Equilibrium is a state of balance of opposing actions that is central in virtually everything that happens, from basic physics to dance and the arts, economics and social ideologies.

Philosophers have discussed the concept for millennia, and scientists have developed sophisticated schemes for characterizing equilibrium systems because they are the simplest. But equilibrium systems are boring because a system in equilibrium does not change.

All natural systems are slightly out of equilibrium, fueled by some kind of impetus. Many are close enough that equilibrium principles can be applied as approximations, but the real workings require more advanced approaches.

Dynamic equilibrium refers to a steady state system in which there is ongoing change, but in opposing directions such that the system as a whole remains in balance. There are many examples: A lake or a bathtub is in a steady state when water flows in at the same rate as water flows out; the oxygen content of the atmosphere remains constant as long as respiration and photosynthesis remain balanced.

Homeostasis reflects a complex dynamic equilibrium that is kept in a fixed state over some time period through moderated changes. Energy and material input is changed to metabolism, motion and output of heat and waste.

A heating/cooling thermostat is a simple physical analog of homeostasis. The control algorithm is simple: too cold, turn on heater. Too hot, turn on cooler. This complex system includes not only the room but also outside the room and all of the possible factors that can influence the temperature of the room. Yet it has very simple controls.

Nature's systems are not so simple. They are always near equilibrium, sometimes straying further than others but never sustaining it. Regardless of the size of the system and its apparent order, there is always some scale at which it is chaotic.

From the shore we see water in turbulent rapids. A bug in the water would see chaos; an observer in an airplane would see a thin line, and an astronaut may not be able to see the river at all.

Time is a factor as well. Water moves downstream despite the turbulent eddies, and on our time scale the river's path is fixed, but over geologic time the river may change its course dramatically.

On a planetary scale we are the atoms and bugs in the rapids of a metaphorical stream and have only a limited ability to see changes in the global systems that are barely perceptible even with instruments in our human time frame.

Being very small and extremely short-lived creatures, we are unable to forecast changes in very large systems whether they be the planetary ecology, global climate, global economy, global politics, or even the traffic during tomorrow's commute. We do the best we can with those limitations and keep getting better. The big Q is whether we are getting better fast enough.

Richard Brill is a professor of science at Honolulu Community College. E-mail questions and comments to .(JavaScript must be enabled to view this email address).