What does and does not have intrinsic spin?
Wikipedia Spin (Physics)
https://en.wikipedia.org/wiki/Spin_(physics)
says:
“In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.”
But it doesn’t say that only those items have intrinsic spin.
Is this list comprehensive? Or do other things have intrinsic spin? (as opposed to orbital angular momentum?) For example: molecules? Buckyballs?Ball Bearings? Schrodinger cats?
Wikipedia Spin (Physics) goes on to say:
“Spin is one of two types of angular momentum in quantum mechanics, the other being orbital angular momentum. Orbital angular momentum operator is the quantum-mechanical counterpart to the classical notion of angular momentum: it arises when a particle executes a rotating or twisting trajectory (such as when an electron orbits a nucleus).[3][4] The existence of spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which particles are observed to possess angular momentum that cannot be accounted for by orbital angular momentum alone.”
Of course every large item has lots of electrons among other things and so it has spin due to the constituent electrons. I mean does the large object have any intrinsic spin of its own, beyond that inherited from its constituents.
Arguing the other way is
http://www.askamathematician.com/2011/10/q-what-is-spin-in-particle-physics-why-is-it-different-from-just-ordinary-rotation/
In its derivation that every three dimensional object is either a fermion or a boson, where it states:
“By the way, notice that at no point has mass been mentioned! This result applies to anything and everything. Particles, groups of particles, your mom, whatevs!”
Is everything either a fermion or a boson?
No matter how large?
And thus perhaps possess its own intrinsic spin?
Or does this only apply to total angular momentum and not intrinsic spin.
I’m confused. Help!
Best Answer
Things have intrinsic spin.
There's no "class of objects" that has spin and another class of objects that doesn't. Everything is a quantum object with a quantum state, and spin is a number that tells you how the state of the object transforms under rotations. It is different from "classical" angular momentum in that spin is not the operator associated to $\vec r \times \vec p$, which would be the usual angular momentum, but it is an angular momentum since it is a conserved charge of the rotation group. In most cases, though, the individual spins of the constituents of macroscopic objects will be completely uncorrelated, and sum to zero on average, so you don't notice it in large objects. A notable exception are permanent magnets, which derive their magnetic properties from the alignment of the individual electron spins.
Not everything is "a fermion" or "a boson". These are terms for elementary particle states for which one can write down creation and annihilation operators, and the property essentially derives from whether these commute or anticommute. Entire systems are not created in such a simple Fock creation/annihilation formalism, it doesn't really make sense to assign the terms "boson" or "fermion" to them because they are not associated to any bosonic or fermionic creation/annihilation operators.
Not even every particle is a fermion or boson, in two dimensions, the spin statistic theorem fails due to the different structure of the Lorentz group, and there are anyons with fractional spins and fractional statistics.