On caustics: a conversation.

Author:McKinlay, Pam

Figure 1 (opposite). Frontispiece for pamphlet originally printed for the Art and Light Exhibition, a collaboration between the Dunedin School of Art and the University of Otago departments of Physics, Botany, Anatomy, Physiology and Computer Science, hosted by the Otago Museum, 15-30 August 2015. Printed by Phototype Press at the P Lab, Dunedin School of Art, on a Risograph RA-5900. Typesetting and layout by Gregory Thomas. Etching from drawing by James Clerk Maxwell, Diagram of the Lines of Force and Equipotential Surfaces, plate from A Treatise on Electricity and Magnetism, vol. 1, 1873. (1) The lines of force depicted here visually resemble some of the caustics which we would later produce whilst experimenting with the light cast from the projections.


Light is the juncture between the known and the unknown. For the scientist, light is a meeting point for classical and quantum physics, it is the location of special relativity and the photon. Because the speed of light is the speed of information, it is the speed of the possibility of knowledge. For the artist, it is first and foremost a natural phenomenon.


The installation step into my light cone emerged during the Art and Light Project as a series of images captured from interactive projections producing caustic effects. They came from a response to ideas about research into the properties of light in vacuums and rainbow caustics and the images explored where we find ourselves situated in our experience of spacetime--within a continuum of personal and intersecting histories (across time) and within the universe (space). They were made with a mind full of light cones and "dark bodies," along with ideas percolating down from the time of Plato--ideas which have been affected by a cast of a thousand bright sparks including Newton (2) and Young, (3) many of which are however now deemed null and void.

Theories about light changed radically with Maxwell and Einstein and underwent rapid evolution within the timespan of special relative and muse Esther McKenzie. Esther was a member of the Society of Friends, better known as Quakers, for whom "light" is a spiritual concept. Great grandmother, and born around the time of the discoveries of special relative-ity, Esther only very recently stepped out of her final light cone. (4) We set about making projections in an experimental project space which we could walk through to encapsulate this myriad of ideas from across time and space. The documentation of the experience of this event eventually settled into a series of silhouette portraits of Esther's great-grandson, exhibited at the Art and Light exhibition.


Following in the footsteps of Henri Poincare, in this International Year of Light, I turned to personal experience to question some of the alluring properties of light. Poincare was a French philosopher and scientist much admired by Einstein, who advocated the analysis of relationships of everyday experience in one's habitual surroundings to aid analysis of scientific concepts. (5)

This summer, on sunny days with blue skies, I spent a lot of time swimming at the saltwater pool at St Clair. I'm no Esther Williams. (6) I like to swim at a certain time of day when there aren't many people around. With the sun behind me, I love to see the light/waves arcing out in front of me and the overlapping curve as the next set of waves push forward and intersect and cross over as I glide behind them. This only happens when you are swimming in one direction in the pool. Swimming back the other way always feels like pushing against the tide--there's no sun-rippling waves to swim with. I don't know the "why" of what is happening, but it is beautiful. It makes me happy and I KNOW something about the world and the way in which light plays amongst us and dances on the bottom of a pool. These are my personal experiences of a property of the radiating waves (water) and the effects of diffraction (light) as the light changes and "bends" as it encounters the boundary at the surface of the pool.

Let me prevail upon you to read a diary entry for 2 May--"What's This ?!"(a 3-D light artefact)

I found the opportunity to delve into this question when I joined the Art and Light Project. I had the good fortune throughout the project to have several conversations with Dr Terence Scott, from the University of Otago--hence the title of these pages, which preserves the tenor of those meetings. I thank him for his extraordinary generosity and time in bringing me up to (light) speed on the properties and behaviour of photons, and sharing his thoughts on the high-speed pursuit of virtual particles (a quixotic allure for many quantum physicists) and new research into the Casimir effect. (7) With these ideas in tow I took a sedate Journey through the annals of light-science history (8) in order to grasp how our understanding of light has come about in the twenty-first century. It was in these travels through virtual dusty tomes (sans dust motes) that I had my first encounter with the writings and etched drawings made by the "father of light," physicist James Clerk Maxwell. In 1873 Maxwell wrote that light and electro-magnetism share the same ultimate nature, both being electro-magnetic radiations. (9) Maxwell's equations, derived from concepts of the duality of electricity and magnetic forces, are now hailed as the beginnings of our current understanding of "light." (10)


From an early age we learn that light is both a particle and a wave. (11) As we daily observe in nature, waves are conveyed through a medium (ripples through water, sound through air). This poses the question that if waves need a medium to travel through, then how do light "waves" travel through a vacuum? What is doing the waving? At the time when Maxwell was devising his theory of electromagnetism it was thought that the universe was filled with a substance called the luminiferous aether, which was thought to be the medium by which natural light travelled through space. (12) This idea held sway until 1905, when Einstein explained that light travelling through space forms sui-generating waves. (13) Einstein's hypothesis that light was in a way its own medium spelled the end for the luminiferous aether, and from that time the aether was consigned to the realm of magic, phantasmagoria and steampunk fictions.


The way we have thought about "seeing" over the centuries has undergone some major shifts, and with it the way we view the world and our place in it. It used to be thought that the reason we "saw" was that the eyes emitted a sight ray, which bounced off objects and travelled back into our eyes in a theory known as extramission. Based on the observation of "fire" gleaming in animals' eyes, this idea was recorded by ancient writers like Pliny and developed into the "visual ray" hypothesis by natural philosophers including Plato and Pythagoras. (14) Following the irrefutable logic of the Islamic scholar Ibn al-Haitham Al Hazan, who argued that since the moon and stars are so far away, it is impossible for a ray from the eye to reach them and thus illuminate them, it became the accepted wisdom that vision was rather the result of rays from light sources reaching the eye by a process known as intromission. (15) Originating from sources such as the sun or a lamp, we characteristically see light scattered off an object's surface; objects that generate light-such as a television...

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