In 1972 Michel Siffre entered a cave chamber 440 feet below the ground, alone and isolated from any natural light & clocks. For six months he removed from all time references which led to his discovery of a human time warp and slowing down time. He found that without time cues, several people including himself adjusted to a 48-hour rather than a 24-hour cycle.
In 1962, a French scientist named Michel Siffre lived alone in a cave for two months, with no clock, calendar, or sunlight. He only slept and ate when he felt like it, to see how living without time would affect the body’s natural rhythms. Over the next ten years, he set up more than twelve similar experiments. In 1972, he went back into a cave in Texas for six months. His work helped start the study of human biological clocks.
Michel Siffre was a trained geologist. In 1961, he discovered an underground glacier in the Alps and initially planned to spend fifteen days studying it. However, he later decided that two months would be more useful to understand it better. During this time, he wanted to live like an animal, without a watch, in the dark, and without knowing what time it was.
Instead of just studying caves, he ended up studying time. He created a scientific method by putting a team at the entrance of the cave to call him when he woke up, ate, and went to sleep. His team was not allowed to contact him, so he wouldn’t know the outside time. Through this experiment, he unintentionally developed the field of human chronobiology. He noted that, similar to rats, which were known to have an internal biological clock since 1922, humans also have a body clock.
Michel Siffre describes his living conditions during the experiment as difficult, with poor equipment and a cramped camp. His feet were often wet, and his body temperature dropped to 34°C (93°F). To pass the time, he read, wrote, and conducted research in the cave, while also thinking about his future.
Each time he called the surface, he performed two tests. First, he measured his pulse. Second, he did a psychological test where he counted from 1 to 120 at a rate of one number per second. Through this test, they made an important discovery: it took him five minutes to count to 120, meaning he experienced five real minutes as if they were only two.
Michel Siffre describes his living conditions during the experiment as difficult, with poor equipment and a cramped camp. His feet were often wet, and his body temperature dropped to 34°C (93°F). To pass the time, he read, wrote, and conducted research in the cave, while also… pic.twitter.com/uFatDku1IT
— Vicky Verma (@Unexplained2020) October 21, 2024
Siffre described experiencing a significant change in his perception of time during his experiment. He went into the cave on July 16 and planned to finish on September 14. However, when his team told him that September 14 had arrived, he mistakenly thought it was only August 20. He felt like he still had another month left in the cave. This showed that his sense of psychological time had compressed, making two months feel like only one.
I’ve been investigating for forty years. I believe that when you are surrounded by night—the cave was completely dark, with just a light bulb—your memory does not capture the time. You forget. After one or two days, you don’t remember what you have done a day or two before. The only things that change are when you wake up and when you go to bed. Besides that, it’s entirely black. It’s like one long day. (Source)
In the interview with journalist Joshua Foer, Michel Siffre shared his experience of being underground without any artificial way to measure time. He described his sleep as “perfect” because his body naturally decided when to sleep and when to eat. This is significant because he found that his sleep/wake cycle was not the typical twenty-four hours that most people experience, but rather around twenty-four hours and thirty minutes.
The key finding was that he had an internal clock that operated independently of the natural day/night cycle. In later experiments with other people in the caves, they also showed longer cycles than twenty-four hours. Many of them even had cycles lasting up to forty-eight hours, which included thirty-six hours of being active followed by twelve to fourteen hours of sleep. This discovery led to significant funding from the French army, who wanted to explore how soldiers could increase their waking activity.
After Michel Siffre’s initial experiment, he conducted more studies by placing a man in a cave for four months and a woman for three months. In 1966, another man stayed underground for six months, followed by two more experiments that lasted four months each. During these studies, they analyzed sleep stages, including rapid eye movement (REM) sleep, which is when dreaming occurs, and slow-wave sleep.
They discovered a link between how long a person stays awake and how much they dream the next night. Specifically, for every ten extra minutes a person is active during the day, they get about one extra minute of REM sleep. Additionally, they found that the more a person dreams, the shorter their reaction time during the next waking phase. After this discovery, the French army sought drugs that could artificially increase the amount of dreaming, hoping to create longer days of thirty hours or more for soldiers.
