Friday 25 Nov 2022: Four geometrical-optics illusions
Michael Berry - University of Bristol
Newman Red 12:30-13:30
Many 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
• Oriental magic mirrors and the Laplacian image. The optics of these ancient objects involves the regime of pre-focal brightening, and the transmission analogue 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. The mirror- reflected rays from an object form caustic surfaces in the air. Images of such objects are organised by those points whose caustics intersect our eyes.