B Polarized Electron in a Rotating Reference Frame

[Dale]

won't the electron also exert a torque on the permanent magnet, causing it to begin to rotate ... over a long timescale

The torque is constantly changing direction as the electron precesses. Every $\pi$ seconds the torque is applied in the opposite direction and undoes whatever minuscule angular acceleration may have happened $\pi$ seconds before. As long as it doesn't affect the magnet over a time scale of 2$\pi$ seconds then it will not affect it over long timescales either.

 

[metastable]

The torque is constantly changing direction as the electron precesses. Every ππ\pi seconds the torque is applied in the opposite direction and undoes whatever minuscule angular acceleration may have happened ππ\pi seconds before. As long as it doesn't affect the magnet over a time scale of 2ππ\pi seconds then it will not affect it over long timescales either.

So to attempt summarize what I think I've learned:

In the absence of an outside magnetic field, the electron cannot precess.

Still feeling unsettled because I can't help but think even if the permanent magnet had no charge, it would require an outside force to counteract the gravitational attraction to keep the system undisturbed over a long timescale.

 

[Dale]

If something that negligible unsettles you then there is little anyone else can do for you. I can’t think of a more negligible effect here.

Are you still interested in rotating reference frames or is your interest now changed to long time scales? I had thought that your interest was in rotating reference frames, and others thought it was in electrons, and now I am unsure.

 

[metastable]

Are you still interested in rotating reference frames or is your interest now changed to long time scales? I had thought that your interest was in rotating reference frames, and others thought it was in electrons, and now I am unsure.

Is there a method that will cause the vector of the electron's magnetic moment to stop precessing & continuously point in a desired direction? Suppose I observe a distant galaxy and I want each measurement I perform of the electron's magnetic moment vector to show that it is substantially parallel with the vector pointing towards that galaxy from my present position within some small margin of error. What forces and methods would I rely on to orient the vector of the electron's magnetic moment in this desired vector?

 

[Dale]

Is there a method that will cause the vector of the electron's magnetic moment to stop precessing & continuously point in a desired direction?

Not that I know of. But why not just use a classical gyroscope instead?

 

[Nugatory]

Is there a method that will cause the vector of the electron's magnetic moment to stop precessing & continuously point in a desired direction?

No, if you’re thinking about an electron and quantum mechanical spin (and look at post #17 above again). Yes, if you’re thinking about a classical charged rotating object like a gyroscope.

 

[metastable]

No, if you’re thinking about an electron and quantum mechanical spin (and look at post #17 above again).

I'm confused... does that mean that for non-precessing electrons, the vector of the magnetic moment can only take one of 2 values-- up or down... or does it mean the vector could be measured to point in any direction, but I have no way to alter this direction according to my wishes?

 

[Dale]

This is going nowhere. Please make a choice:

If you want to learn about quantum mechanical spin and precession of electrons in a magnetic field, open a thread about that in the QM forum. Do not include any complications about rotating reference frames.

If you want to learn about rotating reference frames, choose a classical example and open a new thread about that here. Do not include any complications about quantum mechanical objects like electrons.

This thread is closed.