Re: Understanding MinEP and MaxEP


"William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message news:dhl5ib$ri0$1@xxxxxxxxxxxxxxxxxxxxxx
> "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote in
> news:dgc3bu$te6$1@xxxxxxxxxxxxxxxxxxx:
>
> > I agree with what you are saying both with regard to what Lotka's
> > logic was, and also with regard to the validity of that logic.
> >
> > However you seem to be missing one key point which leads you to
> > mistakenly believe that there is a significant distinction between
> > maximum work and maximum entropy production. The thing you are
> > missing is this:
> >
> > In a 'climax' ecosystem at steady state, biomass does not accumulate!
> >
> > Therefore, you can't use accumulation of biomass as a measure of
> > 'work'. Biomass may represent 'work' to a growing organism, but to an
> > ecosystem it is secondary production. Ultimately, all of the
> > potential energy available to the primary producers is going to be
> > converted to heat. (It may be converted to heat by either biological
> > or non-biological mechanisms, but it is going to become heat in any
> > case). Now heat is not the same as entropy - you have to divide heat
> > by temperature to get entropy. You get the most entropy if the heat
> > production is done at nice low biological temperatures (by leaves or
> > termites) rather than at high temperatures (black-body minerals or
> > forest fires) from the original potential energy source (sunlight or
> > cellulose). So maximum work really does come pretty close to maximum
> > entropy production if you count the 'work' as simply a secondary
> > energy source.
>
> But what if the energy is transferred without producing heat (i.e.
> reversibly). The termites are merrily turning wood into more termites,
> but every step of the reaction is very close to equilibrium.

Not all steps. And in any case, there are so many steps so that the
net process is far from equilibrium and generates considerable entropy.
Also, you have to realize that termites (including symbionts) are producing
more than just more termites. They are producing significant methane.

Plus, let me emphasize again that there is no NET production of termites.
Over the long run, only enough are produced to replace losses to chimps,
birds, and 'old age'.

> This is
> maximum work (in terms of amount of termites produced) but it is MinEP.
> And in the forest fire case, what happens to the heat produced in
> combustion? The answer is it gets successively transferred to other lower
> temperature molecules in the atmosphere until the final transfer is done
> at low temperatures. And all those transfers produce entropy. No, I think
> the only real question is, does biomass accumulate in a climax ecosystem.
>
> > Or are you saying that total biomass production (primary plus
> > secondary plus etc.) constitutes 'work'. Lotka likes ecosystems best
> > when they have many trophic levels? I am not sure that that idea is
> > defensible. To my mind, the ideal ecosystem would have a single
> > species which builds biomass in its youth, but lives off stored
> > biomass in its senescence, eventually withering away to nothing and
> > leaving behind no wastes. Other than its biochemical implausibility,
> > what is wrong with that? Would you count that as a particularly
> > unproductive ecosystem? I would say that as long as it consumes all of
> > the available energy resources and generates its heat at a low
> > temperature, it is doing just fine.
>
> Does information count as work?

Sure. Why not? But information does not accumulate at climax, either.

> If so, then complex ecosystems do contain
> more work than simple ones. So we have accumulation of biomass,
> accumulation of structure, or accumulation of diversity as indicators
> that entropy production is different than work production in ecological
> systems. Now the presence of large deposits of coal and oil, and of coral
> reefs, would indicate that in the earth's past biomass and structure did
> accumulate, but I don't know if that is still true. It is probably true
> in the oceans - the constant rain of organic matter to the ocean bottom -
> and may be true in boreal forests, where leaf litter does in general
> accumulate. The tropics seem to accumulate information (in terms of
> biodiversity) rather than biomass.

And they seem to produce oxygen and consume carbon dioxide, too. But
you and I both know that they don't really do net production of either
information or oxygen. I am always amused when some environmental
activist informs me that the tropical rain forests produce 40% of the
world's oxygen. They are dumbfounded when I ask what fraction of the
world's oxygen they consume. It seems that no one ever taught them that
figure.

Overall, I agree with you that IF biomass or information or structure is
accumulating, then a measure of 'work production' may differ from a
measure of 'entropy production'. My point is simply that when these
things do not accumulate, then MaxEP and MaxWork say pretty much the same
thing. Both principles have heuristic value - neither is an unbreakable
law of nature. And in the cases where they differ, I see no reason to
prefer one heuristic over the other. It is easy to find exceptions to
either one.


.

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