[Question] What is complexity science? (Not computational complexity theory) How useful is it? What areas is it related to?

I’ve been reading “Playing with movement—Hargrove 2019”. This book told me about “complexity science”, which is a field which supposedly studies complex systems and it does it not by reductionism, but by looking at the system as a whole. It seems that some key concepts used in complexity science are: complex system, emergence, adaptivity, nonlinearity, self-organization, constraints, attractors, feedback loops. This book pitched an idea that with many complex adaptive systems, if you want the system to achieve a certain goal, it’s bad to specify a specific plan for it and instead it’s better to specify or build constraints under which the system, being adaptive and all, will achieve the goal on its own, supposedly in a more optimal way. Examples:

  • System: my body. Goal: get healthy by physical exercise. Specific plan: do strength training by doing specified sets of reps, using specific instructions on how to position my body. Alternative (constraints): live in such an environment that a lot of physical activity will happen naturally.

  • System: economics of a country. Goal: make it productive. Specific plan: central planning of what to produce, in what quantities and how. Alternative: free market economy, the organizations will behave however they want, and hopefully the whole system will act in an optimal way.

  • System: my body. Goal: eat healthily. Specific plan: write down a schedule of specific meals for the next year and eat them. A potential problem is I might miss something and that might lead to a lack of some nutrients. If instead I eat whatever I want, I will probably crave those other nutrients and hence I’ll go and eat them. Obviously, this has downsides.

This idea seems plausible and very important. However, I’ve never heard of complexity science before. I’ve been following all kinds of links about complexity science trying to figure out what it is, what fields it’s related to and what subareas it has. Also, I want to know how much of it is correct and how to apply it in the real world. Please help me figure out these questions. So, I guess I want a primer. Except I know that if I find a primer written by a complexity scientist, it’ll claim that complexity science is the greatest invention ever. Instead, I want a sceptical primer which specifies the domain of applicability of complexity science and the domain of applicability of theory of complex adaptive systems. Below, I list some more specific questions.

  • It seems complexity science is also sometimes called complexity theory (different from computational complexity theory) and is somehow related to systems theory and complex systems science. Systems theory is supposedly a synonym for cybernetics. And maybe systems theory is related to systems thinking. How are all these areas related and to which does the study of complex adaptive systems belong?

  • Complexity science is somehow related to a bunch of math areas: chaos theory, differential equations, fractals, and cellular automata. But at the same time, it seems related to sociology, the study of human organizations, and has some applications to medicine and biology.

  • I want to read or study something to better understand the idea described earlier. I want to understand when that idea is true and when it’s false. Any recommendations or thoughts? Is this idea also studied in other scientific fields?

  • In general, how awesome is complexity science? Is it almost entirely correct like math or physics? Or is it full of incorrect information like psychology and other social sciences? It is at least not 100% crackpottery, since some books are published by Princeton university press and Oxford university press.

  • Complexity science seems useful for rationality. Why isn’t it popular on Lesswrong?

And here are some links and sources I found about complexity science: