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What exactly is meant by the word "particle"

  1. Feb 1, 2016 #1
    I was browsing through the content section of my book and see the word particle mentioned many times in many chapters. Each time I read I start thinking that maybe it can mean more than subatomic particles.
    I commonly deal with particles with point masses and things of the sort and I'm not sure exactly what it could mean in layman's terms
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  3. Feb 1, 2016 #2


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    In classical physics, a particle is an ideal point mass.

    In quantum mechanics and especially quantum field theory, the word "particle" is used, but it means something very different - electrons, photons, quarks, and all the rest of the subatomic zoo are not ideal point masses. There's no ambiguity or unclarity in the quantum mechanical description, but it doesn't match our intuition about how objects should behave.
  4. Feb 1, 2016 #3


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  5. Feb 2, 2016 #4


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    We used to speak about material points or point masses, now "particle" is frequently used instead.
  6. Feb 2, 2016 #5


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    All the above is perfectly ok thinking. The problem arose when 'they' started calling photons 'particles', which lumped them in with particles with mass. The properties of photons are, to my mind, sufficiently different for them to deserve a different word. I guess it's too late to do anything about that, unfortunately.
  7. Feb 4, 2016 #6


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    I'd say an electron in qft is a pointlike particle, having no internal stucture. What do you mean precisely by 'not ideal point masses'?

    Edit never mind, I just read

  8. Feb 6, 2016 #7


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    I'd define a "classical pointlike particle" as a macroscopic object for which it is in some given context sufficient to be described just by the position of one geometrical point related to this object. Usually it's convenient to choose the center of mass (or in relativistic physics the center of energy) as this point. E.g., for the description of the motion of the Earth around the Sun, it is not too wrong to describe the Earth as a "point particle".

    Elementary particles like electrons are usually not describable as classical point particles, because they must be described quantum theoretically.
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