"Characteristic of a system where the individual degrees of freedom keep each other in a more or less stable balance, which cannot be described as a "perturbation" of some decoupled state, nor in terms of a few collective degrees of freedom" (P. BAK. C. TANG & K. WIEISENFELD, 1988, p.364).
The authors give as an example: "… ecological systems (which) are organized such that the different species "support" each other in a way which cannot be understood by studying the individual constituents in isolation. The same interdependence of species also makes the ecosystem very susceptible to small changes or "noise". However, the system cannot be too sensitive since then it could not have evolved into its present state in the first place. Owing to this balance we may say that such a system is "critical"… this criticality can be put on a firm quantitative basis" (Ibid).
Further on, the authors state that this class of composite systems "has a specific temporal fingerprint, namely "flicker noise"… characterized by correlations extended over a wide range of time scales, a clear indication of some cooperative effect".
Flicker noise is in fact not noise but reflects the intrinsic dynamics of self-organized critical systems" (Ibid)
"Another signature of criticality is spatial self-similarity" (Ibid).
Thus criticality is characteristic of not strongly integrated systems (as for example ecological or climatic ones) or almost homogeneous systems (i.e. with a very limited number of classes of components).
It seems related to countervailing statistical regulations which maintain the composite system within a channel of dynamic but turbulent stability, which evoques also the concept of chaotic attractor.
Note: In a more recent paper, P. BAK (with K. CHEN) use the label "composite system" in lieu of "dynamic system" which seems more adequate. In this dictionary we also use the expression: "Almost homogeneous system ".
- 1) General information
- 2) Methodology or model
- 3) Epistemology, ontology and semantics
- 4) Human sciences
- 5) Discipline oriented
To cite this page, please use the following information:
Bertalanffy Center for the Study of Systems Science (2020). Title of the entry. In Charles François (Ed.), International Encyclopedia of Systems and Cybernetics (2). Retrieved from www.systemspedia.org/[full/url]
We thank the following partners for making the open access of this volume possible: