Facts of the Matter
Water acts as a prism, bending the sun's light into a rainbow.
Study of light has colorful history
It is easy to understand the mystique of light. It penetrates and permeates simultaneously and its nature has been a matter of philosophical, theological, and scientific speculation for at least 2,500 years, since the ancient Greek philosophers started writing about it.
Color was especially perplexing, since it is not clear how light can carry the infinite variety of colors that we can perceive.
The story is tied in with the aesthetic nature of the paradigms of perfection and purity that needed to be circumvented before there could be progress.
Empedocles (490-430 B.C.) wrote that the eye projects a ray, bounces off of objects, then returns to the eye to create an image in the mind.
Socrates (469-399 B.C.) described a different kind of light, an intellectual illumination of cognitive moral guidance in the form of an inner voice that ". . . whenever it speaks it turns me away from something I am about to do, but it never encourages me to do anything."
Plato (427-347 B.C.), one of Socrates' students, synthesized his mentor's moral philosophy with the mathematical mysticism of Pythagorean numbers and shapes, adopting the circle as the most perfect shape, in perfect spherical universe with an imperfect Earth at the center.
He likened the sun metaphorically as the source of Socrates' intellectual illumination.
Plato's philosophy taught that every human has a moral obligation to seek the truth behind the appearances through logical discourse because he did not trust the easily-deceived five senses.
He found the erratic retrograde movement of the planets against the star background abhorrent and needed an explanation of their motions in terms of circles, in the way that the shadow of a properly contorted hand can produce the appearance of a rabbit.
Plato's student Aristotle (384-322 B.C.) found a way to explain the planetary movements in terms of circular motion, and constructed an elaborate cosmology that was remarkably internally consistent as well.
Aristotle's model retained the imperfect Earth, separated from the perfect, circular heavenly realm by the moon's orbit.
Aristotle added to Socrates' intellectual illumination that makes all things an internal "agent intellect" to process infused knowledge analogous to the way light makes colors visible.
Aristotle's idealized, perfect cosmos evolved philosophically over the next 450 years, culminating in the Ptolemaic system, an astronomical model of planetary motion that satisfied Plato's "circular question" but lacked Aristotle's cosmological unity.
The perfect, circular world view centered around an imperfect Earth for centuries prevented philosophers from thinking outside of the circular box. It was accepted axiomatically that the heavens were perfect, circular, and pure, and the source of both inner illumination and visible light.
Augustine (354-430) later referred to Socrates' cognitive guidance as "divine illumination" because, "The mind needs to be enlightened by light from outside itself, so that it can participate in truth, because it is not itself the nature of truth."
Augustine's position that pure truth should not be sought from the senses remained the dominant view among Christian philosophers for 900 years.
Thomas Aquinas (1225-1274) reexamined Aristotle's view, and in doing so helped to ignite the Renaissance with the view that we require the light of "agent intellect" and denies that divine illumination is sufficient on its own.
He also presented convincing rhetoric concerning the perfection of God and by association light that streams from the heavens.
The status of perfection of the heavens and the purity of light would be safe for another 350 years.
In the first decade of the 17th century Johannes Kepler (1571-1630) found the simplest explanation for the movement of the planets was to have them moving around the sun in ellipses, not in circles and not around the Earth.
His work seriously demoted the sanctity of the circle, although it went unnoticed by scholars at the time.
Thirty years later Rene Descartes (1596-1650) observed that certain material actions do not change and called the rules behind these changes the "laws of nature."
He saw the universe as a smooth-running machine, set in motion by God and governed by natural laws. Accordingly, he thought that light could be completely understood through mechanics.
He verified that the lens of the eye adjusts like a machine to focus, representing the ideal machine. That was evidence that strengthened the mechanical theory of light.
Descartes believed that white light was spinning particles and colors were caused by the slowing or speeding the rotation of the white light particles.
White light represented purity and the perfection of the heavens from which it ultimately came. In Descartes' theory, colored light was merely distortion caused by the pure, white spinning particles passing through the prism.
In England, Isaac Newton (1642-1727) passionately and obsessively believed that Descartes had been wrong. That and his obsession with light nearly drove him mad. He thought of light as a divine principle, but not in the same sense as the ancient "divine illumination."
He began to study it intensely with obsessive energy in 1664. He designed a series of experiments upon which the replicability of his new theory of light would depend.
In 1665 he split a sunbeam into a spectrum by passing it through a prism in a darkened room. He placed a second prism upside down in the path of the colored beams of light emerging from the first triangular prism. The light that emerged from the second prism was single beam of white light.
Newton concluded that white light consists of the color of the rainbow. He deduced that a single color of light passing through a prism would not change color, but would be bent.
He verified the conclusion by screening all but the red light coming from the first prism and passing it through the second prism. Repeating the exercise with the blue portion of the spectrum showed that the blue light was bent more than the red light, meaning that the separation of colors is a secondary effect.
Although they disagreed about the color of light, we owe much of our modern world view and scientific knowledge to Descartes and Newton.
Richard Brill, professor of science at Honolulu Community College, teaches earth and physical science and investigates life and the universe. E-mail questions and comments to firstname.lastname@example.org