Volunteers spent 40 days inside a French cave believing only 30 days had passed
The Deep Time team, deep inside the Lombrives Cave in the French Pyrenees. Image Credits: @HumanAdaptation via X What conditions the volunteers actually lived through
The Deep Time team, deep inside the Lombrives Cave in the French Pyrenees. Image Credits: @HumanAdaptation via X What conditions the volunteers actually lived through How the volunteers' sense of time actually broke down Why the group's days stretched so far beyond 24 hours What researchers hoped to learn from the experiment What the experiment revealed about adapting to isolation On March 14, 2021, fifteen volunteers, seven women and eight men aged between 27 and 50, entered the Lombrives cave in the French Pyrenees to begin a 40-day experiment with no clocks, no phones, no natural light and no contact with the outside world. Known as Deep Time, the project was led by French Swiss explorer Christian Clot through his nonprofit research group, the Human Adaptation Institute, and was designed to study how the human brain tracks time and how a group adapts psychologically and physiologically to prolonged isolation. When the volunteers finally emerged into daylight on April 24, 2021, most of them believed they had spent roughly 30 days underground, having lost track of more than a week and a half of real time despite the experiment's rigorous scientific monitoring throughout.According to the project's own registration on ClinicalTrials.gov, the experiment was designed to evaluate temporal cognitive perception and collective synchronisation in an underground environment lacking any external time cues, alongside the influence of group living on circadian rhythms in a free-running situation, meaning one with no light or dark cycle to anchor the body's internal clock.
The project operated under the oversight of France's Ministry of Education, Research and Innovation.Inside the cave, temperatures held steady at around 10 degrees Celsius with 100 per cent relative humidity, and the volunteers had to draw their own water from a well roughly 45 metres beneath the surface. Three separate living spaces were set up within the cave system, one for sleeping, one for communal living and one dedicated to ongoing scientific work, including topography surveys of the cave's flora and fauna. Participants wore biometric sensors throughout the experiment and swallowed a small capsule containing a thermometer that tracked internal body temperature until it passed naturally, giving researchers continuous physiological data for the full 40 days.Without any clocks, sunlight or outside contact, the group had only one agreed rule, not to wake other members of the team, leaving each person to follow their own emerging internal rhythm rather than a shared, externally imposed schedule. According to reporting from the BBC, Clot said the group's days gradually stretched well beyond the usual 24 hours, describing a shared surprise at how far their internal sense of time had drifted from the calendar by the time the experiment ended.When the volunteers were finally told the project was ending and prepared to leave, the mismatch became clear. According to the PBS NewsHour, Clot told journalists that in the group's own minds, they had entered the cave roughly 30 days earlier rather than 40, while one team member, a maths teacher who had kept himself active by running 10 kilometre loops through the cave system each day, estimated he had only been underground for 23 days, having drifted onto a personal rhythm running as long as 40 hours in a single cycle.Sleep researchers have long understood that the human body's internal clock relies heavily on external cues, particularly natural light, to stay synchronised to a 24-hour day.
The BriefWire