It's the perfect fifth.
That's the most beloved chord in music history.
Don't know what the perfect fifth is?
Well, let George Lucas and John Williams introduce you to this truly perfect chord. It is used (sketched in the intervals of the melody) in the legendary Star Wars theme -- that gargantuan mass of awesomeness that explodes from the speakers when the text scrolls up the movie screen to introduce the plot of the movie:
The two notes in the Star Wars theme that are DAH and DAAAH above are the notes that form the perfect fifth chord.
So what makes this two-note chord so special? And how on earth can something like that exemplify a spiritual truth that is nourishing to the soul?
To answer that, first let's re-think how we perceive musical "notes."
It's dominoes. Just dominoes. A musical note is a vibration -- but not just any vibration; it's a vibration of air molecules that are getting slammed with some kind of force: maybe a singer using his vocal chords to force air out of his mouth and sing or maybe a bassist yanking on a string to make it snap and force pressure into the air around it. Whatever force it is, it hits the air molecules, and the molecules vibrate and hit the ones next to it, and they vibrate and hit the ones next to them. It's a domino effect. When you hear a note, you're hearing the dominoes of air molecules slamming against each other until they spread out across the room and hit your ear.
So why does a note sound "higher" or "lower" than another note? Some sound waves vibrate faster than others. The dominoes fall faster than others. They have what's called a higher "frequency," and it sounds higher to our ears.
With the perfect fifth chord, you got a high note -- the fifth -- and a lower note -- the one (tonic). The fifth has a higher frequency -- a higher rate of vibration -- than the other. It's two lines of dominoes falling at the same, but one line is falling at a faster rate than the other.
In the perfect fifth, the two notes have a ratio of 3:2 in their frequency. For every three dominoes falling in the high note, two dominoes are falling in the low note. It turns out the brain really likes the 3:2 pattern in music. Of all the frequency patterns in Western music, the 3:2 is the simplest pattern for the brain to pick up, and our brains prefer simple frequency patterns because the nerves in the ear can transmit more information to the brain -- like getting a clearer picture on the TV.
Part 2 will explain what this has to do with, well, anything else -- particularly our souls, our relationships with others, and our relationship with Christ.