[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


This came from the American Institute of Physics:

"HIGHLY OPTIMIZED TOLERANCE. Many natural and man-made
systems exhibit power-law statistics. That is, when you plot the likelihood
of an event (e.g., sizes of forest fires, power outages, and web file
transfers, or losses due to hurricanes, floods, earthquakes, and man-made
disasters) as a function of size the resulting graph will fall off
proportionally to the size of the event raised to some exponent.
Interactions or phenomena at many size scales (from very small to very
large) contribute to the overall state of these systems. One theory which
tries to explain all this is "self organized criticality." Jean Carlson of
UC Santa Barbara (carlson@physics.ucsb.edu) and John Doyle of Caltech
(doyle@cds.caltech.edu) now propose another theory, called highly optimized
tolerance (HOT), which they believe does a better job of accounting for the
tendency in interconnected systems to gain a measure of robustness against
uncertainties in one area by becoming more sensitive elsewhere. As with
energy conservation or the inexorable increase in entropy, efforts to
violate the robustness principle will fail. Especially in biological
evolution or in engineering, this means that a system might obtain
robustness against common and designed-for uncertainties and yet be
hypersensitive to design flaws or rare events. For example, organisms and
ecosystems exhibit remarkable robustness to large variations in temperature,
moisture, nutrients, and predation, but can be catastrophically sensitive to
tiny perturbations, such as a genetic mutation, an exotic species, or a
novel virus. Engineers deliberately design systems to be robust to common
uncertainties. Cost and performance tradeoffs force an acceptance of some
hypersensitivity to (one hopes) rare perturbations. In evolved or designed
systems, this tradeoff leads to the "robust, yet fragile" characteristic of
complexity, one feature of which is power laws. Doyle and Carlson have been
exploring the application of their theory to a number of biological and
engineering problems with the help of experts in those fields. (Physical
Review Letters, 13 March 2000; Select Article; a longer version appears in
Physical Review E, August 1999.)"

One has to wonder if this principle can be applied to ALL organized systems,
such as software and mechanical engineering. This would have profound
implications for systems designed to last for untold years in extreme (and
unknown) environments, such as starships.

Lee Parker

"People do love to go to weird places for reasons we can't imagine -- mostly
because they have too much money."
                            - Freeman Dyson