I'll try. I really thought you were taking the mickey, and I think you will see why I thought that.
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In what follows, the quoting refers to [Bill Powers (2008.03.06.0306 MST)] citing Martin Taylor 2008.03.05.22.48.
All control systems are refrigerators. Not all heat pumps are control systems.
Are you replying to the post in which I reminded you of control systems that act by raising the temperature of air and maintaining it in this elevated state despite either heating or cooling disturbances? Not all control systems are refrigerators.
Over the years, the measure of the quality of control used on CSGnet has usually been the ratio between the RMS variation of the controlled variable with the output fed back to the perceptual signal and its RMS variation when the loop is complete. If control is effective, the RMS variation is lower when control is good than when it is poor or absent.
By "increase the stability of molecules," all you mean is slowing down their random motions. That is not control.
No. It is refrigeration. Actually, it's not the slowing down that's the point. That's only a side effect. The point is that their RMS variation is reduced.
But that is precisely what distinguishes thermodynamic equilibrium systems from control systems.
Here is where I began to think you were taking the mickey. I believed that you were well aware that I was talking about the fluctuation in the controlled variable, which, in a refrigerator is the average momentum of the molecules in the region around the thermostat that provides the reference input value.
When you started talking about the Avogadro's number of degrees of freedom of the molecules, and their RMS velocity, and that refrigerators can also heat I began to wonder why you were doing that. Teasing came to mind, but you were so dead-pan about it that I couldn't be sure. Now I'm taking you at your word that you were not.
In a control system positive fluctuations are resisted by actions in the negative direction; negative fluctuations by actions in the positive direction. There is no one action that will reduce the RMS fluctuations.
"...that will reduce the RMS fluctuations" of what? In a physical refrigerator, it so happens that the RMS fluctuations of the molecular velocities are what leads to the evaporation that is the mechanism of refrigeration. The controlled variable is the average velocity, and it the RMS fluctuations of the controlled variable that are reduced. It's a fluke that the controlled variable itself depends on the RMS fluctuations of something else. (Aside: One of my favourite papers from long ago did an analysis of variance which outputs F-ratios, using as data the F-ratios from a whole bunch of analyses done under conditions that varied in several dimensions. The situation is not dissimilar).
I think it's really stretching a point to see RMS variations as primary and molecular motions as side-effects. RMS variations are a calculation, not a phenomenon.
True enough. RMS variations ARE a calculation. No control system works by performing that calculation. But, as analysts, we frequently use that calculation to determine the effectiveness of control. And, to pre-empt the next reason I began to think you really were teasing, I ask "What is the value around which the RMS variation is computed", and I answer "The reference value".
All control systems, whether they are alive or not, are refrigerators, and I repeat what I said to Richard: If you can think of some way that would allow a low-entropy state to persist in a higher entropy environment other than an isolating shield or a control system, then you will be in a position to assert that thermoduynamic considerations do not require PCT as a basis for life.
Not all control systems create and maintain low-entropy states. For example, a dancer deliberately leaps, twirls, lifts, and runs in controlled patterns, creating motion where there was none before. All control of dynamic variables involves generation of variation, not reduction in variation.
Yes. And if that variation is controlled, the perceptions involved will be closer to their changing reference levels that they would be in the absence of control. Their RMS variation about that changing value is reduced by the presence of the feedback loop.
The only way you can say that control always involves decreasing entropy is to ignore the physical nature of the controlled variable and look only at whether it is varying more or less because of the control.
You don't have to ignore the physical nature of the controlled variable at all. You have to ignore the dimensions of the physical situation that are orthogonal to the degree of freedom that is the environmental variable corresponding to the controlled perception (a simple scalar, in an PCT-style elementary control unit).
Only then could you say that maintaining a room at a comfortable temperature in the winter is refrigeration:
I didn't say that at all. I said that all control systems are refrigerators, not that what they do is refrigerate rooms or change temperatures.
But if you ignore the physical nature of the controlled variable, you have converted a systematic analysis into a metaphor, and have lost the rigorous connection to the world of physics.
Quite the opposite. You have removed the metaphoric possibility and limited the analysis to a rigorous domain.
You have looked at control only as reducing variations due to disturbances, which is a narrow view of control.
No. I've looked at it as reducing the variations around a reference value, whether implictly developed or explicitly provided, whether static or variable.
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Actually, most of the above is a school of red herrings (which I assumed you were well aware of, and which is another reason I thought you were likely to be taking the mickey).
The only assertion at issue is that for a low-entropy structure to sustain itself in a higher entropy environment, it must include at least one control system.
If you can find a way for such a structure to avoid decay without invoking control, then and only then will you invalidate my thesis. The thesis itself is that thermodynamic considerations show that PCT is a requirement for all living systems, whether they be the carbon-based ones we know or something else entirely.
Martin