Spontaneous synchronization is a mysterious form of emergent behavior in which the behavior of a system's components or agents tend to align with each other over time and the entropy of the system appears to spontaneously decrease. Examples of synchronization include flocking, flashing, ticking, assimilation, and conforming.
In these systems agents own behavior. When an agent updates itself it "aligns" its behavior with the behavior of a random or influential neighbor or in some cases with the majority of its neighbors. Feedback takes over, as information spreads then echoes back to its origin, releasing another wave of reinforcement, certainty, amplitude. It's positive reinforcement.
Sometimes the way an agent observes its neighbors can be subtle, a mere vibration transmitted through a floor can, over time, cause clocks in a clock shop to start ticking in unison. People walking on a bridge will tend to march in cadence to compensate for the sway of the bridge caused by the cadence, creating a self-reinforcing loop.
TED talk by mathematician Steven Strogatz.
Here's another interesting link: