- #1
msumm21
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As described in the Wikipedia article about the Stern-Gerlach experiment, if an electron passes through the (Z-axis oriented) device it will hit a screen on the other side in one of 2 possible locations, call them the upper and lower locations. Sometimes the electron is "spin up" about the z-axis and it hits the screen in the upper location, other times it is "spin down" and hits the screen in the lower location.
This seems to imply that the electron is in the spin up or spin down state about the z-axis, but why can't it be in the spin up state about the x-axis or in any of the other infinite number of states? I know that a measurement of the spin about the z-axis will cause the spin state to be up or down about the z-axis, but I don't see that measurement taking place. I agree that the measurement of the location of the electron when it hits the screen gives away information about the spin (and therefore constitutes a spin measurement), but I don't see why that measurement is about the Z-axis. Why can't the electron hit the screen in other locations that are consistent with other spin orientations?
Looks like the total magnitude of the spin of an electron is sqrt(3)*hbar/2 and, when measured, its spin about a particular axis is either +hbar/2 or -hbar/2 (so there is another component of magnitude hbar/sqrt(2) in the plane normal to the axis of measurement). So, for example, why can't the electron hit the screen with no z-axis deflection corresponding to maybe a state with hbar/2 about the x-axis and hbar/sqrt(2) about the y-axis?
Thanks
This seems to imply that the electron is in the spin up or spin down state about the z-axis, but why can't it be in the spin up state about the x-axis or in any of the other infinite number of states? I know that a measurement of the spin about the z-axis will cause the spin state to be up or down about the z-axis, but I don't see that measurement taking place. I agree that the measurement of the location of the electron when it hits the screen gives away information about the spin (and therefore constitutes a spin measurement), but I don't see why that measurement is about the Z-axis. Why can't the electron hit the screen in other locations that are consistent with other spin orientations?
Looks like the total magnitude of the spin of an electron is sqrt(3)*hbar/2 and, when measured, its spin about a particular axis is either +hbar/2 or -hbar/2 (so there is another component of magnitude hbar/sqrt(2) in the plane normal to the axis of measurement). So, for example, why can't the electron hit the screen with no z-axis deflection corresponding to maybe a state with hbar/2 about the x-axis and hbar/sqrt(2) about the y-axis?
Thanks