The Sounds Of Invisible Worlds

Like the microscope and the telescope did centuries ago, new technologies to capture and analyze sound are leading to startling discoveries about what the eyes cannot see.

Vera van de Seyp for Noema Magazine
Karen Bakker (1971-2023) was a professor at the University of British Columbia, a Guggenheim fellow and a 2022-23 fellow of the Harvard Radcliffe Institute for Advanced Studies.

More than 400 years ago in the small Dutch town of Middelburg, a father-and-son team stumbled on an invention that would one day change history, but which they dismissed as a dud. By tinkering with glass lenses, Hans and Zacharias Janssen invented the microscope. Yet this was not by design.

The Janssens were leaders in a new and highly lucrative industry: making reading glasses. In their quest for the perfect pair of spectacles, a highly sought-after luxury item, the Janssens discovered that they could magnify objects by aligning two lenses in a cylindrical tube. They were astounded to find that combining two lenses magnifies much more than any one lens does on its own. But the view was blurry and the device too clunky for their clients, so they put their quirky discovery aside.

The Janssens’ magnifying machine lay mostly unnoticed for nearly a hundred years before someone put it to use. Antonie van Leeuwenhoek, a Dutch fabric merchant with a grade school education, first built a few homemade microscopes with a mundane goal: checking the quality of the expensive fabrics he had purchased from overseas. But Van Leeuwenhoek soon turned his attention to the world around him, pointing his microscope at well water, mold, bees, lice, yeast, blood cells, human breast milk (his wife’s) and sperm (his own). Everywhere he looked, his microscopes revealed a strange new world of beings living in every nook and cranny of our world, but unseen by the unaided eye.

Van Leeuwenhoek initially (and wisely) kept his discoveries secret for fear of ridicule. When he eventually revealed what he had seen, polite Dutch society disdained his strange proclivity for magnifying bodily substances; many simply refused to believe in the existence of “animalcules” altogether. Nevertheless, Van Leeuwenhoek penned hundreds of letters to the Royal Society in London, which — after initial suspicion and a visit from a skeptical scientific delegation — eventually accepted his findings. The humble merchant’s research papers were published alongside those of Sir Isaac Newton in the Royal Society’s learned journal.

The new world of microscopic observation soon fascinated scientists and philosophers alike. Microscopes proliferated as a form of visual prosthetics — artificial eyes that helped humanity see new things in new ways, laying the foundation for startling discoveries. The study of the microscopic world renewed interest in atomism — an early theory that the world was composed of fundamental, tiny particles — and would also eventually provide new methods for understanding contagion and disease.

As the historian of science Catherine Wilson argued in “The Invisible World,” the microscope catalyzed the Scientific Revolution. The simple device captured a complex idea: Science could reveal aspects of the natural world that were invisible to naked human perception. Spectacles merely helped us focus on the written word; the microscope enabled humans to perceive entirely new realms, extending the power of both sight and imagination.

“The microscope enabled humans to perceive entirely new realms, extending the power of both sight and imagination.”

At around the same time, another Dutch spectacle-maker was also tinkering with glass and realized that distant objects could be magnified by arranging convex and concave lenses. News quickly spread across Europe; in Italy, Galileo Galilei, then a university lecturer in mathematics, tweaked the design and turned his telescope to the stars.

Most of his contemporaries were using telescopes for military purposes — spying on enemies on land and at sea. Within a year, Galileo published descriptions of the sun, moon, stars and planets in “Sidereus Nuncius” (“Starry Messenger”), which became one of the most widely circulated scientific tracts of the age. Despite persecution by the Catholic Church, Galileo’s discoveries sparked the abandonment of the idea that the Earth was at the center of the universe and laid the groundwork for profound challenges to the foundations of science, philosophy and politics.

In Europe, the science of optics had deep cultural roots: In classical Greek philosophy, sight was the noblest of senses, and philosophers from Plato to St. Augustine exulted in visual imagery. Even basic scientific terms in common use today reflect a preference for vision and the visible: The word “theory” derives from the Greek theoreo (“to see”), and the name later given for this era of reason and scientific triumph — the Age of Enlightenment — is a visual metaphor of light overcoming shadows.

