#### NotEinstein

**Valued Senior Member**

I think hansda got confused a few lines above the one I just quoted:Hansda: my kitchen collander passes grains of sand. That puts an upper limit on grains of sand of about .5cm.

Can we now conclude grains of sand are about .5cm in diameter?

I think hansda saw thatIn classical physics, the angular momentum and magnetic moment of an object depend upon its physical dimensions. Hence, the concept of a dimensionless electron possessing these properties contrasts to experimental observations in Penning traps which point to finite non-zero radius of the electron. A possible explanation of this paradoxical situation is given below in the "Virtual particles" subsection by taking into consideration the Foldy-Wouthuysen transformation.

The issue of the radius of the electron is a challenging problem of the modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.

__completely unsourced__line about the Penning traps (which appears to be talking in terms of classical physics anyway), and ran with it. In doing so, (s)he forgot to read the rest of that section, where it clearly explains it's an unsettled issue.

Edit: Interestingly enough, there's similar discussions on the talk page:

https://en.wikipedia.org/wiki/Talk:Electron#Radius

https://en.wikipedia.org/wiki/Talk:...g_"caused_by"_virtual_photons,_"causes"_spin?

But there too, the statement is unsourced.

Edit2: Yes, it's a fully unsourced addition:

https://en.wikipedia.org/w/index.php?title=Electron&diff=prev&oldid=633949990

Thus it can safely be disregarded.

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