system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we interpret music in the minor key, and dissonance and such, as "creepy," or "sad?"

Whenever there's a scene in a movie that suddenly turns sour-- a character reveals bad news, or a dead body is found-- without fail, the score becomes dissonant or shifts into a minor key. In any horror movie, the music for the "scary" parts is in the minor key. In general, songs feel "sadder" or "creepier" once they change and become more dissonant.

(I've studied singing for years but suck at music theory so please forgive me for my lack of proper terms! hence my need for an explanation like i am five.)

Anyways, why is this?? What in our brains takes a certain succession of musical notes and translates it into an emotion like that? Like, I remember when I was watching Milk, (spoiler for Milk/historical event ahead) when Josh Brolin's character was walking around, suddenly the music switched into a minor key and then I knew something bad was going to happen, and then he went and shot Harvey Milk. 

If anyone could explain to me in simple enough terms why this is, I'd be so curious. I'm not very scientifically minded but this still interests me a lot.
gpt
I think it's just cultural conditioning. In the Middle East, among other places, minor keys are used all the time for celebratory music.

Plus, it's not just minor or major keys, tempo and style have a lot to do with it as well.