This document discusses the physics of sound waves and how they relate to musical scales and harmony. It explains that sounds are waves that can be measured by their high and low points over time. The lower the pitch of a sound, the longer the wavelength. When two sounds interact, they can either be dissonant by opposing each other, or consonant by matching at certain points. Nature creates a harmonic series where sounds mathematically align. Pythagoras discovered this relationship by experimenting with different instruments and realized notes have mathematical relationships that build musical scales. The harmonic series provides the frequency ratios that define each note of a scale.