Title: The Galilean Imperative: A Physicist's search for Simplicity

Abstract: Nearly 400 years ago, Galileo gave us the image of the great Book of Nature, lying open before us. We could read it, he said, only if we understood its language- the language of mathematics. The search for a mathematical description of nature, an activity we now call theoretical physics, has been extraordinarily successful. In a real sense, what we see around us are the consequences of equations that can be written on one sheet of paper. This tremendous success encourages physicists to keep searching for simplicity, even in apparently complex systems. Why do we believe that the world should be described by simple models? Is this just an extrapolation from past successes, liable to fail at any moment? Faced with the evident complexity of the world, is the search for simple mathematical descriptions just a matter of guessing, or are there principles to guide our search? I'll address these questions with lessons from the history of the subject, then turn to one of the modern frontiers: the search for a physicist's understanding of the brain and mind.