Physics Colloquium - Friday, Nov. 3rd, 2006, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Harry L. Swinney
University of Texas at Austin

Fractal Fingers and Torn Garbage Bags

We inject air into oil contained between closely spaced glass plates and observe fingers of air penetrating into the oil, producing complex patterns. The geometrical dimension of the patterns is found to be fractal -- intermediate between a one-dimensional line and a two-dimensional disk. A simple computer algorithm, called Diffusion Limited Aggregation, is shown to yield patterns that have, surprisingly, the same geometrical properties as the viscous fingering patterns. We also examine the wavy edges of torn thin plastic sheets and wavy leaves. Again the structures are found to be fractal.