Engineering Complex Systems

The emergent properties of complex systems are far removed from the traditional preoccupation of engineers with design and purpose

Complex systems can be identified by what they do (display organization without a central organizing authority — emergence), and also by how they may or may not be analysed (as decomposing the system and analysing subparts do not necessarily give a clue as to the behaviour of the whole). Systems that fall within the scope of complex systems include metabolic pathways, ecosystems, the web, the US power grid and the propagation of HIV infections.

Complex systems have captured the attention of physicists, biologists, ecologists, economists and social scientists. Ideas about complex systems are making inroads in anthropology, political science and finance. Many examples of complex networks that have greatly impacted our lives — such as highways, electrification and the Internet — derive from engineering. But although engineers may have developed the components, they did not plan their connection.

The hallmarks of complex systems are adaptation, self-organization and emergence — no one designed the web or the metabolic processes within a cell.And this is where the conceptual conflict with engineering arises. Engineering is not about letting systems be. Engineering is about making things happen, about convergence, optimum design and consistency of operation. Engineering is about assembling pieces that work in specific ways — that is, designing complicated systems.

It should be stressed that complex is different from complicated. The most elaborate mechanical watches are appropriately called très compliqué, for example, the Star Caliber Patek Phillipe has 103parts.The pieces in comlicated systems can be well understood in isolation, and the whole can be reassembled from its parts. The components work in unison to accomplish a function. One key defect may bring the entire system to a halt; complicated systems do not adapt.Redundancy needs to be built in when system failure is not an option.

How can engineers, who have developed many of the most important complex systems, stay connected with their subsequent development? Complexity and engineering seem at odds — complex systems are about adaptation, whereas engineering is about purpose.However, it is robustness and failure where both camps merge.

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