I was thinking asbout the physical existence of E and B fields. I would assume that most devoted physicists would say that they are as real as the chairs we sit on (I forgot the exact quote and the person who said it). But doesn't relativity disprove this fact? For example, consider the following thought experiment: Say there are two observers A and B. Say observer A is on a train which is moving at some speed relative to observer B who is outside on the ground watching observer A pass by. Now, say there is positive charge infront of observer A. Accorrding to observer A there would be no magnetic fields emanating from the charge since the charge is stationary in his frame. However, according to observer B there would magnetic fields emanating from the charge because there charge is moving according to him. Most physicists would resolve this apparant paradox by saying that the combination of E-fields, M-fields, length contraction, time delation etc would make it such that the net effect of that charge on its surroundings would be the same and hence there is no paradox. However, doesn't this imply that magnetic fields are not real (since one person "sees" it the the other doesn't). And only their combined effect(i.e. forces) are real?