The 25-day drift<\/p>\n
The headline result is the date. Told on 14 September that his time was up, Siffre insisted it was 20 August. His internal calendar had fallen roughly 25 days behind the real one.<\/p>\n
The short-term version was stranger still. Each time he rang the surface he ran two tests: he took his pulse, and he counted aloud from 1 to 120, aiming for one number per second. Two minutes, in other words. In a 2008 interview with Cabinet magazine<\/a> he described what happened: it took him five minutes to reach 120. He was living five real minutes as though they were two, and he never felt the seconds stretching.<\/p>\n Something in him had loosened its grip on the outside world.<\/p>\n The mechanism is not the one most readers assume. Siffre\u2019s measured sleep-wake cycle in Scarasson ran to about 24 hours and 30 minutes, slightly longer than the surface day but nowhere near long enough on its own to shed 25 days in two months. His own explanation was memory. In total darkness, with nothing changing but waking and sleeping, one cycle stopped being distinguishable from the next, and the count quietly came apart.<\/p>\n Where the 1962 stay sits in the record<\/p>\n The idea that living things run on internal cycles was not new in 1962. Plants, insects and rodents had all been shown to keep rough daily rhythms in constant conditions. Humans were the open question, and Siffre was not the only person working on it that year.<\/p>\n The first controlled demonstration of a free-running human rhythm belongs to J\u00fcrgen Aschoff and R\u00fctger Wever at the Max Planck Institute for Behavioural Physiology. Their paper \u201cSpontanperiodik des Menschen bei Ausschlu\u00df aller Zeitgeber\u201d<\/a>, spontaneous periodicity in humans with all time cues excluded, was received in January 1962 and published in Naturwissenschaften that August, weeks before Siffre came back into the daylight. Earlier still, Nathaniel Kleitman had gone into Mammoth Cave in 1938 to test whether a human sleep-wake schedule could be pushed off the 24-hour day.<\/p>\n What Siffre added was duration and freedom. Aschoff\u2019s subjects spent days or weeks in a sealed chamber on institutional terms. Siffre spent two months in a cave on a schedule nobody had set for him, and produced a date error large enough that people well outside the field paid attention. He was straightforward about the German work himself, telling Cabinet that a professor in Germany ran more than 150 isolation experiments between 1962 and 1972, all of them shorter than his own.<\/p>\n The longer stays<\/p>\n In February 1972 Siffre went down again, this time for 205 days in Midnight Cave near Del Rio, Texas, in a study backed by NASA and by French agencies including the Defence Ministry, which wanted to know how to schedule sleep for crews on long nuclear submarine patrols. It was there, and among the volunteers he sent underground through the 1960s, that the strangest result appeared: stretches of a roughly 48-hour cycle, 36 hours of continuous wakefulness followed by twelve or more hours of sleep. He caught it twice in Texas, not steadily, and by his own account he could not tell those days from ordinary ones.<\/p>\n What the finding does and does not show<\/p>\n It is worth being careful here. Siffre was one man in one cave, keeping his own notes, and the 1962 stay was in the strict sense a case study with a sample of one. It did not establish a length for the human circadian clock, and the numbers that came out of that era were later shown to be inflated, because subjects in isolation were choosing their own lighting and stretching the apparent period. Under strict light control, Charles Czeisler and colleagues reported in Science in 1999<\/a> that the intrinsic human circadian period averages 24.18 hours, not the 25 hours the cave-and-bunker generation had estimated.<\/p>\n What Scarasson did do was make the question vivid, and fundable. The line from a wet tent on a glacier to modern circadian medicine is not straight, but it is real.<\/p>\n The cost of the experiment<\/p>\n The cost to Siffre himself was not small. He came out of Scarasson disoriented and describing himself as physically and mentally depleted, his memory of individual days collapsed into one long dim stretch. Interviews collected by LADbible<\/a> capture the sameness of it: with no dawn, no dusk and no clock, he lost the ability to tell one day from another after a cycle or two. Only the endpoints, waking and going to sleep, stayed distinct.<\/p>\n His later stays were harder still, and the pattern repeated across nearly four decades. Without light, his sense of time slipped, and it slipped in the same direction every time.<\/p>\n Why it still matters<\/p>\n The practical uses that grew out of this era of work are easy to miss because they are now everywhere. Shift-work scheduling. Jet lag protocols. Light therapy for seasonal affective disorder. NASA\u2019s interest in the astronaut sleep cycle and the French Defence Ministry\u2019s interest in submariners on long patrols both trace part of their lineage to Siffre\u2019s data; by his own account, NASA analysed his 1962 numbers and paid for the mathematical work that followed.<\/p>\n There is a broader point, too, about how much of what a person experiences as time is imported from outside. The sun sets, and it is evening. A clock reads three, and the afternoon is a fact. Strip those cues away and the body keeps counting, but it counts slightly wrong, and it does not know it is counting wrong. Other animals handle darkness differently: dolphins sleep one hemisphere at a time, keeping half the brain awake to breathe. Siffre\u2019s cave was a quieter version of the same lesson. The machinery that governs when a person is awake is not the machinery most people think it is.<\/p>\n Siffre was, by most accounts, unusually clear about what he had and had not done. He described himself as a geologist who stumbled into biology. He heard the criticism, some of it from cavers worried about ecological disturbance, some of it from scientists who thought his methods flashy and undercontrolled, and mostly answered by pointing at the data. Discover Magazine\u2019s survey of extreme isolation<\/a> places him at the head of a line that now runs to hundreds of people in caves and laboratory simulations, including the Italian sociologist Maurizio Montalbini and a 27-year-old woman who spent 131 days underground in New Mexico. In each case the same drift shows up. The clock inside the skull keeps ticking. It just does not tick in step with the one on the wall.<\/p>\n His account of the darkness never changed much. It was complete, unlike anything on the surface, and it did something to memory rather than to the clock. After a day or two down there, he said, you no longer remember what you did a day or two before. The only things that change are when you wake and when you go to bed. Everything else is one long day.<\/p>\n On 14 September 1962, those thoughts were 25 days behind the surface. He came up a few days later with ski goggles over his eyes to shield them from the daylight, into a world that had moved on further than he had, and spent the next sixty years trying to work out why.<\/p>\n","protected":false},"excerpt":{"rendered":"On 16 July 1962, a 23-year-old French geologist named Michel Siffre lowered himself 130 metres into a glacier…\n","protected":false},"author":2,"featured_media":121185,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_share_on_mastodon":"0"},"categories":[16],"tags":[50],"class_list":["post-121184","post","type-post","status-publish","format-standard","has-post-thumbnail","category-alps","tag-alps"],"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ch\/117166630954391623","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/posts\/121184","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/comments?post=121184"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/posts\/121184\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/media\/121185"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/media?parent=121184"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/categories?post=121184"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ch\/wp-json\/wp\/v2\/tags?post=121184"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"glacier](\"https:\/\/www.europesays.com\/ch\/wp-content\/uploads\/2026\/08\/glacier-cave-interior.jpg\")
\nWhat the man himself said about it<\/p>\n![\"vintage](\"https:\/\/www.europesays.com\/ch\/wp-content\/uploads\/2026\/08\/vintage-field-telephone.jpg\")
<\/p>\n