photon emission by the acceleration of electrically charged particles I understand why the acceleration or deceleration of an electrically charged particle creates a ripple in the existing electric field, which is tantamount to an electromagnetic wave. However, I am not clear on why this is accompanied by an emission of energy/photon emission… 
That is to say, generally when acceleration happens there is conversion of energy internally in the relevant object (e.g. potential energy turning into kinetic energy inside a ball that is falling towards planet Earth): but why would there be a quantised emission of energy as part of this process in case the particle is charged?
I tried to think of the emission of this energy as the ability of the wave to move things at a distance (unlike the ball in the example), which would make it seem more logical. However, that ability was also there before the wave, with the stationary electric field (although the direction changes from a straight line towards the charge in case of the stationary electric field to a more wavy pattern to the sides with the EM wave). Either way, this interpretation is faulty in that it does not explain why there is no emission in the stable case, yet an emission in the case of acceleration.
Can anybody clear this up?
Thanks!
 A: You can discuss all this classically then everything is just solutions of Maxwell's equations:


*

*if there is no electric field the charge particle will just move in a straight line and not generated an em wave

*if there is an electric field the field will accelerate the particle and in the process the electromagnetic field will change is a wave like way propagating from the particle location. 

*Electric field energy is transferred to the charged particle but in addition some energy is propagated away from the particle in the form of an em wave.


Classically you are forbidden to talk about photons.
But you want to talk about photons, so now we must do a complete switch of language to the language of quantum electrodynamics (QED).
Everything aspect of the classical story can (if you try hard enough) be derived from quantum electrodynamics considering the case when you have a large number of photons and electrons acting together.
I can't give you the full story but can give some ideas to help you read more:


*

*In QED there are only two types of object (photons and electrons). All dynamics is explained in terms of the local interactions of photons and electrons.

*Conservation of energy carries over from the classsical to quantum language. But now all the energy is stored in particles (not in the field as such or potential energy). So all energy transfer is simply photon-electron interactions.

*So an electron moving in the absence of a classical em field is just an electron moving in the quantum vacuum (no photons to transfer energy to the electron - I'm ignoring vacuum fluctuations).

*Now consider a single electron moving in a classical static electric field: the e-m field is in an excited state so there are lots of photons available which can transfer their energy to the electron.

*In this process the electron can then emit some of its energy as a photon which will propagate away from the electron. If there are lots of such coherent propagations, say from lots of electrons which are part of a large charged object, then these propagating photons will combine together to form a classical electromagnetic wave. 
In summary, its all photons, but depending on the way large numbers of photons combine you can get very different classical behaviours.  
