Actually, sound isnt physically existant, since the air is the same air with a sound wave going through it as it is when its silent. Sound is actually a momental state set by the universe to the matter. Sound also requires time to exist, not only space. A still-shot of something moving will give you its coordinates between its current position and its next position in space-time. Therefore, anything that requires time to 'exist' is not physically existant. I.e. Momentum/Speed.