Why light does not have mass
Because light is a wave, and waves do not have the property of mass. Sound does not have mass either. It is massless, just like light. Contrary to what mainstream physics claims, that is not a special property of light. And because waves do not have the property of mass, they do not have the property of acceleration either (since that is a function of mass). Just like light waves, sound waves do not accelerate to the speed of sound either, and travel at a constant speed in the same medium. So the constancy of the speed of light is not a special property of sound. It is a general property of waves. The speed of sound is also independent from the motion of the source, this is not a special property of light, as Einstein foolishly believed. All waves have these properties, because their speed depends only on the properties of their medium of propagation. So it does not matter whether the source is moving while it emmits the wave. Or if the observer/receiver is moving while it receive...