GB: "Sound, like light, does not have mass ..."
BW: While it is true that sound is a characteristic of the medium, so has no inherent mass, the kinetic energy is passed from one molecule of air to another. It is the mass of that molecule that determines the speed of the sound, so there is always kinetic energy (and therefore, mass) engaged in the process.
Light, IF it is considered a wave, must also be passing kinetic energy from one "molecule" of the "aether medium" to another. Therefore, that medium must have mass and motion. Unlike air, no massive aether "molecule" has ever been detected in any light experiment.
However, there are a multitude of experiments which demonstrate that light is some kind of massive particle with motion, including the home novelty radiometer with four vanes that rotate when exposed to light:
BW: Einstein's only saving grace was his mathematical formulation describing Hertz's "photoelectric effect" (which got Albert his only Nobel Prize). That doesn't work unless light is a massive particle (photon) in motion, independent of any medium.
BW: Of course, that doesn't explain what kind of particle or groups of particles compose the mass of light, nor what proper motion they include. I'm working on that.