin it seems obvious that the energy of the electron doesn't change when it passes a magnetic field (or SG). But then something very peculiar immerges: 1.the state of something changes without any energy exchange 2.the magnet induces a change in the electron but it doesn't change a bit