I’m in the passenger seat of a white van, on a dusty, potholed road somewhere along the northeastern coast of Sri Lanka. It’s 9:00 p.m. and the stars are out. “Is this the right way?” I ask our driver.

He’s a local named Bobby; that isn’t his real name, but that’s what he wants me to call him. Bobby is shaking his head and flashing me a reassuring smile. It’s the same smile he used ten minutes ago when he took a wrong turn into someone’s front yard, the same one he gave me twenty minutes before that when he brought the van to a dead stop in the middle of a two-lane freeway, stepped out into oncoming traffic, and ran across the street to ask a barefoot man on a bike for directions.

“Bobby? Is this the right way?” I repeat.

That smile.

Then Bobby suddenly pulls into a driveway. Through the headlights, it looks like we’ve just pulled into a junkyard. Twelve hours driving through steep mountain roads, jungles thick with elephants, and dusty towns filled with men in baggy slacks selling boiled peanuts and green bananas – and now this.

“Bobby?”

He pulls out of the driveway and takes a left. This road is narrower and bumpier. Bushes scrape the doors. The eyes of unknown animals glow from copses of coconut palms. A dog barks. Bats the size of rats flutter and swoop inches from the windshield.

Minutes later, we come to a stop in a barren sandlot. To the right is a creepy-looking, three-story pink-concrete building. A single, bare light bulb shines over a white plastic table on the patio, giving the scene an Edward Hopper feel. Bobby exhales, pulls the key from the ignition, and smiles. We’ve arrived at our destination, he says: the Pigeon Island View Guesthouse.

Of the twenty or so sperm whale scientists in the field, none dive, film, or interact with their subjects. Schnöller finds this inconceivable. “How do you study sperm whale behavior without seeing them behave, without seeing them communicate?”

That evening, after days of air travel from five different points of the globe, the whale search party has gathered and we are all sitting together around the patio table. On one side sits the expedition leader, Fabrice Schnöller, and Guy Gazzo, a 74-year-old freediving legend, both from Reunion Island, a French outpost located 400 miles east of Madagascar in the Indian Ocean. Across the table is South Africa national-record holding freediver, Hanli Prinsloo, and her aquatic he-man boyfriend, a world-champion swimmer from Los Angeles named Peter Marshall. Belgian photographer, Jean-Marie Ghislain, sits next to Prinsloo. Ghislain tells the group that he has just returned from a trip in Botswana to swim with crocodiles. The trip ended after the first day when a team member had his arm eaten off.

Thirty years ago to the week an American film crew came to this spot – Trincomalee, Sri Lanka — and captured the first footage of sperm whales in their natural habitat. The resulting film, Whales Weep Not, narrated by Jason Robards, became an international sensation and helped spark the Save the Whales movement.

Schnöller and his crew hope to have a similar impact by capturing the first 3-D footage of sperm whales and human-and-whale freediving interactions which Schnöller will use an upcoming documentary. We'll also be recording audio data for a group of researchers in France who are trying to decipher the sperm whale click language.

But for any of this to work we’ll first need to find some whales.

Schnöller, who is 45 years old and wears an uncombed swatch of short gray hair and oversize multicolored shorts, first swam with sperm whales in 2007. He was sailing with a friend from his home in Reunion to neighboring Mauritius, when a pod approached the boat. Schnöller grabbed a mask, snorkel, and fins, and jumped in. Within a half hour the pod surrounded him. Then they oriented their bodies vertically, like obelisks, and stared up with wide eyes. They began echolocating his body; Schnöller could feel their echolocation vocalizations, called clicks, penetrate his flesh and vibrate through his bones, his chest cavity. The whales stayed with him for two hours.

Six months after the encounter, Schnöller sold his lumber store and dedicated his life to trying to understand these animals. He built his own A/V equipment to record sperm whale behavior and communication. He enlisted some of the foremost marine scientists to help him crack their “hidden language.”

In the five years since he began, Schnöller and his team — none of whom have had any formal research experience or even hold scientific degrees — have collected the largest database of sperm whale behavior and vocalizations in history.

What's given them such intimate and immediate access is that they are the only researchers in the field willing to swim with whales. More specifically, they are the only researchers freediving to -40 feet and below, then swimming in whales' deep-sea turf.

“Jane Goodall didn’t study apes from a plane,” said Schnöller. “And so you can’t expect to study the ocean and its animals from a classroom. You’ve got to get in there. You’ve got to get wet.” Schnöller’s renegade band believes that the only way to crack the sperm whale language code, and to truly understand these animals, is by diving with them face-to-face.

This balls-to-the-wall approach puts traditional ocean scientists at a disadvantage. No university or institution would permit its employees to motor miles out to sea in a beat-up boat off the coast of a developing country to swim with sperm whales, which can grow up to 125,000 pounds and 60 feet in length and are the largest predators on Earth. And, freediving isn’t a course offered with most ocean-based PhD’s. Few students would want to take the course if it were. Freediving requires months to years of training to master. And if all the training is successful, it would only bring researchers within chomping distance of the four dozen seven-inch-long teeth that line the sperm whale mouth.

