In a groundbreaking experiment in 1962, French geologist Michel Siffre dared to live like a ‘timeless’ caveman, submerging himself 130 meters beneath a glacier in the Ligurian Alps for over two months. His aim? To uncover the secrets of the human body's internal clock without the interruptions of natural light or time cues. The results of his remarkable journey would lay the foundation for the field of human chronobiology, revolutionizing our understanding of time perception, sleep, and even the psychology of space travel.

Living Underground: A Radical Experiment

Siffre, then just 23 years old, embarked on this radical self-experiment inspired by the psychological challenges faced by astronauts during the space race. “This idea became the idea of my life,” he recalled years later. His methods were deceptively simple; he abandoned his watch, blocked out sunlight, and instructed his team above ground to withhold any information regarding time. Alone with only basic camping supplies and a flashlight, he set out to measure the impact of complete isolation on his sense of time.

The Body's Internal Clock

Unbeknownst to him at the time, Siffre's experiment would yield profound insights. He discovered that humans have an inherent internal clock that can operate independently of external stimuli. According to Siffre, “Without knowing it, I had created the field of human chronobiology.” This revelation suggested that our understanding of time is not only biological but also deeply psychological.

To explore this phenomenon further, Siffre challenged himself with psychological tests during his stay. In one notable test, he attempted to count from 1 to 120, believing he had counted for two minutes, only to find that five minutes had elapsed. This distortion illustrated how our psychological perception of time can become warped without external reference points. “My psychological time had compressed by a factor of two,” he noted, revealing the surreal effects of isolation on mental processes.

The Merging of Days

Siffre recounted how the absence of natural light and routine caused his days to blend into “one long day.” As time passed, he struggled to remember what he had done a mere days prior. His work highlighted not just distortions in time perception but significant implications for memory and cognition, leading to a greater understanding of how isolation can impact our mental faculties.

Impressively, Siffre returned to such experiments multiple times after his initial venture. In the 1970s, he spent six months underground in Texas, and by 2000, during his last foray, he famously miscalculated the turn of the millennium, thinking it was still New Year’s Eve four days after the celebration had occurred.

Shifting Sleep Cycles

Siffre's investigations revealed that, when deprived of time cues, individuals could adapt to a 48-hour sleep-wake cycle, essentially doubling the typical circadian rhythm. This discovery offers critical insights for researchers examining human performance in extreme environments, such as space missions or deep-sea explorations.

A Lasting Legacy

Michel Siffre passed away on August 24, 2024, leaving behind a legacy that profoundly influences various fields, from sleep science and space medicine to cognitive psychology. His pioneering self-experiments have shaped our understanding of human performance in isolation, revealing that time is more than a mere measurement; it is a construct of our consciousness.

In the decades since his groundbreaking research, scientists continue to explore the intricacies of time perception and its implications for human psychology—an endeavor that undoubtedly owes a great deal to Siffre’s daring journey into the depths of the earth, where he discovered not just the passage of time, but the very essence of what it means to be human.