Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Postive feedback systems destroy themselves.  (think of hooking the emitter to the base of a transistor)

Huh? That will simply give you an switched-off transistor... For forward biased operation a positive potential difference between base and emitter is required. One could of course achieve a reverse bias with that configuration, by keeping the collector at a lower potential. That would just give you a diode, though... As would hooking the collector to the base... In short, more than one transistor is needed for a positive feedback loop.

Let it be noted as well that some form of positive feedback can be very useful, and is used often in electronic circuits. The circuits don't usually blow up at all. Examples include astable multivibrators and circuits with input hysteresis, such as comparators and Schmitt triggers. These positive feedback arrangements provide useful benefits, such as voltage controlled frequencies for oscillators and noise immunity.

Positive feedback is only 'bad' when one does not want its effects.

by someone (s0me1smail(a)gmail(d)com) on Wed May 23rd, 2007 at 03:35:37 AM EST
[ Parent ]
The positive feedback circuits don't blow up because first they drive themselves out of the linear regime.

Bush is a symptom, not the disease.
by Carrie (migeru at eurotrib dot com) on Wed May 23rd, 2007 at 04:51:58 AM EST
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Yeah, they saturate, as do many other physical systems... We can't get a real 'population explosion' either... It will saturate. The problem is that 'saturation' for a population might look rather nasty, if undamped. Very ugly oscillations.

In electronics most people are not stupid enough to propose an unlimited growth model. Or rather, the basic model is, sure, for many things, like amplifiers... And it is very, very useful, this model. However, anyone who has ever built a circuit knows that it is indeed bounded, and the region of constant gain/growth is limited... The constant gain model is only useful for a range of inputs... Unfortunately most economists seems to disagree that their discipline, as it is based in the physical world, will have very similar bounds to the constant gain/growth model. They come off a bit like first year electrical engineering students. Confusing the model with the system, and failing to properly take into account how it is premised on limiting the input to a certain range...

by someone (s0me1smail(a)gmail(d)com) on Wed May 23rd, 2007 at 05:05:36 AM EST
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Populations don't saturate, they overshoot and collapse. See Wikipedia: Lotka-Volterra equation [interpret us as the predator and the Earth's carrying capacity as the prey]

Bush is a symptom, not the disease.
by Carrie (migeru at eurotrib dot com) on Wed May 23rd, 2007 at 05:14:04 AM EST
[ Parent ]
Yes, nasty oscillations. Under damped system.
by someone (s0me1smail(a)gmail(d)com) on Wed May 23rd, 2007 at 05:20:26 AM EST
[ Parent ]
That is when each generation lives through many reproduction cycles and takes a long time to mature to adulthood. That gives the system huge delayed feedback.

In the case of magicicadas, as we learnt the other night, each generation reproduces at the end of its life cycle, and so in that case 1) you can have saturation; 2) you could potentially see chaotic logistic mapping behaviour.

Bush is a symptom, not the disease.

by Carrie (migeru at eurotrib dot com) on Wed May 23rd, 2007 at 05:30:38 AM EST
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That oscillation is why I support hunting of deer (as state departments of natural resources take it into account when deciding how many hunting permits to issue during any given year).

you are the media you consume.

by MillMan (millguy at gmail) on Wed May 23rd, 2007 at 01:01:05 PM EST
[ Parent ]
So so I, but mostly because deer is tasty.

On the subject, all will be well, and if it doesn't at least it'll be interesting.

Most likely something like this: a bit bad-> pretty bad for us, very bad for the global poor-> very interesting-> good for us, as bad as usual for them.

Peak oil is not an energy crisis. It is a liquid fuel crisis.

by Starvid on Sat May 26th, 2007 at 05:16:09 PM EST
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Economists are idiots. If they spent at least a year studying some kind of engineering, they'd have much more of a clue. But most of what they do now is just campfire story telling.

As for transistor feedback - the easiest way to destroy certain kinds of transistor is thermal runaway. (Oh, the irony.)

by ThatBritGuy (thatbritguy (at) googlemail.com) on Wed May 23rd, 2007 at 06:39:56 AM EST
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If you're young, can do math, and have a penchant for systems thinking, you're not likely to choose Economics as your field of study, are you?

And so we get the Mathematical Economics that we get.

Bush is a symptom, not the disease.

by Carrie (migeru at eurotrib dot com) on Wed May 23rd, 2007 at 06:46:43 AM EST
[ Parent ]
I think that coupled systems of positive and negative feedbacks "naturally" become cybernetic systems. Any part X of the system that "learns" to react to neighbouring inputs in ways that increases stability of X, logically leads to increaed autonomy of X. Subsystems may "learn" to control their own growths and ocsillations as well. "Learning" may mean just stumbling upon a functional configuration of feedabcks (that then tends to preserve itself), or it may mean development of a cybernetic-mechanical mechanism to copy past reactions in certain distinguishable situations. Once a perception-reaction network is established, the system has a "mind" of its own.

Subsytems with expressive functionality put more structure to the whole system - positive feedbacks will be controlled or exploited by "someone", cooperative and competative feedbacks between functional subsystems will gradually occur. Self-preserving functionality of the whole system may emerge.

In the light of this, we should not assume that our destructive growth can physically continue until it crosses boundaries of its own validity - the boundaries may "come" forward themselves. The positive feedback of our run-away civilization should provoke a reaction of the Earth system. Do we see it? Is the explosion of our civilization so unique that the Earth system, even if existing as a smart self-preserving Gaia, "would not know" what to do with it? Or is human impact already so great that an unmistakable stress signal is already received by a core network of geological/atmospheric processes, but the reaction will take some time (a decade or so)?

by das monde on Wed May 23rd, 2007 at 06:34:30 AM EST
[ Parent ]
I think you're ascribing some intentionality to physical processes. The Earth doesn't care about carbon dioxide or about feedback loops.

It's more of a textbook die-off scenario, that - unfortunately for us - is going to be the biggest in history.

Maybe if we're lucky we'll be hit by an asteroid, and we'll be able to blame that instead.

The real problem is that evolution has bred humans to be smart enough to deal with small-scale survivability issues - like 'Whose brain do I eat today?' - but not smart enough to think globally. The predictive horizon of the average human ends at his or her front door. If they're lucky. Thinking far beyond that is too much of a stretch.

And among the humans who are - possibly - smart enough, there's a persistent brain-eating predator class which has no interest in anything except their own immediate pleasure.

We still cannibalise each other economically. And now we've cannibalised most of the planet too.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Wed May 23rd, 2007 at 09:42:14 AM EST
[ Parent ]
It's functionality, not intentionality. I do not prescribe any intention formation, comprehension, and realisation planning. Just a copied perception-reaction cycle.

People can do big scale things, if they have to. But the modern "progress" and conveninece makes things like long-term planning, resourse conservation, child rearing in families unnnecessary. Ideology speeds up the process of unraveling of "obsolete" habits. The canibalism of this scale started recently, and will not last long.

by das monde on Thu May 24th, 2007 at 11:08:01 PM EST
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