Mengsen Zhang, Ph.D.

complex systems and brain sciences


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Why Complexity

I studied Pharmaceutical Science and Psychology as an undergrad, then Criminology as a Master student. Through this journey across the scales, I have looked at humans as molecular machines, cognitive pipelines, and constituents of a social organism, which eventually led me to Complexity Science. The desire to understand complexity is almost a coping mechanism of my brain to hold together very different perspectives of human identity. Human behavior is an interface between the micro and the macro: on one side, it is a global property coming out of the relations between local properties, and on the other side, it is a local property being an element of a global property. What really got me to wonder is the similarity between the two local-global relations, and the analogy between a person and a social system.

I’m certainly not the first person who felt that way. Plato (or Socrates) made a whole argument about what is justice and injustice based on the value of this very analogy - to know what’s justice in a person, one needs to look for justice in a city.

”[…] lacking keen eyesight, we were told to read small letters from a distance and then noticed that the same letters existed elsewhere in a larger size and on a larger surface. We’d consider it a godsend, I think, to be allowed to read the larger ones first and then to examine the smaller ones, to see whether they really are the same. […] there is the justice of a single man and also the justice of a whole city […] and a city is larger than a single man […]. Perhaps, then, there is more justice in the larger thing, and it will be easier to learn what it is. So, if you’re willing, let’s first find out what sort of thing justice is in a city and afterwards look for it in the individual, observing the ways in which the smaller is similar to the larger.” (Republic, 368-369)

This is almost a research statement. What is justice and injustice of a complex system then?

”[…] each of the other citizens is to be directed to what he is naturally suited for, so that, doing the one work that is his own, he will become not many but one, and the whole city will itself be naturally one not many. […] Then it turns out that this doing one’s own work - provided that it comes to be in a certain way - is justice.” (Republic, 423d-433b)

In other words, a complex global structure can be achieved by simple local principles - do what you got to do. Now in all honesty, Plato’s “justice” is not really about the “complex” part of a complex system - it’s about the “a” part. Before getting into whether something is complex, you have to make sure you are talking about one thing. It is perhaps at the heart of Complexity Science to figure out how many things can be one, without becoming simple. Nevertheless, Plato’s “justice” may imply complexity if diversity in individuals’ nature is assumed.

With this being a constant source of wonder, I simply want to take things a bit more formally via scientific means.

I need first a proper language to characterize complex structures (or spatiotemporal patterns), then to figure out how this (now formally represented) structure serves the system as a whole (the “one”), and eventually how to get there (path of evolution). More or less, I’m at the first stage, which turned out to be non-trivial. It is one thing to come up with some functional that can map any complex structure to a scaler and call it a “measure of complexity” (or other fancy concepts of your choice), but it is entirely another thing to really describe that structure. If there is an organism whose survival depends on solving various complex problems on a daily basis, it is insufficient for the organism to just match the level of complexity (or other fancy measures) without matching the structure of behavior to the problem. Thus I am working towards a meaningful way of describing structures (topological? geometrical?) of complex behavior, and hopefully soon got to systematically study how these structures are organized in biological and social systems.

And of course, only then I may know what is justice in complex systems. ;-)