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Complex Systems Science: An Informal Overview — Part II: Organization and Scale

This is part 2 of a series informally introducing and discussing ideas in complex systems science, and their relevance to how we build our world. Here is part 1. 

Complex Systems Science and the Special Sciences

We are familiar with science being broken down into different categories depending on what is being studied: particle physics (e.g. electrons), chemistry (molecules), biology (organisms), psychology (minds), sociology (groups of humans), etc. Call these the special sciences as their role is to look into a certain kind of stuff.

Complex systems science is not defined by what the stuff under study is, but rather how one asks and attempts to answer questions about whatever stuff is of interest. Recall that in complex systems, the properties we are interested in might emerge from interactions among components, i.e. emergent properties. For this reason, in complex systems science we pay special attention to the interactions and relationships among the parts, and how they give rise to (emergent) patterns of behavior.

We can do this in physical systems, biological systems, social systems, or any other system of interest. The answers we get will often look remarkably different than those from the special sciences.

Organization and Interdependence

When we attend to the interactions and relationships in a system, the organization of the stuff becomes more central to our understanding than the stuff itself. To illustrate this point, imagine a mad scientist takes each cell of your body one by one and relocates it to a random location — would you feel much like yourself? I think not. When the organization is disrupted, so are the interactions, and the nature of the system changes.

This also means when you change one part of the system, you may affect a larger portion of, or even the whole, system. This is because the behavior of the parts are interdependent. What part A is doing affects what part B & C are doing (and perhaps vice verse) — what my heart is doing affects what my lungs and muscles are doing. Interdependent behavior presents all kinds of challenges to standard statistical approaches which assume the independence of parts of a system.

Whether or not the change in one part of a system has affects on other parts of the system depend on its organization. If you had to choose between losing a kidney or a heart, which would you choose? Would a tree do better off losing ten-thousand leaves or one trunk?

These are hints to be cautious of centralization, and to use redundancy for robustness when possible. When we build systems we should ask ourselves, “what would happen if X failed?” — even if we are pretty sure X won’t fail.

More is Different

‘More is different’ is another way of saying ‘emergence happens’. It is no easy task to predict what the emergent effects will be when we scale a system (i.e. increase its size/number of components), especially when operating under reductionistic assumptions (emergent effects will always surprise the reductionist).

When engineering systems, emergent effects are often detrimental, or even catastrophic, to the integrity of the system, and therefore the purpose it was intended to fulfill. This is because, at the smaller scale, what appear as irrelevant side-effects (which may not have been noticed or attended to at all) are able to be absorbed or dissipated into the system’s environment in some way or another. When we grow the system, these ‘side-effects’ can coalesce and become relevant to the behavior of the system.

This is why we don’t see land animals much bigger than elephants throughout Earth’s history: the mechanical forces that are mere side-effects for smaller critters become causes of failure. Darwin puts a harsh limit on the scale of a design motif.

There are countless engineering failures that are of enormous cost to society (e.g. F-35, USS Zumwalt, the global financial system). Overgrown elephants.

The holy grail of systems engineering is to leverage emergence rather than fighting against it. Nature manages to do this via evolutionary tinkering. Perhaps we can take a cue from her.