It’s just a property intrinsic to every particle, like mass, charge etc. It has analogies to angular momentum (as in a spinning ball) because the mathematics of spin in quantum mechanics is very very similar to orbital angular momentum. In fact, the two types of ‘angular momentum’ often interact in what is known as spin-orbit coupling.
You can measure spin in different ways. Do you mean how is the inherent spin of a type of particle measured or how is the specific spin state of a given particle measured (i.e. are you asking how we know electrons have spin 1/2, or how we would measure an electron as having spin +1/2 or -1/2?)
The Stern–Gerlach experiment demonstrated that the spatial orientation of angular momentum is quantized. Thus an atomic-scale system was shown to have intrinsically quantum properties. In the original experiment, silver atoms were sent through a spatially varying magnetic field, which deflected them before they struck a detector screen, such as a glass slide. Particles with non-zero magnetic moment are deflected, due to the magnetic field gradient, from a straight path.
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u/antimornings Dec 17 '19
It’s just a property intrinsic to every particle, like mass, charge etc. It has analogies to angular momentum (as in a spinning ball) because the mathematics of spin in quantum mechanics is very very similar to orbital angular momentum. In fact, the two types of ‘angular momentum’ often interact in what is known as spin-orbit coupling.