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Particles vs. Virtual Particles vs. Fields

  1. Jun 5, 2015 #1
    It's easy to find references which explain that the photon is the force carrying particle for the electromagnetic force (ie https://en.wikipedia.org/wiki/Force_carrier). Similarly there are force carrying particles for other forces, like W and Z bosons carry the weak force.

    This has always been confusing to me though. For example, I remember learning in school that an electromagnet, supplied with power, produces an electromagnetic field. That field is what attracts a piece of iron. But now I know that the iron is actually being attracted by the force carrying particles, photons. So photons are constantly shooting out of the electromagnet and when they hit the piece of iron, then the iron experiences an attractive force.

    So then why don't I see photons shooting out of electromagnets?

    Also, if photons are the force carrying particle, does that mean that there is no actual field? It's just the photons? I've read that force carrying particles are "not real" in the sense that they are actually excitations of their respective fields. I'm not entirely sure what to make of that. It seems to imply that when a photon is shooting through the vacuum of space (say, on its way from a distant star to a telescope on Earth), that there must exist an electromagnetic field which permeates all of space for the photon to travel through. Since obviously a field has to exist to being with in order for there to be an excitation of that field. But then how is that any different from the old and debunked aether theory? (see https://en.wikipedia.org/wiki/Luminiferous_aether for reference)

    Speaking of fields, I thought it was possible to have a magnetic field without any accompanying electric field, and vice versa. This implies photons with only one component, electric, or magnetic. Do the photons coming out of my flashlight have both components? Do they have to?

    Finally, virtual particles. I've also read in some places that force carrying particles are actually virtual particles. To my understanding, this means that you can model interactions with forces as though quantized packets of energy were being exchanged between the objects in question. So this would mean that a magnet attached to my fridge is not transferring real photons to the surface of the fridge (real in the sense of being like photons you'd see from a flashlight), but rather only virtual particles are being exchanged.

    But then I never see anything talking about virtual vs real for other types of particles, only photons. Are there both real and virtual W bosons? Are there both real and virtual Higgs bosons? I assume no, since I've never read about them, but then plenty of stuff exists which I've never heard of...

    This has all been rather rambly, so I'll wrap it up with one final question. If photons are the force carrying particle for the electromagnetic force, then why can't I place a magnet between myself and a light-source, and see a visual effect produced from the interaction between the photons coming from my light source and the magnetic field from my magnet?
  2. jcsd
  3. Jun 5, 2015 #2


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    Staff: Mentor

    That's not what happening. The electromagnet is creating an electromagnetic field just like you always thought, and the interaction between that field and the iron is creating a force drawing the iron towards the magnet just like you always thought. The virtual photons appear as part of the mathematical description of how the iron interacts with the field.
  4. Jun 5, 2015 #3


    Staff: Mentor

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