For the Scientific Revolution, optics offered both instrumentation and insights, both machines and metaphors. As Claire Webb has argued, telescopes mediated parallel revolutions in science and philosophy from the 16th century to the present day, and they continue to reform our understanding of the universe and our sense of being in the world.

Marshall McLuhan argued years ago that the cultural, political and scientific revolutions that took place in the West were spurred not only by optics — the microscope and telescope — but also by an equally important technology: the printing press. Invented in the mid-15th century, the printing press with movable type enabled the rapid spread of print media and the standardized and automated cultural production of knowledge. As McLuhan noted, the printing press changed human behaviors and cultural habits, and also our perceptual patterns. Oral traditions receded; visual culture became ascendant. As the written word permeated our lifeworld, the importance of the spoken word — and the use of hearing as a method for exploring and understanding the world — dwindled.

Listening To The World

Senses that are not cultivated tend to atrophy. Ethnographers have long commented on the seeming deafness of Western peoples — raised in a culture obsessed with vision and the written word, whose sense of hearing is less developed than peoples of other cultures.

The Brazilian anthropologist Rafael José de Menezes Bastos wrote a few years ago about traveling with the Kamayurá, an Indigenous community in the Amazon rainforest. One evening, crossing Lake Ipavu in northeast Brazil by canoe, his friend Ekwa stopped rowing and went silent. When Bastos asked why they had stopped, Ekwa responded: “Can’t you hear the fish singing?” Bastos heard nothing. “Back in the village,” he wrote later, “I concluded that Ekwa had experienced some kind of hallucination, a fit of poetic inspiration or holy ecstasy, the whole event just a flight of imagination.” 

Years later, Bastos went to a bioacoustics workshop organized by scientists at the University of Santa Catarina, where he heard the sound of fish songs. Suddenly, Bastos realized, Ekwa “appeared more like a diligent ichthyologist than an inspired poet, a victim of hallucination or holy rapture.” Bastos’ ears had been closed, but Ekwa’s ears were open. Even Kamayurá children, Bastos wrote, were able to hear the sounds of planes and boats arriving well before he could.

In the Kamayurá language, the word anup (“to hear”) also evokes “to comprehend,” in a manner superior to the word tsak (“to see”), which evokes “to understand” only in a narrow analytic sense. Over-reliance on vision alone is associated with anti-social behavior, but hearing well is associated with holistic, integrated forms of perception and knowledge.

“By privileging vision over hearing, we stopped learning how to listen.”

Good listeners among the Kamayurá are often those with virtuosity in music and the verbal arts. A special accolade — maraka´ùp (“master of music”) — is given to those who, like Ekwa, are able to sense, remember, reproduce and relate the sounds of other beings. This ability arises from both innate talent and intensive training over a lifetime.

The Kamayurá’s interpretive abilities are equal to and even in some cases surpass Western scientific understanding: They are able to draw precise and accurate inferences of which species or objects make certain noises, as well as where and why. This is practical and relational knowledge because the Kamayurá are in constant dialogue with the nonhuman life around them. They move through the forest listening and conversing with animals, plants and spirits, telling them that they mean no harm and asking in return to remain unharmed. Bastos argues that this acoustic-musical “world listening” — which combines the precision of Western science with practices of spiritual attunement — is a form of sacred ecology.

The ancestors of modern Westerners may once have possessed this ability, but we ceased to cultivate it many generations ago. By privileging vision over hearing, we stopped learning how to listen. But in the past decade, new generations of scientists have begun exploring the neglected world of sound — from the cosmos to individual cells — leading to some remarkable discoveries that, like the microscopists in centuries past, reveal hidden and unsuspected worlds.

Sounds Of The Cosmos

For millennia, the movements of the celestial bodies in the heavens above, from shining planets to the faintest of stars, have provided practical guidance to navigators and spiritual direction to oracles. But some signals created by the stars are invisible to the naked human eye.

