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French geologist and speleologist Michel Siffre (1939–2024) became world-famous for his bold experiments that transformed our understanding of human biological rhythms. He is widely regarded as one of the pioneers of chronobiology — the science that studies the body’s internal clock and its natural cycles.
Life Without Time
In 1962, Siffre launched a groundbreaking experiment: he spent 62 days in the Scarasson Cave in the French Alps, completely isolated from all external cues — no clocks, no calendar, and no sunlight. He slept and ate purely according to his own perception of time.
When he finally emerged, researchers discovered that his internal sense of time had drifted by several weeks. His subjective day was far longer than 24 hours, proving how easily human time perception can distort in isolation.
The Most Famous Mission — 205 Days Underground
Siffre’s greatest experiment took place in 1972 in Midnight Cave, Texas. This time, he pushed the limits even further, remaining underground for 205 days — commonly described as “five months below the surface.”
During this period, scientists observed something extraordinary: the human biological rhythm does not automatically follow the standard 24-hour cycle. Without daylight or external cues, Siffre’s day often stretched to nearly 48 hours — roughly 36 hours awake, followed by 12 hours of sleep.
Impact on Science and Space Exploration
Michel Siffre’s work laid the foundation for modern chronobiology. His discoveries attracted the attention of NASA, which used his data to understand how astronauts might react during long-duration space missions where natural day-night cycles are absent.
The military also studied his results to learn how sleep, fatigue, and biological rhythms affect soldiers’ performance, endurance, and reaction times.
Legacy
Michel Siffre proved that humans do not live entirely by external rhythms — we operate according to a powerful internal clock, one that can dramatically diverge from the standard 24-hour cycle under extreme conditions.
His daring experiments remain a cornerstone of chronobiological research and continue to inspire scientists studying the human mind, sleep, and resilience in isolation.
