# Moving charges: Describing its field as photons

1. Apr 10, 2012

### McLaren Rulez

Hi,

I was studying Cherenkov radiation and here's what I read. A charged particle moving through a medium has an electric field. This is equivalent to the particle emitting photons which are absorbed by the atoms of the medium and causes them to reorient themselves.

I am a little uncomfortable with the electric field being viewed as photons. For instance, a static electric field has nothing to do with photons. Also, electromagnetic radiation is quantized as photons. But a moving charge seems to be something in between the two so how is it explained? And does this mean that a moving charge (just moving, not accelerating) emits light? I'm quite muddled about this connection so I'd appreciate an explanation or a good source.

Thank you!

2. Apr 11, 2012

### vanhees71

A classical electromagnetic field is not described by photon-Fock states but by coherent states. I don't know, why many people think the photon picture is better than classical electromagnetic fields, if you deal with a situation where classical electromagnetics applies!

3. Apr 11, 2012

### Fr34k

The photons are used when you want to describe interactions of particles. Ie. if you have 2 electrons with their own electric fields. "How do they know where and what the other one is"? It's easier for us to imagine that they exchange something that gives both a sense of their surroundings, in this case a photon.
Now for Cherenkov light, actually particle doesn't emitt light, the medium does. When a particle faster than light in that medium travels through it, it "rearranges" the molecules and atoms with it's field, or as your professor put it, it gives off imaginary photons so the atoms in material "see" where particle is and where is it going. When the particle passes the molecules and atoms rearrange themselves back and that emitts photons you see as Cherenkov light.

4. Apr 11, 2012

### McLaren Rulez

Thank you. I think I get it now.