Fascinating piece by Kathryn Schulz about chronobiology, the science of internal body clocks. Here is just a snippet:
Roenneberg cites experiments in which subjects were confined to bunkers and deprived of all temporal cues. While most subjects maintained a day-night periodicity of roughly 24 hours (circa one day: hence, “circadian”), some people’s cycle doubled, to about 48 hours. Amazingly, they were oblivious to the change. They continued to eat three meals a “day,” and their sense of smaller time units doubled, too. Asked to estimate an hour, they estimated two instead.