The Department of Physics is delighted to welcome Professor Sir Michael Berry (University of Bristol) to give the fifth Physics Department Colloquium of 2024/25. Please join us to listen to Professor Sir Michael Berry's seminar.

A reception will be held directly after the seminar, where tea and coffee will be provided.

The seminar is open to anyone from the university, students are encouraged to attend.

Title

Four geometrical-optics illusions

Abstract

Centuries after the laws of geometrical optics were established, they still have nontrivial and varied applications. Illustrating this are some illusions:

Mirages, and Raman’s error. Understanding why he denied the applicability of geometrical optics requires careful exploration of the continuum limit of a discretely-stratified medium, to reveal its nonuniform convergence.

Oriental magic mirrors and the Laplacian image. The optics of these several-millenniaold objects involves the unfamiliar regime of pre-focal brightening. The transmission analogue (‘Magic windows’) raises a challenge for freeform optics.

The squint moon and the witch ball. The moon sometimes appears to point the wrong way because we perceive the sphere of directions as a distorted ‘skyview’, on which geodesics appear curved. This can be conveniently viewed and analysed by viewing the sky in a reflecting sphere.

Distorted and topologically disrupted reflections in curved mirrors. Mirror-reflected rays from each point of a continuous object form caustic surfaces in the air. Images are organised by those points whose caustics intersect our eyes, and can be systematically understood in terms of the elementary catastrophes of singularity theory.

Professor Sir Michael Berry's abstract can also be found here.