String Theory

Physicists in the lab have produced hard data for string theory! Well, for a theory about strings. Actually, knot theory might be technically a more accurate label. Okay, the truth is that the only reason I'm writing this post at all is so I could make a pun about string theory in the title.

This research evidently made the news when it was published a couple of months ago, but I missed it until Keith Devlin mentioned it in passing last week on NPR. Physicists Doug Smith and Dorian Raymer at the University of California at San Diego have developed a mathematical model for how loose string in a box becomes tangled when the box is jostled. Their paper, Spontaneous knotting of an agitated string, was published this past October in the Proceedings of the National Academy of Sciences (PNAS). (The full article can be accessed without a subscription here.) There have been numerous write-ups about it in science and math publications; a couple of particularly nice articles were in Science News Online and in The Mathematical Tourist column in MAA Online.

The experimental apparatus consisted of clear acrylic boxes of various sizes which were rotated by a computer-controlled motor. Strings of various lengths and stiffnesses were placed in the boxes, and after being spun, the strings were analyzed to see what knots had formed. This was done in large part by taking digital photos of the ending configuration of the strings and using a computer analysis to compute the Jones polynomials of the knots. The PNAS website contains Quicktime movies of the apparatus in action, which are definitely worth a look.

As for any practical advice from the study, the bottom line seems to be that you should pack your loose cords tightly to prevent them from moving around. I don't think that's going to be of much help when I put away the Christmas lights next week. Each year they inevitably come out of the box a tangled mess, in spite of being packed more snuggly than sardines. Perhaps Smith and Raymer can do a follow-up study using Christmas lights instead of string, that are shaken side-to-side instead of being spun. (My Christmas lights, despite being tangled, are usually not knotted at all in a strict mathematical sense, and I don't think that Smith and Raymer examined this type of phenomenon in their study.)