Johannes Kepler: The Mysterious Music of the Spheres
The quixotic search for a “theory of everything”, to finally explain how the universe works in the simplest terms, has consumed contemporary theoretical physicists and twenty-seven kilometres of the Franco-Swiss border. But they are certainly not the first to look — and in 1619, a German astronomer believed he had found the answer.
Johannes Kepler regarded Harmonices Mundi, or the Harmony of the World, as his greatest achievement, though he is now best remembered for his eponymous three laws of astronomy and the discovery that the orbits of planets are not circular, but elliptical. The assertion that planets move in anything less than perfect circles may no longer seem revelatory, but in Kepler’s time it was extraordinary, and he paired it with the radical belief that we literally orbit the sun. Until then, the Copernican system had been largely interpreted as a convenient trick that improved the accuracy of astronomical predictions, not as a true description of the universe. However, Kepler was hardly a scientific rationalist; indeed, neither “reason” nor “science” can be said to have entered their own as the devastating, internecine Thirty Years’ War raged around him. Deeply religious but unconventional in his beliefs, Kepler thought that because man was made in the image of God, man was capable of understanding His creation. His investigations into light, astronomy, and optics were therefore primarily devotional — they brought him closer to the mind of God. And what was on God’s mind? Harmony.
In some ways, it was an old idea; the ancient Greeks had had similar intuitions that there was something mystical about numbers and their relationships. But where they were disturbed by the irrational numbers their inquiry produced, Kepler took them as a fundamental epistemological insight: things are knowable precisely in the way that they relate to each other. He then set about to demonstrate that these relationships, or harmonies, existed not only in geometry and music but also among the planets.
If you divide a string in half, you get an octave; at 3:4, you get a fourth. In total, Kepler found seven ways to divide a string so that the interval is consonant (that is, pleasing to the ear) in relation to both the whole string and the other intervals. What if, he thought, these proportions apply to the very heavens? Could the “music of the spheres” be more than a metaphor?
Kepler’s orbital ellipses provided a way to test his theory. He knew that planets were slowing down as they increased their distance from the sun, and speeding up as they got closer. This action was for him analogous to the way a string vibrates back and forth. Comparing the planets’ maximum velocities with their minimum velocities, he found something astonishing: not only does the difference in each planet’s speed approximate a harmonic ratio, but each planet is further in harmony with its neighbours. Kepler believed, through this unusual symmetry, that he had discovered an organizing principle of the universe. The same proportions that make the sound from a struck string pleasurable govern the skies.
Perhaps Kepler said it best himself:
“The ways by which men arrive at knowledge of the celestial things are hardly less wonderful than the nature of these things themselves.”
P.S. Did I mention that Kepler wrote out the musical notation for each planet’s movement? You can listen to an artist’s rendition of it here.
- Alex Tesar