“We climbed, he first and I behind, until though a small round opening ahead of us, I saw the lovely things the heavens hold, and we came out to see once more the stars.”
― Dante Alighieri, The Divine Comedy
One July day in 1962, Michel Siffre descended into the underworld. This, however, was no heroic epic, no retracing the steps of Dante or Odysseus. Indeed, the trip may have been wholly unremarkable, save for one small detail: Siffre left his watch behind, and descended with no means of measuring time.
In doing so, he entered a timeless void; an abyss that would end up shaking our knowledge of human psychology. Siffre’s voyage into the underworld became not a voyage into hell, but rather a journey into a timeless existence, a realm that few have ever dared imagine.
That, however, was what the journey became, not how it started out. Siffre, then a twenty-three year old geologist, was originally looking for ice —and a year earlier he had found some, a glacier buried deep in the Scarasson chasm. There, on the border between France and Italy, the ice had lain undisturbed for centuries, perhaps millennia.
He wanted to explore this glacier, and thought that fifteen days would be enough to do so and return to the surface. That idea was simple enough — and properly equipped, carried little risk of physical or psychological harm. But ideas, once they take root in the mind, have a way of burrowing deeper, and morphing into something greater.
Michel’s mind turned not just to the darkness of the caves, but also to a place that seems utterly unrelated: the far reaches of space. As Siffre was contemplating his subterranean voyage, the two global superpowers — the USA and USSR — were competing to conquer the heavens.
Months earlier, the Russians had sent the first cosmonaut, Yuri Gagarin, into orbit. NASA soon followed, sending Alan Shepard soaring above the atmosphere. Thoughts were already turning further afield — to the Moon, to Venus and to Mars.
How, NASA wondered, would people cope with such long periods alone and adrift in space? And not just alone — they would be without any of the familiar reference points that guide our daily lives. Without the sunrise or sunset, without a steady rhythm of night and day, without, even, a sensation that time was passing at all.
The question intrigued Siffre, and the parallels with life deep underground struck him as obvious. His trip into the caves, already extending in length, acquired a new purpose. Michel Siffre would study the human biological clock, and find out what happened when all our reference points were stripped away. And he would use himself, alone, as a test subject.
So what started as fifteen days became two months, and what began as geology became something altogether more human. And when he finally left the caves, shielding his eyes from the Sun, he was famous; perhaps the most famous man ever to emerge from isolation.
Michel descended in July 1962. He found the cave to be a cold and wet place, his tent pitched next to a freezing glacier. There was an element of danger — at times rocks would fall and smash into the cave floor, leaving him shaking with fear. His only contact with the outside world was a phone line to the surface; his only light was that he lit himself.
In the cave he had no way to measure time. He had no watch or clock, no rhythm of day and night. He would make a phone call when he awoke, to allow his support team to monitor his sleep cycle. It was a one directional call only: they could answer but never call him, never allowing him to mark time through the ring of a telephone.
Siffre stayed in the cave for two months, passing the hours by reading, writing and researching. With no night or day he slept whenever he felt tired, and ate whenever he felt hungry. Before long his perception of time started to warp — he lost contact with the true cycle of night and day, and the minutes themselves started to expand.
Every time he called the surface he counted out the seconds, up to one hundred and twenty. The task should have taken two minutes, but before long Siffre was taking more than five minutes to complete it. When his team finally told him that the two months were up, he was shocked. By his reckoning he had spent half that time — just one month — underground.
By then, of course, he was famous. News about his underground sojourn had spread around the world, making headlines across Europe and America. On his exit from the caves, film crews gathered around the tiny exit, filming as he emerged into the light.
At the time nobody was quite sure if humans had an innate sense of time. As early as 1729 botanists had found a daily cycle in plants, even without cues from the Sun, and others had found patterns in animals and insects. But no one knew if humans had the same cycle, a perception of time even in the absence of day and night.
To find out, scientists needed an experiment that stripped away all idea of time. Subjects would need to be isolated from the outside world — deprived of all clues about night and day, evening or morning. They would need to act entirely on their own instincts — to eat when they felt hunger, to sleep when they felt tired.
