Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Virtual Photon

  1. Nov 24, 2009 #1
    In my lecture this morning i was told that charged particles interact by the exchange of virtual photons and that they serve as carriers of momentum and force. But it says that a photon is a boson with spin number 1, massless and zero charge.

    The question is basically how can a massless particle carry momentum ?
  2. jcsd
  3. Nov 24, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    I would ask you: on what mathematical grounds does a massive particle carry momentum ?
  4. Nov 24, 2009 #3
    It is irrelevant if it is virtual or not. Real photons are also masless, but they carry momentum. Massless = no rest mass, you are probably thinking about the 'relativistic' mass.
  5. Nov 24, 2009 #4

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Elaborating a bit on what Dmitry67 wrote, according to special relativity, the energy, momentum, and rest mass of a particle are related by

    [tex]E^2 - \left( cp \right)^2 = \left(m c^2 \right)^2.[/tex]

    For a photon, [itex]m=0[/itex] and [itex]E = cp[/itex].

    Even classical electromagnetic fields carry momentum.
  6. Nov 24, 2009 #5


    User Avatar

    Staff: Mentor

    And with the same relationship, if you considerf E and p as the energy and momentum densities of the fields.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook