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I How fast do fundamental forces propagate?

  1. Jun 14, 2016 #1
    So, I've been looking at this chart
    four-fundamental-forces-1.jpg

    Only Electro-magnetic force is carried by massless particle - photon. And it propagates at the speed of light. Now take Weak and Strong force. They are carried by bosons and gluons. They have mass. So, what is the speed of propagation of Weak and Strong forces, if that question makes any sense. It seems that it can't propagate at the speed of light because you can't have mass traveling at the speed of light.
     
  2. jcsd
  3. Jun 14, 2016 #2

    mfb

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    Gluons are massless as well.

    As far as it makes sense, the speed is still the speed of light, but especially for the weak interaction that concept is not really meaningful. You don't need a particle going from A to B to have an interaction - you need the fields at B change as a result of whatever happens at A. The fields are not particles.
     
  4. Jun 14, 2016 #3
    I have trouble understanding why we have force carrier particles. As you said, and I understood that, for electric force to act on something there has to be electric field. But I don't understand why do we have particles that carry weak and strong forces. Can't we also have some kind of field for each of those two forces, like we have electric and magnetic field for electric and magnetic forces?
     
  5. Jun 14, 2016 #4

    mfb

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    Sometimes the exchange of particles is a good model. Sometimes it is not. Depends on the process.
     
  6. Jun 14, 2016 #5
    Alright, what about electric force. If we have positive charge located at distance "d". There is an electric field going from positive charge. For an electron in that field there is a force F=E*q.
    Now if we look at force carriers of the electric force - photons. How does electric force acts? Does positive charge produces photons and electron absorbs them? Can we see those photons?
     
  7. Jun 14, 2016 #6

    mfb

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    It is possible to model the interaction via the exchange of virtual photons, but they are just mathematical tools to approximate the field, because working with the field can be too challenging sometimes.
    No, there are no real photons involved.
     
  8. Jun 14, 2016 #7
    Disclaimer: I almost don't know anything about this.
    I am very confused, because I always thought there was some physical reality to virtual particles.
    That they are only a "mathematical tool" is completely new to me.
    I heard that there were some interactions that could only really be explained through them.
    For example Hawking radiation or the casimir effect.(both of which haven't been measured to my knowlege, but thats besides the point)

    Am i somehow confusing virtual force carriers or gluons with other virtual particles ?:confused:
     
  9. Jun 14, 2016 #8
  10. Jun 14, 2016 #9

    mfb

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    Physics is not about reality, but how real is something you cannot detect in any way, something that is present in approximations only and does not appear at all in more precise calculations?
    Nothing needs the concept of virtual particles.
    The Casimir effect can be derived using virtual particles, but they are not necessary.
    The calculations for the Hawking radiation do not have virtual particles at all. The description with particle/antiparticle pairs sounds nice, but it is wrong.

    Edit: weirdoguy was faster with the links.
     
  11. Jun 14, 2016 #10
    Thanks for clearing up that confusion, although i got to say it is a little shocking to me. :nb)
     
  12. Jun 14, 2016 #11

    phinds

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    Hawking said early on that the "virtual particle pair" explanation of Hawking Radiation is an ANALOGY, not an actual description of what happens. It was the only way he could think of to explain in English something that really can only be explained in the math.
     
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