A_COMPLEXITY_MODEL_FOR CATASTROPHES LIKE SEPT.11Th

[Gość: Zsypek]

Complexity theorists are devising an elaborate model based on the effects of
catastrophic events like Sept. 11. It's meant to aid the insurance industry,
but it also could "test the very young science of complexity theory."

www.discover.com/feb_02/featsurprise.html

< img src=https://www.gazeta.pl/img/g.gif>

[Gość: ЯR]

. The flock's fluid movements appear to be choreographed, even though most flocks
do not have a leader. A flock acts in concert because each individual bird
follows a set of basic rules. In one of the most successful complexity
simulations to date, computer scientist Craig Reynolds created a flock of
artificial "boids," as he calls them, that spontaneously navigate around random
obstacles in a synchronized and orderly fashion, even though there is no master
design for group behavior. (For a demonstration, surf to
www.red3d.com/cwr/boids.) Reynolds programmed each individual bird to avoid
collisions, match the speed and direction of its closest neighbor, and move
toward the center of the flock.

Examples of systems that self-organize, what Kauffman and other complexity
theorists call emergent behavior, are everywhere: The organized foraging of an
ant colony is determined not by the dictates of the queen but by local
interactions among thousands of worker ants; neighborhoods in a modern industrial
city evolve not by the dictates of a central planning board but by the
independent choices made by individual people.

But perhaps the most stunning application of complexity theory and emergent
behavior is Kauffman's attempt to explain the origin of life on Earth. Long
convinced that Darwin's theory of natural selection does not fully account for
the patterns of order and diversity in the natural world, Kauffman designed an
elaborate computer simulation to demonstrate that individual enzymes—protein
molecules—could organize themselves into a self-reproducing collection of
enzymes. In the model any particular enzyme might have a one-in-a-million chance
to catalyze a given reaction, thus forming another enzyme. Kauffman theorized
that with enough enzymes and enough energy, a self-perpetuating, self-
replicating, nonequilibrium system would emerge—in other words, a model of life.
The system might use DNA to replicate itself, but it might not. In Kauffman's
view, only two things mattered: N, the number of potential enzymes in the system,
which had to be a big number, and P, the probability that any enzyme could
catalyze a particular reaction.

The Rediscovery of Time -Dr. Ilya Prigogine

[Gość: Zsypek]

Let us observe that curiously, the two great revolutions in physics over the
century have been precisely connected with the inclusion of impossibilities in
the frame of physics. In relativity a fundamental role is played by the
velocity of light which limits the speed at which we may transmit signals.
Similarly Planck's constant h limits the possibilities of measuring
simultaneously position and momentum. As noticed by Fritz Rohrlich, "The
implications of the finiteness of Planck's constant (h is greater than o) for
the quantum world are as strange as the implications of the finiteness of the
speed of light (c is less than infinity) for space and time in relativity
theory. Both lead to realities beyond our common experience that cannot be
rejected."

In addition to the "impossibilities" which are the result of Planck's constant
or of the finiteness of the speed of light, we have the impossibilities which
come from irreversibility, the second law of thermodynamics. Only processes
which increase entropy in isolated systems are possible. Such a limitation on
the macroscopic scale must express also some type of limitation on the
microscopic scale. The second law has therefore to appear, as we shall see, as
a kind of selection principle propagated by dynamics. The inclusion of this
supplementary restriction brings us even further away from the intuitive vision
of space and time as used in classical science.

www.magna.com.au/~prfbrown/ilyatime.htm