[Martin Taylor 960723 14:00]
Bill Leach (960718.16.17) To Hans Blom
I do not believe that your energy efficiency remarks (made several times)
are applicable to living systems.
...
In terms of the controlled variable, the force applied must of necessity be
exactly the same for both cases. In general, the more components involved
and the more signal processing involved, the greater the energy consumption
unless the increase in energy efficiency of the components in the more
complex system is enough greater than the simpler system to provide the net
gain in efficiency (a condition that often exists in engineered systems).
These two comments may not relate exactly what you were saying to Hans,
but then again they may...
1. Efficiency may mean something to living systems insofar as there is a
cost of acquiring energy resources (food). If there is a cost, and if there
is competition for limited resources, then the more efficient organism
is able to control better (though it might not actually do so). In
evolutionary terms, the more efficient organism has a better chance to
be the fitter organism. In the long haul, it is likely to be the one
whose descendants are still around.
2. "In terms of the controlled variable, the force applied must of necessity
be exactly the same for both cases." This sentence applies only to the force
applied to the CEV, and therefore to the energy used for control. It
ignores the energy wasted in side effects. And if the control is dedicated
to keeping the CEV steady (I mean the simple case of an object being
moved about by disturbances and restored to its position by the control
system), exactly zero energy (force times distance) would be dissipated
if control were perfect.
All the energy would be used because control was imperfect, and because
of non-control (side-)effects on the world. The more efficient organism
is the one that controls best and that minimizes side effects.
Your comment about complex systems possibly losing efficiency because of
their complexity even while gaining efficiency in the actual control
output of the one loop is well taken. I just thought that you overdid it
a bit in saying that energy and efficiency considerations are irrelevant
to living things.
Martin