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Photons radiated by free electron?

  1. Jul 29, 2011 #1
    There is something that I don't understand .A free electron radiates photons in every possible direction as long as it exists so it emits an infinity of photons with Infinite energy ??????
  2. jcsd
  3. Jul 29, 2011 #2
    A free electron does not emit any photons. It requires a potential to accelerate the electron.

    I think you are confusing the electrostatic force with a photon which is a permutation in the electrostatic force. It is the measure of energy transferred like if you pull on a rope, but if you just hold the rope you are not emitting an infinite amount of energy.
  4. Jul 30, 2011 #3
    Very well put -- I've often wondered the same thing. When you read that photons are the quanta of the electromagnetic field, it sure sounds like a field must be "made up of" photons...and when you hear that forces are mediated by the exchange of particles -- and electrostatic fields exert forces on charged particles just as well as changing ones -- that just confuses things more.

    I'm still not totally convinced, though -- that electrostatic field, once "established", can still do work on particles (including test particles) that are brought inside of it, and therefore it "contains" energy, which must be quantized, right?

    I'm sure there's an equally simple answer / analogy, but for the life of me I can't figure it out what it could be.
  5. Jul 30, 2011 #4
    Why should the field contain energy and not the test particles themselves?
  6. Jul 30, 2011 #5


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    No, the fundamental forces of nature do NOT require energy to function. Energy is a measure of the ability to perform work. A proton and an electron bound in a Hydrogen atom do not constantly use energy to stay together. The electromagnetic force from both particles is always there though.

    Also, the view that virtual particles mediate forces by exchanging themselves is simply a way to visualize the process of interaction and make the math easier. There is more than one way to interpret interactions and this is simply one of them.
  7. Jul 30, 2011 #6
    Now , I understand thanks .
  8. Jul 30, 2011 #7
    Well, the cop-out answer is that I read that the energy in a field is proportional to E^2 + B^2.

    But from an intuitive standpoint, the answer would maybe be that it unarguably took energy (required work) to establish the field (it had to change to its current value from something).

    But I guess what is confusing is that the energy just hangs around "in the ether", even after the "photons" have gone.

    I've also always been a little confused as to how a field is established equally in all directions from a charged particle, but in establishing that field it could necessarily only emit a finite number of photons...
  9. Jul 30, 2011 #8
    Sure -- that's fair enough. But we agree that there IS energy in the electromagnetic field, right? It required work to establish (quantitatively, ~ E^2 + B^2), and it can do work on a test particle (whether it does or not on any particular particle is a different question).

    So I guess the question is -- is the energy in that established field (for simplicity, let's say it's electrostatic) quantized into photons? Since they're always moving at the speed of light, that would necessarily require that they be constantly emitted in all directions, right?

    The only picture that I can make work is that the field is established when the photon zips past a point -- like it leaves a trail of changed EM field behind it (a "'groove' in the ether", perhaps)...but while that sounds sort of feasible, I'm pretty sure that's not the standard description.

    Yeah, I was reluctant to bring that in -- it was just an example of how the picture gets muddied even more by the traditional lay exposure to modern physics...
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