the theater

Chiaramonte col Teatro e arcobaleno

We know many things about light, but our ability to explain a phenomenon does not necessarily show our knowledge or awareness of what happens.
In this room the actor becomes a scientist, who notices analogies among seemingly very different phenomena, develops models for their explanation, formulates predictions and verifies their validity in nature. But this is not enough. Finally, he tries to create a virtual reality, a performance, a fiction with his own hands. A mise en scene that behaves according to the laws that he believes play a fundamental role in nature. Many scientists use this approach and call it a "simulation". We will call it simply and, in a provocative way, "the theatre". What is a rainbow? Is it a band of colours in the sky, caused by the reflection of the sun light from water droplets? In order to explain the phenomena, we put on stage several experiments.

the "droplet bow"

After having entered the room, visitors' eyes turn to a glass sphere, which seems to be pending in nowhere, illuminated by a beam of light coming from the sky. The glass sphere retro-refracts a cone of light projected towards the sky. Surprisingly, the bow of colours demarks an inner area, featured by bright white-light reflection, from an outer one, reached by no light. The scene represents a single drop of water illuminated by the sun, and reveals us how each independent drop generates its own colourful light bow.

the "laser rainbow"

To better understand what happens, we use a water-filled glass cylinder, which precisely reproduces processes of reflection and refraction on a single plane. Using white and colourful lamps and three lasers (red, green and blue), whose beams, simulating the sun rays, scan the cylinder from the outside inwards, we reveal the secret: laser rays are retro-refracted just inside the cone, limited by a maximum deviation angle ("limit" angle), while outside of it there is darkness. Around this angle an extended portion of impinging light sums up coherently, thus leading to the appearance of the peak. Since different angles are associated with different colours, this accounts for the separation of colours, which appear between light and darkness.

the "1D- rainbow"

What happens when we look at a large number of drops, illuminated by the sun? Walking alongside an array of hundred cylinders, illuminated by a powerful projector, the spectator can see a dark area and a bright one, separated by an intermediate third section, in which each cylinder shines in a different colour. How is it possible? All cylinders are identical. Indeed, each cylinder sweeps all colours, from deep red to orange, yellow, green, and finally blue, each colour determined by a given angle between the incoming light and the direction of observation. This observation suggests that the rainbow is a virtual object, whose location is defined by the position of the observer, and that the sky below the bow has to be bright.

the "raining rainbow"

When we approach a real illuminated waterfall, we can finally see the rainbow. It outlines a spectacular colourful bow in the sky. But not only that! The bow clearly separates the brighter (internal) part of the sky from the darker (external) one. Nobody has ever noticed it. So, the truth is that the mise en scene reveals unexpected phenomena that might have passed unnoticed in nature. And above the dark part of the sky, there is a second bow with inverted colours and with a faint light outside it. This is the second rainbow, ready to be discovered.


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