So, how would you like to live totally in the dark, in a cave, with no hint of the outside world? No clocks, no natural light, nothing that can give you any hint as to what’s going on. Personally, I think it would be pretty cool. I’d love to spend a month or so underground reading, and living on my own.
That’s exactly what Michel Siffre did for two months with the goal of discovering the natural rhythms of life. Eating when he felt hungry, not a breakfast, lunch or dinner, sleeping when he felt like it. The results are impressive.
He was able to attain the 48 hour cycle, being awake for 36 hours, and asleep for 12 hours, but to him, that was a single day. The way it worked was he went into a cave, set up shop with some books and stuff, and left a team of people at the entrance of the cave. He’d call them when he woke up, when he ate, and when he was gonna go to sleep. The team wrote this info down, but didn’t tell him anything. One of the more interesting things they found is that in counting from 1 to 120 at 1 digit a second, it took him five minutes, so what felt like two minutes for him, was in reality five. That’s cool.
There’s a ton more information in this interview with him, you should read it it’s really interesting.