Speed of field ?

1. Mar 20, 2007

BeauGeste

"speed of field"?

Is it correct to say that a field (i.e. electric) travels at the speed of light?
We've been taught that only electromagnetic radiation in a vacuum travels so can we say that the effect of E travels at c also?
I always thought this to be the case but someone argued that fields are not physical and are 'just there'. Can anyone elaborate please?

2. Mar 20, 2007

Staff: Mentor

It is better to say that changes in a field propagate at some speed. For electric and magnetic fields in a vacuum, that speed is c.

3. Mar 20, 2007

BeauGeste

ok that makes sense now.
I was a little confused because when using retarded times, it appears that the potential or field 'influences' at c but it's really because when using retarded times, a charge is moving and therefore the field is changing (and the change propagates at c).
thanks.