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Meaning of size in subatomic

  1. May 16, 2008 #1
    What is, and is not meant, by size when it comes to the subatomic world?

    The FAQ's of this forum, and a wikipedia article I read recently seem to agree that "the very notion of a discrete 'particle' has been ultimately replaced by the concept of something like wave-packet of an uncertain boundary".

    I think I like that statement, but I still read from time to time that subatomic particle P has size less than 10^-M meters, for example. How would one conclude that without assuming a certain boundary? In what ways do these size statements have meaning and in what ways do they not have meaning subatomically?
  2. jcsd
  3. May 16, 2008 #2
    I think that a good measure for the size of a particle is the size of an area where the probability density of subparticles (that construct the original particle) is high enough. Example are atomic orbitals: they are defined as the volume that has 95% chance to contain electron (although complete definition should also say that the volume drops 5% of the space with minimal probability density).
  4. May 18, 2008 #3
    Okay, that sounds reasonable for compound particles.
    If I have an elementary subparticle, say, a standalone electron. I think I'm supposed to be able to accept a zero, point-like width on one hand, and also accept an uncertain boundary on the other hand. A point seems to be an absolutely certain boundary, so I don't understand the apparent conflict in the language.
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