Asking myself how I and most of my colleagues seem to use the word, I would have said the system is that what is described by a model (see also: Models and Theories). Then however I made the mistake of looking into the matter (e.g. in Bossel, "Systems and Models") which produced the rather abstract definition that a system is a set with elements that stand in some relation to each other, and generally has an environment that possibly provides input and absorbs output. A dictionary further explains:
- System: from Gk. systema "organized whole, body"
After I had halfways reconciled these matters, I read a book called
- The Systems View of the World
A Holistic Vision for Our Time
By Ervin Laszlo
(it's only 90 pages), which is essentially about systems and piles, and sub-systems and supersystems, life and love and reproduction, atoms and cats, self-reflective consciousness - and then manages in one full sweep to declare capitalism an outdated model, ventures for all-volunteer armies, and finishes with proclaiming a new kind of religion "celebrating [...] the sudden synthesis of the quarks and of the wide diversity of microparticles as well as of atoms and molecules throughout the expanding reaches of cosmic space". Wow. The author certainly had a vision. And if you want to get really confused, try reading this.
Either way, this didn't quite clarify what a system is either. To maybe explain why my confusion, let me ask instead: What is not a system?
Lazlo goes and piles rubbish as an example (p.25). Systems, so he argues, change qualities with the elements added. But to a pile of rubbish you can add more rubbish, and all you get is a larger pile of rubbish. It makes only a quantitave difference, he writes, it does not change the 'system' as a whole.
Now if I think in terms of mathematical definitions I can very well understand there's things that are not systems. But if I look at the real world I can't find no example for that. Everybody who is familiar with rubbish (and as a blogger I certainly am) knows that rubbish usually doesn't just orderly add up -it can develop some dynamics on its own. The pile Lazlo discusses just reminds me of the sand-pile model, a well known example for a dynamical system with self-organized criticality. So, here it goes again, we have a 'system'. The only example I can think of where one could have, in Nature, a set of somethings without any relation (interaction) between the somethings is some sort of multiverse. The analogy to Lazlo's pile of rubbish is striking.
But if everything is a 'system' then what is it good for talking about systems? Well, the usefulness of thinking in terms of systems is one of classification. One can have varios forms of systems with specific properties. Open and closed systems. Systems in equilibrium. Biological systems. Self-aware systems. Political systems. Social systems. Academic systems. Complex systems. Their elements are typically sub-systems and they are further part of super-systems, so one gets a whole hierarchy of nested systems within systems - that span all of science.
And then you go make models of these systems, find suitable variables, extract relevant parameters to try to understand the system and make predictions. Within the appropriate limits you can neglect the details of the sub-systems and talk about the system and its properties as an 'organized whole'. Might that be neglecting the quark content of molecules in a system called 'cell', or neglecting the hair color of scientists in a system called 'academia'. This procedure of neglecting finer structure and details is widely used, even within physics itself, e.g. if you think about effective theories.
I guess what confused me about this book is the author's proclamation of a paradigm shift and a change towards a "holistic vision", against reductionism, and for abandoning the "mechanistic worldview of the classical disciplines" (he seems to have a problem specifically with physics). Anyway, I think this paradigm shift just passed me by.
PS: Has clarified, thanks to Andreas.