huy there! everyone says that light has wave particle duality. it means light is a wave and also consists of a particle. now, wave is a disturbance in a medium. but, we know that light can travel without a medium. then why do we say it is a wave? (i know that it is a non mechanical wave then why do we define wave as a disturbance in a medium if it can be non-mechanical?) also light is a transverse wave. in this particles of medium move up and down about their normal positions. which are the particles that move up and down when light travels in space?