Not getting crushed, drowned, or eaten by sperm whales is only one of the challenges of studying them. Another is actually finding the animals. Sperm whales migrate from the north and south poles towards the warmer waters along the equator every summer. If you're lucky enough to see a pod, chances are you’ll never get close enough to dive with them. Schnöller predicts he sees sperm whales about 1 percent of the time he’s at sea looking for them; he’ll dive with them about 1 percent of the time he sees them. In other words, this is hard work with few rewards. It’s made even harder by the fact that most countries with coastlines prohibit swimming with sperm whales.

In late 2012, Schnöller heard that huge pods of sperm whales were congregating off the coast off Trincomalee, a Podunk town along the northeast coast of Sri Lanka. In fact, the whales were regulars in this spot. They've come each spring to hunt, socialize, and mate in the Trincomalee Canyon, an eight-thousand-foot-deep chasm that stretches twenty-five miles across the Indian Ocean, from the northern tip of the country into the Trincomalee harbor. They've come here each spring from around March through August for as long as anyone can remember, and probably for millions of years before that.

Best of all, researching sperm whales in these waters was easy — there are no permits required, no authorities to evade, no cruise ships, no recreational swimmers or divers, no whale-watching industry to speak of. Over the course of a few months in 2012 and 2013, Schnöller shook loose enough funding to send him and a team of expert freedivers to the Trincomalee Canyon for a ten-day expedition in March 2013. He asked if I wanted to come along.

Our first two days treading the Trincomalee Canyon are a disaster. We spend them in two tiny, shadeless fishing boats juddering around the ocean without seeing any whales. The film crew’s cameraman gets seasick the first day and refuses to go back out. Without a cameraman, and still without any usable footage, the documentary director threatens to pull the plug on the documentary.

On the evening of the second day, I meet Schnöller on the second-story patio. He’s sitting alone, haloed in mosquitoes. The blue fluorescent beam of a headlamp shines down on a table filled with half-assembled underwater-camera casings. Behind him, a waxing moon hangs low over a tinseled sea.

“This is very hard work, you see,” he says, looking up as I take a seat at the table. He’s wearing an American flag headband and knockoff Facebook sandals that he picked up at a junk store on the way here, and he looks as ridiculous as that description makes him sound. “Ocean research takes patience, lots of patience, persistence, and is very physically exhausting.”

Schnöller grew up in the west African nation of Gabon, the son of a former French army lieutenant who worked for then dictator Omar Bongo. The family’s house was located beneath a canopy of mango trees at the shoreline of an unpopulated beach, which was where Schnöller spent much of his youth. He told me earlier how he remembered watching crocodiles from a nearby river crawl up the front porch and eat food from the dog bowl. Sometimes while the family was eating dinner, giant mambas would slide in through wooden planks in the roof and drop down on the dining-room table. Schnöller’s father kept a shotgun close by, and after a few years, the roof was peppered with holes.

On weekends, Schnöller would sail along Gabon’s wild coast and make camp on unexplored islands. He learned how to navigate through the ocean’s many moods, keep cool in crises, and improvise his way out of trouble. He learned to be patient.

“There are no fast results in this research,” he says. “That’s why so few people bother doing it.”

Actually, he corrects himself, nobody is doing it.

Of the twenty or so sperm whale scientists in the field, none dive, film, or interact with their subjects. Schnöller finds this inconceivable. “How do you study sperm whale behavior without seeing them behave, without seeing them communicate?” He’s convinced that to understand sperm whales, one must first understand their communication, and to understand their communication, one needs to understand their language, which he believes is transmitted through clicks.

The idea that sperm whales and other cetaceans (dolphins, belugas, orcas, etc) share some form of sophisticated communication is not a New Age theory, and it's not as nuts as it sounds.

At 17 pounds, the sperm whale has brains that are five times the size of ours; it's the largest brain ever to have know to have existed on Earth. The sperm whale's neocortex, which governs higher-level functions in humans such as conscious thought, future planning, and language, is estimated to be about six times larger than ours. Sperm whales also have spindle cells, the long and highly developed brain structures that neurologists have long associated with speech and feelings of compassion, love, suffering, and intuition — those things that make humans human. Sperm whales not only have spindle cells, but they had them in far greater concentration than humans. Furthermore, scientific evidence suggest that they evolved them more than 15 million years before us. In the realm of brain evolution, 15 million years is a very long time.

