"A state of a system which keeps certain properties invariant" (G. PASK, 1961, p.114).
This is merely one of the many more or less complementary definitions that can be encountered in the literature. It is sufficiently general to include different kinds of equilibrium (see hereafter).
For PASK: "The term includes not only static equilibria – an object at rest - but also dynamic equilibria and statistical equilibria" (Ibid)… which of course are quite different situations.
W.R. ASHBY gave examples of three basic types of equilibrium:
"Stable equilibrium" typified by "a cube resting with one face on a horizontal surface".
"Neutral equilibrium", the case of "a sphere resting on a horizontal surface".
"Unstable equilibrium", the case of "a cone balanced on its point" (1960, p.44).
More recently K.De GREENE distinguishes four kinds of equilibria: equilibrium per se, restorable disequilibrium, multiple equilibrium and nonequilibrium/far-from-equilibrium.
He states: "The major emphasis of system dynamics, at least formally, is on the first two conditions. The third condition is studied by catastrophe theory. The fourth condition is emphasized by dissipative-structure theory and by synergetics" (1994, p.7).
Generally, equilibrium is a state in which a system tends to remain if no disturbance deflects it from the same.
Homeostatic systems (i.e. systems endowed with dynamic equilibrium). when disturbed, tend to return, to "bounce back" from their stability thresholds, through negative feedback and thus to remain within a well defined stability channel.
A system in equilibrium is "short-sighted ", i.e. has no sensitivity to long term trends. Curiously enough, our own appreciation of equilibrium in systems whose duration is very large in relation to our own life-time also tends to be "short-sighted ": it is very difficult for us to develop a sensitivity to long or very long rhythms of change.
Equilibrium can also be an instantaneous and transient state of a system submitted to a periodic process.
A. BOGDANOV called such variations "a dynamic equilibrium of changes" wherein "Preservation is always only a result of immediately equilibrating each of the appearing changes by another opposing change" (1980, p.78).
This is in fact an extension of LE CHATELIER Principle. The transition from an unstable to a stable and definitive equilibrium reflects the action of some asymptotic attractor, which corresponds to a gradient characterizing the successive values of the variable.
W.R. ASHBY expresses this as follows: "Given a field, a state of equilibrium is one from which the representative point does not move" (1960, p.46).
Arguably, ASHBY could have added "…anymore", since in the very next paragraph he states: "Notice that this definition, while saying what happens at the equilibrium state, does not restrict how the lines of behavior may run around it. They may converge into it, or diverge from it, or behave in other ways" (Ibid).
Static equilibrium – and subsequent destruction – is anyway the final state of any living 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: