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Quantum angular momentum is a different thing from the ordinary spin of a spinning top. It's not about mass revolving around a physical center. It's just there, almost as if you painted "The angular momentum is 10^-34 Joule-seconds, pointing to the left wall of the laboratory" on it. Despite that, a magnet acts on it exactly the same as if it were a spinning piece of charged metal. So it doesn't start as a spatial difference, but it becomes one once you pass it through the field. And one of the ways you can tell it's not the same as a spinning piece of metal is that the amount of spin is always exactly the same, regardless of how you orient the field. It's always that number I gave you above, called h-bar. The only question is whether it's positive or negative; it's going to be exactly one or the other. That's not what would happen to a regular object. For a regular object, you'd sometimes get 100% of h-bar, and sometimes 50%, and sometimes 0%, and sometimes -100%, depending on the angle between the spin and your apparatus. Just like if you were trying to measure the width of a piece of wood with a ruler: it depends on how you angle the ruler. Somehow, for quantum things, it's always exactly 100% or -100%. 100% things go one direction; -100% things go the other direction. You get exactly two lines, separated physically in space, even though there was no such separation in the original charged particle. |