Invisibility: The History and Science of How Not to Be Seen
by Gregory J. Gbur
Yale University Press, 280 pp., $30.00
Transparency: The Material History of an Idea
by Daniel Jütte
Yale University Press, 502 pp., $45.00
Some twenty years ago the radio program This American Life asked listeners which of two superpowers they would choose: flight or invisibility. These are “two of the superpowers which have fascinated humans since antiquity,” said the host, Ira Glass. It was a test of character and a probe of the zeitgeist. The humorist and actor John Hodgman explained that he had been asking people this question for years at meetings and dinner parties, and that their choice revealed primal desires and unconscious fears.
He was disappointed that no one wanted to use their superpower to fight crime.
People who chose invisibility imagined themselves lurking, eavesdropping, and peeping. They were sneaky. “I think actually,” one woman said,
if everybody were being perfectly honest with you, they would tell you the truth, which is that they all want to be invisible so that they can shoplift, get into movies for free, go to exotic places on airplanes without paying for airline tickets, and watch celebrities have sex.
They want to see without being seen.
To fly is heroic, à la Superman. To vanish is antiheroic. Still, we crave invisibility in response to a growing sense of ubiquitous surveillance: our images captured and displayed everywhere, our inner souls turned out for all to see. “Transparency” is a watchword and a virtue—so we are told—and the desire for invisibility might be a natural reaction.
Over the past two decades, scientists studying optics have considered invisibility not just as a fantasy but as a practical possibility. We know about stealth aircraft, aspirationally invisible to radar. One automaker is now offering a “stealth” paint option—“a dark, enigmatic look,” for “an entirely new personality.” Gregory J. Gbur, an optical physicist at the University of North Carolina, has made invisibility something of a hobby. It informs his research, and he collects headlines: “Invisibility Cloaks Are in Sight”; “Researchers Create Functional Invisibility Cloak Using ‘Mirage Effect’”; “Scientists Invent Harry Potter’s Invisibility Cloak—Sort Of.” His new book, Invisibility, explores the phenomenon as a catalyst for research as well as for science fiction—because across several centuries the science of light and the fiction of invisibility developed side by side, each inspiring the other.
First the invisible man feels exalted, free to do anything he wants, superior to mere mortals, like a “seeing man in a city of the blind.” Unfortunately, to be invisible he has to be naked, and it’s winter in London.
Harry Potter has his cloak, Frodo has his ring, James Bond has a car, Wonder Woman has an airplane. They are mere newcomers to the art of vanishing at will. In ancient mythology Perseus, Athena, and Hermes took turns donning the helm of invisibility, aka the Cap of Hades, when they needed to evade the sight of their enemies. For the same reason, organisms like chameleons and octopi have evolved camouflage skills. Gbur takes his subtitle from the famous Monty Python sketch “How Not to Be Seen,” in which a series of people hide in bushes, leaf piles, and a water barrel before being shot or blown up. The desire to be invisible seems deeply embedded in our psyches. Yet it’s not obvious how a scientist ought to define it.
“The word ‘invisible,’” Gbur writes, “is simultaneously very suggestive, conjuring a specific image (or lack thereof) in a person’s mind, and very vague, in that it can mean many different things.” Everything is invisible in the dark; everyone else is invisible when you close your eyes. Bacteria and quasars are invisible by virtue of being small or far away, until we use microscopes and telescopes. Extending our vision, enabling us to see the unseen, has been a long-standing program in science, so scientists seeking invisibility might seem to inhabit a backwash from the main current.
Invisibility could mean perfect blackness or perfect transparency. A British company in 2014 announced a “super-black” coating called Vantablack that absorbs virtually all the light that strikes it. Jack London wrote a story in 1903, “The Shadow and the Flash,” in which a scientist paints himself perfectly black and battles a rival who achieves near-perfect transparency. Their conflict ends with a surreal and fatal game of tennis: “The blotch of shadow and the rainbow flashes, the dust rising from the invisible feet, the earth tearing up from beneath the straining foot-grips.”
~
In an odd bit of serendipity, Yale University Press has simultaneously published Transparency: The Material History of an Idea by Daniel Jütte. Transparency is invisibility’s obverse. It makes visible what would otherwise be hidden. With impressive detail and wide-ranging erudition, Jütte charts the history of a single material, glass, as a product of human ingenuity developed across centuries, beginning in Mesopotamia in the third millennium BCE. In Roman times the story of glass became the story of windows. “Window views and worldviews are more closely entwined than we might assume,” Jütte writes. As a technology for letting us observe the outside from the inside—and vice versa—the window calls attention to the act of seeing. It frames our vision and “epitomizes the idea of looking at the world from a protected or otherwise privileged perspective.” It becomes a metaphor. We speak of windows onto the world and windows into the soul.
