# Information in electromagnetism and electromagnetic waves

I'm reading Griffith's electrodynamics and in it he mentions in section 10.2.1 that news travel with the speed of light in electromagnetism. To my understanding the news he is talking about are the electromagnetic waves, which travel through space. Later in the example 10.4 he calculates the electric and magnetic field of a point charge moving at constant velocity. Now my question is: if a charge moving at constant velocity doesn't produce EM waves, how does it create an EM field in a point in space if the charge and the point can communicate only via EM waves?

• The computer you are using - and if you use DSL internet connection, that as well - are not using EM waves yet you have information coming to you. You are confusing EM waves with electric (and magnetic) fields. May 20, 2020 at 15:00
• I know I'm confusing something but I can't understand how an electromagnetic field can be created without electromagnetic waves, also in Griffith's in example 10.2 he talks about how a suddenly created current creates and electromagnetic field. For time less than s/c (where s the distance from the cable in which the current is produced) there is no electric field. This means that the electric and the magnetic travel through space. Still even in this case we don't talk about em waves. I hope I made clear what exactly is causing my confusion May 20, 2020 at 15:10
• Unfortunately I dont have time to post a comprehensive answer, but I will try to alleviate confusion with a, maybe not completely accurate, metaphor. Image EM waves as sound. They exist and are regions of low and high pressure. Now the fields is just the pressure. It can be higher or lower. You have wind from big regions of high and low pressure for example and it is not sound. Yet if sound exists or not comes from how this pressure is excited. Maybe it is not the most correct metaphor. I am hoping that someone with a good grasp of ED can give you a comprehensive answer, though. May 20, 2020 at 15:20
• (just a quick comment. A suddenly created current will have to create an EM wave, a pulse with large bandwidth. But then you need to distinguish between what is an EM wave and which are the created electric and magnetic fields) May 20, 2020 at 15:23
• To my understanding EM waves travel to create the EM field. Just like my voice for example will create the sound wave that will create the pressure difference at someones ear. Is this reasoning wrong ? May 20, 2020 at 15:29

If a charge is moving at constant velocity for inertial frame $$A$$, it is always possible to make a change of coordinates, applying Lorentz transformation, to the inertial frame of the particle, say $$B$$.
For frame $$B$$, the field is static all over the space. And frame $$A$$ is moving around this static field. So, there is no signal or information to be transmitted.