A French scientist emerged from a cave after 63 days living in total isolation away from natural light on September 14, 1962.
Michel Siffre had nothing more than a four-volt lamp for illumination in his two months underground.
Though a trained geologist, his time underground had nothing to do with rocks.
Michel Siffre was unable to walk easily when he emerged from his cave. (Gamma-Rapho via Getty Images)
Instead, he was conducting an experiment on how the body clock operates without sunlight.
And quickly, he stopped operating on the same sleep cycle as everyone on the surface.
His waking hours began to extend to 25 hours.
Consequently, his two months underground felt to him more like one.
“After one or two days, you don’t remember what you have done a day or two before,” he told Cabinet magazine.
“The only things that change are when you wake up and when you go to bed.
“Besides that, it’s entirely black. It’s like one long day.”
Michel Siffre survived two months alone in a cave with no natural light. (Gamma-Rapho via Getty Images)
His research was funded in part by the French Army, who wanted to know if they could keep soldiers awake longer.
NASA also contributed funding, because they wanted to know if removing people from the Earth’s solar cycle would harm their sleep patterns.
When he came out, Siffre had to wear special sunglasses to cope with what felt like blinding sunlight to him.
He also had to be helped to move around as he was so unused to walking.
He later supervised other cave experiments.
In 1964, Siffre planned a rescue mission after hearing silence on another cave-man’s microphone for an alarming amount of time.
But his health was revealed by a snore. The subject had been asleep for 34 hours.
Michel Siffre returned to a cave in 1999 where he spent two months underground. (Sygma via Getty Images)
Siffre would return to a cave for three months in 1999, spending the turn of the millennium underground.
To mark the New Year’s, he brought champagne and foie gras to celebrate by himself.
But by then, he had lost track of the days, actually celebrating on what turned out to be January 4.