Many incompletely understood phenomena lurk in the borderlands between physical theories - between classical and quantum, between rays and waves... These borderlands - the domain of physical asymptotics - are my intellectual habitat, with an emphasis on geometrical aspects of waves (especially phase) and chaos.
A source of delight is uncovering down-to-earth or dramatic and sometimes beautiful examples of abstract mathematical ideas: the arcane in the mundane. Examples are:
mathematical singularities in rainbows and the patterns on the bottom of swimming-pools;
a laser pointer shone through irregular bathroom-window glass, illustrating abstract aspects of wave interference;
optics with transparent overhead-projector plastic sheets, illustrating polarization singularities, matrix degeneracies, and quantum measurement, and Anderson localization;
a levitating spinning-top, illustrating adiabatic stability and geometric phases;
twists and turns with a belt, illustrating the behaviour of identical particles in quantum mechanics, responsible for the impenetrability of matter, lasers, superconductivity...
Oriental magic mirrors, directly displaying the Laplacian.
Tsunamis, which are caustics in spacetime, and, when focused, spacetime caustics on a cusped caustic
