15 People Lived 40 Days in a Sunless Cave Without Clocks to Study Time

Fifteen people emerged from a cave in France on Saturday, after spending 40 days living in its depths without sunlight, clocks, or contact with the outside world. 

The volunteers were part of an experiment, called “Deep Time,” which was designed to probe the human brain’s conception of time in an environment without chronological bearings, and to study the group’s overall adaptation to life in isolation.

In the absence of natural cues to regulate circadian sleep patterns, many of the participants lost their sense of time as the weeks rolled by in Lombrives cave, an enormous and well-explored network of subterranean passages in southwest France that served as the site of the experiment.   

The “Deeptimers” were alerted that the experiment was coming to an end on Friday, so that they could prepare for their exit the following day. Led by project director Christian Clot, an explorer and founder of a nonprofit research group called the Human Adaptation Institute, the participants were greeted with applause from team members when they re-emerged into the sunlight at 10:30am local time on April 24. 

"And here we are! We just left after 40 days," said Clot, according to the Associated Press. “For us, it was a real surprise...in our heads, we had walked into the cave 30 days ago."

The experiment’s volunteers ranged in age from 27 to 50, and included seven women and eight men, including Clot. The team had to pass mental and physical evaluations before they were selected for the Deep Time project, and each person had assigned tasks during the 40-day period, which began on March 14. Food and equipment were supplied for the participants, but their water was harvested onsite from the cave. 

Some volunteers had professional experience that was relevant for a cave expedition, including medical specialists and outdoor exploration experts, but the group also included a jeweler, a business intelligence analyst, and a public affairs specialist for a defense industry company. The idea behind the selection of the participants, according to the project website, was to produce “a varied group” that corresponded to “daily life.”

Though the Deeptimers were not in contact with the outside world, their sleep patterns, social behavior, and vitals were monitored by a team of researchers through sensors used for the duration of the experiment. The volunteers even ingested tiny thermometers inside capsules that transmitted body temperatures inside the digestive system, until they were excreted. 

The medical tests continued even after their exit, as the participants had MRIs conducted in Paris less than 24 hours after leaving the cave, according to a post on the institute’s Facebook page. The broad conclusions of all these observations will take time to assess, but many of the participants shared their initial thoughts about their time spent in the cave.

"It was like pressing pause," said Marina Lançon, an outdoor guide, AP reported. Lançon added that the feeling of sunlight and sounds of birdsong were refreshing, but that she could have easily spent more time in the cave.

Deep Time was conducted with support from research centers across France and Switzerland, and is one of many projects that have investigated the behavioral and medical effects of long-term social isolation in extreme environments. Clot thinks these experiments can help anticipate the challenges of long-term submarine missions, deep space and interplanetary exploration, and adaptation in the case of “severe climate disturbances,” according to the project website.

“Our future as humans on this planet will evolve,” Clot said. “We must learn to better understand how our brains are capable of finding new solutions, whatever the situation.”