Self-organizing systems illustrated

This video shows a physical, self-organizing system.

These days a lot of people talk about such kinds of systems for information technology, called self-X systems. Self-X like self-healing, self-organizing, self-stabilizing. The self-X paradigm envisions software systems that come with some inherent dynamics to automatically keep a complex system in a “good” state while it is constantly under “bad” influences. A “bad” influence are request to a web server, the “good” state is that the server responds. State-of-the-art technology allows that a web server stays “good” as longs as there are not too many requests. In case of a (distributed) denial-of-service attack the server will no longer respond to each request; “bad” influence. A self-X web server would be able to deal with this by

  • distinguishing “bad” from “good” requests,
  • automatically providing additional capacity (in memory, CPU and network) for the “good” requests, and
  • efficiently denying all “bad” requests with minimal effort.

This sound too good, to be true. And its obviously not easy to achieve – otherwise we would already have such kinds of systems everywhere. The automatic software updates your operating system and web browser performs these days is one of the first industrial applications of this idea. The skype login mechanism is another example. I guess you want more of this. That’s why a lot of people are researching self-X systems, mostly by thinking of clever algorithms, architectures, network technologies etc.

But the development of these systems requires some profound understanding of self-organization. The good news is that many disciplines have some concept of self-organizing system. The bad news is that these concepts are different although they have something in common. Of course, chemistry, physics and informatics cannot have the same definition of self-organizing system – each talks about different things. But this does not help when one tries to build such a system.

As a starting point, though, I think the five self-organizing metronomes are very illustrative. Let’s have a look on them again:

Each metronome on its own is a single entity that can swing if it is pushed. The movement of one metronome’s pendulum is independent of the other metronomes. That’s why the five metronomes swing non-synchronized in the beginning of the clip. Think of yourself trying to synchronize all of them. By stopping and pushing each metronome one after the other. You will most likely not succeed.

What then happens in the clip is that the metronomes are coupled. This coupling is key in this self-organizing system. The coupling happens by putting all metronomes on a common board and placing this board on two rolls such that the board can move in the direction of the pendulum movement. The metronome was not changed, or more precisely, the mechanism of the pendulum was not changed. But by the laws of physics, the movement of the pendulum applies a force to the ground of the metronome, which is the board. So now, the metronomes are coupled – each applies “its” force to the board – the sum of these forces pushes the board, which moves, which pushes the metronomes. As a result each pendulum is “pushed” by the others. Instead of five independent metronomes we got five coupled metronomes.

Now by another law of physics, the entire system seeks an energetically optimal point. This optimal point lies in a synchronization of the moving parts such that the entire system looses as few energy as possible. If one pendulum is out-of-sync with the others, its movement will dampen the movement of the others and vice versa, and dampening means loss of energy. Actually, because of dampening, the system gets into a synchronized state at all. In the worst case, all metronomes have to stop to get the system synchronized. But luckily, each metronome can give away energy on its own (each metronome has its own dampening mechanism). Therefore, the system can reach a state where each pendulum has been dampened such that it is no longer dampened by the movement of the other metronomes.

I am no physicist, so I am not aware of all details of this process, nor can I explain them appropriately. But what I can say for sure is that the synchronization was achieved by two things:

  1. The coupling mechanism allows communication (i.e exchange of energy) between the parts that shall be synchronized.
  2. Each part is designed in a way that the part can be influenced via the coupling mechanism, most importantly by push and repulsion.

The difficulty in computer science is that we have to find such coupling and interaction mechanisms in a world where there are no laws like the laws of physics – well, not yet.


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