Alan Lightman, a physicist and novelist, is Professor of the Practice of the Humanities at MIT. His two latest books are “The Accidental Universe,” and “Screening Room.”
One evening during Isaac Newton’s years as a student at Cambridge, alone in his room lit by candlelight, a chamber pot in the corner, the budding scientist stuck a needle in his eye to test the nature of vision. If he wiggled the needle, he saw colored circles. If he held the needle still, the circles disappeared. When he took the needle out of his eye and looked at a dark wall, the circles reappeared for a few moments, “a motion of spirits.”
Bruce Watson’s new book, a sweeping cultural and scientific history of our understanding of light, is filled with such vivid and charming scenes. With his trademark good storytelling and wide reading, Watson takes us on a delightful journey from the earliest creation myths, to Chinese ideas of the duality of light and darkness, to 10th-century Islamic scientist Ibn al-Haytham’s construction of a light-refraction apparatus from a cylinder with holes on opposite sides, to Newton’s work with prisms, to Vermeer’s use of a pinhole camera to project onto his canvases scenes to be painted, to Scottish physicist James Clerk Maxwell and his mathematical theory of electromagnetic light waves, to Einstein’s work on the quantum nature of light. In fact, Watson’s book feels like one long story of human history, with fairly detailed explanations of evolving scientific ideas alternating with intimate glimpses of daily life in various eras alternating with portraits of the scientists making the discoveries.
Watson’s enthusiasm for his subjects is infectious. The author of articles on a wide range of subjects for Smithsonian magazine, Watson’s best-known prior book is “Bread and Roses,” a narrative about striking textile workers at a mill in Lawrence, Mass., in 1912. In the introduction to his new book about light, Watson writes that he aims to “reconcile the battles between science and humanities, between religion and doubt, between mathematics and metaphor.” He succeeds, as much as one can with such marching orders.
In ancient times, there was great confusion about whether light originated in the eye (with a light beam emerging from the eye and illuminating objects) or, instead, originated in sources outside the human body, such as fire. The same with color. Was it an intrinsic property of objects or of the light striking those objects? Such controversies seem preposterous to us now, with our modern comprehension of nature, but Watson succeeds in peeling back the centuries and conveying the mentality of an earlier world.
Another historical debate about light has been whether it is wavelike, as are water waves, or particle-like, as are baseballs thrown out of a pitching machine. There is good evidence for both views. In the mid-17th century, a Jesuit priest named Franceso Grimaldi let a shaft of sunlight enter through a tiny hole into a darkened room, travel past a small object in its path and then fall upon a white screen. The object’s silhouette on the screen was odd. Where there should have been only shadow, directly behind the object, there was an invasion of light, and where there should have been only light, there were curious dark marks.
Evidently, the rays of light were not traveling in straight lines, as had been predicted by scientists and philosophers for centuries. Grimaldi had discovered that light is a continuous fluid. Upon meeting an obstacle, the fluid will split into secondary ripples, which can overlap and interfere with one another downstream, producing a complex pattern of light and dark.
On the other hand, light sometimes acts like a collection of separated particles. In 1922, American physicist Arthur Compton shined light on electrons and carefully measured the wavelengths of the light rebounding at different angles. He found that the results were perfectly explained if the incoming light consisted of individual particles, called photons, and the interactions consisted of single photons bouncing off single electrons, like two billiard balls colliding with each other.
Parallel to such attempts to understand the scientific nature of light runs the decisive role of light in ordinary human existence. In one wonderful passage we learn about the unpleasant ordeal of candlemaking. First, an animal like a deer or a yak had to be “slaughtered and stripped of its fat. Soon kitchens and huts reeked with the stench of the unctuous, oily suet boiled in vats of quicklime.” Sulfuric acid was poured in to decompose the lime, leaving a greasy melt. Then, “strings dangling from wooden rides were dipped and dipped again until a finger of white wax clung to each wick.” For millennia, until Thomas Edison, human beings had only candles to light their houses and huts in the night.
In another passage, Watson describes an evening in the summer of 1798 when Parisians went to a light/fright show called Fantasmagorie. Soon after a man stepped from behind a curtain, “the far wall exploded with bolts of lightning.” Skeletons and witches floated in the blackness, and smoke filled the room, sliced by light. Police closed the show, fearing that it might bring back to life the guillotined Louis XVI.
A few quibbles. Many of the scientific explanations would be clearer with illustrations. More serious, Watson should have checked his science with physicists. His explanations of the photoelectric effect, black body radiation, Maxwell’s work predicting electromagnetic waves and other topics suffer from misunderstandings, and he commits some real bloopers, such as saying that forces obeying the inverse square law weaken “exponentially with distance.”
If the book has a climax, it is in one of the final chapters, titled “Einstein and the Quanta, Particle, and Wave,” where Watson celebrates the ultimate enigma of light — that it acts both like waves, simultaneously spread over an extended region of space, and particles, each located at only one point of space at a time. Such seemingly mutually exclusive descriptions violate our human experience with the world. That enigma reaches far beyond light. It applies to all of reality at the tiny scale of the atom. Above all else, modern physics has shown us that what we humans perceive with our limited bodies, and all of our notions based on those perceptions, are an illusion, an approximation of a strange cosmos we can touch only with our instruments and equations.
By Bruce Watson
Bloomsbury. 282 pp. $27