I know it's happened to you before. You put your earbuds neatly away in your pocket or purse, but when you pull them out again an hour later, they're impossibly tangled.
How in the world does that happen? Do you have a gremlin in your pocket that loves to annoy you, or is there something more going on here?
The headphone cord tangling conundrum has actually undergone scientific study, and we finally have an answer. As it turns out, those impossible constrictor knots are caused by physics.
Dorian M. Raymer and Douglas E. Smith of the University of California at San Diego Department of Physics demonstrated this in a paper titled "Spontaneous knotting of an agitated string."
Simply put, there's a sweet spot where the most tangles happen in headphone cords, and Apple iPhone earbuds are smack in the center of it. Cords that are less than 18 inches will never tangle themselves, but when the cord is between 18 inches and five feet, the chances of them spontaneously knotting rises to 50 percent.
Apple iPhone earbud cords are 55 inches long, and are up there in the 50 percent tangling range.
The pocket conditions were simulated in the experiment by putting the headphone cords into a sealed box and agitating it. What the researchers found is that it only takes the end of the wire crossing over another part of itself twice to start spontaneously knotting itself up.
Interestingly, the percentage of a knot forming does not go higher than 50 percent. This is because the cord inside the experiment box wedges itself into the corners of the box and refuses to tangle any further.
The image below from PNAS makes a little more sense of this phenomenon.