B and E *are* in phase, as you say. E is max where B is max. So, what propagates the radiation? Let’s be more careful.

I said that a change in E creates a B and a change in B creates an E. That’s not exactly true. A change in E over *time* creates a variation in B over *space*. [In math-speak, dE/dt gives rise to a curl in B]. And vice versa, a change in B over *time* creates a variation in E over *space*.

So, let’s go back to the example of shaking a charge. Here’s what happens.
1. Shake charge, that creates a changing E field in time.
2. That changing E in time creates a curl in B.
3. However, there was no B to begin with, so that curl in B is new. So, that’s a changing B in time.
4. That changing B in time creates a curl in E.
5. That curl in E changes in time as B changes in time, so that means that the value of E itself is changing over time.
6. Return to step 2, lather rinse repeat.

The PheT simulation at http://phet.colorado.edu/simulations/emf/emf.jnlp shows step 1 nicely.

If anyone else can explain this well, go for it!

Q: What propagates the electromagnetic radiation

A: “… the electric and magnetic fields swap energy between each other, as one grows the other diminishes.

I’ve been considering this phenomenon lately and have been all over the web trying to answer this for myself. The answer given to the question here doesn’t seem consistent with what I’m getting from other sources. Wouldn’t the energy swapping hyposthsis require that the propogating electric and magnetic fields be 90 degrees out of phase with one another. Everything I’m reading says that the E and M fields are completely in phase with one another (ie, both reach their max and min at the same time). So what am I missing here?

Regarding this post: I love Paul Doherty’s balloon demo! On what listserv did this take place? I’d love to join!