Sperm whales are the loudest animals on earth. Their vocalizations are loud enough to be heard several hundred miles away, and possibly around the globe. At their maximum level of 236 decibels, these clicks are louder than two thousand pounds of TNT exploding two hundred feet away from you, and much louder than the space shuttle taking off from two hundred and fifty feet away. Sperm whale clicks could not only blow out human eardrums from hundreds of feet away, but vibrate a human body to pieces. The extraordinary power of clicks lets whales use them to perceive an intimately detailed view of their environment from great distances. They can detect a ten-inch-long squid at a distance of more than a thousand feet and a human from more than a mile away. Sperm whales’ echolocation is the most precise and powerful form of biosonar ever discovered.

Not only are sperm whale vocalizations extremely loud; they are also incredibly organized. They sound unremarkable to the human ear — something like the tack-tack-tack of a few dozen typewriters — but when slowed down and viewed as a sound wave on a spectrogram, clicks, which range in length from 24 o 72 milliseconds (thousands of a second), reveal an incredibly complex collection of shorter clicks woven within them. Inside one click is a series of smaller clicks, inside those smaller clicks yet even smaller clicks, and so on, each unfolding like a Russian nesting doll.

Sperm whales transmit these clicks at very specific and distinct frequencies, and can replicate them down to the exact millisecond and frequency, over and over again. They can control the millisecond-long intervals inside the clicks and reorganize them into different structures, in the same way a composer might revise a scale of notes in a piano concerto. But sperm whales can make elaborate revisions to their click patterns then play them back in the space of a few thousands of a second.

“These patterns are very structured; this is not random,” says Schnöller, taking a sip of beer. The only reason sperm whales would have such incredibly complex vocalizations, Schnöller suggests, is if they were using them in some form of communication.

Schnöller isn’t alone. Most marine biologists believe that sperm whales are in fact communicating through their clicks. They just have no idea what they’re saying. Schnöller hopes to be the first.

Sperm whale echolocation, even from miles beneath the ocean’s surface, is strong enough to vibrate five feet of wood and make an audible clicking sound. It sounds like a signal from another world, which, in a way, is precisely what it is. I get chills listening to it.

“When you think about it, human language is very inefficient, it is very prone to errors,” Schnöller says. Humans use phonemes—basic units of sound, like kah, puh, ah, tee—to create words, sentences, and, ultimately, meaning. (English has about forty-two phonemes, which speakers shuffle around to create tens of thousands of words.) While we can usually convey phonemes clearly enough for others to understand them, we can never fully replicate them the same way each time we speak. The frequency, volume, and clarity of the voice shifts constantly, so that the same word uttered twice in a row by the same person will usually sound discernibly different, and will always show clear differences when viewed on a computer. Comprehension in human language is based on proximity: If you enunciate clearly enough, another speaker of the same language will understand you; if you bungle too many vowels and consonants, or even pronunciation (think of French or a tonal Asian language), then communication is lost.

Schnöller’s research suggests that sperm whales don’t have this problem. If they’re using these clicks as a form of communication, he believes, it would be less like human language and more like fax-machine transmissions, which work by sending out microsecond-length tones across a phone line to a receiving machine, which processes those tones into words and pictures. (Perhaps it’s no coincidence that a pod of socializing sperm whales sounds a lot like a fax transmission.)

Human language is analogue; sperm whale language may be digital.

“Why do they have such huge brains, why are these patterns so consistent and perfectly organized, if they aren’t some kind of communication?” Schnöller asks rhetorically. He mentions that sperm whales have more brain mass and brain cells controlling language than humans do. “I know, I know, this is all just theory, but still, when you think about it, it just doesn’t make sense otherwise.”

To illustrate his point, Schnöller relates an encounter he had the previous year with a pod of sperm whales. The pod whales, both adults and their young, were hanging out in the water, clicking and socializing, when Schnöller approached them with a camera attached to a bodysurfing board. A calf swam over and faced Schnöller, then took the camera in its mouth. A group of adults immediately surrounded the calf and showered it with clicks. Seconds later, the calf let the camera go, then backed up and retreated behind the adults without ever looking at them. To Schnöller, the young whale looked ashamed. “It got the message not to mess with us.” He laughs. “That’s when I knew, they had to be talking to it. There’s just no other way.”

Schnöller says he’s also witnessed, on numerous occasions, two sperm whales clicking back and forth to each other as if they were having a conversation. He’s seen other whales pass clicks and then suddenly move in the same direction. He’s watched a whale bend its head in exaggerated motions to face one whale head-on and pass one pattern of clicks, and then bend in another direction to face another whale and pass a completely different pattern. To Schnöller, it all looked like they were talking.

But neither Schnöller nor anyone else will be translating the cetacean language anytime soon. It’s too complicated, and both resources and personnel are too scarce to study it closely. The DareWin team has come here to collect data in the hope of simply proving that sperm whales use clicks as some form of communication. They’ll record as much sperm whale socializing as they can, then correlate coda clicks with specific behaviors. The crazy-looking pod at Schnöller’s feet, called a SeaX Sense 4-D, uses a underwater-camera housing with twelve minicameras and four hydrophones to document the sperm whale interactions in high-definition audio and video, in all directions at once.

