Collective Motion
Collective Motion
The emergence of global ordered movement in a system of individual particles. This broad term includes all sorts of different systems: traffic flows, bird flocks, bacterium collectives. The thing I find interesting is that normally, each part of the collective (an agent), has some local rules managing their behaviour. Local means it depends on their surroundings somehow, and isn't controlled by a hive mind or a function of the whole group. For example, a driver wants to keep a safe distance to the car in front and behind. These local rules are normally considered to be the same (or at least qualitatively similar) for each agent. One or two agents can interact freely without issue or surprising behaviour, but as the system size grows, some global behaviour emerges. Note the connotation with "emerges". From not being present to appearing, global behaviour is a function of all the agents moving together. For example, an overly-cautious driver who brakes too early or a distastracted driver who brakes hard can send a shockwave of braking backwards through traffic. This is an emergent phenomenon that appears at sufficient traffic densities. None of the drivers plan to be part of this display, but due to their personal driving methods, the wave permeates through the congestion.