The history of architectural glass implicates the cultural meaning of light. For physicists, light on earth comes first from the sun. In religion, it first came from God. Culturally, it has symbolized divinity, inspiration, knowledge, and political power. Darkness, as in “the Dark Ages,” was its antithesis. Jütte emphasizes that medieval times, far from being dark, were when Christian churches drove the demand for architectural glass, at first usually colored and then, as the technology of glassmaking improved, colorless, clear, and more perfectly transparent.
Glass windows let the light in, a plain fact that becomes a metaphor: “For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light.” In practical terms light meant safety. Jütte quotes Michel Foucault: “A fear haunted the latter half of the eighteenth century: the fear of darkened spaces, of the pall of gloom which prevents the full visibility of things, men, and truths.” Light-skinned people in Europe turned the vagaries of pigmentation into an ideology of genetic superiority. As a counter to the darkness, whiteness was idealized and light suggested enlightenment. Then industrialization made light an object of technology: oil lamps, gas lamps, and finally electrification—turning night into day, as people began to say.
For the natural philosophers of the scientific revolution, glass was a substance to be shaped into lenses and prisms, to investigate the mysteries of light as a building block of nature. Glass reflects light and refracts it, focuses it and splits it into the colors of the rainbow. As the developing science of optics made its way into public knowledge, it revived old dreams of invisibility. In 1859 an Irish American writer, Fitz James O’Brien, published a story in Harper’s Magazine that imagined an invisible monster haunting a boarding house. The creature attacks the narrator, Harry, in the dark, and when he turns on a gas light he sees, to his horror, “nothing! Not even an outline,—a vapor!” After a struggle involving ropes and poorly aimed blows, he and his friend Hammond finally overpower “the Thing,” as they call it. The strangeness leaves them terrified and confused, until they start to think scientifically. “Let us reason a little, Harry,” says Hammond.
Take a piece of pure glass. It is tangible and transparent. A certain chemical coarseness is all that prevents its being so entirely transparent as to be totally invisible. It is not theoretically impossible, mind you, to make a glass which shall not reflect a single ray of light.
Air, too, is felt but not seen. What if transparency is the natural state, and only a certain chemical coarseness makes things visible? No less than Isaac Newton, the first great pioneer of optical science, had speculated along those lines. He suggested that “the least parts of matter” are transparent in themselves, until light passing through them is reflected and refracted every which way. Glass loses its natural transparency—becomes opaque—when it is scratched or crushed to powder. Conversely, paper, woven of discrete fibers, can be made transparent by soaking it with oil of equal density, to smooth the passage of light.
As Gbur tells it, the quest for invisibility ran closely alongside the search for the least parts of matter, beginning with the recognition that everything consists of invisible particles surrounded by emptiness and bound together by forces of attraction. Ancient Hindu sages and Greek philosophers had suggested this, and Newton favored the idea, though the atomic view didn’t take hold until the nineteenth century, when John Dalton developed a theory of tiny particles, identical and interchangeable, as the elementary constituents of matter. This laid the groundwork for modern chemistry. Even then scientists were still speculating—using inference and guesswork to construct a theory of things too small to be seen directly—and fiction writers speculated with them.
The imaginary scientist in another O’Brien story is an explorer with a microscope. “I imagined depths beyond depths in nature,” he says. “I lay awake at night constructing imaginary microscopes of immeasurable power, with which I seemed to pierce through all the envelopes of matter down to its original atom.” We have those now: electron microscopes and scanning tunneling microscopes, which can resolve particles far smaller than the wavelengths of ordinary light.
Also driving the fascination with invisibility was the paradoxical discovery that light itself can be invisible. William Herschel, musician turned astronomer, realized in 1800 that the sun emits “invisible rays”—what we now understand as infrared and ultraviolet light, radiation at wavelengths too short and too long to be detected by the human eye. It turns out that the visible spectrum is pitifully narrow. Of the universe’s full electromagnetic splendor, our eyes perceive only a sliver.
The notion of invisible rays made other forms of invisibility all the more plausible. “The human eye is an imperfect instrument,” says the narrator of “The Damned Thing,” an 1893 story by Ambrose Bierce:
Its range is but a few octaves of the real “chromatic scale.” I am not mad; there are colors that we cannot see.
