[Note: there is a companion web application and source code on GitHub for this article.]
When I first started dating my wife, one of the little things that impressed me about her was that she would always know when it was about to rain. We were living in Pittsburgh at the time, where sudden downpours and thunderstorms are common. This ability to predict the weather was a valuable skill to have. Finally, I asked her how she was so good at predicting a storm. “The leaves on trees,” she replied. “They turn upside down right before the storm hits. It’s something I learned in Girl Scouts.”
Ideas have a funny way of spreading. Sometimes a concept that has become ubiquitous in a particular field of study can take years to be widely understood in another field that could have equal use for it.