Point particles

Discussion in 'Physics & Math' started by quantum_wave, Jun 4, 2008.

  1. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    http://en.wikipedia.org/wiki/Point-like_particle

    What does theory say as to how a point particle has energy? Are we talking wave form, or standing wave, or how is the energy of a point particle ... manifested or demonstrated? I'm not talking string theory, but quantum field theory standard model fundamental particles with no detectable component parts?
     
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  3. Vkothii Banned Banned

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    There does seem to be a bit of misunderstanding about what a fundamental particle or a quantum is, what its components are, as you say.

    A particle with mass has energy because it has a rest mass, it has inertia and that means it interacts with gravity, and if it has momentum, that's because it isn't at rest. "At rest" of course, means not moving in respect of some other particle. Even at rest, a particle with mass has an equivalent energy.

    Photons are particles because they are composed of electric and magnetic moments, they have a momentum and a direction, they interact with external electric and magnetic fields, they diffract, or scatter like particles, but like waves too, depending on how you look at it, literally. The only thing they don't have is mass. If they did, they wouldn't travel so fast, and they would couple to the EM field or have a charge as well.

    Point particles are a good model for things like electrons and quasiparticles in semiconductors, especially as a classical "group" of individual objects with a collective motion. Electrons diffract and scatter like waves too though.

    At least that's what I found out in the lab, as it were.
     
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  5. Reiku Banned Banned

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    Personally, i don't like the point particle notion at all. I wonder if it will ever change...
     
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  7. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Thank you; the reason I was asking was to get an informed view like you have given and to understand the usage of the phrase "point particle". From what you say about energy and fundamental particles we can differentiate between the the usage of the phrase "point particle" as a model of the fundamental particle and the extreme usage in my opinion, i.e. an infinitely dense zero volume point energy like you get if you backtrack General Relativity to a point origin.

    I've heard it said that fundamental particles have vacuum energy or ground state energy that is far greater than "rest" energy and that is a good part of the incompatibility between GR and quantum theory. This vacuum energy comes from symmetry breaking which in the case of the point origin in GR would have corresponded with the cause of expansion and with the matter anti-matter described at the earliest point of the formation of the universe.

    Thank you for helping me sort out the difference in usage of the term.
     

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