Ten years after his first time-isolation experiment, Michel Siffre went back underground himself, this time in Midnight Cave near Del Rio, Texas, and spent 205 days.
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Michel Siffre explains that he returned to an underground environment in 1972 after his first time-isolation experiment for two main reasons. First, he wanted to study how aging affects psychological time, planning to conduct an experiment every ten to fifteen years to see if his perception of time changed. Second, he noticed that everyone else he sent underground developed a forty-eight-hour sleep/wake cycle, while he did not. He decided to stay underground for six months to see if he could align with that cycle.
When asked why people fall into this forty-eight-hour cycle, Siffre stated that he did not have a theory about it; he only observed facts. He acknowledged the existence of this phenomenon but admitted that no one really understands why such a significant desynchronization in the sleep-wake cycle occurs. He also mentioned that, since the end of the Cold War, it became harder to secure funding for further research, leaving it primarily to mathematicians and physiologists to explore this area.
In this part of the interview, Michel Siffre discusses how significant events in 1962, like the Cuban Missile Crisis and Yuri Gagarin’s journey into space, influenced people’s views about living underground. He mentions that during the Cold War, there was a lot of interest in bomb shelters, and there was little understanding of how the human sleep cycle worked in outer space.
At that time, both the U.S. and Russia were competing to send humans into space, and France was starting its nuclear submarine program. The French military did not know how to manage the sleep cycles of submariners effectively. This lack of knowledge is likely why Siffre received substantial financial support for his research. NASA analyzed his first experiment from 1962 and funded him to conduct more detailed mathematical analysis.
What is it about the underground that both attracts us and scares us?
Michel Siffre said: 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 celebrated the new millennium 2,970 feet underground in Clamouse Cave with foie gras and champagne, but he was three-and-a-half days late and also missed his sixty-first birthday.
He took almost thirty years to go underground again because, when he came out of Midnight Cave in 1972, he found himself $100,000 in debt. He had underestimated the costs of bringing his experiments from France to Texas, which forced him to leave the field of chronobiology.
In 1999, he decided to return to a cave in southern France for two months to study the effects of aging on the circadian cycle. He was inspired by John Glenn, who went back into space at the age of seventy-seven.
Michel Siffre celebrated the new millennium 2,970 feet underground in Clamouse Cave with foie gras and champagne, but he was three-and-a-half days late and also missed his sixty-first birthday.
He took almost thirty years to go underground again because, when he came out of… pic.twitter.com/FfQic9XpHd
— Vicky Verma (@Unexplained2020) October 21, 2024
Did you ever succeed in catching a forty-eight-hour cycle?
Yes. In the 1972 experience in Texas, there were two periods where I caught the forty-eight-hour cycle—but not regularly. I would have thirty-six hours of continuous wakefulness, followed by twelve hours of sleep. I couldn’t tell the difference between these long days and the days that lasted just twenty-four hours. I studied the diary I kept in the cave, looking cycle by cycle, but there was no evidence that I perceived those days any differently. Sometimes I would sleep two hours or eighteen hours, and I couldn’t tell the difference. That is an experience I think we all can appreciate. It’s the problem of psychological time. It’s the problem of humans. What is time? We don’t know.
When he finally emerged from the cave on September 5th, on Day 205, he found himself a changed man. His eyesight had worsened, he had developed a chronic squint, and some psychological troubles bothered him. He concluded that, even though he was able to develop a 28-hour day without the constraints of time, future space travelers would have serious trouble adapting to long-distance travel in confined areas.
Siffre died on Aug. 25, 2024, at the age of 85 in Nice. He was the leading figure in the field of chronobiology, the study of how the human body understands time. Previous scientists had speculated that, contrary to the prevailing idea at the time, our internal clocks are independent of the solar cycle, even as we usually adjust to its influence. Through decades of experiments beginning with that 1962 descent, he proved it.
