When Time Slips: From a French Cave to Future Mars missions

Author: Mary Upritchard

InnovaSpace Admin Director & Space Fan!

When scrolling through the endless nonsense recently that appears on Facebook, I came across a rare post of interest detailing the remarkable work of French geologist Michel Siffre, who died a year ago this Sunday (24 August 2024), aged 85 years. In 1972, Siffre conducted an extraordinary isolation experiment in which he lived alone for 180 days in a cave 440 feet underground. He had no sunlight, no clock, and no contact with any other person, having only basic supplies, a sleeping bag, and instruments for recording his activities and observations.
His aim was to study how the human mind and body behave when deprived of all natural time cues. The results of this work, now more than 50 years old, continue to be relevant for research into human endurance, circadian rhythms, and the psychological effects of extreme isolation. They are also especially relevant for human space exploration, with space agencies considering the realities of sending people to live for months, or even years, in sealed environments on the Moon or Mars.

Michel Siffre in Midnight Cave, 1972, during his six-month underground isolation experiment. Image credit: Michel Siffre / CNRS Archives

Initially, Siffre relied on hunger and fatigue to regulate his days, but within weeks it was observed that his perception of time changed. He often believed a day had passed when nearly two had gone by. His body abandoned the 24-hour cycle, adopting a 36-hour waking period followed by 12 hours of sleep.
Scientists monitoring the experiment saw this as evidence that humans have an internal clock that can operate independently of the Sun. The changes, however, came with cognitive and psychological costs, like hallucinations, difficulty speaking, memory lapses, and a need to create artificial social interaction, such as talking to insects or to himself. By the time the experiment ended, Siffre believed only 151 days had passed, rather than the actual 180 days.

Translating from Cave Walls to Space Frontiers: Lessons for Life Beyond Earth

Image credit: author

Life Without a Sunrise - Astronauts aboard the International Space Station (ISS) see 16 sunrises every Earth day. This constant cycling of light and dark is managed by strict schedules, carefully calibrated lighting systems, and oversight by mission control, ensuring that body clocks remain aligned with a 24-hour rhythm. Without such controls, circadian rhythms can rapidly drift, affecting alertness, decision-making, and even physical health.

Mars missions bring a different set of problems. Just getting there will take about nine months, with no sunlight or natural day–night cycle during the trip, and messages to and from Earth taking up to 22 minutes each way. Once on Mars, the day is slightly longer than on Earth - 24 hours & 39 minutes - which doesn’t sound like much, but if a crew are living inside a sealed base with no view of sunrise or sunset, they will rely completely on artificial lighting to keep body clocks in sync. If lighting systems fail or if their routine breaks down, Siffre’s work suggests that their sense of time could quickly become confused. That loss of time awareness could put the mission at risk, disrupt essential tasks, and even make it harder to deal with emergencies.

The Psychology of Deep Isolation - When considering long-term space missions, the focus is generally on technology, such as rockets, life-support systems and protection from radiation. Nonetheless, isolation and confinement and the psychological effects these have are equally important and can be dangerous. Siffre’s months in the cave showed how being cut off from the outside world can damage memory, disrupt mood, and distort perception.

"Desolation overwhelms me"  -  1972 Diary entry, Michel Siffre

Siffre was so overwhelmed by loneliness he attempted to befriend a mouse for companionship, an attempt that ended tragically when he accidently killed the mouse, causing him to suffer a deep sense of despair and suicidal thoughts.

NASA’s HERA (Human Exploration Research Analog) program and the European Space Agency’s Concordia Antarctica research station have explored some of these effects, but have not gone as far as the sensory deprivation that Siffre endured, i.e., no daylight, no fresh stimuli, and no sound beyond his own. The first humans on Mars are more likely to experience a psychological environment closer to Siffre’s cave, even more so than crews on the ISS, facing monotony, restricted movement, and communication delays that make real-time emotional support from Earth impossible. Without robust countermeasures like structured social interaction, planned activities, and ways to break up the routine, mental health decline could slowly build up and threaten the mission.

​Autonomy and Control - Time management in space is both a technical and social challenge. On Earth, Siffre’s experiment had a clear endpoint, and his return could be organised on schedule. On Mars, early crews will have no such guarantee, with no quick return. They may have to decide collectively whether to impose strict schedules, adopt flexible routines based on personal needs, or even invent entirely new timekeeping systems. Each choice will have its pros and cons, for example, synchronising with Earth time might ease communication and data transfer, whereas adopting Martian time could improve alignment with local environmental conditions. But considering Siffre’s research once more, it showed that creating your own time structure can be risky, having the potential to erode cognitive stability and alter social cohesion. The question of who can decide and enforce “official time” in a space settlement is also open to political and ethical debate and will need to be resolved.

​From Darkness to the Stars - Siffre called his cave stay “a slow slide into madness”. He emerged with memory loss and lingering psychological effects, yet he chose to repeat the experience under different conditions, building a valuable dataset on human adaptation to extreme environments.
Today, his work helps scientists understand how people cope, or struggle, in extreme environments. For astronauts, it’s a reminder that training must prepare them not only for technical jobs but also for the absence of natural time cues, monotony, and long periods of isolation. In the vacuum of space or under Martian skies, maintaining a stable perception of time could be as vital to survival as oxygen, clean water, and functioning life-support systems.

Michel Siffre’s dedication to his research pushed the boundaries of both science and human endurance. Few would risk their health, and even their sanity, to reveal how our minds cope with isolation and distorted time. Does it make you wonder how far you would you be willing to go in the name of discovery?