These volunteers spent 40 days in a cave with no sunlight or way to tell time : The participants had no access to clocks, phones or communication devices. They had no idea what time, or even what day it was, and no way to find out what was happening in the outside world.
Their only technology were cameras and devices used to track their movements and measure their sleep patterns.
15 French volunteers leave cave after 40 days without daylight or clocks: Fifteen people have emerged from a cave in south-west France after 40 days underground in an experiment to see how the absence of clocks, daylight and external communications would affect their sense of time.
Deep Time Project from Human Adaptation Institute