Nobody has ever recorded sperm whale interactions and behaviors with such sensitive equipment before, because no such equipment had existed. And even if it had, academic and institutional scientists couldn’t get in the water to use it because none freedives with whales. Schnöller and his crew are allowed such intimate access to whales because they approach them in their natural, most unthreatening forms, by freediving with them. The whales don’t scare off, they don’t swim away, and they don’t attack. They become curious. Often, the whales welcome him and other freedivers into their pods and try to communicate with them.

At seven in the morning on the third day, the boat captains arrive and lead us back to our hired beat-up “research vessels — two decades-old pangas with wooden planks for seats.”

I’ll be on a boat with Hanli Prinsloo, Peter Marshall, and Jean-Marie Ghislain. The plan is for the two boats to head out together, several miles off the coast, to a spot in Trincomalee Canyon where the seafloor drops off to a depth of more than six thousand feet. From there, we’ll split up and look for whales. Should someone on either boat spot any, he’ll use a mobile phone to alert the other boat. We’ll then trail the whales, wait for them to slow down or stop, and then get in the water.

We pack up, squeeze in, and set off south toward the horizon, our rickety craft riding low in the water. Hours later, we're tweny miles off the coast, floating in a dead-calm sea. Still, no whales.

“There were just so many out here last year,” Prinsloo says, who had travelled here last year and had a half-dozen whale encounters. She’s curled up in a sheet wet with seawater and sweat, leaning against Peter Marshall. Both of them are wearing T-shirts around their faces, so only the lenses of their sunglasses peep through. “I don’t know,” Prinsloo laments. “I don’t know what happened.”

Ghislain, the photographer who told us the unfortunate crocodile tale earlier in the week, wipes his sweaty palms against his T-shirt. He emits an exaggerated sigh, takes a sip of water, and turns to stare into the open ocean. A minute becomes an hour; an hour becomes two. I check my dive watch: the temperature gauge reads 106. Even my fingers are sunburned.

The notion of all of us trying to arrange a peaceful encounter with whales is bit ironic, given the way humankind has treated them for centuries.

According to legend, in 1712, an American ship captained by Christopher Hussey was hunting right whales off the southern coast of Nantucket Island when a gale suddenly blew the vessel dozens of miles south, beyond sight of land, to a barren stretch of deep water in the middle of the Atlantic Ocean. The crew struggled to regain control of ship and were readying the mast to tack back to shore when they noticed columns of mist shooting up at odd angles from the water’s surface. Then they heard heavy, heaving exhalations. They had floated into a pod of whales. Hussey ordered the men to draw lances and harpoons and stab the whale closest to the ship. They killed it, tied it to the side of the boat, fitted the mast, and sailed back to Nantucket, then dropped the whale’s body on a south-facing beach.

This was no right whale. Hussey knew that the mouths of right whales are filled with baleen, a hairlike substance used in filtering out krill and small fish. The whale he had just caught had enormous teeth, several inches long, and a single nostril on top of its head. The bones of its flippers looked eerily like those of a human hand. Hussey and his crew cut open the whale’s head, and hundreds of gallons of thick, straw-colored oil oozed out. The oil must be sperm, they thought (wrongly); this strange whale must be carrying its “seed” within its oversize head. Hussey named it spermaceti (Greek sperma, “seed”; Latin cetus, “whale”). The English version of the name took hold: sperm whale.

From that point forward, the sperm whale was screwed.

By the mid-1700s, whale ships had flocked to Nantucket to join a thriving industry. Sperm whale oil, the straw-colored seed taken from the whale’s head, turned out to be an efficient and clean-burning fuel for everything from streetlamps to lighthouses. In its congealed form, it made top-quality candles, cosmetics, machine lubricants, and waterproofing agents. The Revolutionary War was fueled by sperm whale oil.

By the 1830s, more than 350 ships and 10,000 sailors were hunting sperm whales. Twenty years later, those numbers would double. Nantucket was processing more than five thousand sperm whale corpses a year and reaping upwards of twelve million gallons of oil. (A single whale could yield five hundred or more gallons of spermaceti; oil from boiled blubber could produce about twice that amount.)

But hunting the world’s largest predator didn’t come without dangers.

Whalers in the eighteenth and nineteenth centuries were attacked regularly. The most famous incident occurred in 1820. The Nantucket whale ship Essex was off the coast of South America, its crew hunting whales, when they were rammed twice by a charging bull. The ship was lost. A crew of twenty men escaped in smaller boats and drifted off into the open ocean.

Nine weeks later, still drifting, the crew was close to starvation. Following maritime custom, the men drew lots to see who would be eaten. The captain’s cousin, a seventeen-year-old named Owen Coffin, was chosen. Coffin put his head on the side of the boat; another man pulled the trigger of a gun. “He was soon dispatched,” wrote the captain, “and nothing of him left.”

