Molecular music: Patterns of vibrations at the quantum level


Hearing of the fire at Notre Dame de Paris a year ago broke my heart. I have only been there once in my life, but that visit is one of my most cherished memories. Before studying chemistry and joining the Center for Sustainable Nanotechnology, I earned a music education degree, with a major in voice and a minor in piano. I sang in a choir that toured France my senior year. We visited and sang in some of the most beautiful cathedrals, but the one that impacted me the most was Notre Dame de Paris. Its stained glass is breathtaking, and I could almost feel the centuries of Catholic history those walls have witnessed.

Notre Dame de Paris, taken in 2011. The vaulted ceilings and reflective stone made for great acoustics. (photo by Laura Kesner)

Have you ever heard a choir singing in a cathedral? It’s so beautiful. It’s really an unparalleled sound you just have to experience in person at least once in your life if you can. The vaulted Gothic architecture in many European cathedrals is more than just visually beautiful—it carries and beautifies the sound. The massive stone walls and arches reverberate, or reflect sound so that it bounces all around, lasting seconds after the source stops. This reverberation smears the sound together a little, like the blending of paint colors. This actually brings out notes that may otherwise not be noticeable, because they weren’t actually sung or played. They are overtones , which our Center director talked about in this blog post regarding overtones and color. Watch this video and note both the reverberation from the room and the overtones produced from just a few voices.

Overtones are found in a variety of things: sounds, colors, and even quantum mechanics. Quantum mechanics may sound intimidating, but don’t let it scare you. It’s like cat logic: my cats like attacking my shirt even when I’m shaking a much nicer feather toy to distract them. Why they prefer playing with my shirt, even when I’ve picked them up and put them next to their real toys, I’ll never really know. The rules of quantum mechanics themselves don’t make a whole lot of sense to us (even to many of the scientists who study it), but accepting what we observe and using those rules does help explain many scientific phenomena, even better than cat logic explains cats!

Overtones in Music

We’ll get back to quantum a little bit later. But first, let’s talk overtones in music. Music is made when vibration of a string, air column, or other part of an instrument (or person!) causes the air around it to compress at specific intervals. The faster these air molecules compress and decompress, the higher the frequency of the sound wave; the higher the frequency, the higher the pitch.

Sound waves are intervals of compressed air (image from Popular Science, 1878 , US Public Domain)

To see how this applies to overtones on a musical instrument, let’s look at the A...

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