In a Cold War-era bunker-turned-Airbnb situated 50 feet below ground in Arkansas, journalist Lynne Peeples conducted an experiment to better understand her internal clock. She’d always struggled with sleep — growing up in Seattle, the long, dark winters contributed to the effects of seasonal affective disorder (or SAD). From an early age, she says, she understood her circadian rhythms — the body’s measure of time that drives everything from the sleep-wake cycle to appetite — were generally disrupted.
For 10 days, she cordoned herself off from all of the signals the body uses to tell time. She deprived herself of light, from both the sun and electricity, clocks, most screens and other people. (Peeples did have some light: She set all the LED lights in the Airbnb to a dim red light, which wouldn’t impact her circadian rhythms.) She strapped herself up to devices that tracked her temperature, glucose levels, sleep, and…