And, God help me! the Damned Thing is of such a color!
Of course, the Damned Thing is another invisible monster.
~
With the progress in optics came a growing understanding of the gulf between what we see and what is really there. Light does strange things on its way from the object to the eye, and the brain has to do its best—which is often not very good at all—to make sense of the signals being passed its way.
Whether as particles or waves or both, light rays interfere with one another, sometimes even canceling each other out. Interference patterns mix darkness with light—a mind-bending fact properly appreciated by Thomas Young, a medical doctor turned physicist, whose studies of the eye led him to the study of light itself. Young’s wave-based theory of interference, contradicting Newton’s particle-oriented (“corpuscular”) theory, provoked controversy and derision in the early 1800s. One contemporary explained why it was so counterintuitive:
Who would not be surprised to find darkness in the sun’s rays,—in points which the rays of the luminary freely reach; and who would imagine that any one could suppose that the darkness could be produced by light being added to light!
The relationship between light and darkness was not so simple.
It was the electricians—especially Michael Faraday and James Clerk Maxwell—who created a unified theory of light as nothing more or less than an oscillating wave of electricity and magnetism. A disturbance in the field. Maxwell’s theory brought together every natural form of luminance: lightning bolts and auroras, glowworms and fireflies, fluorescent jellyfish and bioluminescent fungi. It also predicted, as a matter of pure mathematics, all the invisible versions of electromagnetic radiation: radio waves (soon made in Heinrich Hertz’s laboratory in Karlsruhe), microwaves, and gamma rays. The sexiest were discovered and named by Wilhelm Röntgen in 1895: X-rays. Invisible themselves, X-rays penetrated solid matter and revealed what lay within. Röntgen made an image of the bones inside his wife’s hand. She said, “I have seen my death,” and he won the first Nobel Prize in physics.
We’re so accustomed to advanced medical imaging, from MRIs to PET scans, that it’s hard to grasp how powerfully X-rays affected the popular imagination. “Misinformation spread almost as quickly as news of the discovery itself,” Gbur writes. “If X-rays can see through anything, might people be able to use them to spy on their neighbors and see through their clothing?” (A similar fear arose about a decade ago when the American government installed full-body scanners at airports: invisible rays revealing our naked forms.) When Thomas Edison learned of X-rays, he confidently announced that they would allow the blind to see. “I can make a Röntgen ray that will enable me to see through the partition in this laboratory, and possibly through the brick walls,” he said. He was wrong, but the foundation had been laid for Superman’s “X-ray vision” and novelty-store X-ray spectacles, and also for the first great novel of invisibility, H.G. Wells’s The Invisible Man.
Wells’s first book, The Time Machine (1895), had been a sensation—a pseudoscientific fantasy that brought him instant success. The Invisible Man, published two years later, was almost as original. It drew straight from the headlines—“Röntgen vibrations” are part of the narrator’s bag of tricks—and the influence went both ways. Its readers included future scientists. It was “a turning point in the history of invisibility physics,” Gbur writes, “when the possibility of invisibility—and its dangers—entered the public consciousness, where it has remained to this day.”
As in The Time Machine, Wells dresses his story in an armor of plausible mumbo jumbo. His protagonist, a former medical student named Griffin who has turned to the study of optics, explains, “The whole subject is a network of riddles—a network with solutions glimmering elusively through.” Griffin is pondering the ways a body may absorb light or reflect it or refract it, when “suddenly—blindingly! I found a general principle of pigments and refraction—a formula, a geometrical expression involving four dimensions.” He makes a “gas engine” powered by “dynamos” and creates drugs that “decolourise blood.” We’re being conned, but generations of readers have been happy to go along. As for Griffin, he is euphoric: “I beheld, unclouded by doubt, a magnificent vision of all that invisibility might mean to a man—the mystery, the power, the freedom. Drawbacks I saw none.” What could go wrong?
First the invisible man feels exalted, free to do anything he wants, superior to mere mortals, like a “seeing man…in a city of the blind.” Unfortunately, to be invisible he has to be naked, and it’s winter in London. Practicalities begin to weigh on him. He is jostled in crowds and growled at by suspicious dogs. In his mind’s eye he becomes “a gaunt black figure” with a “strange sense of detachment.” Eating is a problem—think of undigested food making its way through the gastrointestinal tract.
