The answer “because they just do” may be your first response to this question (indeed, it was mine), but its knot a good one (Yeah, yeah, I know…)
Actually, it has to do with Entropy (the second law of thermodynamics) and things tending toward disorder. In fact, the universe seems to exist in a state of ordered chaos (or chaotic order, whichever way you choose to see it) and your headphones are obeying the order of the Universe by causing chaos whilst in your pocket. Maybe.
Alternatively, Summer Ash of ‘NPR.org’ says that,
“Mathematicians have studied knots forever and developed all sorts of theories and classifications of their variations, but physicists have only recently began to explore what equations govern their formation”.
She goes on to describe an experiment, carried out by Physicists Douglas Smith and Dorain Raymer, which involved spinning a length of string with a motor to see if it was tangled or not, they did this 3,415 times. Why that precise number?
Well, according to Smith, “The scientific answer is that 3,415 was around the point where we had statistically compelling results. The human answer is that 3,415 times was about as much as we could stand.”
You wouldn’t expect a guy who appears to have taken the term ‘String Theory’ literally to have a sense of humour, but there you go. I’ll let Summer explain the rest;
“They concluded that with a minimum length of string (18.124 inches) and sufficient space for the string to shift around in its container, knots formed fairly quickly, often within the first few seconds. Inputting these results into a computer model, they even managed to create a program that could identify the “Jones polynomial” for each resulting knot, a mathematical property based on parameters such as the number of string crossings”.
Ergo, when you consider the length of your headphone chord and how much space it has to move around in your pocket (especially when you’re out and about, going to/from work, jogging, walking the dog or whatever), it becomes clear that you’re knot going to avoid the odd entanglements (sorry. I’ll stop now). Its just physics. In fact, if it doesn’t happen all the time, you’ve probably beaten odds close to winning a decent amount on the lottery. Think about that.
Anyway, to sum up, today, we’ve now learned together that knotted headphone cables are a natural symptom of business as usual in the Universe. It is indicative of the great wide somewhere winking down at us and reassuring us that it’s all going to be alright and that everything is going exactly according to plan. A way of saying that the days of our lives are as predestined as every grain of sand on every single beach on every single world in every single galaxy…
Or, if you prefer, the Universe is basically a Grant Morrison re-write of a Phillip K. Dick wet dream.
Or, if you prefer:
Headphones get tangled up in your pocket. Why? Because they just do.