The Remarkable Underground Voyages of Michel Siffre

On life without time and company

“I was reading Plato's Symposium aloud. It was a textbook and it was wonderful to talk aloud. But I was like that... there's a photo that I think is the most representative of my life there, of the breakdown I had. This photo was really very hard.” Credit: M. Siffre.

We climbed, he going first and I behind,
until though some small aperture I saw
the lovely things the skies above us bear.
Now we came out, and once more saw the stars.

― Dante Alighieri, The Divine Comedy

One July day in 1962, Michel Siffre descended into the underworld. Ostensibly he did this for science: his goal was to learn how the body and mind reacted to being stripped of time, to being placed in an abyss beyond the familiar rhythms of the day and night, of the changing seasons, and of the ticking of a clock.

He thus went to live by himself in a cave. He left his watch behind, climbed deep into an Alpine chasm, and pitched a tent next to an underground glacier. For the next two months he remained there, in a place where he had no view of the outside world, no marker of the passage of time, and no light beyond that which he lit himself.

His only connection with others was a single phone line strung out to the surface a hundred metres above. But this he used sparingly, making only a brief call whenever he awakened, ate, or prepared to sleep. That was a necessary evil: a support crew on the surface monitored the calls, and used them to track how his cycles of sleep were drifting deep underground.

The cave was, he later recounted, a perilous place. Not only did the glacier make it freezing cold, but it was also wet, and pools of freezing water stretched across its surface. His feet were constantly soaked, and from time to time rocks would fall from the cave roof, smashing with a sudden intensity into the floor and leaving him shaking with fear.

More insidiously, however, Siffre’s perception of time began to alter. With no day or night he slept whenever he felt tired, and ate whenever he felt hungry. But the seconds, he later said, began to stretch out, and long periods of time could pass in what seemed to him like a mere instant.

This was more than an illusion. Every time he called the surface he counted out the seconds, up to a hundred and twenty. The task should have taken two minutes to complete, but before long Siffre was taking more than five minutes to finish. When the experiment was over, and his team told him that his two month stay was up, he was shocked. By his own reckoning, kept in a handwritten journal, he had counted only thirty-five days in the cave.

It was the first indication of what later underground experiments would find over and over again. When isolated and stripped of the natural rhythms of time, the body adopts a free-running cycle of its own. Time begins to stretch and bend, and perceptions of how much of it has passed become increasingly unreliable.

By the time Siffre emerged blinking from his cave he was, of course, famous. News about his underground venture had spread around the world, making headlines across Europe and America. On his exit from the cave, curious journalists gathered around the chasm, filming as he was hauled out into the light.

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A year before Siffre ventured into the cave, Alan Shepard had become the first American to fly in space. It was a short flight, one that lasted no more than fifteen minutes. But NASA, then newly founded, was already looking further. Kennedy had set them the goal of reaching the Moon, and others were dreaming of more distant destinations — of Venus, of Mars, and beyond.

These proposed flights into space would be profoundly unlike anything experienced by past travellers. Once beyond Earth orbit, astronauts lose the steady rhythm of day and night, of sunrise and sunset, and can thus only track the passing of time via the digital tick of a clock. They experience intense isolation. Voyagers to Mars, if they ever set off, will be separated from the rest of humanity by a light-speed delay of more than eight minutes.

How, NASA wondered, would people cope with such long periods alone and adrift in space? Would they go mad? Or could they find more efficient ways to sleep and eat when freed from the restrictions of the Earth’s rhythms? The question intrigued Siffre, and he saw obvious parallels with his life deep underground.

At the time, nobody was quite sure if humans had an innate sense of time. As early as 1729 botanists had found a daily rhythm in plants that persisted even without cues from the Sun, and others had found similar 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.

After Siffre emerged from the cave, NASA, keen to find out, agreed to fund the analysis of his results. So too did the French military, who were interested in finding better ways to manage the life of sailors stationed on nuclear submarines for months on end. If the body had an innate clock, they reasoned, then perhaps it could be manipulated with drugs, and if so, perhaps sailors could adopt a longer working cycle deep under the waves.

To Siffre, at least, his experiment did reveal the presence of this internal clock. Even without any way to measure time, his sleep cycle had fallen into a steady rhythm. It did not last exactly twenty-four hours — he found it drifted closer to twenty-five — but it did seem to show that humans had some innate sense of time even when stripped of all reference points.

