# what does it mean for a particle with no size to have angular momenta?

I recently was reading about higgs boson and particle spin recently and I stubble upon an question that contains an answer to what a spin is.

It explains that electrons etc. have no size yet they have angular momenta. I dont understand what exactly is meant by that. Does it refer to the angular momenta of the magnetic field? I just dont imagine something with no size having any sort of angular momentum.

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You've check marked wrong answer. Spin is an attribute of individual electron.. not of a collection of electrons. –  Sachin Shekhar Jul 7 '12 at 10:10
Please do not accept wrong/vacuous answers, it dilutes the value of the site. Sachin Shekar's answer is not good. The spin angular momentum is a real honest to goodness angular momentum, not a mathematical analogy. It can be seen in the Einstein deHaas effect. –  Ron Maimon Jul 8 '12 at 7:33
Thank you for your comment I will look into it. I do not know enough about it to decide which answer is the best yet but i will read the Einstein deHaas effect and then try to judge. I dont know what to do in a situation like this If there is a way to start a discussion about which answer is better or have community resolve this problem in another way. Otherwise I will do my best. –  Xitcod13 Jul 8 '12 at 20:58

As a answer, first I'd like to ask why you're asking a quantum mechanics problem with classical mechanics mental model.

There are two types of angular momentum in quantum mechanics:

1. Orbital angular momentum, which is a generalization of angular momentum in classical mechanics (L=r×p). I think, you shouldn't have problem with this because Orbital has size.

2. Spin, which has no analogue in classical mechanics. You can understand it as a number appeared in quantum equation. It can be understood like charge(with physical dimension), which is a number to denote one of basic attributes of particles. Yes, Spin does have physical dimension of angular momentum. But, its because it is a type of angular momentum, mathematically.

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to answer your first question is because i would understand quantum mechanics i would not ask questions about it. Q.M. has a lot of confusing vocabulary which means something else in "regular" english. Also what exactly do you mean by "which is a number (with physical dimensions)" numbers cant have physical dimensions. You mean the charge with physical dimensions? –  Xitcod13 Jul 6 '12 at 13:08
@Xitcod13 I meant charge is ((just a number)) with physical dimension.. Ofcourse, numbers don't have physical dimensions. :) –  Sachin Shekhar Jul 6 '12 at 13:17
Spin is not a type of angular momentum, it is angular momentum, period. This is demonstrated by the Einstein deHaas experiment detailed in my answer. –  Ron Maimon Jul 8 '12 at 6:45
@Ron That experiment is out-dated. At that time, there wasn't any concept of Orbital. –  Sachin Shekhar Jul 8 '12 at 7:21