# Electromagnetic waves propagation

Initially it was considered that if em waves travel across vacuum then vacuum must contain certain some mass which does not interact with normal matter but transfers em wave called AETHER they were comparing these waves with normal mechanical waves

Modern concept : It is disturbance in em field which is em wave.

My questions:

1. If they are disturbances in em field then why don't em waves arise when we move source charge with uniform velocity? Why on acceleration only?

2. E M field contains energy in the form as in any field energy density is given as: U equal to Half epsilon Electric field square

And energy is equivalent to mass; then these two theories may be considered equivalent (besides some non applicable points)

1. If this is true then certain modifications like that of stokes can be used after certain required amendments. Or even Michelson Morley experiment could be adapted to sense em field. Edit :

There is extract from principle of relativity original papers by Einstein and minkowski :

"Fresnelian ether cannot be said to behave in any respectable physical fashion,and this led stokes,in1845-46,to construct a more material type of medium, Stokes assumed that viscous motion nensues near the surface of separation of ether and moving matter ,while at sufficiently distant regions they remains wholly undisturbed.He showed how such a viscous ether would explain aberration if all motion in it were differentially ir rotational. "

Can field too become something like viscous near materials

On Q2. This doesn't seem to be a question. Note the energy density in the EM field has a magnetic part too. That is $$U =\frac{1}{2}\left(\epsilon_0 E^2 +\frac{B^2}{\mu_0} \right)$$