What produces the electromagnetic fields in the light wave when photons are chargeless?

Question

If there’s an electromagnetic field in the propagating light wave there must be an electric charge producing it, but photons are charge less, so how are these electric and magnetic fields produced and sustained if photons are chargeless? Besides,why are photons chargeless if they’re nothing but packets of Energy propagating through alternating Electric and Magnetic fields?

Answer 1

Electric charges are not the only thing that can generate electric fields. Changing magnetic fields can also create electric fields. Also, changing electric fields creat changing magnetic fields.

So for light the procedure is that somewhere a charge oscillates creating a changing electric field. This changing electric field generates a changing magnetic field which in turn generates further changing electric fields. These changing fields propagate in space to form electromagnetic fields, the quantized form of which are photons.

In short: it is not only charges that create electric fields.

Answer 2

There is a difference between an electric field and a charge, the former being an effect caused by the latter.

Consider a classical charged sphere. It is responsible for a static electric field that is uniform in all directions and gets progressively weaker with the square of the distance outwards. The charge is localised but the field associated with it is spread over space.

If you are happy with that image, consider what would happen to the field if the charged sphere were moved to one side. The field lines all have to be reoriented so that they point at the new position of the charge. The change in the orientation of the fields has to propagate outwards at the speed of light, so you get an outwardly moving kink in the field lines as the realignment happens.

Now imagine the sphere is moved from side to side in a periodic way. Now the field lines are continually having to realign, first one way then the other. A periodic series of kinks propagates down the field lines. The charge which causes the field lines, and the movement of the charge that causes the kinks, remain localised, but the kinks travel outwards at the speed of light.

So, crudely, you can think of EM waves as simply outwardly propagating changes to field lines emanating from moving charges.

The description I have given is, clearly, not at all rigorous, but it should provide a conceptual model of how a change in an EM field in one place can be brought about even though the charge responsible for the change is elsewhere.

The quantum mechanical description of what happens is far more complicated. But again you can consider the photons to be outwardly propagating effects triggered by charges at other locations.

Answer 3

Let's start with the properties of the electron. The electron is an electric charge and a magnetic dipole and has both an electric and magnetic field. When excited, the electron emits quanta of energy aka photons.

If one accelerates many electrons in an antenna rod, the field of the emitted photons can be measured. Heinrich Herzt was the first to measure both an oscillating electric field and a corresponding magnetic field.

Although photons are treated as massless, they are particles (and are listed as such in the Standard Model of Physics). Each photon travels at the speed of light and it can be seen that a photon inherits its field components from the emitting particle.