AAAI Fall Symposium - Nov. 5 - 7, 2009 - Arlington, VA

Complex Adaptive Systems and the Threshold Effect: Views from the Natural and Social Sciences

Most interesting phenomena in natural and social systems include constant transitions and oscillations among their various phases. Wars, companies, societies, markets, and humans rarely stay in a stable, predictable state for long. Randomness, power laws, and human behavior ensure that the future is both unknown and challenging. How do events unfold ? When do they take hold ? Why do some initial events cause an avalanche while others do not ? What characterizes these events ? What are the thresholds that differentiate a sea change from a non-event ?

Complex Adaptive Systems have proven to be a powerful tool for exploring these and other related phenomena. We characterize a general CAS model as having a large number of self-similar agents that:

1. utilize one or more levels of feedback;
2. exhibit emergent properties and self-organization; and
3. produce non-linear dynamic behavior.

Advances in modeling and computing technology have led not only to a deeper understanding of complex systems in many areas, but they have also raised the possibility that similar fundamental principles may be at work across these systems, even though the underlying principles may manifest themselves differently.

Econophysicist Predicts Date of Chinese Stock Market Collapse

The Shanghai Composite Index was supposed to burst before July 27 but didn't. A few days after that deadline, however, it dropped by 20 percent. Coincidence ?.

Last month, we looked at a prediction that the Shanghai Composite stock market index was about to crash. The forecast was made by a team lead by the econophysicist Didier Sornette at the Swiss Federal Institute of Technology in Zurich, who has made a study of economic bubbles and how they burst. His thinking is that bubbles are the result of some kind of feedback mechanism that creates faster-than-exponential growth. This kind of growth rate is straightforward to measure, and so bubbles should be easy to identify. In July, he and his buddies pointed out that the Shanghai Composite stock market index was following exactly this kind of trend. But they also made an extraordinary prediction. They said that this bubble would burst between July 17 and 27.

Formalismo de Keldysh (Keldysh Technique)

This technique provides the correct evaluation of the quantum mechanical average of an observable. It means that there is not any assumption about the final system state whenever we perform the above mentioned average. As a consequence, it is a suitable tool to study small systems in contact with macroscopic systems which are in "different" thermodynamic equilibrium states.

See the original Keldysh's papers:

• L. V. Keldysh, ZhEFT 47, 1515 (1964)
• L. V. Keldysh, Soviet Physics JEPT 20, 1018 (1965)

How to Avoid Yourself

Every Sunday morning you go for a walk in the city, heading nowhere in particular, with just one rule to your rambling: You never retrace your steps or cross your own path. If you have already walked along a certain block or passed through an intersection, you refuse to set foot there again.

This recipe for tracing a loopless path through a grid of city streets leads into some surprisingly dark back alleys of mathematics—not to mention byways of physics, chemistry, computer science and biology. Avoiding yourself, it turns out, is a hard problem. The exact analysis of self-avoiding walks has stumped mathematicians for half a century; even counting the walks is a challenge.

My own initiation into the trials of self-avoidance came when I began experimenting with a simple model of the folding of protein molecules, a story I told in an earlier "Computing Science" column (see Hayes 1998). Protein folding is close to the historical roots of the self-avoiding walk, which was first conceived as a tool for understanding the geometry of long-chain polymer molecules. A polymer writhing and wriggling in solution forms a random tangle—random, that is, except that no two atoms can occupy the same position at the same time. This "excluded volume effect" in the polymer is modeled by the walk's insistence on avoiding itself.

Steven Weinberg: From BCS to the LHC

Steven Weinberg reflects on spontaneous symmetry breaking, and the connection between condensed-matter physics and particle physics, in a talk at the University of Illinois in Urbana, celebrating the 50th anniversary of the BCS theory of superconductivity. It was a little odd for me, a physicist whose work has been mainly on the theory of elementary particles, to be invited to speak at a meeting of condensed-matter physicists celebrating a great achievement in their field. It is not only that there is a difference in the subjects that we explore. There are deep differences in our aims, in the kinds of satisfaction that we hope to get from our work. Condensed-matter physicists are often motivated to deal with phenomena because the phenomena themselves are intrinsically so interesting. Who would not be fascinated by weird things, such as superconductivity, superfluidity, or the quantum Hall effect? On the other hand, I don't think that elementary-particle physicists are generally very excited by the phenomena they study. The particles themselves are practically featureless, every electron looking tediously just like every other electron.

Guilt by Calculation

This kind of statistical gumshoeing has a long history. In 1936, for example, English biologist and statistician R. A. Fisher went gunning for Gregor Mendel, whose experimental results Fisher believed had been tweaked to be more favorable to Mendel's ideas. "Fictitious data can seldom survive a careful scrutiny," Fisher wrote, "and, since most men underestimate the frequency of large deviations arising by chance, such data may be expected generally to agree more closely with expectation than genuine data would." In other words, it was precisely the beautiful agreement of experiment with theory that exposed Mendel's thumb on the scale. Only once in 15,000 times, Fisher computed, could one expect such strong conformity. ( The controversy over Mendel's research practices continues to this day, with notable scientists lining up on both men's sides ).

AWT and mechanical models of entanglement

By AWT explanation of quantum entanglement is closely related to wave function collapse. Try to imagine, you're a sailor, who is staying at night on the end of floating wharf, to which some boat is attached. Because night sea is stormy, everything ( both sailor, wharf and boat ) are wobbling up and down, but in different phases. From the perspective of sailor this boat sways randomly. The observation of quantum particle is analogous to situation, when sailor touches the boat for a moment, thus exchanging some kinetic energy with it. What will happen, after then ?

Do particles have a free will ?

Mathematicians John H. Conway (inventor of the cellular automaton Game of Life, between many other) and Simon Kochen of Princeton University have proven that if

human experimenters demonstrate 'free will'

in choosing what measurements to take on a particle, then the axioms of quantum mechanics require that the free will property be available to the particles measured, or to the universe as a whole.

The Anderson-Higgs mechanism

To understand the Higgs mechanism, imagine that a room full of physicists quietly chattering is like space filled only with the Higgs field....

... a well known scientist walks in, creating a disturbance as he moves across the room, and attracting a cluster of admirers with each step ...

... this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field ...

... if a rumour crosses the room ...

... it creates the same kind of clustering, but this time among the scientists themselves. In this analogy, these clusters are the Higgs particles.

References

P. W. Anderson. Plasmons, Gauge Invariance, and Mass.
Phys. Rev. 130, 439 (1963)
 
Peter Higgs. Broken Symmetries and the Masses of Gauge Bosons.
Phys. Rev. Letters 13, 508 (1964)

Tunneling Effect (Efecto Túnel)

http://physweb.bgu.ac.il/GROUPS/HIGHLIGHTS/ymeir1.html

Read more... Thanks to Mi Tribu Urbana Gracias a Mi Tribu Urbana