Ninety-five days later, the boat was rescued. There were two survivors: the captain and the man who had pulled the trigger. The harrowing tale served as the basis for Herman Melville’s novel Moby-Dick and, more recently, Nathaniel Philbrick’s nonfiction bestseller In the Heart of the Sea.

As sperm whale stocks decreased in the ocean near Nantucket, and whalers had to search farther away, the cost of oil increased. Meanwhile, a Canadian geologist named Abraham Gesner invented a method of distilling kerosene from petroleum. This process produced a substance close to whale oil in quality, but much cheaper. In the 1860s, the whale-oil industry collapsed.

The discovery of petroleum sounds like a death knell for whaling, but ultimately, this new cheap fuel would hasten the sperm whale’s destruction.

In the 1920s, new diesel-powered ships could process whale bodies so quickly and easily that whaling become profitable again. Sperm whale oil became a primary ingredient in brake fluid, glue, and lubricants. It was used to make soap, margarine, and lipstick and other cosmetics. The whale’s muscles and guts were mashed up and processed into pet food and tennis-racket strings. (If you own a top-quality wooden tennis racket made between 1950 and 1970, chances are it was strung with the sinew of sperm whales.)

Whaling went global. From the 1930s to 1980s, Japan alone killed 260,000 sperm whales—about 20 percent of the total population.

By the early 1970s, an estimated 60 percent of the ocean’s sperm whale population had been hunted, and the species was nearing extinction. While the world had grown proficient at hunting sperm whales, the whales themselves were a complete mystery. No one knew how they communicated or socialized; no one even knew what they ate. They had never been filmed underwater.

The documentary Whales Weep Not, which was seen by millions of people in the 1980s, offered the public the first view of sperm whales in their natural habitat. Sperm whales seemed far from the image handed down by history and literature. They were not surly brutes munching boats and men but gentle, friendly, even welcoming. The global antiwhaling movement gained support throughout the early 1980s and eventually ended all commercial whaling by 1986.

The general increase in awareness of the sperm whale’s intelligence and human-like behavior has not deterred some countries from trying to hunt them again. As of 2010, Japan, Iceland, and Norway have been pressuring the International Whaling Commission to end its thirty-year moratorium on whaling. Schnöller and other researchers predict the moratorium could be lifted as soon as 2016, and hunting of sperm whales could again become legal.

Sperm whales have the lowest reproductive rate of any mammal; females give birth to a single calf once every four to six years. The current sperm whale population is estimated at about 360,000, down from approximately 1.2 million just two hundred years ago, where it probably hovered for tens of thousands of years before whaling began. Nobody knows for sure, but many researchers fear the population has been declining once more. Continued hunting could significantly decrease the population for generations and eventually push sperm whales back toward extinction.

Back on the boat, another hour passes. And another. I check the thermometer on my dive watch and notice the temperature has climbed to 109.

Then, suddenly, an electronic chirp blasts from the back of the boat. It’s Schnöller, calling our captain’s cell phone. The DareWin team has just spotted a pod of sperm whales near the Trincomalee harbor. Schnöller says the whales have probably been there the whole time; we just hadn’t been far enough out to spot them. They’re following slowly behind the pod, waiting for an opportunity to get in.

The captain starts the motor and we shoot south.

“You see the ploofs?” says Prinsloo, pointing east at the horizon. What look like little mushroom clouds shoot from the surface at a 45-degree angle. A sperm whale has only one external nostril, which is located on the left side of its head and causes its exhales to emerge at an angle. These distinctive blows can go about twelve feet high, and on a windless and clear day, they’re visible for a mile or more.

“They look like dandelions, don’t they!” says Prinsloo. Three hundred yards to our right, another blow erupts.

“Get your mask,” she says.

Our team has agreed to put only two people in the water at any one time, to avoid scaring off the whales. I’m on the first shift. The captain turns and pulls parallel to the pod so that we’re a few hundred feet in front of them.

“You can never chase down a whale,” Prinsloo explains as she yanks off the sheet and grabs her fins. “They always need to choose to come to you.” If we move slowly in predictable motions, just in front of the whales’ path, they can easily echolocate the boat and get comfortable with our presence. If they’re disturbed by us, they’ll take a deep breath and disappear beneath the surface. We’ll never see them again.

As the boat edges closer, the whales still haven’t dived—a good sign. Prinsloo says it’s not a full pod, just a mother and calf. Another good sign. Calves get curious around freedivers, and their mothers, in Prinsloo’s experience, encourage them to investigate.

Both whales are four hundred feet from the boat when they slow down, almost to a stop. Our captain cuts the motor. Prinsloo nods to me; I pull on my fins, mask, and snorkel, and we quietly submerge.

