Re: experimental measurement of electron diameter?

In article <daui150vqb@xxxxxxxxxxxxxxxxxx>, Bob Cain <arcane@xxxxxxxxxxxxxxxxx> writes:
>
>
>mmeron@xxxxxxxxxxxxxxxxxx wrote:
>> Do you see, in *classical physics* any
>> problem with two point particles interacting?
>
>Yeah, I do but that doesn't mean there is one. :-)
>
>How is a range of interaction different than a finite size?

That's getting into the semantics of how we do define "size". Two
masses interact gravitationally over an infinite range but we don't
take it to mean that their size is infinite. We could take it this
way but then the word "size" would mean something different than it
means now.

Basically we evaluate the differential cross sections for particle
interactions for all the known fields (the dreaded "force over a
distance" but if you don't like it you can use exchange of virtual
particles instead) assuming zero size and compare with the measured
scattering data (for the case of electrostatic interaction, as well as
Newtonian gravity the cross section you get is the famous Rutherford
cross section). If, within the error margins, the data agrees with
the "zero size" calculation then we say that, again within the error
margins, the particle size is zero. Mind you, this doesn't mean that
it actually necessarily is zero, just that within the accuracy of the
data the size cannot be distinguished from zero.

> If there is a finite cross section for all interactions
>what does it mean to define the particle as a point?
>
See above.

Mati Meron | "When you argue with a fool,
meron@xxxxxxxxxxxxxxxxx | chances are he is doing just the same"
.

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