Doubts about the electron magnetic moment.

[carllacan]

Hi.

According to this page and other sources I found the z-component of the electronic magnetic moment is greater than the classically calculated value due to relativistic effects. Which makes me wonder:

1) What about the x and y components? I am completely lost as to why only the z axis is mentioned. I'm thinking that it is assumed that the axis of rotation of the electronand therefore the moment are aligned in that direction and therefore the x and y comps are 0. Am I right?

2) How are relativistic effects sneaking in here? There isn't anything going really fast, which I thought (perhaps naively) was necessary for them to be relevant.

Thank you.

 

[mfb]

1) What about the x and y components? I am completely lost as to why only the z axis is mentioned. I'm thinking that it is assumed that the axis of rotation of the electronand therefore the moment are aligned in that direction and therefore the x and y comps are 0. Am I right?

Right. The z axis is chosen to be aligned with the spin.

2) How are relativistic effects sneaking in here? There isn't anything going really fast, which I thought (perhaps naively) was necessary for them to be relevant.

To make quantum mechanics compatible with special relativity, you need a different description of electrons - and spin is one result of that different description.

 

[carllacan]

Does that different description of electrons happen to be the Dirac equation?

 

[mfb]

Sure.