The invisible man puts on clothes, wraps his face in bandages, and grows desperate and deranged. As Wells’s son Anthony West wrote, he becomes
an invisible madman, a person impenetrably concealed within his own special frame of private references, resentments, obsessions, and compulsions, and altogether set apart from the generality of mankind.
He has found that invisibility, far from being a superpower, is the ultimate in alienation. Nowadays every selfie-snapping Instagrammer and TikTokker seems to feel this instinctively.
No wonder Ralph Ellison chose this theme for his 1952 masterpiece, Invisible Man. His narrator is invisible because he is Black in white America. In the novel’s famous opening he declares:
I am an invisible man. No, I am not a spook like those who haunted Edgar Allan Poe; nor am I one of your Hollywood-movie ectoplasms. I am a man of substance, of flesh and bone, fiber and liquids—and I might even be said to possess a mind. I am invisible, understand, simply because people refuse to see me.
The invisible man is unnamed, marginalized, living literally underground, in an abandoned coal cellar illuminated by exactly 1,369 light bulbs. (He steals electricity from Monopolated Light & Power.) He listens on his record player to Louis Armstrong’s “What Did I Do to Be So Black and Blue,” which he describes as poetry of invisibility. Invisibility gives him an altered sense of time: an awareness of its nodes, an escape from strict tempo, a sense of being out of sync. Invisibility has its advantages, he tells us, but sometimes he begins to doubt his own existence. He feels like a phantom in someone else’s nightmare. “All life seen from the hole of invisibility is absurd,” he says.
Yet the quest for invisibility persists. Maxwell’s electromagnetic theory has been upgraded to quantum electrodynamics, which has sidestepped the question of whether light is a particle or a wave by embracing both views, combining them in one uneasy package. Quantum control of light provides communication and medicine with applications weirder than science fiction. Physicists manipulate light like wizards. Lasers make beams of coherent light that cut diamonds and blast kidney stones. Holograms manipulate interference patterns to create three-dimensional images. Optical fiber channels light to carry information far more efficiently than any electrical wire.
In 1975 Milton Kerker, an expert on the scattering of light by small particles, wrote what Gbur calls the first scientific paper about “a truly invisible object.” Kerker calculated that under certain circumstances the light striking an object could excite electrons so as to generate electromagnetic waves perfectly out of phase, rendering the object invisible. Alas, nothing seems to have come of this discovery. The research was funded in part by the Paint Research Institute, possibly in hopes of discovering invisibility paint.
The most persuasive progress toward true invisibility—the “game changer,” says Gbur—came in 2006, with strategies for making objects disappear by bending light around them. On astronomical scales, the gravitation of black holes warps space to alter the path of light, and physicists suggested designing optical materials—“metamaterials”—that could produce a similar effect. Every transparent substance has a refractive index, the measure of how much light is bent when it enters the material. A Ukrainian theorist, Victor Veselago, speculated that materials could be created with a negative refractive index and that such metamaterials would bend light in counterintuitive ways. “With the introduction of metamaterials,” Gbur writes, “researchers were now asking, ‘How can we make light do whatever we want it to?’” (Metamaterials are now transforming the design of lenses for smartphones and other applications.)
An English optical physicist, John Pendry, thought “it would be a good joke to show how to make objects invisible.” He proposed creating a metamaterial that could guide light around it “like water flowing around a rock in a river, so that the object inside it cannot be seen.”
My wife suggested that I [make] reference to someone called Harry Potter, of whom I had never heard but who apparently had something to do with cloaks. However, the joke was taken extremely seriously, and cloaking has since become a major theme in the metamaterials community.
When Science published Pendry’s paper in 2006, it generated a flurry of newspaper headlines of the sort Gbur treasures.
In 2011 Japanese researchers reported finding a chemical reagent that bleached biological tissue almost to a state of transparency, in an effort to reveal brain structures to their microscopes. They pursued basically the same approach as a fictional lab worker named Flack in an 1881 short story, “The Crystal Man,” by Edward Page Mitchell, using chemical solvents to clear pigmentation. But they were working with mouse embryos, and their methods don’t seem suitable for live humans.
It’s fair to say that scientists’ imaginations continue to run ahead of their practical success. Their computer simulations achieve better results than their experiments. The invisibility cloaks that work by bending light are mainly ad hoc. They’re limited in size—Baile Zhang, from Singapore, demonstrated an invisibility cloak that hid a pink Post-It note at a TED conference in 2013, and later reported having expanded it to hide goldfish in a tank and a cat—and they cast shadows or operate over a limited range of wavelengths. Even Gbur, who includes an appendix optimistically titled “How to Make Your Own Invisibility Device!” lets us know, somewhat wistfully, that the invisibility of our science-fictional dreams might remain forever impossible.
