From Scientific American, an interesting theory of the mass of sound:
In a paper published in Physical Review Letters, a group of scientists has theorized that sound waves possess mass, meaning sounds would be directly affected by gravity. They suggest phonons, particlelike collective excitations responsible for transporting sound waves across a medium, might exhibit a tiny amount of mass in a gravitational field.
And although the amount of mass carried by the phonons is expected to be tiny—comparable with a hydrogen atom, about 10–24 grams—it may actually be measurable. Except, if you were to measure it, you would find something deeply counterintuitive: The mass of the phonons would be negative, meaning they would fall “up.” Over time their trajectory would gradually move away from a gravitational source such as Earth.
“Collective excitations” is somewhat of an interesting resolution to the wave-particle theory. If waves move through matter, they create these little particle-like objects and apparently, these have mass, but so little that in the case of sound, they drift away from Earth.
A more perfect metaphor for music would be hard to find. It inspires us to give up on our cares here, and dream of what is great, so that someday we can make it real and push aside all of the tedium here on this overcrowded, polluted, corrupt, and idiotic globe.