Sometimes, when studying music, it’s easy to forget that music is a physical phenomenon. What’s really happening when we hear a sound is changes in air pressure, caused by vibrations, move tiny hairs in our ears which create the sensation of hearing.
Believe it or not there are people who primarily study the way sound moves through air, water, and other substances inside of a variety of spaces.
But why is this relevant?
Harmony happens when sound waves of different speeds (or frequencies) are combined. Typically simpler ratios between the speed of the sound waves are preferred. These simple ratios correspond to harmonic intervals.
In a global sense, the music of the Western European tradition is an harmonic outlier. Very few musical traditions have developed a formalized system for handling harmonic motion. The vast majority of cultures center their harmonic language on the octave (2:1), fifth (3:2), fourth (4:3), and thirds (5:4 and 5:6). This is why there are some harmonic similarities when listening to the music of different cultures.