Astrophysicists have developed techniques to convert data from light signals into digital audio, using pitch, duration and other properties of sound. Wanda Díaz-Merced, a blind astronomer, sonifies plasma patterns in the upper reaches of the Earth’s atmosphere and invented new methods to detect subtle signals in the presence of visual noise.

But the conversion of data into acoustic signals — called sonification — is now being used by scientists who are not vision-impaired because listening to the stars helps detect patterns that may be missed by visual representations. Sonification has led to several surprising discoveries, including the presence of lightning on Saturn and the ubiquity of micrometeoroids smashing into spacecraft.

“Listening to the stars helps detect patterns that may be missed by visual representations.”

Even the origins of the universe can be sonified. Shortly after the Big Bang, giant waves traveled through the dense, hot matter that comprised the early universe. These waves compressed (and thus heated) certain regions while stretching (and thus cooling) others. The resulting temperature variations can still be detected today as temperature variations in the cosmic microwave background radiation — like echoes of the original shockwaves of the Big Bang.

The cosmic microwave background radiation (also called “relic radiation”) occurs at a frequency that we cannot detect with our eyes. (Humans can typically perceive light from approximately 380 to 750 nanometers in wavelength, but the electromagnetic spectrum extends well beyond this range. Cosmic background radiation is everywhere around us, but invisible to the naked eye.) When John Cramer, an astrophysicist at the University of Washington, converted these signals into sound, they resounded with a loud hum that he described as “rather like a large jet plane flying 100 feet over your house.”

In addition to scrutinizing graphs and charts, scientists are once again listening to the music of the stars. The ancients would be pleased.

Hearing The Tree Of Life

The science of bioacoustics similarly opens up a novel window into worlds of sound unheard by human ears. Across our planet, sound is a primordial form of conveying complex ecological information; a vast range of species — even those without ears — are remarkably sensitive to sound.

In the past two decades, scientists and amateurs have begun using digital recorders to record the sounds of life from the Arctic to the Amazon. Much of what they record is inaudible to humans, above or below our hearing range. The science of digital bioacoustics can thus be compared to the early days of optics: Digital recorders, like microscopes or telescopes, extend the human sense of hearing beyond the perceptual limits of our bodies.

The painstaking work of bio-acousticians has revealed that many more species than we previously realized actually make noise. Moreover, we are realizing that many species that are vocally active are capable of conveying complex information through acoustic communication.

A good example is elephant infrasound. Elephants emit powerful, very low sound waves (well below human hearing range) that travel long distances through both forest and savannah and help herds and families coordinate behavior across vast expanses of terrain. Even more surprising are the specific signals and sounds that elephants convey for certain situations, which scientists have compiled into a dictionary with thousands of sounds. African elephants, for example, have a specific signal for honeybees. They are keen listeners too, able to distinguish between humans from tribes that hunt them and those that don’t merely by listening to their voices and discerning their dialects.

“Sound is a primordial form of conveying complex ecological information; a vast range of species — even those without ears — are remarkably sensitive to sound.”

Even some voiceless creatures, it turns out, are exquisitely attuned to sound. Steve Simpson, a biologist at the University of Exeter, has demonstrated that coral larvae are able to differentiate between the sounds of healthy and degraded reefs (they prefer the former), and even between a random reef and their home reef (they prefer the latter). Yossi Yovel, a neuro-ecologist at the University of Tel Aviv, has found that flowers will respond to the sound of buzzing bees by flooding themselves with more and sweeter nectar within minutes. Even animals in the soil make noises: an underground Twitter.

The world is alive with nature’s sounds, most of which are undetectable by the naked human ear. But by combining digital bioacoustics with artificial intelligence, scientists have begun unveiling the extent of interspecies communication across the Tree of Life. Yovel’s team has trained an AI algorithm to detect minute changes in the high ultrasound emitted by plants; in one experiment with tobacco plants, the algorithm was able to detect whether the plants were dehydrated, healthy or wounded simply by listening. These high ultrasonic frequencies are well above human hearing range but audible to insects.

