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How come there is a particle with zero mass?

  1. May 2, 2009 #1
    How come there is a particle with zero mass??

    My question is probably very lame, please excuse me

    how come there is some particle that has no mass and no charge? (like photons) does such a particle really exist? or they are just "virtual" particles thought for better understading of some phenomenons?
  2. jcsd
  3. May 2, 2009 #2


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    Re: How come there is a particle with zero mass??

    They aren't really particles in everyday terms - a photon is a lump of electro-magnetic fields.
  4. May 2, 2009 #3
    Re: How come there is a particle with zero mass??

    A photon does not have any mass and charge, indeed, but it is real.

    A photon has energy and momentum to transfer/obtain, so it can interact. If you remember that a photon is an electromagnetic wave that appears in the electron equations of motion, you will have a clear picture of photon-electron interaction. This interaction is rather strong, so it cannot be neglected without getting in trouble (infrared catastrophe).

    Last edited: May 2, 2009
  5. May 2, 2009 #4


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    Re: How come there is a particle with zero mass??

    If a photon isn't a particle in everyday terms, then neither is an electron, or any of the other particles of the standard model. Particles are quantum systems with Hilbert spaces that are the representation spaces of irreducible projective representations of the Poincaré group (or representations of its covering group). Massless particles can exist because there are massless representations. Electrons can exist because there are massive spin 1/2 representations.

    To the OP: I don't think there's any way to explain this in less mathematical language.

    Actually, what I wrote is an oversimplification. That stuff only defines the mathematical description of non-interacting particles. There seems to be no end to how much you have to learn to really understand interacting particles.
  6. May 2, 2009 #5
    Re: How come there is a particle with zero mass??

    photons are definitely real; if you're having trouble thinking of them as particles try thinking of them as packets of energy proportional to their wavelength which transmit the electromagnetic force
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