What are complex systems? How are they different from complicated systems?

While there are many definitions of complex systems, over the past two decades, a general consensus has emerged on how to distinguish complex systems them from those which are merely complicated. A car engine, for example, is complicated, being composed of many interrelated parts which must be machined in very precise ways. That said, an engine is not generally considered 'complex' (in the sense used by 'complex systems researchers') for a variety of reasons.

1. Complex systems are self-organizing. A car engine didn't organize itself, but a colony of ants does.

2. Complex systems are generally controlled in a manner which is distributed, rather than centralized. So, while a single driver controls the performance of a car engine during use, a colony of ants building a nest has no central director. Rather, local actions of many actors contribute to an overall macro-behavior.
3. A complex system leads to the emergence of behavior which is greater than the action of the sum of its parts. In a car engine, the engine, all the parts fit together to create the action of the whole, but nothing unexpected should emerge unless the engine malfunctions.

   With an ant colony building a nest, however, the nest will never get built unless the micro-rules exercized by many ants, each with limited insight and information, could lead to a macro-structure which cannot be predicted from the micro-rules used by each ant - namely, the structure of the nest.

For all the reasons listed above, a car engine is a complicated system, but a colony of ants building a nest is considered complex.

Complex systems abound in nature, from vortexes in a drain-pipe to weather patterns, mass-migration of bees to a food source, to the reactions of crowds doing 'the wave' at a baseball game. While there has been extensive research in complex systems in nature, there is also a growing literature on complex social systems.

Our goal is to help bring the insights in the study of complex systems to a wider public seeking to make the world a better place.