Physical picture of electron spin? Can the spin of an electron be understood as originating from an open string rotating around a perpendicular axis through its midpoint?
 A: I copy from my answer here,

When measurements started to look at the microcosm of atoms and particles, the conservation rules of energy, momentum were found to hold in the interactions, BUT unless an intrinsic angular momentum was given to particles, conservation of angular momentum would not hold. So by experimental observations a fixed angular momentum, called spin, was assigned to all elementary particles so that the observations would fit the quantum theory that was developing. This has been validated over and over again with all measurements.

If you are talking about strings as in string theory , where the electron is an excitation of a string, the same holds, because the excitation is chosen so that it fits the data known for the electron, it is an "assigned" mathematical location to fit the existing symmetry groups of the standard model. They are quantum excitations , not classical states rotating .
A: The spin of elementary particles can be understood as a rotation in the mathematical sense, due to it formally behaving like the ordinary angular momentum of three dimensional space. In that regard, you can assimilate it with the image of a top (for example) spinning about its axis, provided that you quantize the motion. But that's about as far as analogy goes. In your example of an electron, the property itself has nothing to do with a physical body rotating about an axis attached to it. But curiously enough, in a way it behaves as if that were true.
The  original experiment of Stern-Gerlach revealed the quantization of angular momentum, while the angular momentum picture of spin was first proposed by Goudsmit and Uhlenbeck a few years later.
A: Fundamental particles are  point like so they cannot be spinning.The quantum spin of a quantum particle is just something which gives the quantum particle angular momentum.
