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Light Reading

THE FIRE WITHIN THE EYE A Historical Essay on the Nature and Meaning of Light By David Park; Princeton University Press: 372 pp., $29.95

July 20, 1997|SIDNEY PERKOWITZ | Sidney Perkowitz is author of "Empire of Light: A History of Discovery in Science and Art" (Henry Holt). He is Charles Howard Candler professor of physics at Emory University

If you could turn your eyes inward so as to examine the busy neurons within your skull, you would have graphic evidence of how important light is to the human organism. Nearly one-third of the billions of nerve cells in your brain do nothing but interpret the light entering your eyes to present a world rich in color, detail and meaning. That striking neurophysiological fact demonstrates how central to humanity is our highly developed vision.

Many centuries before neurons were dreamed of, however, or the structure of the eye was known, "light" was a compelling idea because in its speed and intangibility, it seemed ungraspable. And we have not yet penetrated to the deepest heart of light. Although we understand it better than we once did, it still carries an apparently insoluble quantum puzzle, that it is both wave and particle. Although we use it for ordinary purposes like playing the latest compact disc or telephoning a friend, it carries spiritual weight. Like space, time and other vast concepts, the idea of light has always drawn us; we have never stopped thinking about it.

In "The Fire Within the Eye," David Park shows us how that thinking has progressed. An emeritus professor of physics at Williams College, Park could undoubtedly explain in great detail how a laser works or how light produces sound from a CD. But he is after different game than the modern gadgetry of light or even its profound quantum discrepancy. His book, he writes, is "a history of thought about light, rather than the story of a gradual climb toward truth."

It is good to hear from a physical scientist steeped in history and philosophy who knows that the latest scientific knowledge is not the only truth that has accrued around light. Of course that scientific knowledge carries special weight because the physical nature of light is extraordinary. (Light acts in some ways like a stream of tiny billiard balls and, in other ways, like an undulating ocean wave. This enigma emerged after Einstein discovered those tiny particles, which came to be called photons, in 1905. It has baffled the finest scientific minds since, from Einstein to Richard Feynman who, with two colleagues, won a Nobel Prize in physics in 1965 for the modern theory of light, called quantum electrodynamics, or QED.)

"The Fire Within the Eye," however, concentrates on the period dating from before the time of Socrates to the 19th century. Only the book's last chapter is devoted to the recent intense activity in the science of light, which is characteristic of this century. "Ideas ripen slowly," says Park, who believes that the 20th century has not been more important for the scientific understanding of light than the three preceding centuries. He adds, "We who live in this century do not need to have its leading intellectual assumptions explained to us." I do not fully agree with either position. The uncovering of the photon and QED theory are unique and historic achievements, as is the vast progress in the technology of light (which may finally explain the wave-particle paradox). And many teachers of science, like myself, find they can hardly do enough to explain to their students the "leading intellectual assumptions" of the day.

But for the story of light before this century, Park is an excellent guide. He begins with the early Greek philosophers, who had no way to sense and analyze light other than through their eyes and minds. For them, the objective properties of light were entwined with the subjective nature of vision, whereas we moderns know that the light we see is electromagnetic radiation of certain wavelengths, radiation that is emitted at other wavelengths as well, such as those of invisible ultraviolet light.

The first philosophers lacked this physical knowledge and found it difficult to answer even the very first question about vision: How is the image of an object conveyed to the viewer? Now we know that light travels to the eye, either directly from a source or after modification by the material world. To the viewer, however, the act of seeing requires a directed focusing of the eye and one's attention. That subjective reality may explain why the philosopher Empedocles (who gave us the four elements) wrote in 450 BC about a "visual ray" that left the eye in order to seek out and sense the thing that was seen. Plato also accepted this idea and introduced a "fire within the eye" as the origin of the visual ray. I know from my own experience that some people still find the notion of a ray from the eye eminently reasonable. To them, the contemporary scientific view is not obvious; it takes some explanation to present the modern version of things.

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