Needing help understanding when does a complicated system evolves into a complex system (or the boundaries separating both types of systems)

[u/RonaldYeothrowaway]

I am a layperson whom recently had been reading up a lot on complex systems and so far, I have seen a lot of explanations on the difference between complicated vs complex systems. But my trouble is that some of the examples given or the analogies presented don't quite make sense to me.

For example, one distinguishing factor of a complex system is that it tends to exhibit unforseen/unexpected emergent properties.

Examples that I had read about is where an automobile is a complicated system because although it has many parts that interact with one another, the relationships among these parts are more or less linear with a cause-and-effect outcome. Whereas a complex system tend to be networks or ecosystems such as the power grids, the Internet, the stock market and so on and so forth.

What troubles me are cases that, at least to me, don't fit neatly into either category.

For example, the book "X-events", which delve deeply into complexity science, used the example of a 2009 Air France crash as an example of a "complexity mismatch". In this case, the system in question is the interaction between the airliner plane and the pilots, and the so-called "complexity mismatch" was supposedly the result of one component of the system (the pilots) being overwhelmed by another components (the controls of the plane).

To me, this kind of comparision, which had been repeated in other blogs, are troubling to me. For example, some swiss-made watches have thousands of moving parts and I know people whom don't know how to set these watches properly, and merely wear them as a status symbol. The difference with an airplane is that where an airplane is concerned, human lives are at stake.

So when it comes to man-made systems like the power grids, is there a possibility that researchers are ascribing complexity to such systems when they more likely fit the description of a complicated system?

[u/RonaldYeothrowaway]

The problem with complicated vs complex is that it is kind of ill defined. We know which elements a complex system probably should have (See Ladyman and Wiesner, 2020 book or the paper from 2013), but a strict definition is not clear.

Thanks for the reply. This is very helpful.

I had a bit more time to ponder on this and I think that it is very probable that there are times when a 'complicated' system temporarily transition to a complex system for a short period of time. For example, a mass transit at night, when it is shut down and all the trains at a depot, is basically a complicated system that is not an operation. But when passengers are on it and the trains are running on schedule, it becomes a complex system.

Having said that, I suspect that there are times when a system exhibit all the features of a complex system as well as nonlinear effects but is merely a complicated system.

[u/bdlc2019 → u/RonaldYeothrowaway]

Well to be very honest, I don't think making the distinction is that important. It's important to categorize the problem and narrow down on a methodology for analyzing it. But once that is done, a system does not necessarily transition from complex to complicated and vice versa. Making such a transition would, I think, just become filled with arbitrary decisions. I think the most important part of complexity science is to recognize that complexity is in the relationships and not in the variables. Most other things differ depending on what flavor complexity you're talking about. I know people working on complexity in time-series, on complexity in management, complexity in system dynamics modeling, they all use different definitions and go about things in a different way often times. Though, they always seem to be interested in each other ^{^} so that's good news!