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As we know light travels as an electromagnetic wave...but electric fields and magnetic fields are interactions between charges...they are the forces acting on stationary and moving charges respectively. But when there is no charge how can these fields propagate through free space??


marked as duplicate by John Rennie electromagnetism Aug 5 at 16:32

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  • $\begingroup$ The electromagnetic field does not “need” charged particles to exist, any more than charged particles need an electromagnetic field to exist. It is easy to imagine a universe in which the electromagnetic field exists but fields for charged particles do not. Such a universe would not be very interesting (you would just have free photons flying around, not interacting with anything), but it would not be inconsistent. So I think you just have the wrong conception of the electromagnetic field. Electrodynamics is the story of how the electromagnetic field and charged particles interact. $\endgroup$ – G. Smith Aug 5 at 16:38

Charges are the source of electromagnetic waves, not the medium that the waves travel through.

As an analogy, say you're on a boat on a lake, and another boat moves past. The waves from the wake of the other boat will make your boat rock. That's an interaction between the other boat and your boat caused by the water waves produced by the other boat.

But there didn't have to be any other boats between your two boats for the wave to reach you.

  • $\begingroup$ Good answer. It is intriguing that we always seem to need an ether - or water - to explain such matters. $\endgroup$ – my2cts Aug 5 at 16:33
  • $\begingroup$ You don’t need an aether for electromagnetic waves. This was a key finding of the Michelson-Morley experiment $\endgroup$ – Jake Rose Aug 5 at 16:35
  • $\begingroup$ @JakeRose, I don't think I said you did. I said whatever source produces your wave, you don't need more of that source in the space where the wave travels. The fact that water waves and EM waves differ in the nature of the medium that carries them is immaterial to that point. $\endgroup$ – The Photon Aug 5 at 16:37
  • $\begingroup$ To be clear: the medium that EM waves travel through is not a material medium, it is the electromagnetic field itself. $\endgroup$ – The Photon Aug 5 at 16:39
  • $\begingroup$ @my2cts, It's a (pedagogical) problem that EM waves are pretty much the only waves that we deal with in everyday life that aren't carried in a physical medium. $\endgroup$ – The Photon Aug 5 at 17:01

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