“Take my hand,” she says. “Now, follow.” Breathing through our snorkels with our faces just below the surface, we kick out toward the whales. Today, the visibility is mediocre, about a hundred feet. We can’t see the whales in the water, but we can certainly hear them. The blows grow louder and louder. Then the clicking begins; it sounds like a playing card stuck in the moving spokes of a bicycle. The water starts vibrating.

Prinsloo tugs my arm, trying to get me to hurry up. She pops her head above the surface for a moment and stops. I stick my head up and see a mound a hundred feet in front of us, like a black sun sinking on the horizon. The clicking grows louder. The mound pops up from the surface again, then disappears. The whales leave; we don’t see them depart. But we can hear them beneath the water, their blows softening as they drift off. The waters calm, the clicks slow like a clock winding down. And they’re gone.

Prinsloo lifts her head and faces me. “Whale,” she says. I nod, smiling, take the snorkel out of my mouth, and begin to tell her how incredible the experience was. Then she shakes her head and points behind me.

“No. Whale.”

The mother and calf have returned. They’re stopped and are facing us in the other direction, a hundred and fifty feet away. The clicking starts again. It’s louder than it was before. I instinctively kick toward the whales, but Prinsloo grabs my hand.

“Don’t swim, don’t move,” she whispers. “They’re watching us.”

The clicks now sound like jackhammers on pavement. These are echolocation clicks; the whales are scanning us inside and out. We watch from the surface as they exhale. With a kick of their flukes, they lunge toward us.

“Listen,” Prinsloo says urgently. She grabs me by the shoulder and looks directly at me. “You need to set the right intention now. They can sense your intent.” I know how dangerous human-whale interactions can be, but I strive to set my fear aside, calm myself, and think good thoughts.

Behind Prinsloo, the whales approach, hissing and blowing steam like two locomotives. “Trust this moment,” she says. The whales are a hundred feet, seventy-five feet away. Prinsloo grips my hand. “Trust this moment,” she repeats, and she pulls me a few feet beneath the surface.

A hazy black mass materializes in the distance, growing larger and darker, like a drop of ink on a paper towel. Details emerge. A fin. A gaping mouth. A patch of white. An eye, sunk low on a knotted head, peers in our direction. The mother is the size of a school bus; her calf, a short bus. They look like landmasses, submerged islands. Prinsloo squeezes my hand and I squeeze back.

The whales approach us head-on. Then, thirty feet from colliding with us, pull softly to the side and languorously veer left. The rhythm of the clicks shifts; the water fills with what sounds to me like coda clicks. I believe they are identifying themselves to us. The calf floats just in front of its mother, bobs its head slightly, and stares with an unblinking eye. Its mouth is turned up at the end, like it’s smiling. The mother wears the same expression; all sperm whales do.

They keep their gaze upon us as they pass within a dozen feet of our faces, shower us with clicks, then retreat slowly back into the shadows. The coda clicks turn to echolocation clicks, then the echolocation fades, and the ocean, once again, falls silent.

Trying to save and study sperm whales is not without dangers either.

One of my companions tells me about a freediver-whale encounter in the Azores, off the west coast of Africa. After more than an hour of friendly contact and observation, a young bull approached and apparently got jealous. The bull turned and shot the freediver with clicks that left the man with hours of debilitating pain in his stomach and chest. (Long term, he suffered no ill effects.)

Schnöller told me a similar story. He was diving with sperm whales in 2011 when a curious calf approached and started bumping him with its nose. Schnöller held out his hand to push the calf back and felt a sudden shock of heat rush up his arm. The energy from the clicks coming out of the calf’s nose was strong enough to paralyze Schnöller’s hand for the next few hours. He too recovered.

Prinsloo and Ghislain had their share of close calls in Trincomalee last year. After spending hours in the water with a pod, a bull approached Ghislain at a fast clip. Prinsloo motioned to Ghislain to get out of the way. Just then, the bull turned, raised his twelve-foot fluke above the surface, spun it, and slapped it down. If Ghislain hadn’t moved, his head would have been crushed. Prinsloo and Ghislain claimed the fluke slap was possibly a playful interaction, not meant to harm. But when you’re in the water with an animal five hundred times your weight and ten times your size, such play can be fatal.

The fact is that nobody—not Prinsloo, Schnöller, or Buyle—really knows how risky these kinds of encounters are. Up until ten years ago, Schnöller told me earlier, nobody was diving with whales.

“Everyone thought it was too dangerous,” said Schnöller. Today, only a handful of divers attempt it, and most have had their share of narrow escapes.

Few people — and no other researchers — would dare risk their careers — and lives — to dive with these animals.

Luke Rendell, a sperm whale researcher at the University of St. Andrews in Scotland, told me in an e-mail that Schnöller’s research approach looked like “a pile of hokum” and was probably a “pretty flimsy scientific cover to go swimming with whales.” His team was perfectly capable of “collecting data without freediving with the animals, thank you.” To be fair, Rendell said he welcomed more researchers to the field, but he thought the DareWin’s website looked suspiciously like pseudoscience.

