““Theory and experiment both show us that light does not need a material medium for propagation. We would have no trouble understanding this if light were nothing but particles zooming along through empty space. But that is not the way it goes: Light is a vibration, an oscillation made up of elementary oscillations we call photons. But there is no substance that oscillates when light propagates; thus we cannot impede the propagation of light when we remove substances from some given space.””
