Talk:Twelve leverage points

Wikipedia system is a growing system, where information accumulate, to reach (an impossible ?) goal of being the repository to all human knowledge.

Positive and negative here don't mean one has positive or negative final effect, it refers to the direction of the change.

The negative feedback loop tends to slow down a process, while the positive feedback loop tends to accelerate it. That's all.

Negative effect will promote backward direction, and positive effect will promote forward direction. Of course, forward and backward are all relative. It depends of the goal. It depends whether the goal is to progress, or regress, or tend to stability.

In a system going forward, the negative loop will tend to promote stability (stagnation in this case). The positive feedback loop will tend to speed up the growth (ie, the accumulation of knowledge).

But, both can, without control, get so much influence that they may completely break up the system. Be they meant to speed it up, or to slow down the process. Both can get wild.

Example of positive feedback loop going wild

a nuclear reaction, such as in Tchernobyl

eutrophication of a lake, which first lead to increase of productivity (biomasse increases), to lead to an oxygen-deprived system where microorganism cannot assume biodegradation of dead matter any more, to end up with a dead lake where anoxic conditions caused the death of all oxygen-dependent life

Example of negative feedback loop going wild

deforestation of Amazonian forest. While many people would imagine soils in these forests are rich, they are usually not (except in places where Indians have been making sort of tertres of accumulated wastes). Remove the trees for agricultural production. The bare thin soil will not resist long with few plants on it to tropical rain falls, and will suffer erosion. It will quickly loose the little organic matter it has, resulting in ever less species thriving on it, resulting in even naker soil...to the point where the mother rock is reached and no vegetation grow any more.

When Google is indexing Wikipedia, it is making Wikipedia better known to readers, and can bring new editors, so potentially more knowledge. That's positive ! Then, more editors mean more articles, more links, so more google hits, so more editors again. That's a positive feedback loop !

However, in indexing, it is strongly increasing connexion times, hence driving usual contributors away : that is a positive feedback loop going wild !

And here, the bottle necks are 10 and 9

If Google brings too many new editors at the same time, it may brings more basic vandalism, and may take up all the time of sysops trying to cope with vandalism and new comers welcoming and teaching. To the point they are not authoring articles any more. That is a positive feedback loop going wild ! (though...it may make sense to prevent some sysops to edit...)

I think you have your definitions of en:feedback wrong.

Sorry Martin, but I don't really get it. What do you mean by "your". I sure havenot written definitions of the en:feedback. If you say the definition of en:feedback is wrong, well, I certainly do agree there are strongly restricted to electronic field. If you say what I explain is wrong, please explain. Also, a feedback is different from a feedback loop.

The person who wrote en:feedback is essentially right. The use of "feedback" and in particular "negative feedback" above is wrong.

essentially right. As long as you view the definition of feedback from an electronician or mathematician perspective. Which is clearly not a biologist perspective. Fact is I think you view it from the input and output perspective only. Not from a system perspective. Biologists see feedback both from the output perspective and system perspective. It might be that our definitions are different.

"negative feedback" is feedback that acts so as to reduce its own cause. An example is body temperature - if I get too hot I sweat more, and this negative feedback reduces my temperature.

Notice the wikipedia definition is saying that a Feedback is a process whereby some proportion of the output signal of a system is fed back to the input, in order to change the dynamic behaviour of the system.

This is quite right on the most basic system, but not taking into account that sometimes, this is not the output that is fed back. The output signal can be fed first to another system, which output will act on the first system. Or it can be transformed by a function.

It also says Feedback may be negative, thus tending to reduce output, or positive, thus increasing output.

That is forgetting most systems work with threashold values. And until the theashold is reached, the system is changing, not the output. Besides, syneresis also impact system, without impacting output necessarily so.

Positive feedback is feedback that acts so as to increase its cause. There is no such thing as a "negative feedback loop going wild" - what you describe is a positive feedback loop with negative consequences. Similarly a nuclear meltdown is a positive feedback loop with negative consequences. MyRedDice

Negative feedback is for neutralization/regulation of the system (homeostasis), while positive feedback is an amplification. Both feedbacks are not linear, nor parallele to each other. Which is why a tiny little thing like a butterfly can have a huge impact, for its little effects may be amplified by a positive retroaction. I agree there may not be negative feedback loop going wild, but I still maintain a positive feed back loop can certainly get wild by an un-controlled amplification. Which is why in most biological systems, processus are controlled both by positive and negative feedback loop (well...usually by several). Often, the process is slightly too slow that required, so a positive feedback loop is accelerating it more or less for it to have the necessary effect. But, there is usually a negative feedback loop acting as a guardian, to ensure no excess amplification occur. Typically, heart rate with vagual system.

I may not use the right words to express myself, so I will probably not convince you, but it will take much more for you than just saying "you are wrong and wikipedia is right" to convince me :-)

- feedback : stabilisation

+ feedback : amplification

I certainly agree with you that excess/unrestrained positive feedback can "go wild". I maintain that negative feedback loops cannot "go wild" - only stagnate, and your deforestation example is an example of positive feedback, because the loss of soil causes a loss of species which causes a further loss of soil which causes a loss of habitat which causes.... and so on until the ecosystem collapses. That's positive feedback because, to quote your own words, a "positive feedback loop tends to accelerate [a process]". In this case the process is deforestation, and the positive feedback acts to accelerate it so that it occurs faster than one would otherwise expect.

true. That is a perfect bad exemple ;-)

I think we might be in "heated agreement" here - perhaps it was just my misreading of what you wrote coupled with a poor choice of example in deforestation that caused this whole spat? --MyRedDice

perhaps

Thanks anyway for acknowledging my discomfort

Rename this page?

Rename this page maybe to "some leverage points"? Some means at least one, so then the number of leverage points could vary without causing the name to be incorrect.

WHat is this about??? Jaberwocky6669 05:13, 4 Jul 2005 (UTC)

system theory applied to Wikipedia; Anthere