Metastable:
I have been guilty of playing fast and loose with a phrase: meta stable, or you can say metastable. This is a well defined concept in physics and chemistry. It denotes a state that can last for an appreciable period of time; a small disturbance will lead to the condition returning to the original condition, but a larger disturbance will result in the system leaving its condition and finding a new more stable state.
For instance consider water freezing. Over a range of temperatures water will remain a liquid indefinitely (assuming constant pressure on it). When it gets cold enough it will freeze. That, too, can last indefinitely. But as you cool water you can cool it past the freezing point by a small amount and it will not freeze. It is super cooled. But if you drop a tiny ice crystal into the super cooled water the whole thing will freeze. The super cooled state is meta stable.
More simply consider a picture hanging on a hook on the wall. With a small bump the picture may rock a bit but then will continue hanging. But hit it hard and you can lift the wire over the tip of the hook and the picture will fall to the floor from where it will not return to the hook unless some outside agency puts it back where it belongs.
That is the standard definition, well thought out by others and quite useful.
I use it in a different sense. In fact I use it in two senses. If you consider some ancient empire, day follows day and generation follows generation for quite some time. But as the 300th birthday of the empire approaches the empire becomes more and more likely to fail until with very few exceptions at about year 300 it has no possibility of surviving much longer. Similarly in modern reasonably rich countries the birth rate has fallen to below replacement and almost always the age at first marriage for women has commenced an inexorable climb. This can last a long time; it looks reasonably stable. The birth rate is not substantially falling, but the words mene, mene, tekel, upharsin have been written on the wall. That could be “numbered, numbered, tested and shattered,” if my reading of Daniel is correct. Sounds sort of like the same thing, eh what?
The second sense in which I use “meta stable” is that on a different time scale, every time a regime changed in lower Mesopotamia there was always another ready to step in and take over. This has not been true everywhere. Great empires in Africa have fallen and not been replace. The same has been true in the Western Hemisphere.
So my excuse is this: meta stable means stable on one time scale and not another. Run to the bathroom and flush a wad of tissue down the toilet. Being pretty dry, the wad will float for a while. As the water rushing into the siphon the wad will circle around. It looks like it is going to be stable for some time. But then the water closet above runs out, the inflow stops and with a gulp from the siphon the tissue goes down. The condition of the tissue was meta stable, stable on a scale of seconds but not on a scale of minutes.
The problem is this. The situation is not really stable after the flush. On a longer time scale other things will be flushed. But after the event the toilet will return to its resting state. On an even longer time scale, the mechanism will wear out. But it will be repaired. Eventually the technology will change. On a very long scale it will change any number of times.
So whether the toilet is stable depends entirely on the time scale you choose. Nothing lasts forever.
If that is true of the toilet, then it is true of everything. Every process is either grossly unstable or meta stable until the earth becomes uninhabitable in the unknowable mists of the future. And of course a word that can be applied to anything really has no meaning because it doesn’t distinguish between what is described and anything else.
So the word has serious problems the way I use it. But I do find it useful to call attention to the fact that apparent stability depends on time scale and the transition from what appears to be stable to what is obviously completely unstable can happen abruptly. I shall attempt to be more careful when the issue arises again.
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