On Lambertian reflections and stirring coffee

The Lambertian distribution, also known as Knudsen's Law, is a model for random reflections of light or gas particles from rough surfaces. I will present a mathematical "justification" of the Lambertian distribution. Then I will discuss a deterministic model inspired by stirring coffee. The analysis of the model will be partly deterministic, and partly based on the Lambertian distribution.

Joint work with O. Angel, M. Duarte, C.-E. Gauthier, J. San Martin, and S. Sheffield.