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Colloquium - John Gemmer, Brown University

Date: Monday, February 1, 2016

Time: 4:30PM

Location: Rockefeller Hall 310

Title: Why is lettuce so wrinkly?

AbstractMany patterns in Nature and industry arise from the system minimizing an appropriate energy. Examples range from the periodic rippling in hanging drapes to the six-fold symmetries observed in snowflakes. Torn plastic sheets and growing leaves provide striking examples of pattern forming systems which can transition from single wavelength geometries (hosta leaves) to complex fractal like shapes (lettuce). These fractal like patterns seem to have many length scales - the same amount of extra detail can be seen when looking closer (“statistical self-similarity”). It is a mystery how such complex patterns could arise from energy minimization alone. In this talk I will address this puzzle by showing that such patterns naturally arise from the sheet adopting a hyperbolic non-Euclidean geometry. However, there are many different hyperbolic geometries that the growing leaf could select. I will show using techniques from analysis, differential geometry and numerical optimization that the fractal like patterns are indeed the natural minimizers for the system. Along the way I will provide an introduction to the field of “energy driven pattern formation” and present a mysterious proof that 1=2.

Tea at 4:15 in RH305