Science in Society

Bryn Mawr College

Emergent Systems Working Group

September 27, 2002
Doug Blank and Deepak Kumar
"Emergence Systems: Ideas and Examples"

Prepared by Panama Geer
Additions, revisions, extensions are encouraged in the Forum and/or at

Doug Blank began the discussion by presenting some of the core ideas of emergence.

One hallmark of emergence is the notion of the whole being greater than the sum of its parts. The local interaction of small, "simple" pieces, or agents, gives rise to global behavior. Global behavior "emerges" as a result of "simple" parts interacting on a lower "level." This global behavior results from the interactions of the parts. The global behavior that is not evident in the parts alone. 

Systems that exhibit emergence are often driven by self-organization. A system is self-organizing if, left alone, it tends to become more organized. This is counter to the ideas of entropy and the second law of thermodynamics, roughly that all systems tend to run down, or tend towards disorder, over time. Many biological systems are self-organizing.

Often, phase transitions appear as the number of interacting elements in the system increases. That is, an observer sees a quick, dramatic change in the global behavior of the systems; for example, the transition from ice to water. Pairing this with self-organization, often one globally sees something that appears random and then quickly becomes organized. Sometimes complexity is referred to as the "edge of chaos."

The emergent, global behavior may create a novel "level". This level can be thought of as an actual new entity, or possibly a new level of description. There may be multiple "levels of complexity", but, for a system to exhibit emergence, there does not need to be more than the initial level (where the parts reside) and the global level. One person stated that, in practice, some of the most interesting phenomena occur when there are many levels to the system, that is, when there is a tendency towards increasing complexity. 

Some questions arose with regard to these "levels". (1) Are multiple levels of organization essential for defining emergent systems? (2) How do you get a system to propagate levels of organization? (3) How do you get both bottom-up and top-down causality in such systems? (4) Is this causality an essential part of an emergent system?

The global behavior is often said to be unexpected, a surprise, or unpredictable. Some participants felt that the words "unexpected" and "surprise" are often not stated precisely.

Often, emergent systems can be described by so-called "Power Laws". That is, little things happen often, while big things happen rarely.

Examples of emergent systems were briefly discussed. Life can be thought of as an emergent system. Is it a "typical" example or a special case? Other examples included biological and artificial evolution, the development of urban structures, cellular automata, Conway's Game of Life, etc.

Deepak Kumar provided a demonstration of the movement of a robot that was given a few simple rules. The rules were (1) if the sensor was touching something it moved diagonally left and (2) if the sensor was not touching anything it moved diagonally right. The global behavior that the robot exhibited was that it followed a wall. If one looked closely, a slight zigzag motion could be detected. The wall-following behavior was described as emergent. 

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