Saturday, September 23

Complexity and Robustness

9:15 AM-10:00 AM
New Hampshire Ballroom
Chair: George Cybenko, Dartmouth College

Through design or evolution, complex systems in engineering and biology develop highly structured, elaborate internal configurations, with layers of feedback and signaling. This makes them robust to the uncertainties in their environment and components for which such complexity was selected, but also makes the resulting system potentially vulnerable to rare or unanticipated perturbations. Such fragility can lead to large cascading failures from tiny initiating events. Perturbation of one gene or a single line of software code, or the introduction of an exotic specie or trace amounts of a toxin, rarely causes significant system-wide impact, yet occasionally can cascade into complete system failure.

This ?robust, yet fragile? character of complex systems severely complicates the challenge of connecting phenomena on widely different time and space scales, and in particular, exactly those phenomena most critical to understanding and preventing large cascading events. This talk will argue that ?robust, yet fragile? is not an accident, but is the inevitable result of fundamental tradeoffs. It is the single most important common feature of complexity in technology and biology, with profound implications for computational issues. Motivating examples will be drawn from shear flow turbulence, quantum computing, gene regulation and signal transduction networks, web/internet traffic, power outages, forest fires and other large ecosystem events, stock market volatility, distributed software, commercial aircraft design, automobile airbags, weather and climate forecasting, and formula one racing.

John Doyle
Control and Dynamical Systems Department
California Institute of Technology, USA
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