Per Bak Reading Notes

/ Reading Notes /

Per Bak, How Nature Works: The Science of Self-Organized Criticality
2015 05 19

Crystals and gases and orbiting planets are not complex, but landscapes are.

History is unpredictable, but not unexplainable.

Self-organized criticality is a new way of viewing nature. The basic picture is one where nature is perpetually out of balance, but organized in a poised state—the critical state—where anything can happen within well-defined statistical laws. The aim of the science of self-organized criticality is to yield insight into the fundamental question of why nature is complex, not simple, as the laws of physics imply.

Good science is not necessarily expensive science.

Things happen by revolutions, not gradually, precisely because dynamical systems are poised at the critical state. Self-organized criticality is nature’s way of making enormous transformations over short time scales. … To predict the event, one would have to measure everything everywhere with absolute accuracy, which is impossible. Then one would have to perform an accurate computation based on this information, which is equally impossible.

Nature has no obligation to obey our ideas; our intuition could be entirely wrong.

Recently, Vicsek has constructed a fascinating model for self-organization of a flock of birds. He showed that it was possible for the birds to fly in formation in the same direction without a leader. The individual birds would simply follow their neighbors. The flock migration is a collective effect, as is SOC.

I once raised this issue among a group, not of geophysicists, but of cosmologists at a high table dinner at the Churchill College in Cambridge. “Why is it that you guys are so conservative in your views, in the face of the almost complete lack of understanding of what is going on in your field?” I asked. The answer was as simple as it was surprising. “If we don’t accept some common picture of the universe, however unsupported by the facts, there would be nothing to bind us together as a scientific community. Since it is unlikely that any picture that we use will be falsified in our lifetime, one theory is as good as any other.” The explanation was social, not scientific.

You don’t get rich from doing physics, but you do get an opportunity to go to all the places the rich would go to if they had the time.

Thus, the three models are mathematically identical; if you have studied one, you have studied them all!
So if any of my readers should happen to have ideas of their own, don’t be shy. Go full speed ahead, and don’t let any professional scientist intimidate you.
It seems that the human brain has not developed a language to deal with complex phenomena.
we tend to experience phenomena as periodic even if they are not, for example, at gambling casinos and in earthquakes and volcanos.

Complexity is a consequence of criticality.

Real life operates at the critical point between order and chaos.

I really love this book. I was reminded of it as Jan and I read Tom Wolfe’s history of “Silicone Valley” in Hooking Up. First the engineers work for the exploiters: then the engineers defect, then redefect. I don’t doubt a statistical pattern is being followed, that the statistical pattern is very different from any history we develop with psychological principles: as though we know what we are doing and why.

I’m in Chap 6, about 2/3 of the way through. It looks like some really incridible stuff is on its way, relating SOC of a range of kinds to the evolution of biological life. Yay!

Above I quote, “You don’t get rich from doing physics, but you do get an opportunity to go to all the places the rich would go to if they had the time.” Gotta comment: I launched PK Fine Arts, Ltd. with a capital of consigned art, with trust of the artists, but no cash. So: I was a poor man peddling middle brow art in snooty communities. I had no money but I was broke in Palm Beach, on Fisherman’s Waft, in ritzy neighborhoods of Phoenix … I went hungry in luxury.

2015 11 05 Back reading Bak again, sure is great. I’m about 2/3 of the way. He’s said something so profound but I’ll paraphrase, weave my own diction, not quote:
If you’re at an apex, any step, in any direction is down!
Correspondingly, like the song Hey, Look Me Over says in Wildcat: “I figure whenever you’re down and out the only way is up! Yes: if you’re at the absolute nadir then any step in any direction is up!

Quotes resume:

we cannot extrapolate directly from the microscopic scale to the macroscopic scale.

interface growth is a self-organized critical phenomenon.

One can think of this as a learning process in which nature creates a network of functionally integrated species, by self-organization rather than by design. The “blind watchmaker” is at work.

Darwin’s mechanism of selecting the fitter variant in an ecology of species leads not to a gradually changing ecology but to an ecology in which changes take place in terms of coevolutionary avalanches, or punctuations. Our numerical simulations had demonstrated that there is no contradiction between Darwin’s theory and punctuated equilibria. Our model is in the spirit of Darwin’s theory, but nevertheless exhibits punctuated equilibria.

We are “fit” only as long as the network exists in its current form.

Ah, bravo.

they share one another’s fate.

One could argue that it is actually the sensitivity of real life to minor spurious events that makes fiction possible, or believable.

acquiring insight is in itself a worthwhile effort

The obsession with the simple equilibrium picture probably stems from the fact that economists long ago believed that their field had to be as “scientific” as physics, meaning that everything had to be predictable. What irony! In physics detailed predictability has long ago been devalued and abandoned as a largely irrelevant concept. Economists were imitating a science whose nature they did not understand.

Agents in reality are not perfectly rational. In discussions with traditional economists, I used to argue that their economics theory has to include me, and that I certainly am not perfectly rational, as they themselves have argued so convincingly.

Explanations for why the stock market goes up or down belong on the funny pages,” says Claudia Goldin, an economist at Harvard.

I gotta memorize this book.

[Traffic] jams are fractal, with small subjams inside big jams ad infinitum.

… One unintended consequence of these flow control technologies is that, if they work, they would in fact push the traffic system closer to its underlying critical point, thereby making prediction, planning, and control more difficult, in sharp contrast to the original intentions. Note the analogy with attempts to regulate economy (or sandpiles). Self-organized criticality is a law of nature for which there is no dispensation.

That is so wonderful! I repeat: Self-organized criticality is a law of nature for which there is no dispensation.
I repeat another Bak line: “They [researchers] observed a curve similar to that of light from a quasar.”
I’ve been reading about fractals since Gleich’s book on Chaos theory came out in the mid-1980s. One arresting report was that early observers and theorizers of modern chaos ideas noticed correxpondences between phenomena not formerly associated: rainfall in the Amazon / cotton prices in Brazil. (I make-up, not look-up, an example.) People are used to seeing correspondenes familiar from mythology: beaucoup sin / beaucoup suffering. This was different. This was showing deep patterns in nature, in the cosmos not iterated by church or state. !

The self-organized critical state with all its fluctuations is not the best possible state, but it is the best state that is dynamically achievable.

Man, oh man, what a great book.

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About pk

Seems to me that some modicum of honesty is requisite to intelligence. If we look in the mirror and see not kleptocrats but Christians, we’re still in the same old trouble.
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