# Electron spin problem

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1. Nov 29, 2015

### Sheldon Cooper

Hello,
I've been reading the Stern-Gerlach experiment, and where the concept of electron spin is introduced, am facing a problem, i.e., if you consider electron a charged rotating sphere, then the electromagnetic energy and size of the electron becomes huge!! So how do you deal with this?

2. Nov 29, 2015

### Staff: Mentor

By not considering the electron as a (classically) charged rotating sphere.

3. Nov 29, 2015

### cree_be_mee

I'm pondering the implications of the inherent spin of an electron as not having any classical comparison. The spin is 1/2 yet we have no evidence that an electron is more than a point particle. I have no idea how it is a point particle while it has mass. Yet consider the neutrino which only recently was found to have mass.

I'm working on a mechanism for electron - photon interaction that I'm hoping will describe an electron's "motion" despite having no evidence that they move through space at all. What is the linear momentum if not p=mv proportional to the velocity? Then how may it have angular momentum if there's no volume which may spin?

4. Nov 29, 2015

### Staff: Mentor

Quantum mechanics gives a good description and does not have all those issues a classical description would have.
That is the wrong approach. Learn about the existing experiments and theories first. To think outside the box you have to know where the box is first.

5. Nov 29, 2015

### Staff: Mentor

It's very hard to discover something new if you don't know what's already been discovered.

6. Nov 29, 2015

### DrChinese

As already mentioned, there is no need to re-invent the wheel. As to the idea that an electron is "only" a point particle: there is plenty of evidence to the contrary. Any electron interference experiment is such evidence (that its position is smeared out across a substantial volume of space). The Heisenberg Uncertainty Principle describes this phenomena.

7. Nov 29, 2015

### vanhees71

All evidence of electron tells us that it is not a point particle in the classical sense. That's why we describe it with quantum theory (in the most general sense in terms of relativistic quantum field theory within the Standard Model of elementary particles). As far as we know, it is an elementary spin-1/2 Dirac fermion with a mass of around $0.511 \; \mathrm{MeV}$. That's all you can say precisely about what an electron is, and this is a lot!

The only "mechanism" of electron-photon interaction is, as is implied by the very use of these words, quantum electrodynamics. An (asymptotic) free electron has a momentum $\vec{p}=m \vec{v}/\sqrt{1-\vec{v}^2/c^2}$. Only in the non-relativistic limit, i.e., for $|\vec{v}| \ll c$, it's $\vec{p} \simeq m \vec{v}$.

Last edited by a moderator: Nov 29, 2015