One of the problems with being a physicist is that I start seeing physics happening everywhere I look. Here’s an example. Last week I was sitting in a cafe on Dunedin’s George Street enjoying a coffee with my wife, when the moment was utterly ruined by a completely inconsiderate couple on the other side of the street choosing to demonstrate a physics phenomenon for me.
Their crime? Walking arm-in-arm down the street exactly in step with each other. I mean exactly in step, for an entire block. They were unwittingly demonstrating the phenomenon of synchronization of coupled systems. Basically, if you take two things that oscillate at nearly the same frequency, and link them together in some way, you’ll get the two oscillations synchronizing. Huygens described it with his clocks, and there are lots of other examples (one oft-mentioned one is the synchronization of menstrual cycles in women who live together – not that I have experience of that one). Walking is a form of oscillation (swing your left leg, then swing your right leg, and swing your left again), and it has a defined frequency (number of left-swings per second – or half the total number of swings per second, because one cycle consists of a left leg swing and a right leg swing ). If someone measured the frequency for each member of the couple individually, I speculate that the two frequencies would be very similar, but not quite the same. If they separated, they would slowly get out of step. But, have them walk together, and the swing of one left leg influences the swing of the other left leg, and they end up walking in perfect synchrony.
I wonder if those who are experts in other fields suffer the same problem – of seeing their field of expertise in action everywhere they look?