Welcome to Spotlight.
I'm Marina Santee.
And I'm Patrick Woodward.
Spotlight uses a special English method of broadcasting.
It is easier for people to understand, no matter where in the world they live.
A group of people crowd around a large hole in a rock.
A rope hangs down into the hole.
Soon, the rope moves.
A man comes out of the hole wearing a hard hat and climbing equipment.
The man in the hard hat has his arm around another man.
The first man moves very weakly. and is only just able to climb.
He closes his eyes as he enters into the light.
It is too bright for him.
He has not seen the sun for six months.
This man's name is Michel Siff.
He is a French geologist.
A geologist is a person who studies the Earth.
But today, Sif is not studying the earth.
Instead, he is studying how people experience time.
Sif locked himself away under the ground for half a year.
He did not have clocks.
He did not have the sun to tell him when to sleep.
He slept as long as he needed.
And he stayed awake as long as he wanted.
The experiment was very bad for him.
It troubled him a lot.
But while living underground, Michel Siff discovered something very important, the internal clock.
Today's Spotlight is on Michel Siff and the internal clock.
Sif did not train to study how people experience time.
Instead, Sif went to school to be a geologist.
As a young man, he explored underground and studied different kinds of rocks.
But one day in 1962, Sif explored a cave that would change his life.
He had discovered an underground glacier.
The glacier was in the French Alps.
He was supposed to lead a trip to the mountains to study the glacier.
The trip was to take 15 days.
But Sif did not believe that this was enough time.
He decided that he would go for two months instead.
And, as an experiment, He would go without bringing a clock.
He would live in the cave alone.
His goal was to have no connection to time passing in the outside world.
He wanted to see what his body would do.
Joshua Foer is a writer.
He spoke to Michelle Seif about his experiment.
Seif said, I invented a simple scientific method.
I put a team at the opening of the cave.
I decided I would call them when I got up, when I ate, and just before I went to sleep.
My team did not have the right to call me.
I would have no idea what time it was.
The cave was not a great place to live.
Living near a glacier, Sif was often wet.
His body temperature would get very low.
It would go as low as 34 degrees Celsius.
He also did not have much to do.
He studied the glacier.
He read his books and wrote in his journal.
But there was no one to talk to.
He lived by himself and lost all sense of time.
Sif told Joshua 4, There were two tests I did every time I called the surface.
First, I checked my heartbeat.
Second, there was a mental test.
I had to count from 1 to 120.
I counted at a rate of one number each second.
With that test, we made a great discovery.
It took me five minutes to count to 120.
In other words, I experienced five real minutes as if they were only two minutes.
When two months had passed, Sif's team called him.
They told him it was time to leave.
Sif was very confused.
He was supposed to leave on the 14th of September, but he believed that it was only the 20th of August.
He had lost 25 days.
But Sif also discovered something even more amazing.
He discovered that each of us has an internal clock.
This clock tells our bodies when to sleep and get up.
Usually, we sleep and get up because of light from the sun.
We live in a 24-hour sleep cycle.
Sif also lived in a cycle.
But his sleep cycle was 24 and one half hours long.
This proved that the sun was not the only thing organising sleep.
Instead, humans have a natural cycle.
Without the sun, we sleep and get up when our bodies tell us to.
Sif knew that what he had discovered was very important.
So, he devoted his life to studying this eternal body clock.
In fact, he is considered the father of the new field of study called Chronobiology.
Chronobiology studies how these internal cycles of time affect both mind and body.
He performed many other experiments.
In some, he sent other people into caves.
They also stayed for months.
These people had different sleep cycles than Sif did.
Instead, they developed 48-hour cycles.
They would stay awake for 36 hours.
Then, they would sleep for 12 hours.
This meant that each person's sleep cycle was different And most are longer than 24 hours.
These experiments were very important at the time.
Countries had just begun to send people to space.
But no one knew how going to space would change people.
They did not know how it would affect sleep.
Being alone in a cave is a little like being alone in space.
So people going to space could prepare better for the effects of travelling in space on their bodies.
Then, in 1972, Sif decided to do another experiment on himself.
He would go down into a cave again.
He was older and he wanted to study how this changed the results.
But he also wanted to stay underground longer.
He would live in the cave for six months.
Sif's six months underground affected him very differently than before.
Two months underground did not change him much.
But the six months caused him great mental disturbance.
He began to fear the fungus that grew on the cave walls.
He feared he would catch diseases from the cave dust.
And he felt extremely sad.
Once, he was so lonely that he tried to befriend a mouse.
He tried to catch the mouse so he would have something living to talk to.
But he was not able to.
He killed the mouse by accident.
This made him so sad he thought about taking his own life.
But he continued with his experiments.
He did not give in to his sadness.
By the end, he could only say a few words, and it was very difficult to think.
Sif had everything he needed to survive.
But without others, his mind stopped working well.
Sif's experience damaged his mind.
But this experiment was a success.
His discoveries helped inform scientists how sleep works, and he helped confirm the importance of physical touch.
Being touched by other people is not just nice.
It is important to survive.
People can live without other people for a long time, but it can be dangerous to their health.
After his six-month stay, Sif stopped his experiments for eight years.
He moved away from his home in France and divorced his wife.
His time in the cave changed him.
He needed time to recover.
Soon though, Sif began experimenting again.
And today, he is one of the most well-known people who study time.
And his experiments are still the only ones of their kind.
Franz Halberg is a professor at the University of Wisconsin.
He also studies how we experience time.
In 1988, he spoke to the Los Angeles Times about Sif.
He said, Some people think he is a bad boy, but Sif does what no one else will do.
He has by far the longest records of people being alone.
Others who have studied similar things have done it for weeks.
He has done it for months.
Would you live by yourself for two months?
What about six months?
Why or why not?
You can leave a comment on our website or email us at radio at radioenglish.net.
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You can also get our programmes delivered directly to your Android or Apple device through our free official Spotlight English app.
The writer and producer of this programme was Dan Christman.
The voices you heard were from the United Kingdom.
All quotes were adapted for this programme and voiced by Spotlight.
You can listen to this programme again and read it on the internet at www.radioenglish.net.
This programme is called Living Without Time, Michel Sif and the Internal Clock.
We hope you can join us again for the next spotlight program.
Goodbye.
