zlacker

>>qqqqqu+(OP)
Quantum spin. Electrons aren't really spinning, right? But why do we call it spin? I know it has something to do with angular momentum. What are the possible values? Is it a magnitude or a vector? Is there a reason we call it "spin" instead of "taste" or some other arbitrary name? How do you change it? What happens to it when particles interact?

>>pjungw+uk
No, they are not really spinning. However the spin quantum property does make the particle deflect as if it were spinning when it moves through a magnetic field, thus the name.

It is techinically a two-component spinor, which is why the direction of the spin 'moves' if you measure it along different x,y,z axes. It is also quantized unlike a normal vector: All fermions have quantized half-integer spin magnitudes and all bosons have integer magnitudes.

Magnetic fields can be used to change the spin.

When particles interact, opposing spins tend to pair up in each electron orbital which cancels the magnetic field. This is why permanent magnets must have unpaired electron orbitals.

>>aetern+pr
Can you please formally define what a spinor is? Like, mathematically, what are they?

>>bollu+DQ
A quaternion is a (more-commonly known?) type of spinor which is often used in 3d graphics in matrix form to perform rotations.

Spinors are difficult to describe in an HN post since they require a good amount of linear algebra, but my favorite explanation is probably here: http://www.weylmann.com/spinor.pdf