Monday, April 23, 2012

Le Chatelier's Principle

John Gall's Systemantics, making the point accurately but more humorously as usual, describes it thus:
A large system, produced by expanding the dimensions of a smaller system, does not behave like the smaller system.
Gall was an engineering type, adapting the scientific principle beyond merely physical systems to systems of all kinds. A nine-member Supreme Court behaves differently than a tribunal; fifty states behave differently than thirteen.

Remember that when the cry goes up about how expanding Medicare must be the solution if the ACA is struck down by the courts. Medicare is not a terrible system, at least from the points where my hospital interacts with it. Neither is it wonderful, and Tim Geithner apparently thinks it's going to go broke in ten years so we'd better do something fast. (I didn't hear the rest of that story, but I'll bet I can guess.) The blithe confidence that expanding a system that already leaks...hmmm.

I had first heard Le Chatelier's principle, or something like it, years ago at college:
Any change in status quo prompts an opposing reaction in the responding system.
Turns out that's not quite it either. In its precise form in chemistry - which I did not take in college - it's
If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established. (emphasis mine, to connect to the topmost quote.)
Unfair, you say, to try and apply physical laws to political questions. Just because such things happen among gasses and turbines and cooling systems doesn't mean those apply to human systems.

Actually, it's likely to be worse. A physical model on, say, a one-tenth scale has at least some reasonable chance of vaguely illustrating what will happen full-scale and giving hints as to where problems may arise. The physical system is, if anything, more likely to be useful. But viruses, cats, kindergartens, or - gulp - restaurants will be far more complicated and work unpredictably.

Which of course gives us great confidence in the predictability of the delivery of health care via government insurance in a mixed free-market/redistributive system.


Sam L. said...

Complexity is not just a multiplier, it's an exponential.

And the fudge factors are worse.

Texan99 said...

I took the reference to a change in volume to be something different from what we would call "scaling up." In a chemical reaction, they probably would be referring to keeping the same number of molecules but expanding the volume they were contained in; i.e., decreasing the density. Le Chatelier's principle is about systems that are limited by negative feedback loops, so if you make a small change to the system, it adjusts until it reaches equilibrium again: homeostasis.

Gringo said...

Then there is the folk version of Le Chatlier's principle: "It is difficult to make predictions, especially about the future."

Sam L. said...

Does RS Gold's comment make sense to anyone, or is it just what is an arcane subject to me? Given the links, I'm guessing SPAM.

Assistant Village Idiot said...

I'm guessing World of Warcraft spam

Anonymous said...

Le Chatlier's principle is the heart of the Haber process: hydrogen gas and nitrogen gas are ultra-compressed to drive them into combination -- as ammonia liquid.

While the reaction is actually exothermic, the reaction rate is astoundingly slow because the activated complex/ rate limiting step involves the cleavage of nitrogen gas -- which is extremely stable.

Even with its great stability, at least some trivial fraction of nitrogen gas will be energenic enough to permit a colliding molecule of hydrogen to snap it apart. In the crowded pressure, the NH radical is instantly snapped up by more hydrogen to form ammonia.


Thermodynamics DOES apply to us and our economy. It is universal law.

Assistant Village Idiot said...

Good, more science guys. We were short on them for so long around here, and it's nice to be back on the upswing.