I'm still amazed that the EM field requires no medium to propagate.
In the 19th century, while electricity was being discovered and used to kick-start the Industrial Revolution, many people thought that something they called the
ether was responsible for EM propagation.
So Michelson and Morley tried to measure the effect that Earth's motion around the Sun, plowing through the
ether so to speak, would have on the propagation of visible light. Their conjecture was that the speed of light would vary according to the direction of propagation in the
ether. Their experiment, while cleverly designed, did not yield the expected result. There was NO indication that the
ether, if it existed, had any effect on how light propagated.
Part of the problem has to do with how the
ether was defined. It was supposed to be massless and pervasive but invisible. That pretty much says the
ether is unobservable, directly. After many years and repeated demonstrations failed to reveal any evidence for the existence of the
ether, the idea that some sort of medium was necessary to propagate EM waves was abandoned.
I propose another (untestable) explanation: God. God has many attributes that are similar to what is expected of the hypothetical
ether, so if you insist on requiring a medium to propagate EM radiation, God is as good an explanation as you will find. Attach whatever religion pleases you. While contemplating this, consider also gravity and what effect the
ether (God) has on that.