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Force carriers / standard model

  1. Mar 24, 2005 #1
    I've heard electromagnetic wave propagation described as a 'swarm of photons'. This makes sense to me in terms of the standard model, wrt. the photon being the 'carrier particle' for electromagnetism. However, what about something with a static electric field - what's the 'carrier particle' for that? Likewise with a magnetic field around, say, a permanent magnet?

    I don't really understand why in the standard model, the electroweak force doesn't have a unique carrier particle but the electromagnetic does - would the electroweak only have a carrier particle at the extremes where the EM and WN are unified?

    Sorry if these seem like dumb questions, I'm very rusty :eek:
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  3. Mar 24, 2005 #2
    Interaction Type | interaction particle
    EM photon
    Weak (W+,w-,Z)
    Strong gluon
    Gravity graviton
    From my understanding, the electroweak needs the three so that charge and or flavor can be exchanged. Both of the W's can exchange electric charge or flavor and Z is neutral.

    Any electromagnetic interaction is through the exchange of a photon(static or dynamic). Rember that these interactions transfer momentum and energy.
  4. Mar 25, 2005 #3
    it sounds like the poster is asking the age old question - "how does a magnet work?" - and i think the answer is we just do not know. exchange of photon does indeed transfer momentum, but cannot apparently explain a resulting attractive force. also, the effect of a permanent magnet does not steadily diminish through "use" which it would if it were continuously emitting the amount of photonic energy required to sustain a force on nearby metallic objects.

    now, if you do happen to be able to explain to the rest of us exactly how a magnet works, i will be positively thrilled... over the years, i have nearly fried my poor little brain pondering virtual photons, et al, with virtually no success at any understanding. carry on...
  5. Mar 25, 2005 #4


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    I think the theory of magnetism as it is described in QM,Q statistics & Solid State Physics books is (for me,at least) more than satisfactory...Magnetism comes from atomic magnetic moment which includes both spin & orbital angular momentum.
    It's true that this picture is not complete,but at least is more than "we just do not know".

  6. Mar 25, 2005 #5
    daniel - the poster was asking about mechanism, ie, what is actually happening? how is an attractive force transmitted to the object? the answer to this question is that "we just do not know." sure, we can obfuscate with elaborate equations and discourses on virtual photons, and loftily pretend that we understand things beyond the ken of mere mortal laypersons, but while QM satisfactorily can explain what occurs mathematically, it does not address how this works at a fundamental level. this is generally true of literally every aspect of fundamental reality. we dont know what energy is. we dont know what gravity is. we dont know what time is. telling a questioner that something like magnetism or gravity can be explained by an equation is not helpful. sadly, that is pretty much all we can do however...
  7. Mar 28, 2005 #6
    How then would electrons scatter off of and transfer momentum to a nucleon or nucleus? That would imply we need another interaction particle that is not virtual. Also, how would you describe the make up of a nucleon without virtual particles? Without sea quarks I do not see the possibilty to do so.

    Now as far as the magnetic material, we are dealing with a macroscopic material. There are many electrons which will always be "moving". If you were to question an individual particles magnetic moment such as an electron, I cannot answer your question. This is one area I have a tough time with. If it is an intrensic property, then maybe the electron is not a point like particle. If it is due to the confinement of an electron, Heisenburg gives us an answer: the electron is moving yet again. I am leaning to think it is due to confinement.

    Does a charge diminish while in the presence of other charges? i may be simplistic in this arguement but I believe it to be the best way to look at this. An electron must be in a conduction band for this to work right? The electron is in motion. But why? Well doesn't it work much like an H2O molecule, there are shared electrons between the metallic ions. Where does the attraction come from? The overall net charge of the ion. Well we can keep going untill we ask where does the original energy come from?. I would look at the Coulomb Potential then. So now their is an energy in the electric field. This energy is used to try to hold these conduction electrons, but the ion does not produce a strong enough field to hold this last electron, so it is "shared". So now we have many electrons (on the order of a few Na(avagadro's number)) moving. This would constitute a magnetic field. No matter what the temperature. Only an external electric or magnetic field would alter this.

    If my arguements are really flawed please let me know. I am not trying to be hostile, but rather submit what I understand. If it is wrong, please let me know, and I will research the matter further.
  8. Mar 28, 2005 #7


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    This is incorrect. The magnetism properties do not originate out of the conduction electrons. Conduction electrons have no magnetic properties. Rather, magnetism in matter depends highly on the unpaired orbital of the valence shell of atoms that make up that matter. These unpaired orbitals first result in a net magnetic moment of each atom. Then the nature of the coupling with its neighbor and next near neighbor, etc... (as in the Heisenberg coupling term) will determine the nature of that magnetic property, either ferromagnet, antiferromagnet, paramagnet, etc.

    Elementary treatment of magnetism in material is usually presented in a solid state physics text (such as Ashcroft and Mermin). A more complete treatment of quantum magnetism can be found in Auerbach's classic text.

  9. Mar 29, 2005 #8
    What exactly do you mean by static and dynamic ?

  10. Mar 29, 2005 #9
    Thanks Zapper, I have had one course in Solid State with a horrible professor. He is a great researcher, but not a very good teacher. I have Kittel and will look into it some more. I will see if I can find Auerbach's since I have heard good references elsewhere on that book.

    Marlon.... I was thinking about a moving charge system. Mainly the fact that the interacting particles do not have to be static.

  11. Mar 29, 2005 #10
    After looking in Kittel, I see where I made my mistake. The only contributions from conduction electrons comes from paramagnetic responses. They contibute to the paramagnetic susceptibility of the material. Thanks again for letting me know.
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