Interestingly, during the subsequent experiments I did with other research subjects, all of the people in the caves showed cycles longer than twenty-four hours. But the important thing is that we proved that there was an internal clock independent of the natural terrestrial day/night cycle. We showed that my sleep/wake cycle was not twenty-four hours, like people have on the surface on the earth, but slightly longer-about twenty-four hours and thirty minutes. My sleep was perfect! My body chose by itself when to sleep and when to eat. It might be said that you achieved perfect sleep. When you were underground, entirely isolated from any artificial measurements of time, your body slept exactly when it wanted to, and for exactly as long as it wanted to. I decided to live like an animal, without a watch, in the dark, without knowing the time. And then this idea came to me-this idea that became the idea of my life. I shall see nothing.” So, I decided to stay two months. At first, my idea was to prepare a geological expedition, and to spend about fifteen days underground studying the glacier, but a couple of months later, I said to myself, “Well, fifteen days is not enough. In 1961, we discovered an underground glacier in the Alps, about seventy kilometers from Nice. Michel Siffre: You have to understand, I was a geologist by training. What made you decide to live underground in complete isolation for sixty-three days? Joshua Foer: In 1962, you were just twenty-three years old. His work helped found the field of human chronobiology. Sleeping and eating only when his body told him to, his goal was to discover how the natural rhythms of human life would be affected by living “beyond time.” Over the next decade, Siffre organized over a dozen other underground time isolation experiments, before he himself returned to a cave in Texas in 1972 for a six-month spell. In 1962, a French speleologist named Michel Siffre spent two months living in total isolation in a subterranean cave, without access to clock, calendar, or sun.

Siff and then there was light