Antennas work by accelerating electrons to emit EM radiation. In fact, my understanding is that any accelerating electron will emit EM radiation.
But in relativity, no frame of reference is preferred. Therefore, an electron in an antenna can claim that every other electron in the universe is moving around it.
So does that mean that when an antenna creates a signal, every other electron in the universe sends the same signal back to it?
But in relativity, no frame of reference is preferred.
This isn't exactly correct. The first postulate of special relativity is:
"The laws of physics take the same form in all inertial frames of reference."
Note the key word "inertial" in the statement of the postulate. No inertial frame of reference is preferred over any other inertial frame of reference. However, an accelerating charge's rest frame is not inertial. So the laws of electromagnetism do not follow the usual Maxwell's equations in the charge's frame, which is non-inertial. Therefore you cannot infer that the rest of the charges in the universe are sending the same signal back.
