This post is basically a video about the so called Einstein de Haas effect from the Action Lab (a video channel). This experiment is often mentioned as experimental validation that electrons have so called “Intrinsic angular momentum”. The experimental setup is very easy to explain, look in the next picture:
A metal cylinder is hanging from a wire (the guy in the video uses tooth floss because that has no winding twist in it so the cylinder will not rotate). If placed in a vertical magnetic field or such a vertical magnetic field is flipped on, the cylinder rotates a little bit.
Often in the experimental setup a coil magnet is used, but it can be any more or less perfect vertical magnetic field. The effect of the rotation is rather small so in video’s like this you often see some shiny or reflecting metal glued to the cylinder and with a light the rotation is amplified for us to see.
The explanation you always see is that the unpaired electrons in the metal cylinder align themselves with the applied magnetic field. So that’s the logic for the explanation of this experiment.
How different is it for the Stern Gerlach experiment that is very similar because it is about the behavior of unpaired electrons in a vertical applied magnetic field. In the SG experiment the beam of silver atoms is split in two and now the logic is as next, quote:
This means that when you take a beam of electrons whose angular momenta are all randomly oriented, if you measure the z component of angular momentum you get one of only two different values.
But if your explanation in the Einstein de Haas effect would be this 50/50 percent probability in spin up or spin down, that would imply zero rotation and therefore once more day the physics professors will talk out of their necks and now it must be logical that all electrons align.
Source of my above quote:
Measuring Electron Spin- the Stern-Gerlach Experiment
Furthermore it is a fundamental basis of quantum computing that it must be possible to have superpositions of quantum states. So if the explanation of the Einstein de Haas effect would be correct, there is no randomness in electron spin measurements via application of external magnetic fields. You just can’t eat it from both sides: either all electrons will do the same or the probabilistic nature of quantum mechanics is true. Anyway here is the video with the title: Do Electrons Really Have “Intrinsic” Angular Momentum?
https://www.youtube.com/watch?v=uQ5w4_0S2l4
That was it for this post on magnetism in particular the very different explanations you hear when we are talking about the same thing: The reaction of an electron on a vertical magnetic field.