It is dark. You need a light. And if your light goes out, you’re dead. In the Middle Ages, caves were the place where demons lived. But at the same time, caves are a place of hope. We go into them to find minerals and treasures, and it’s one of the last places where it is still possible to have adventures and make new discoveries.

~ Michel Siffre

Others followed Siffre into the timeless underworld. 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 distorts 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.

But not everyone settled into the regular pattern of sleep and wake that Siffre had found in his first journey into the caves. Some slept for hours — one man was asleep for more than thirty hours, and only awoke as his crew, fearing he had died, prepared to descend into the cave. Others were awake for days, sometimes 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 placed themselves in horrific conditions, locked in a place of absolute darkness and silence. Under such extreme isolation, it is perhaps no surprise that madness was a constant danger.

Many of those who went underground reported hallucinations, loss of vision, and depression. They suffered, too, when they returned to the surface. After months in darkness, their eyes could not cope with the glare of the Sun. And having lost any semblance of night and day, they struggled to regain the normal patterns of life. One — a woman named Véronique Le Guen — committed suicide shortly after she emerged from her four month stay underground.

Life alone in the timeless void, it became inescapably clear, was something akin to torture.

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Still, Siffre was convinced his experiments had been worth the torment. They had proved, he thought, that humans had an internal body clock, a sense of time that persisted even in eternal darkness. But in most people the clock seemed to run slow. Over time, deprived of natural cues like sunlight, the body clock gradually lengthened, until it often reached a forty-eight-hour cycle of sleeping and waking.

That meant thirty-six hours awake, followed by twelve hours of sleep. Dreaming, too, increased: the more 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 controlled and 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?

Sadly, later studies would conclude that many of Siffre’s discoveries about time and sleep were wrong. One of the biggest flaws was their setting: isolated caves are not ideal places to study sleep, and his subjects were often under immense psychological stress. Separating the effects of timelessness from the devastating impact of extreme isolation was too hard, and too unethical to properly repeat.

A second problem came down to artificial lighting. True, Siffre’s cave dwellers had been denied natural light. But deep in the caves, they had control over their own electrical lighting. The more tired they became, the more they tended to light brighter lights — and every time they did this they prolonged the onset of sleep. Over time this gradually shifted their rhythms further and further from the true twenty-four-hour day.

Other studies, performed using controlled lighting, found no real evidence that the forty-eight-hour cycle existed. Instead they all found an inbuilt circadian rhythm that, like the rest of the natural world, almost exactly matches the Earth’s rotation.

These discoveries, however, did not come until the 1990s, and by 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, when he himself had descended into the cave.

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Thus it was, ten years after his first stay underground, that Michel Siffre decided it was time to go back. His failure to achieve the fabled forty-eight-hour cycle bothered him, and he reasoned that a longer study might reveal that he too could reach such extremes.

But he also had something to prove: people were talking about him, he worried, saying that he was afraid to go back into the darkness. He wanted to show that he was not scared of the dark, and not fearful of returning to the caves. Six months underground would prove that, he was sure, and perhaps he might at least get some good science out of the experience.

So Michel returned, heading to Midnight Cave in Texas. His team spent months preparing the site, carefully relaying equipment one forty metres down a shaft. The cave was magnificent, he later wrote, but filled with powdery ash mixed with bat droppings. Whenever he walked he disturbed the unpleasant mixture, throwing up dust that he feared would destroy his lungs.

Life in the cave was harder than he had remembered or 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. At one point he broke off contact for days, and all but abandoned the experiment.

Later, overwhelmed by feelings of guilt and loneliness, he resumed contact and restarted the experiment. But out of desperation he sought to befriend a mouse living in the cave, his fear of isolation overcoming his worries about disease.

When those efforts failed — he killed the mouse by mistake — desolation and despair threatened to consume 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. The nightmare was over.

During his six-month stay in Midnight Cave, it turned out, Siffre did at least briefly achieve a forty-eight-hour day. But until he came out he no idea he had reached his goal. Whether he slept for two hours or eighteen, it seemed to make little difference amidst the solitude of the caves.

Even 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 , one no doubt worsened by the vast debts incurred by running the experiment , and he suffered from poor eyesight and memory.

This, then, 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 break that oath, briefly and 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 and verdant forests. And when he escaped his self-inflicted torture, that is where he went. The next years of his life were spent in Guatemala; hunting not the secrets of time, but of the lost civilizations of the past.