The Physics of Mass Gatherings and the Trump Inauguration

Sometimes, things get out of control. Take, for example, mass gatherings. Usually they're safe, but every now-and-again, we hear about a disaster where a number of people are crushed to death or injured in a stampede. In retrospect, it seems so avoidable, but is that always the case? I recently wrapped up a study with some colleagues from Uppsala University's Mathematics Department, and it looks like, at least in some cases, that the risk for injury in mass gatherings naturally emerges from mechanics and the physics of disorder. Here's what it comes down to: in a crowd packed shoulder-to-shoulder, the random positioning of people relative to their neighbors creates a physical network of contacts. Networks like these have a number of interesting physical properties, but three specifically caught our attention given their ability to drive a disaster: 1) Broken symmetry = massive collective motion. Circles are very symmetric. Neatly packed oranges at your favorite grocery store also have symmetry, but a little less-so. A dense crowd of people packed together, say at a presidential inauguration, has essentially no symmetry at all. The term of art is called a "broken symmetry," and one of the immediate physical consequences is that a large scale "wave" can propagate through the crowd like sound through air or vibrations on a string. While this massive collective motion has a fancy physics name - a Goldstone mode in case you want to look it up on Wikipedia - the important poi...
Source: Science - The Huffington Post - Category: Science Source Type: news