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Unformatted text preview: Chaos, Complexity, and Entropy A physics talk for nonphysicists Michel Baranger Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics Massachusetts Institute of Technology, Cambridge, MA 02139, USA and New England Complex Systems Institute, Cambridge, MA 02138, USA MITCTP3112 The twentyfirst century is starting with a huge bang. For the person in the street, the bang is about a technical revolution that may eventually dwarf the industrial revolution of the 18th and 19th centuries, having already produced a drastic change in the rules of economics. For the scientifically minded, one aspect of this bang is the complexity revolution, which is changing the focus of research in all scientific disciplines, for instance human biology and medicine. What role does physics, the oldest and simplest science, have to play in this? Being a theoretical physicist to the core, I want to focus on theoretical physics. Is it going to change also? Twentiethcentury theoretical physics came out of the relativistic revolution and the quantum mechanical revolution. It was all about simplicity and continuity (in spite of quantum jumps). Its principal tool was calculus. Its final expression was field theory. Twentyfirstcentury theoretical physics is coming out of the chaos revolution. It will be about complexity and its principal tool will be the computer. Its final expression remains to be found. Thermodynamics, as a vital part of theoretical physics, will partake in the transformation. CHAOS For theoretical physicists the revolution started a few decades ago with chaos. Chaos is a purely mathematical concept; it is an undeniable mathematical fact. We know that theoretical physics is built on mathematics, and that all theoretical physicists are applied mathematicians. The first question that I want to examine, then, is: why is it that, among all the practitioners of science, applied science, engineering disciplines, and human sciences, physicists were practically the last ones to be interested in chaos and to use it in their work? There were exceptions, of course. The people who built the large particle accelerators knew about chaos; in fact they discovered much of it. There are many other exceptions. But the majority of physicists did not know about chaos, and still does not. Engineers of many sorts, meteorologists, some types of chemists, population biologists, cardiologists, economists, and even psychologists, seized upon chaos long before the physicists did. During my teaching career at MIT, twice I introduced some simple chaos in an undergraduate course for physics majors; I wanted these future physicists to be exposed to it. But in the MIT physics department, faculty members do not teach the same course for very long. After two or three years, they move you to another course to keep you from getting stale. And so, twice 1 Michel Baranger — Chaos, Complexity, and Entropy the person who succeeded me took chaos out of the curriculum, saying “Sorry, I don’t know...
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 Spring '10
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 Physics, Chaos Theory, Fractal, Chaos, Michel Baranger

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