Crackling Noise and Avalanches: Scaling, Critical Phenomena, and the Renormalization Group

In the past two decades or so, we have learned how to understand crackling noise in a wide variety of systems. We review here the basic ideas and methods we use to understand crackling noise - critical phenomena, universality, the renormalization group, power laws, and universal scaling functions. These methods and tools were originally developed to understand continuous phase transitions in thermal and disordered systems, and we also introduce these more traditional applications as illustrations of the basic ideas and phenomena.Comment: Lecture notes for Les Houches summer school on Complex Systems, summer 200