🚀 go-pugleaf

In article <3369749D.3D21@midusa.net>, T. Haug <tjhaug@midusa.net> wrote:
>John:
>How do you define equilibrium?

In physics (and I'm posting from sci.physics), "equilibrium" is 
a condition in which a physical system remains in the same state
as time passes.    According to this definition a sleeping dog is 
not in equilibrium, because while it might look static to the casual 
observer, it is actually breathing, metabolizing, pumping out heat 
into the environment, and so on, and eventually it will wake up
and walk off.  By this definition, living systems are never in 
equilibrium; you only reach equilibrium when you die and completely 
decompose.

There is a sense in which living systems act to maintain the constancy
of certain parameters (body temperature, chemical concentrations, etc.).
A nice word for this is "homeostasis".  It's quite different from the
above sort of equilibrium, since it typically requires expenditure of 
free energy.  It's not too terrible in certain situations to use the
word "equilibrium" for "homeostasis", as long as one knows what's going
on.  For example, when one speak of someone being in "psychic equilibrium"
one doesn't usually mean that their brain has rotted completely away; one
means that they are homeostatic.   Also we might speak of an ecosystem 
being in "stable equilibrium" if it returned to its initial state after
small disturbances, though again this is really a kind of homeostasis. 

In fact, it's pretty tricky to make precise the sense in which living
systems, ecosystems, etc. maintain a kind of constancy.  For example,
it used to be thought that the "balance of nature" meant that when small
natural disturbances in an ecosystem pushed it from its homeostatic
state, it would automatically move back to that state.  Now it seems
that this rarely happens so neatly.