Quantum Oil Slick: This image is a photograph of a naturally occurring oil slick off the coast of Santa Barbara. This oil slick illustrates the phenomenon of diffraction from thin films. We use it to illustrate the quantum theory of light in educational materials based on Feynman’s QED book, which uses arrows and simple rules to describe quantum phenomena by “drawing arrows on a pieces of paper.” The Air Force is supporting evaluation work on the learning that takes place in this course.