Self-Organized Criticality

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Basic Principles
Natural Selection
Red Queen Effect
Swarm Intelligence
Self-Organized Criticality
Butterfly Effect
Control Loop
Lever Point
Frozen Accidents
Path Dependence
Complexity, Simplicity
Edge of Chaos
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The abbreviation SOC is sometimes used for "Service Oriented Computing" or "System On Chip". It can also mean Self-Organized Criticality, a concept coined by the Danish physicist Per Bak (1948-2002). It is the most physical form of self-organization, which can occur even in inanimate matter. The term is closely related to the concept of the edge of chaos and means that a system evolves towards a critical state, where the state of the systems can change suddenly. It is characterized by high complexity, which means unity in diversity: stability in instability, simplicity in intricacy, and predictability in unpredictability. The price for this complexity is usually low uniformity, it is a point of permanent change, continuous fluctuations and constant variation.

The criticial point is point of high complexity, because it combines stability and instability: the system evolves automatically to a certain state (which increases stability, certainty, and predictability), but at these state chain reactions can lead to avalanches and cascades of any size (which increases instability, uncertainty and unpredictability). Thus the criticial point in self-organized criticality is a "metastable" and complex state characterized by instability in stability, uncertainty in certainty, or unpredictability in predictability.

The SOC concept can be applied for example to tectonic plates (earthquakes) or to sand piles (avalanches). If grains are added to a pile constantly, the slope of the sand pile develops itself automatically towards a certain critical value, where avalanches of all sizes can occur. Although the system is stable (it develops towards a certain critical point despite disturbances), it is instable at the same time (there can be avalanches and cascades of all sizes). It shows a high complexity in form of stability in instability.

SOC means also often a high complexity in form of simplicity in intricacy. On the one hand the behavior is simple and can be described by a few parameters, but on the other hand the behavior is intricated, characterized by long-range fluctuations and correlations, and can not be predicted at all. Although the detailed behavior and the precise occurence of avalanches is hard to predict, the overall behavior of the system can be described by a few parameters named "critical exponents". They are typical for phase transitions. The distribution of avalanches at a critical point follows typically a power law. Small events are very frequent while large events are rare.

Like other concepts, for example Autopoiesis, Self-Organized Criticality is not a complete science or a theory, rather an observation, a phenomenon, or a principle. The idea of SOC is useful to explain cascades and avalanches (for example in sand-piles or producer-consumer networks) that can be described well by simple power-laws.


  • Per Bak, How Nature Works - The Science of Self-Organized Criticality, Springer, 1996, ISBN 0387947914


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