How come when you drop a totally untangled cord and then pick it up two seconds later it always transformed itself to the Gordian knot?

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For example earphones.

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Probability. Think about how many millions of configurations a set of headphone cords can take. Now realize that only one of those configurations is untangled.

One of the laws of nature. An untangled string will always become tangled (tied). Whereas a tangled (tied) string will always untie itself. In science this is known as “string theory”.

This had been observed for many years – but never described as a scientific phenomenon until about a decade ago. So this is relatively new knowledge for humans!

Raymer & Smiith wrote in *Spontaneous knotting of an agitated string* (PNAS October 16, 2007 104 (42) 16432-16437):

* A average string (diameter 3mm) of length less than 46 cm (or 1.5 feet) will *almost never* tangle itself up, even if you put it in a sealed box and shake it for an hour
* The stiffer your string, the less likely a knot; headphone wires, for instance, are less likely to knot than a soft string, but more likely than thicker steel wire.
* The longer your string, the higher the probability of a knot… but it tapers off quickly at around 50% (under their conditions)! Longer strings do *not* always mean higher chance of knotting.
* The knotting happens because a knot-forming crossing is roughly as likely to happen as a knot-undoing crossing; but if a string is coiled (and thus touches itself in many places), there are *multiple chances* for a knot to form, and it’s very likely that at least one will occur.