Question

Statistical Physics of Hair Knots?

Answer 1

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In everyday life, no matter how hard people may try, they end up discovering that they have knots in their hair every morning. What is the physics behind this phenomena?

A priori, it seems non-trivial to me that a hair knot would develop. This requires hair to pushed and pulled in such a particular way that effectively it curves in on itself, which seems difficult. However, we see this is a generally observed phenomenon due to "random" forces moving hair about.

Various parameters seem to control how many knots one might develop. For example, longer hair or curlier hair seems to have a higher propensity for knots. There could be other factors at play, such as hair stiffness, hair-hair interaction, hair density, etc.

As complex system with a large number of constituents with relatively simple macroscopic observables, maybe it's possible to understand what's happening from a statistical physics perspective? What controls the "phase transition" between knotted hair and straight hair? What are the properties of said "phase transition"? Does the state of hair settle into "thermodynamic equilibrium", or is it more like a "glassy phase", or perhaps does it not "thermalize" at all?