What is it to live without clocks, daylight, or simple communication with people outside your immediate surroundings? In the name of science, fifteen people descended into a cave in southwest France for 40 days to find out. The experiment, which was part of a wider project called Deep Time, witnessed fifteen people live and explore a cave where there was no natural light, the temperature was 10C, and the relative humidity 100 percent.

The participants had no way to tell time and no ability to communicate with the external world. As expected, all fifteen people in the cave completely lost their sense of time. “And here we are! We just left after 40 days … For us it was a real surprise,” said Christian Clot, the director of the project. “In our heads, we had walked into the cave 30 days ago.”

A big crowd awaited the volunteers as they left their “isolation cave” in the Lombrives. “It was like pressing pause,” said Marina Lançon, one of seven women to take part in the experiment.

Although Lançon was happy to feel the wind and hear birdsongs again, she said that she did not feel any rush to do anything and even wished she could have stayed in the cave a few days longer. She also said that she will avoid looking at her smartphone for a few more days in order to avoid a “too brutal’ return to real life.

As reported in The Guardian, scientists monitored the 15 team members’ sleep patterns, social interactions, and behavioral reactions via sensors. One sensor was a tiny thermometer inside a capsule that participants swallowed like a pill in order to measure body temperature and transmit data to a computer until it was expelled naturally. The participants tried counting days not by hours, but in sleep cycles, and simply followed their biological clocks to know when to wake up, go to sleep, and eat.

“It’s really interesting to observe how this group synchronizes themselves,” Clot said while recording in the cave. He also mentioned that working together on projects and organizing tasks without being able to set a time to meet was a particulate challenge. Living in a cave for 40 days may not sound all too appealing, but in fact, two-thirds of the participants expressed a desire to remain underground a little longer to finish group projects started during their stay.

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