What is a Complex System?

In this video you will find what is the answer of  IFISC young researchers to this question.

What do ants, the brain and society have in common? They’re all complex systems! And “What is a complex system?”, you might be wondering.

We will say, in a very generic way, that a system is a set of connected elements. Just a group of things, alive or inanimate, which are able to interact between them giving rise to a certain behavior. And here comes the tricky part. A non-complex system can be entirely understood through the study of its individual units. On the contrary, for a complex system understanding its behavior requires more than just adding up the contribution of each element. 

Why? Well, it all comes down to the interactions. The components behave individually but their actions influence the other components. This leads to the system being capable of adapting to the environment and to the emergence of unpredictable collective behavior.

Ants do not seem that complex. In fact, these insects are quite simple creatures, not too smart you might think. However, they exhibit some incredible features. For instance, an ant has different working duties depending on the needs of the colony at a particular moment. That means they are able to adapt to the environment. There is no leader telling each of them what to do, yet they know. Not so dumb after all.

In the case of the brain, our ability to think is due to a team of neurons working together. It is well known how a single neuron functions. But when they get together, their collective behavior is not what we could have expected. A single neuron cannot “think” by itself, but an ensemble of them can. This shows that thinking arises from the interaction of many neurons.

Another characteristic of complex systems is that they are usually made up of a large number of elements. There are approximately 7.7 billion people in the world. That's pretty large. Besides, our individual behavior is constantly changing as a result of relationships and that leads to the emergence of particular social phenomena.

Complicated vs complex.

Although these words have not the same meaning, they are often used interchangeably. A complicated system might have a large number of components but they follow cause-effect relations that are well understood and can be precisely predicted. However, as we stated before, in a complex system the interactions between elements give rise to emergent phenomena that cannot be derived just from the study of the behavior of each part separately.

Plane vs brain.

An example of the difference between complicated vs complex is given considering a plane vs the brain. A plane is made up from millions of pieces of different sizes, materials, resistance, etc. But somehow, when we put all of that together, the result is a machine capable of flying. We know every detail of each component and what is its function. The plane is just the sum of all of them. It is indeed something very complicated, but not complex.

The brain is complex. It is basically a collection of neurons interacting among them. We know quite well what is a neuron. Its anatomy and structure have been studied for decades. But when we have a bunch of them interacting, the resulting behavior is more than the sum of the individual contributions.