Driven by the realization that nature is full of interspecies communication, interdisciplinary research teams — computer scientists, biologists, linguists — are now attempting to use AI and digital bioacoustics to develop tools for translation. This raises profound ethical issues. When do we have the right to gather nonhuman acoustic data? Who should have access to that data? Hunters? Fishers? And what are the risks or potential harms, given the biases inevitably embedded in AI algorithms?

Equally, this raises profound philosophical questions. Does the existence of complex communication in other species challenge the supposed uniqueness of language as a solely human capacity? And do these discoveries create new possibilities for enabling a political voice for nonhumans, who might influence environmental governance or, more broadly, human conduct?

Sonifying Cells

If sound is universal and primordial in the cosmos, life might somehow be attuned to acoustic communication, and living phenomena — from diseases to brain activity to symbiotic relationships — could be translated and understood through acoustics.

Scientists are sonifying data in innovative ways — for example, biophysicists have used sonification as a teaching tool about protein folding. In medicine, neuroscientists are using sound to hone diagnoses of Alzheimer’s, and sonification has been used to assist doctors in detecting barely visible details of subtle yet important variations in heart rate and electrocardiogram signals. Sonification techniques have also been used by doctors looking for irregularities in brain waves to detect signals of cognitive impairment that might otherwise go undetected, and to find early signs of epileptic seizures in children.

The benefits go beyond the ability to detect small signs that might otherwise be overlooked. Our field of vision is limited to approximately 180 degrees, and the eyes can close. But we can hear sounds from 360 degrees, and the ears are always listening. Visual data requires the attentive gaze of a healthcare provider. But audio data can be projected, calling for rapid attention. Sonification is both subtle and insistently immediate.

In addition to its diagnostic utility, sound is important for our health in another important way: It is regenerative. For example, music benefits older adults with dementia, a well-documented phenomenon that illustrates how our neurons respond to songs and rhythms long after memory and cognition fade. And the mammalian responsiveness to sound goes well beyond mere relaxation. A team of medical scientists based in St. Louis recently completed a study where they targeted low-frequency sound waves at specific parts of the brains of mice, inducing them to a hibernation-like state. They also recreated the same effect in rats — animals that don’t normally hibernate.

Since most mammals naturally hibernate, and since most — including humans — share similar brain structures, does this mean that humans might possess a latent capacity for hibernation? Perhaps one day, sound could be a useful tool to keep space voyagers in a state of suspended animation as they travel between worlds.

“Sonic data and technologies expand our perceptual and conceptual horizons.”

The Sonics Revolution

Centuries ago, before the invention of the microscope, no one had any idea that there was a microbial world full of strange life. Before the invention of the telescope, humanity was able to perceive only the smallest glimpses of celestial bodies. No one could foresee the discovery of DNA and the ability to manipulate the code of life, nor the development of space travel and the ability to visualize distant regions of deep space. Optics decentered humanity within the solar system, within the cosmos.

Sonics is the optics of the 21st century. Like the microscope, sonic technologies function like a scientific prosthetic — as it extends our sense of hearing, it expands our perceptual and conceptual horizons. We are encountering new soundscapes throughout the cosmos and across the Tree of Life, learning about the universality of acoustic meaning-making and the primordial sensitivity of living organisms to sound. Sonics decenters humanity within the Tree of Life, while connecting us more closely to the cosmos.

In the 16th and 17th centuries, the early days of optics, the term “revolution” was used to refer to celestial bodies revolving, implying cyclical movements rather than linear progress, a restoration of alignment rather than a break with the past. The notion of revolution as a violent rupture and rejection of the preceding scientific, political and economic order came to prominence only in the 18th century.

Sonics is a revolution in the newer sense, but it might also be a revolution in the older sense too, a circling back to something we had once known but have since largely ignored or forgotten: the primordial importance of sound to life, to the universe, to our bodies. The world is sounding all around us. Choosing to listen, and developing new data sonification techniques enabled by advanced technologies, will enable us to sense the cosmos, the Earth and our own selves anew.