Pictures, Models, Approximations and Reality:
Phase transitions and our understanding of the physical world

Michael Fisher

The ways in which theoretical physicists look at the real world and try to understand it will be explored. Through the medium of a domino game on a large checkerboard, the rapier-like specific heat of a superfluid helium, and the visual effects seen when a liquid and its vapor merge to form a supercritical fluid, the talk will address the question: "What is the role of the theorist in modern science?" The power of analogy based on physical pictures and simple models will be illustrated in the context of ideas concerning phase transitions and critical phenomena in fluids and magnets, in alloys and plasmas. The significance of the concepts of shape and singularity in the search for universality will be explained; the role of symmetry and dimensionality in our insights will be touched upon.