A new Discovery Channel show, Darkness, sends three strangers into a cave or abandoned mineshaft, giving them six days to find each other and a way out — with no light, at all, at any time. For Esquire, Patrick Blanchfield takes a deep look at the premise, the participants, and the crew, who also have to spend the week in the dark. Leaving aside the cold, and the hallucinations, and the high potential for physical injury, there’s the issue of sleep: how do you sleep normally with no light or social cues? You don’t.

Brandon’s experience gets at another challenge of surviving underground, in the dark or otherwise: what happens to your sense of time. Brandon fell asleep twice, and only for thirty or forty minutes at a go. But when he awoke, he was certain that he’d been asleep for two eight-to-ten-hour stretches. When the safety crew came to retrieve him, Brandon was adamant he’d been underground for two full days. In reality, he’d only been below for twelve hours.

Scientists have documented this phenomenon extensively. Researchers who have undertaken simultaneous but separate sojourns into caves for extended periods will emerge with radically different estimates of how long they’ve been below—different from one another by weeks, and different from the calendar by yet more. Absent cues from the aboveground natural world or data from clocks or phones, our conscious perception of time can get weird, fast.

But that’s nothing compared to what goes on inside our bodies. When people talk about your “circadian rhythm,” they’re actually referring to dozens of different physiological processes, cycles governing everything from your heart rate to your breathing to your immune system to your digestion to your body temperature. These sub-systems operate on their own timelines, but are largely kept in sync with each other as long as the body follows a roughly 24-hour cycle that tracks changes in ambient light and various social cues. In situations of irregular light and darkness, everything goes out of whack within a couple of days. It is not uncommon for test subjects living underground to start sleeping and waking in forty-eight-hour cycles, or to experience bizarre changes in their behavior or sense of self. Michel Siffre, a European scientist, spent months at a time in half-lit caves in the Alps and Texas as part of research he carried out for NASA. Siffre not only got hypothermia, but also went off the rails, in one instance desperately trying to befriend a mouse for companionship but instead accidentally crushing it and falling into near-suicidal despair. When asked about the impact of those experiments on his mind and body, Siffre, who’s now in his seventies, describes it as “hell” and speaks of feeling like “a semi-detached marionette.”

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