Biological evolution chose the wavelengths our eyes can see—from about 400 to 700 billionths of a meter—and it chose well. Those are light rays that pass through the atmosphere with a minimum of scattering and absorption but do not pass through solid matter in most of its forms. However we have manipulated visible light, at least so far, objects reflect it and cast shadows. Even transparency is rare. The people who have best learned how to bend light around objects to make them disappear are stage magicians, with mirrors. They have the advantage of stationary audiences, happy to be fooled.
Even when the idea of invisibility attracts us, we still fear the darkness. Ellison’s invisible man, in his windowless space underground, needs his army of light bulbs to keep the darkness at bay. “I doubt if there is a brighter spot in all New York than this hole of mine, and I do not exclude Broadway,” he says. Fear of the dark may be primitive and instinctual, but Jütte’s Transparency charts a change in attitudes in the West during the Enlightenment. “In previous periods of history, darkness was first and foremost a practical problem—an obstacle to the conduct of certain domestic and professional activities,” he writes. The Enlightenment gave it a moral coloration: darkness was associated with “cultural backwardness and social inferiority”—dungeons for criminals, hovels for the poor. Light was modern. It brought safety and health. When the early Massachusetts colonists built a courthouse in Boston in 1713, they took particular pride in its windows: “May the Judges always discern the Right…Let this large, transparent, costly Glass serve to oblige the Attorneys alway [sic] to set Things in a True light.”
Windows were prized as a luxury and a mark of civilization. One measure of their importance is that from 1696 to 1851 England imposed a window tax. Windows let people look out upon the landscape—ideally onto their gardens. Or the windows let people look in, which was another virtue, the antithesis of furtiveness. Jütte cites Jean-Jacques Rousseau as a champion of righteous transparency. His own heart, Rousseau said, was “transparent as crystal,” and he praised transparency in architecture: “I have always regarded as the worthiest of men that Roman who wanted his house to be built in such a way that whatever occurred within could be seen.” Continuing the metaphor to this day, transparency—in social relations, in government, in corporate practice—has come to be seen as an unalloyed good. Morality has combined with aesthetics to make glass the quintessential material of modern architecture.
Frank Lloyd Wright championed glass to let us “escape from the prettified cavern of our present domestic life as also from the cave of our past.” The picture window became a status symbol. Mies van der Rohe brought glass-faced towers to Chicago; under his influence, Philip Johnson designed his trademark Glass House in Connecticut; I.M. Pei shocked France by adding a glass pyramid to the Louvre. Le Corbusier hailed skyscrapers with “immense geometrical façades all of glass, and in them is reflected the blue glory of the sky.” They continue to rise in every city. Meta’s headquarters in Menlo Park, California, designed by Frank Gehry, is entirely transparent, the company boasts: “One can see through it from one end to the other.” In its center is the chairman, Mark Zuckerberg, his office encased in bulletproof glass. Everybody loves glass.
And yet. In the history of Western architecture, the paradigmatic glass building is the panopticon, designed by the English philosopher and reformer Jeremy Bentham in 1791. Long before walls and large windows of glass became feasible, he made transparency the “characteristic principle” of his plan. He explicitly associated transparency with good government. The panopticon was a marvel. But it was intended as a prison—a new national penitentiary for Britain. The inmates were to live in transparent rooms, visible from all sides and from above, always watched, never unseen. “There ought not any where be a single foot square,” Bentham wrote, “on which man or boy shall be able to plant himself, no not for a moment, under any assurance of not being observed.”
Jütte wants us to see that glass architecture, along with the dream of a transparent society, has “a nightmarish side”—that it is “an architecture of power.” It tends toward homogeneity and control. To see something is the first step toward subjugating it. “Tightly sealed windows keep the city’s smells at bay,” he writes, “and the development of soundproof glass has turned windows into highly effective barriers against the exterior soundscape.” A glass wall is still a wall.
The same applies to the vision of perfect transparency promised by Zuckerberg and the other purveyors of social media. We are told that a transparent society will replace stealth and secrecy with openness and accountability. But living in glass houses means that someone is always watching. The panopticon rises all around. Invisibility seems no longer to be an option.