Schnöller brushes off the criticism as “normal scientist reaction.” And he’s finding legitimacy with partnerships with researchers at the University of Paris and other oceanographic institutions. “This will all be official, it will all be scientific,” he says.

Institutional scientists study sperm whale communication by recording clicks with a hydrophone from the deck of the boat, without ever knowing which whale is clicking and why. One of the longest-running sperm whale research programs is the Dominica Sperm Whale Project, headed by Hal Whitehead. The group studies sperm whale behavior by, among other things, following pods around and snapping photographs of flukes when the whales come up for air.

Meanwhile, last year Schnöller had a face-to-face encounter with five sperm whales that lasted three hours. The entire dive was documented in three-dimensional video and high-definition audio and is, to date, the longest and most detailed footage of sperm whales ever recorded.

Schnöller insists he’s not trying to subvert the scientific system—he wants to work within it—he is simply trying to speed up the collection of data, which, at the institutional level, happens at a glacial pace. For Schnöller, and perhaps for the whales, that pace may be too slow.

If hunters don’t eradicate sperm whales, pollution might. Since the 1920s, PCBs (polychlorinated biphenyls), carcinogenic chemicals used in the manufacture of electronics, have slowly seeped into the world’s oceans and, in some areas, reached toxic levels. For an animal to be processed as food, it must contain less than 2 parts per million of PCBs. Any animals that contains 50 ppm of PCBs must, by law, be considered toxic waste and be disposed of in an appropriate facility.

Dr. Roger Payne, an ocean conservationist, analyzed sea life for PCBs and found that orcas had about 400 parts per million of PCBs—eight times the toxic limit. He found beluga whales with 3,200 ppm of PCBs, and bottle-nosed dolphins with 6,800 ppm. All of these animals were, according to Payne, “mobile Superfund sites.” Nobody knows how much more pollution (PCBs, mercury, and other chemicals) whales and other oceanic animals can absorb before they start dying off en masse.

Payne and other researchers point to the baiji dolphin, a freshwater native of China’s Yangtze River, as a possible portent of the sperm whale’s fate. Considered one of the most intelligent of all dolphin species, the baiji dolphin has become functionally extinct due to pollution and other manmade disturbances. (At last count, there were about three baiji dolphins left.)

For Schnöller, sperm whale research isn't recreation; he doesn't spend months away from his family, using his own money, just to go “swimming with whales.” He's in a race to understand these animals before humans wipe them off from the face of the Earth.

On the fourth day, the film crew leaves. The cameraman had been violently seasick since the first day and refused to spend another ten hours motoring around in a rickety boat. The director, Emmanuel Vaughan-Lee, was exhausted.

“You never told me it would be this hard,” said Vaughan-Lee when I’d talked with him the previous night. He was scratching his bald, sunburned knees beside the patio table. I had warned him, repeatedly, but the point was moot. He told me he’d decided to cut his losses and take the next flight home to San Francisco.

They left a day too soon.

That morning, the remaining team of seven, plus the hired boat hands, cram into a single boat designed for half our number. With the motor coughing and wheezing, we head south. Hours later, we’re fifteen miles from the coast and idling over the deep water of Trincomalee Canyon again. Schnöller checks his GPS, putting us near where they saw the whales yesterday.

“Turn the motor off. I listen for them,” he says. From the bow of the boat, he grabs a sawed-off broomstick with a metal pasta strainer tied to the end. He inserts a small hydrophone into the center of the strainer and drops the whole contraption into the water, then puts on a pair of ratty headphones.

This strange device, which is wired to an amplifier, works like an antenna to home in on sperm whale clicks. By spinning the strainer around, Schnöller can determine what direction they’re coming from. Frequency and volume give him an idea of how deep the whales might be.

“They sell these to institutions for fifteen hundred euro,” he says, laughing. “I make mine from junk, and it works just as good.” Click Research, a new oceanographic manufacturing company he’s now building, will offer a version that works as well as the institutional model for only $350.

Schnöller puts the headphones over my head and hands me the broomstick. “What do you hear?” he asks. I tell him I hear static. Schnöller cups the headphones tightly over my ears. “Now listen. What do you hear?”

He takes the broomstick from my hands and spins the strainer slowly around below the surface. Through the static, I begin to hear a syncopated rhythm, like distant tribal drums. I tell Schnöller to stop moving the strainer. Everyone on the boat falls silent. The rhythm speeds up and grows higher in pitch, the patterns overlapping. What I’m hearing isn’t drums, of course, but the echolocation clicks of sperm whales hunting in the deep-water canyon miles beneath our boat.

Schnöller grabs the headphones and passes them around the boat. Everyone is entranced. A boat hand listens for a moment, then passes the headphones back to Schnöller. He gingerly walks to the bow and picks up a worn, wooden oar, then dips the paddle in the water and sticks the end of the handle in his ear.

