Originally posted by Farn
Ivan, you mention a 'changing electric field' and a 'changing magnetic field' in your explanation. When I think of an electric field I think of electrons when I think of a magnetic field, I think of a current of electrons. However...as its been said an EM wave doesn’t require electrons to be present for it to propagate and of course this is true because we know they cross space. So I'm still at a loss for how these changing fields take place without electrons. What am I missing?
At the deepest levels, I am not qualified to answer this question correctly. To the extent that I can answer this I will try. Electrons have an electric field. The electron is one concept; the field is the other. It is not correct to think of the field as an extension of the electron. The field is a consequence of the internal workings of the electron - we would have to talk about quarks at this point and I'm not qualified to do so. But the key point is that the field and the particle are two different things.
Next, we get in deep quickly with Maxwell's equations and the implicit relativity theory therein. Maxwell tells us that an electric field is produced by a collapsing magnetic field. Also, as the electric field forms, it produces a magnetic field. This, at one level, is the best description of these two fields to be found. Anything else is just a less precise way of thinking about it. Also, each of these fields contains energy. The total energy of the photon could be found [in principle] by simultaneously measuring each field and then calculating and adding up the energies.
At another level, and I resist telling you this because it can easily cause confusion especially in this context, but, here we go. We do have a better explanation for the nature of these two fields. An electric field is just an exchange of photons! So, you seek to understand how the electric field manifests as a photon, and yet the photon IS the essence of the electric field. Honestly, I don't know how to explain the apparent contradiction. Perhaps someone else can help here. But it gets even worse.
Imagine that you are standing next to a wire in which current flows. As you mentioned, you could measure a magnetic field around the wire due to the flow of charge in the wire. Now, instead of a wire, imagine that we are talking about a stream of electron moving through a vacuum. Here comes the relativity part: If you could pace the flow of electrons moving through the vacuum by running alongside the stream of charge, the electrons would no longer appear to be moving. Correct? It would appear that they are motionless as compared to you. Guess what? If we have no moving charge, we don't have a magnetic field. Right? So when we started, you could measure a magnetic field as you stood next to the stream of electrons. But as soon as you start to move with the electrons, for you, the magnetic field disappears! A magnetic field is just an electric field viewed relativisticly!
