One Man's Quest To Prove Humans Prefer a 48 Hour Sleep Cycle

In 1962, a 23 year old geologist named Michel Siffre entered a dark cave with the intention of living there for two weeks completely cut off. He had no watch or light and could only make a call when he awoke to let his team monitor his sleep cycle. Siffre soon lost track of time and began to settle into a 48 hour cycle, staying awake for 36 hours and sleeping for 12. When he emerged, he thought he had been down there for less than half the time that had actually passed. Afterwards, he wondered whether there was such a thing as a natural body clock.

His life is the subject of an engrossing article from writer Alastair Williams, and it's a movie-worthy story of an obsessed scientist and an all-consuming journey to answer a fundamental question about our body clocks that nearly drove him to madness.

Was he right? In the 90s, research showed that the 48 hour day was likely a product of his artificial lighting at the time, and that humans seem to have “an inbuilt rhythm that, like the rest of the natural world, almost exactly matches the Earth’s rotation.” Still, it's an interesting question, and one that we only tried to answer because one man back in the 1960s decided to dedicate his life to asking it.