Could You Survive an Endless Night?

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dark-nightSunrise follows sunset, and we as a species rely on the golden light of our sun to wake. Shift workers and residents north of the Arctic circle know that we can cope with a sleep and wake schedule that doesn’t quite sync up with the daylight hours.

But what if daylight hours didn’t come at all? How would humans respond?

If there was darkness with no natural light, would the way we sleep change?

Some sleep researchers have experienced these kinds of endless nights personally. To find out what they saw, we’ll need to visit some deep caves. But first, we head north.

In the Arctic Circle

The land of the midnight sun, the Arctic Circle contains parts of Canada, Greenland, Alaska, Russia, Finland, Sweden, Iceland, and Norway.

Besides being cold, the region is best known for the fact that it experiences extreme light – and extreme darkness. Between the June and December solstice, the day shrinks from one of 24 hour daylight to one of 24 hour darkness.

These long nights, ironically, don’t just mean that people sleep all day. “Midwinter Insomnia” describes the specific form of insomnia that afflicts people living in the long nights of the Arctic circle winter.

That being said, plenty of residents are able to cope. Tatiana, a teacher in the Russian village of Korzunovo, said of the darkness: “No one likes the polar nights: when it’s dark you just want to sleep all the time. But then, during the polar days, by the time you want to go to sleep the new day has begun. And, actually, you get used to it. Humans can get used to anything…”

As difficult the climate may be for the population, theirs is not an endless night. Aside from the December solstice, the sun does appear each day, at least for a short time.

Aside from that, there are other factors that would work to define the human sleep cycle. Most notable, our alarm clock. That, and other social forces (like getting to work on time), mean that life in the Arctic circle doesn’t go totally off the rails with minimal sunlight.

In order to see what happens to humans in a long, perfect night, we need to cut out all those stimuli.

In A Deep Dark Cave

Mammoth cave, Kentucky is 150 below the surface, and completely free from all light. It has no regular population, the temperature is the same all year round, and is deathly quiet. It is completely devoid of any clues that the body could use.

And it’s just where Nathaniel Kleitman spent over a month in 1938.


Kleitman, the grandfather of sleep research and co-discoverer of REM sleep, wanted to investigate the 24-hour sleep cycle. Are there internal factors that determine our sleep/wake patterns, or does the human body rely on environmental cues? To find out, he removed these cues by descending into Mammoth cave.

Along with his research partner Bruce Richardson, he attempted to adapt his body to a 28-hour day that did not correspond with the daylight hours above ground.

By measuring internal temperature curves, the two researchers were able to accurately track their bodies’ responses to the longer day.

Once their four week stay was complete, the results were out. A press release from the University of Chicago announced the findings as: “Dr. Kleitman’s temperature curve tended to remain that which prevailed during a normal twenty-four hour day, but Mr. Richardson’s curve was readjusted to the longer cycle.”

So although one of the two did adjust to the longer day, Kleitman himself did not. One theory about why this may be so is that Kleitman was older than Richardson. He had more experience with a 24-hour day – this could have made his sleep cycle more persistent than his younger counterpart.

But this experiment was only with two men – what if there were more test subjects and more time?

Into A German Bunker

Twenty years after Kleitman, the study of sleep had another hero in Jurgen Aschoff. Understandably, Aschoff was not eager to subject himself to pitch-black caves for weeks on end. Instead, he took to more regulated studies of test subjects.

The bunker used to house test subjects wasn’t just free of natural light, temperature changes, and other elements like the Kentucky cave – it was even shielded from the Earth’s electromagnetic field. With stays of up to eight weeks, the volunteers were able to turn on lights and determine their own activity levels, but they had no idea of the time outside the bunker. Some subjects were isolated, some were not.

Most participants, with no idea of the “real” time outside of the bunker, naturally moved toward a 24-hour day. After two decades of research (with many different volunteers) he was able to determine that humans in fact do have internal sleep regulators.

Of course, there were some exceptions, who assumed extreme sleep cycles such as 48 hours waking followed by 16 hours sleeping. However, even these outliers maintained the same 24 hour physiological pattern (measured through body temperature). Journals kept by the volunteers showed that they typically felt best when their sleep/wake pattern was closest to a 24 hour day – even if they didn’t know it.

Although we do have an internal regulation of our sleep cycles, it isn’t necessarily permanent. With a process dubbed entrainment, humans and other organisms can change their internal clock.

Light and dark do contribute to re-enforcing or changing our sleep cycle, but they actually have relatively minor force. Much more powerful are social cues, and these often go hidden. Meals, Aschoff found, are one of the strongest ways to establish a sleep cycle.

Along with this, Aschoff had a discovery significant enough to be called Aschoff’s Rule. The first of these states that for diurnal (that is to say, non-nocturnal or daytime active) organisms exposed to constant darkness, their active period will shrink while their sleep time grows.

Under A French Glacier

Geologist Michel Siffre never planned to live in complete isolation under a glacier in the Alps.

But, in 1962 his interest was piqued by the space race heating up in the early sixties. Hoping to contribute to an understanding of how astronauts might cope with sunless living in space, he found a cozy little glacier in the Alps. It was 375 feet down, below freezing, damp, and dark – and he stayed there alone for two months.

With no clocks and no natural light, Siffre wanted to see how his body would respond, and what would be the effect on his sleep cycle. Using one way communication, he would report his meals and sleep to his research assistance topside. Although he did not know it at the time, he would maintain a roughly 24-hour day for his time under the glacier. Like Kleitman many years earlier, and Aschoff’s test subjects, his internal clock maintained the same speed.

However, there was a strange side effect. Even though Siffre’s body maintained the 24-hour schedule, his mind lost track of time. When he finally left the cave on September 14, he estimated that the actual date was only August 20.

This wasn’t the only time Siffre spent alone in the dark. He would later spend 205 days in a Texas cave, and over two months in a French cave. The latter was done at the age of 61, and both were devoid of all natural stimulus or human contact. He would eat, sleep, and wake, only when he felt that he wanted to.


The Texas cave, and subsequent studies, showed a marked difference in sleep patterns from before. Although he kept to his standard 24-hour cycle for the first month or so, after that point his sleep cycle began to shift. He experienced “days” that ranged from 18 to 52 hours in length. His sanity and his emotional well-being also hit extremely low ebbs, reaching their nadir when he accidentally crushed a small mouse that he was attempting to befriend.

More details about Siffre can be found in this interview from Cabinet.

At Home

Today, between rapid transit across time zones, night shifts, and all-nighters, most of us have experienced a disconnect between our sleep cycle and the 24-hour day. These researchers laid the groundwork for a scientific understanding of this phenomena.

With our current knowledge of circadian rhythms, we know that the 24-hour day will persist as an internal human clock. But we also know that external stimulus can alter that clock.

In darkness with no stimulus at all, the 24-hour clock may stay the same, or it may begin to lose, gain, or otherwise shift. Luckily enough for anyone with jetlag, exposure to natural light patterns, meals, social cues, and other stimulus can eventually reset a broken sleep clock.

photo credit: StefaniaVS via photopin, Cabinet, and Wellcome Collection.

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