In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
That’s the primary difference between an axiom like “Curiosity Killed The Cat” and an axiom like “You Are Not Your User. ” The former rings true in common experience. It’s test-able, like striking a tuning fork or dangling a bit of yarn in front of a kitten. The latter is just some stuff that somebody said.
Sometimes, axiomatic sayings like “You Are Not Your User” no longer have a who that’s saying them. They cease being an actual instruction, and instead serve as a kind of identity, to identify the person who’s repeating the axiom as One Of Us.
The technical term for when an axiom devolves into an ID card is shibboleth: a custom, principle, or belief distinguishing a particular class or group of people, especially a long-standing one regarded as outmoded or no longer important.