Siffre’s time in the cave provided exactly that. And, for him at least, it did appear that he had an inbuilt sense of time. Without any external indications of time, he naturally settled into a steady rhythm of wakefulness and tiredness. It wasn’t exactly twenty-four hours — somehow the days stretched closer to twenty-five hours in the depths of the caves. Even so it was proof, of a kind, that humans did have an inbuilt sense of time.
Others followed Siffre into the caves. In Italy, Maurizio Montalbini spent months alone in the 1980s. In America another Italian, Stefania Follini, isolated herself for sixteen weeks in New Mexico. Siffre himself went back, spending six months underground in Texas, an experience that drove him to the brink of madness, and then another two months at the age of sixty, exploring the effects of age on the body clock.
Again and again these studies showed that profound isolation distorted the impression of time. Montalbini spent 210 days underground, but felt that only 79 had passed. Follini, denied even the sound of a human voice for months, thought she had spent just eight weeks underground, half of the true amount.
Not everyone settled into the regular pattern of sleep and wake that Siffre had reported in his first journey into the caves. Some slept for hours — one man was asleep for more than thirty hours, and only awoke as scientists, fearing he was dead, prepared to descend into the cave. Others were awake for days, up to fifty hours at a stretch. Many reported settling into a forty-eight hour cycle.
It was not just the perception of time that changed. Participants were subject to horrific conditions, locked in a place of absolute darkness and silence. Under such extreme isolation, it is perhaps no surprise that both Siffre and Follini befriended small animals — seeking relief in the company of bats, rats and mice.
Madness was a constant danger. Many subjects reported hallucinations, loss of vision and depression. They suffered, too, when they returned to the surface. After months underground, their eyes could not cope with the glare of the Sun. Having lost any semblance of day and night, they struggled to regain normal patterns of life.
Life underground, it became clear, was something akin to torture. Human beings — evolved to swing in the trees and run across vast open plains — could not cope well with cramped, dark places, isolated from the rest of society.
The voyages into the underworld were not conducted for fun, nor as a feat of endurance. They were performed, ostensibly at least, for science. Much of the funding came from the military, or from NASA; people who were willing to pay for crazy and outlandish research in the hope of gaining a slight edge in war, spaceflight or torture.
Siffre, after he emerged from his Alpine cave, found support from the French government. They funded more cave expeditions, hoping to apply the results to crews of nuclear submarines immersed for months in the deep ocean. Their world, military strategists reasoned, was little different to an underground cave.
Like cave dwellers, submariners enter a realm stripped of reliable reference points. In the depths of the oceans they encounter eternal darkness buried in a profound silence. They spend months, even years, under the waves, the demands of nuclear secrecy and security isolating them from humanity.
Absent the regular twenty-four hour cycle of day and night, military leaders wondered if a more efficient pattern could be found. Could, as some studies seemed to indicate, a forty-eight hour cycle be possible, with thirty-two hours of duty and sixteen hours of sleep?
The military wanted to find out, and they handed Siffre the money to repeat his experiments. He sent more people into the caves, each spending several months alone, and analysed their sleep carefully. His findings confirmed the experiment he had done on himself.
Everyone who entered the cave lost track of time, becoming de-synchronized from the world above. People kept, more or less, a regular cycle of waking and sleeping, proving the existence of an internal body clock. But in most people the clock was not too reliable. Over time, deprived of natural cues like sunlight, the body clock gradually lengthened, until many people followed a forty-eight hour cycle instead.
That meant thirty-six hours awake, followed by twelve hours of sleep. Dreaming, too, increased — the longer people stayed awake, the more they seemed to dream when they finally slept. None of this he could explain biologically — after all his training was in geology — and studies outside the caves, in more artificial settings, did not always reach the same results.
Even so, the idea of the forty-eight hour day remained a tantalizing puzzle for years. Did it reflect an underlying, “natural” body clock that all humans possessed, deep down? Was it something that could be trained into people in more normal situations, like doctors or soldiers? Or was it a freak result, something that only emerged in extreme places?
Ten years after his first long stay underground, Michel Siffre decided it was time to go back. His failure to achieve the forty-eight hour cycle of sleeping and waking bothered him, and he reasoned that a longer study might reveal that he too could reach such extremes.
He had something to prove as well: people, he felt, were talking about him. He wanted to show that he was not scared of darkness, not afraid to return to the caves for even longer. Six months underground would demonstrate that, he was sure, and to boot he might get some good science out of the experience.
