Lecture Theatre 2, Hudson Beare
Prof James Sethna, Cornell University
A piece of paper or candy wrapper crackles when it is crumpled. A magnet crackles when you change its magnetization slowly. The earth crackles as the continents slowly drift apart, forming earthquakes. Crackling noise happens when a material, when put under a slowly increasing strain, slips through a series of short, sharp events with an enormous range of sizes. There are many thousands of tiny earthquakes each year, but only a few huge ones. The sizes and shapes of earthquakes show regular patterns that they share with magnets, plastically deformed metals, granular materials, and other systems. This suggests that there must be a shared scientific explanation. We shall hear about crackling noise and that it is a symptom of a surprising truth: the system has an emergent scale invariance – it behaves the same on small, medium, and large lengths.
James Sethna is Professor of Physics at Cornell University, and member of the Fields of Computational Biology, Computational Science and Engineering, and Applied Mathematics. He has a BA from Harvard (1977) and a PhD from Princeton (1981, under P. W. Anderson). Sethna has made extensive contributions to condensed matter theory, materials science, statistical mechanics, and the dynamics of disordered systems under strain. In systems biology, his group has led the investigation of the sloppy dependence of model predictions as parameters are varied, crucial to the understanding of prediction errors and model falsifiability. Sethna has written a textbook, “Statistical Mechanics: Entropy, Order Parameters, and Complexity” (Oxford University Press, 2006).