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<\/p>\nI was worried that a discussion of hair gel would have a certain bias toward men, but my wife assures me that women are just as likely to use a leave-in hair product.\u00a0 I\u2019m going to rely on that unstatistical assurance and roll right on.<\/p>\n
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We want to consider two tasks: putting hair gel in and taking it out.\u00a0 The first case is easier, so let\u2019s tackle that right away.\u00a0 You get some gel, smear it around on your hands, and then give yourself a head massage with those gelly hands.\u00a0 (Better smear it around your hands first, for quicker homogenous application.)\u00a0 So that\u2019s it, the gel gets on your hair, and all would be \u2018cut-and-dry\u2019 so to speak, except that your hands still have a bunch of gel on them.\u00a0 In fact, you can rub your hands on your hair for quite a while and you still won\u2019t get all the gel off \u2026 and that is genuinely interesting in a statistical physics context.\u00a0 In essence, you have established an equilibrium between the gel in your hair and the gel on your hands.\u00a0 OK, now wash your hands, and keep reading.<\/p>\n
Let\u2019s imagine you arrive at work and decide you look a little too much like John Travolta astride Greased Lightnin\u2019 and not enough like a scientist.\u00a0 Time to get rid of some of that gel. We can think of a few ways to get the hair gel out of your hair.\u00a0 One is to take a shower.\u00a0 Another would be to stick your head in the sink under running water (but don\u2019t bump your head).<\/p>\n
But you can get out that excess gel and avoid bumps and splashing by thinking statistically.\u00a0 Recall our observation about putting in hair gel: some of it stays on your hands, in an effective equilibrium with the gel in your hair.\u00a0 So you can use the principle underlying that observation to remove gel.\u00a0 Put your clean (maybe wet) hands in your hair and rub them around to establish an equilibrium.\u00a0 Some of the gel is on your hands.\u00a0 Wash it off and repeat til you transform yourself back to a respectable nerd.<\/p>\n
For those of you in the business, the analogy to protein-ligand binding is obvious.\u00a0 Your hair is like a set of proteins and the gel represents ligands (ions, small molecules or other proteins).\u00a0 Maybe your hands are the proteins\u2019 environment.\u00a0 Allow ligands to interact with proteins and they will reach a binding equilibrium.\u00a0 But we can stretch the analogy a step further to invoke signaling in the cell.\u00a0 Say a burst of calcium ions is released in the cell in response to a biological signal and the ions bind to calcium-receptor proteins.\u00a0 We can imagine the signal can be reversed (the hair gel removed) if the unbound <\/em>calcium concentration is reduced (you rub clean hands in your hair): the equilibrium between proteins and ions will re-adjust due to constant binding\/unbinding events.\u00a0 Eventually, almost all the proteins will lose their calcium ions as the signal is removed \u2013 from John Travolta to nerd.<\/p>\n Lesson: Look for statistical physics in the world around you \u2013 it\u2019s better than texting while walking.<\/p>\n <\/p>\n