okay i'm not a physicist myself, but this is how i understand it. sound (ie pressure) waves require a medium to propagate through. the wave itself can travel ov

okay i'm not a physicist myself, but this is how i understand it. sound (ie pressure) waves require a medium to propagate through. the wave itself can travel over a long distance, but the actual particles involved are displaced only locally. now if you have a light and point it in a particular direction, the EM waves will propagate even through a vacuum. rather than local displacement of a medium, the photons themselves actually travel.