# Are there any regulating condition on the spin of particle?

Are there any regulating limit on spin of particle?.E.g why spin of electron is 1/2 but not 3/2,spin of photon is 1 but not 2 e.t.c
Thank you very much in advance.

Related Quantum Physics News on Phys.org
Currently, what is assumed is that an electron's spin is an intrinsic property. That it originates from the angular momentum of the particle.

In quantum mechanics, angular momentum is quantized (meaning that it is not only comprised of energy but also of particles). Since physical particles are enabling this spin to occur, there should be a countable, finite number of them. Perhaps that explains why the numbers are finite ratios of integers, and not weird repeating decimals.

I cannot answer WHY every particle has some intrinsic angular momentum (probably due to the conditions under which it was formed).

One of the "regulating conditions" you ask about is most likely the quantization of angular momentum. Generally when you think of angular momentum, you think of some kind of energetic value, not chunks of matter that are rotating the object in question around.
If you want to know why angular momentum is quantized, you can refer to this thread: https://www.physicsforums.com/showthread.php?t=194897

This is a good source to read further: http://www.electronspin.org/
Also, this Wikipedia page explains how in relatively simple terms (but not why): http://en.wikipedia.org/wiki/Spin_(physics [Broken])

Last edited by a moderator:
So,are there any relations between symmetry(e.g Lorentz symmetry) and quantization of energy(because we think of angular momentum as some kind of energy)?

Are there any general transformation of spinor(or field operator of high spin particles) under Lorentz symmetry?

A. Neumaier
2019 Award
I cannot answer WHY every particle has some intrinsic angular momentum (probably due to the conditions under which it was formed).
Because it is part of the defining conditions. If one observes a particle with different quantum numbers (mass, spin, and charges) from one of the standard ones, one concludes that it is not one of the standard particles.

A. Neumaier