So Michel returned, heading to Midnight Cave in Texas. His team spent months preparing the cave, carefully relaying equipment from the surface to the cave floor, one hundred feet down a shaft. The cave was magnificent, he later wrote, but filled with powdery ash mixed with bat droppings. Wherever he walked he disturbed the unpleasant mixture, throwing up dust that he fretted would destroy his lungs.
His health continued to preoccupy him. He heard mice rustling in the darkness, and, fearful of disease, set out to trap them. He succeeded — much to his later regret — in killing all but one of the mice. By the time the sole survivor emerged, late in his stay, his mind was already fracturing, leaving him on the very edge of sanity.
Later studies would conclude that many of Siffre’s discoveries about time and sleep were wrong. Caves are not ideal places to study sleep — there are too many confounding variables. Separating the effects of timelessness from the devastating impact of extreme isolation was too hard, and too unethical to properly repeat.
Siffre was, after all, a geologist, not a biologist. He could not explain why some people seemed to sleep for days in the caves, while others woke after a few short hours. Neither could he explain why, after staying awake for thirty-six hours, people experienced vivid dreams, far more intense than those who slept after only a few hours.
Decades later, researchers concluded that artificial lighting was to blame. True, participants were denied natural light. But deep in the caves, they had control over their own, electric, lighting. As the circadian rhythm dipped, and the cave dwellers became more tired, they lit brighter lights — thus prolonging the onset of sleep. Over time this gradually shifted their rhythms further and further from the true twenty-four hour day.
Later studies, under more controlled lighting, found no real evidence that the forty-eight hour cycle, or thirteen hour cycle, or any other odd cycle existed. Instead they found an inbuilt rhythm that, like the rest of the natural world, almost exactly matches the Earth’s rotation.
As for submariners, the military experimented for years with an eighteen hour schedule of sleep and wake, believing it to be more efficient for onboard life. But as the evidence of the twenty-four hour cycle became overwhelming, and research on crew members showed mounting psychological problems, the US Navy eventually switched back to a twenty-four hour schedule.
These discoveries did not come until the 1990s, however, and in 1972 the question was still very much open. Siffre was convinced of the existence of the forty-eight hour day — after all, he’d seen, or thought he’d seen, it emerge in every experiment he’d done. That is, in every experiment bar one, the very first one, where he himself had descended into the cave.
Life in the cave was hard, harder, perhaps, that Siffre had imagined. After weeks alone, in profound darkness and silence, his mind began to break. He begged his crew to release him, and when they refused he began to contemplate suicide. He broke off contact for days, all but abandoning the experiment.
Later he would relent, as feelings of guilt and loneliness — no doubt amplified by his extreme stress — overwhelmed him. In desperation he sought to trap and befriend the one surviving mouse, his fear of isolation overcoming his worries about disease.
When those efforts failed — he killed the mouse by mistake — desolation and despair threatened to overwhelm him. “I am living through the nadir of my life”, he wrote in his diaries, “I am wasting my life in this stupid research!”. Nine days later, after more than twenty-five weeks underground, his crew finally called him back to the surface. His nightmare was over.
In his six months in Midnight Cave, Siffre did, at least briefly, achieve a forty-eight hour day. Until he came out, however, he had no idea that he had done so. Whether he slept for two hours or eighteen, amidst the solitude of the caves it seemed to make little difference.
After Siffre emerged, blinking in the harsh light of the Sun, his troubles continued. Like others, he struggled to readapt to the natural rhythms of life. He fell into a depression — no doubt worsened by the vast debts the experiment had accumulated — and suffered from poor eyesight and memory.
For Siffre, this was almost the end of his cave experiments. His descent into the underworld, though no retracing of Dante’s voyage through hell, proved a torment equal to anything he could have imagined. He swore never to return — and though he would, briefly, roughly thirty years later —it was another vision, one that came to him in the caves, which guided his next steps.
In the darkness he had dreamed of Central America, of searching for lost Mayan relics. He had tried to imagine the Sun, the sounds of living creatures, the green verdant forests. And when he escaped his self inflicted torture, that is where he went, spending the next years of his life in Guatemala; hunting not the secrets of the soul, but the lost civilizations of the past.
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