Spin is an operator with components (Sx,Sy,Sz) but do these represent "spatial" components. The question arose because the spin of an electron sets up an angular momentum L = -e/m * S (S and L are vectors) So inverting the spatial coordinate system and requiring that the physical result must be the same, the spin has to be reversed right? So what is spin up and what is spin down seems to be fixed by our choice of coordinate system. Is that correct or am I misunderstanding something? It just seems a bit weird to me, since spin is not really a true angular momentum but something intrisic and non spatial if I remember correct.