He explains in stilted English that this was how Sri Lankan fishermen used to listen for whales hundreds of years ago. Sperm whale echolocation, even from miles beneath the ocean’s surface, is strong enough to vibrate five feet of wood and make an audible clicking sound. I give it a try and hear a faint tick-tick-tick. It sounds like a signal from another world, which, in a way, is precisely what it is. I get chills listening to it.

Schnöller puts the headphones on and spins the strainer dexterously. He tells us the whales will switch from making echolocation clicks to codas as they ascend. By listening to these subtle shifts in click patterns, and the volume and clarity of the clicks, he has taught himself to predict the location and moment that the whales will surface, with startling accuracy. I ask him: How accurate? Then he demonstrates.

“They are two kilometers that way,” he says, pointing west. “They are coming up. They will be here in two minutes.” We sit, staring westward. “Thirty seconds...” he says. “They are moving to the east, and... right...”

Exactly on cue, a pod of five whales surfaces about fifteen hundred feet from our boat, each exhaling a magnificent blow. He grins, obviously proud of himself, takes off the headphones, and throws the strainer and broomstick in the bow. I give him a high-five. The boat captain looks dumbfounded.

“Okay, now,” says Schnöller. “Who wants to go in?”

After dinner, Schnöller, Gazzo, and Ghislain are sitting around the patio table going over the day’s footage. The clips are hypnotizing. Each of us had short encounters with half a dozen different whales. Schnöller and Gazzo recorded the interactions in 3-D high-definition video. He says this is the first time some of these behaviors have been documented at such at close range. The most impressive footage, he says, comes from the dive that Guy Gazzo and I took at the beginning of the day.

A pod of about five whales turned and approached our boat. Schnöller told me to grab my mask and follow Gazzo, who was carrying the 3-D camera, into the water. At first the whales were moving away from the boat, but as we swam out farther they changed direction to meet us face to face. Some two hundred feet in front of us, a shadow expanded, then separated into two forms—two enormous whales, perhaps thirty-five feet long. One whale, a bull, came directly at us but then unexpectedly spun around so that its belly was facing us. We couldn’t see its eyes or the top of its head. As it approached, it dove just beneath our fins and let out a rapid burst of coda clicks so powerful that I could feel them in my chest and skull. The bull, still upside down, released a plume of black feces, like a smoke screen, and disappeared. The entire encounter lasted less than thirty seconds.

Schnöller boots up the video on his laptop and plays it back for me. This time, he turns up the volume on his laptop speakers.

“You hear that?” he says, then reverses the video again, and again. I listen closely. The clicks sound harsh and violent, like machine-gun fire. “That’s not a coda.” Schnöller laughs. He plays the clicks back again. “And he’s not talking to you.”

What Gazzo and I heard and felt was a creak—the echolocation click train that sperm whales use when they’re homing in on prey. The whale flipped on its back so it could process the echolocation clicks more easily in its upper jaw, much as a human might cock his head to focus on a sound. Schnöller plays the video again and again, laughing.

“He was looking at you to see if he could eat you!” he says. “Lucky for you, I guess you didn’t look too delicious.”

But this brings up a question I’ve had ever since we first boarded the boats. Why didn’t they eat us? We’re certainly easy prey.

Schnöller believes that, when the whales echolocate our bodies, they perceive that we have hair, big lungs, a large brain—a combination of characteristics they don’t see in the ocean. Perhaps they recognize that we’re fellow mammals, that we have the potential for intelligence. If this theory is correct, then sperm whales are smarter than us in one crucial way: they see the similarities between our two species more readily than we do.

He then brings up another file on his computer, a ten-second audio loop he recorded with the hydrophones earlier in the day. He clicks Play.

“Well?” He looks at me. I tell him the only thing I hear is distant echolocation clicks, which sound like random emanations from a drum machine. He orders me to put on his headphones, turns up the volume, and blasts me with what sounds like an enormous bomb exploding from miles away.

“I think this is something big,” he says. I ask him if the hydrophone just bumped into the side of the boat. “No, impossible,” he says. “This is something important. I promise you, this is big.”

Excerpted from James Nestor's DEEP: Freediving Renegade Science, and What the Ocean Tells Us About Ourselves (An Eamon Dolan Book/Houghton Mifflin Harcourt). Available Tuesday, June 24, 2014.

On June 23, 2014, Schnöller took his sperm whale research public. He launched a crowd-funding campaign, called THINK!, to raise funds for four sperm whale research expeditions over the next year. High-level contributors to the campaign will be able to join the expeditions at research points around the globe—Oman, Sri Lanka, Guadaloupe, and more—and swim face-to-face with sperm whales as Schnöller and his crew document the encounters. All proceeds go to sperm whale research, specifically, to cracking the cetacean language code.