I thought that electrons, neutrons, and protons DID have a defined size.

However, even if they don't, they can still have a "scattering
cross-section", which is the volume which represents how close they
have to come in order to interact. Imagine, for example, a planet with
an asteroid passing by. Depending on how fast the asteroid is going,
there will be some distance of closest approach from which the
asteroid will be "captured" by the planet and pulled in. This would be
the scattering cross-section of that planet (which is a function of
speed in this case).

Sean


On Thu, Jul 5, 2012 at 8:13 PM, Nicola Perotto <nicola@nicolaperotto.it> wr=
ote:
> On 05/07/2012 20.56, Electron wrote:
>
>> One thing I don't get is... if the particles are "volumeless", how can t=
hey "collide"?
>
> Because aren't particles but waves! ;-))
>
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