An expanded version of chaos theory, complexity theory looks to uncover a system's beginning (its “initial conditions”) and to trace development as variables and subsystems are added to combine and shape outcomes in ways that are unpredictable.
What's fascinating about complexity theory is that it's not just about unpredictability... it's also about finding patterns within that unpredictability. Complex systems often exhibit self-organization, where order emerges without central control. Think of how cities develop distinct neighborhoods, how ecosystems stabilize into food webs, or how free markets coordinate resources without anyone orchestrating the whole system.