Time may feel a lot slower when you're in a dark cave, experiment finds

Fifteen French volunteers have spent 40 days in a cave with no sunlight or any connection to the outside world in an experiment that sought to better understand our perception of time, and how people adapt to drastic changes in living conditions. 

The volunteers, aged between 27 and 50, made up from biologists to primary school teachers, exited the cave on April 22, 2021, visibly tired, but smiling. They all wore sunglasses to allow their eyes to adjust to sunlight again. 

"And here we are! We just left after 40 days," said Christian Clot, founder of Human Adaptation Institute and the director of the experiment called “Deep Time.”

“For us, it was a real surprise...in our heads, we had walked into the cave 30 days ago." 

At least one volunteer said the time inside the cave felt like 23 days, as the group recorded their individual biological clocks based on their sleep cycles.

"Losing time is the greatest disorientation there is," said the project website. 

"And it is this aspect that the mission Deep Time wants to understand better. Because to this day, we do not know how our cognitive system understands and manages this indefinite continuity, this environment where the succession of events and phenomena takes place, even beyond this variable that we could call the biological clock in chronobiology."

Living in under 10 degrees Celsius and relative humidity, which stood at 100%, the Deep Timers were responsible for generating electricity with pedal bikes and drawing water from a well 45 metres below the earth. 

The researchers, meanwhile, were able to track the group’s body temperatures and monitor their behaviour thanks to a thermometer swallowed by pill and through other sensors. Over the 40 days, the experiment followed 50 scientific experimental protocols, from genetics to olfactory perception. 

With no way to reference time inside a cave, organising tasks together had been a particular challenge, Clot told AP. 

"It's really interesting to observe how this group synchronises themselves," he said earlier in a recording from inside the cave.

Such an experiment, which saw the removal of references to time and space, as well as studying the brain and genetics, is a first. That said, in 1962, Michel Siffre, a 23 year-old speleologist studying caves, conducted a similar experiment when he went into a cave, alone, for two months. The experiment was conducted in an attempt to study caves, but later, Siffre said he changed his attention to time. Unwittingly, he had created the field of human chronobiology, discovering that humans have a body clock like lower mammals, such as bats, whales and mice.

The findings of the Deep Time study could be useful in other fields, such as defence, and trips into space, as well as educating us on human survival when faced with confinement scenarios, especially in the case of crises such as climatic disturbances, the experiment’s website read. It pointed out that what the world is experiencing during the Covid-19 pandemic is in fact a real-time test of these scenarios.

Less than twenty-four hours after leaving the cave, the volunteers were taken to a Paris hospital to conduct MRIs in order to compare data collected before they entered.

Research centres across France and Switzerland supported the experiment that cost 1.2 million-euro ($1.9 million).