00:00So, what's the longest you can survive without looking at your phone or watch to
00:05check the time?
00:07My personal record is about 13 minutes.
00:10But someone has no trouble living without knowing the time for 63 days!
00:15In the summer of 1962, a French chap named Michel Siffra took off his watch and went
00:21down into a cave in the French Alps.
00:24The then 23-year-old spent the next couple of months in complete isolation and without
00:29seeing the sun.
00:31And that's how he accidentally became the founder of a whole field of science called
00:35chronobiology, or the study of biological rhythms.
00:40Michel's original plan was to study an underground glacier he had discovered earlier.
00:46He wanted to spend 15 days underground, but then thought it wouldn't be enough to do
00:51serious research and decided to stay there for two months in the dark.
00:56It wasn't the comfiest of vacations, as his feet were always wet, and his body temperature
01:01was way lower than usual.
01:03He spent his free time reading, writing, thinking about his future, and studying his surroundings.
01:08He also slept well and ate when he felt like it.
01:12There was a team waiting at the entrance of the cave.
01:15They agreed the scientists would let them know when he woke up, ate, and before going
01:19to sleep.
01:20The team wasn't allowed to contact him, just to record when he was sending signals
01:25to make sure he was safe and sound and keep track of his life cycle.
01:29Cifra also informed them of his pulse and counted from 1 to 120 one digit per second.
01:36And that's how they found out his perception of time was seriously off.
01:40It took him 5 minutes to finish that task instead of the regular 2 minutes.
01:45When the team told him it was time to get out of the cave, he was confident it was only
01:49August, but it was already the 14th of September.
01:53Cifra thinks it had to do with an almost total absence of light.
01:57He had just a little light bulb in the cave.
02:00It all felt like one long day to him, and his memory couldn't keep track of what he
02:04was doing yesterday or two days before.
02:10The most important result of his experiment was proving that people, just like animals,
02:15do have an internal clock that doesn't depend on the day and night cycles.
02:20Cifra didn't stop there and went on dozens of expeditions to spend some time inside caves.
02:26Ten years later, he started a 6-month experiment in Texas.
02:30All this helped him to find that when people don't have time cues, they switch to a 48-hour
02:36cycle, not the 24-hour one we're used to.
02:38It would be 36 hours of activity and 12 to 14 hours of sleep.
02:43NASA used the results of his experiments to help astronauts who had short-term memory
02:48issues after some time in isolation.
02:54In 2021, a Spanish woman beat Cifra's cave record.
02:58Beatriz Flamini spent 500 days in a cave outside of Granada with basically no contact with
03:05the rest of the world.
03:06She insisted that the support crew wouldn't give her any news at all, even if something
03:11happened to her family members.
03:13The idea of this rough experiment was to test her own limits and also help scientists
03:18understand how staying in such extreme conditions affects the human mind and body.
03:24During the experiment, called Time Cave, Flamini received food from a drop-off point and sent
03:30GoPro videos of herself to the support crew.
03:32They checked the footage to make sure she was physically and mentally fine.
03:37Flamini spent the entire time working out, reading books, painting, weaving, and making
03:43food.
03:44She didn't shower, but the support team took out her natural waste once every 5 days.
03:49At some point, flies filled the cave, but Flamini braved on and continued the experiment.
03:55Around day 300, she had to leave the cave and stay in a tent in isolation for about
04:008 days because of a technical issue.
04:03When 500 days elapsed, the support crew found Flamini sleeping.
04:08She had lost track of time completely and said it always felt like 4am to her.
04:13She didn't want to leave as she hadn't finished the book she was reading.
04:17Although she started hearing things that weren't real and had a strong craving for roast chicken,
04:22the extreme athlete never even considered leaving the Time Cave earlier than planned.
04:28Researchers from several Spanish universities will analyze the data from this unusual experiment.
04:37Intricate biological rhythms govern our lives, from the smallest cellular processes to the
04:42functioning of the entire body.
04:45These rhythms regulate various aspects of your physiology, including sleep patterns,
04:50body temperature, hormonal balance, metabolism, and cardiovascular activity.
04:55Many diseases get stronger during nighttime or in the morning.
04:59Shift work disrupts the balance between internal rhythms and external time, so scientists blame
05:05it for diseases.
05:06Jet lag is a good example of how your internal clock gets out of whack because you move to
05:11a different time zone.
05:13But light, especially when you catch it at certain times, can help reset your body clock.
05:19When you see light at the end of the night, it nudges your clock forward, and early evening
05:23light can push it back a bit.
05:26It takes about a day for your body to catch up with each hour of time difference.
05:31And since our natural body clock ticks around 24.2 hours, it's easier for us to adjust
05:37to longer days out West than shorter ones out East.
05:41That's why when athletes or researchers live underground for a while, they end up feeling
05:45like they're in a time warp.
05:49Back in the 70s, scientists found the circadian clock mechanism in a fruit fly.
05:55It has to do with different genes.
05:57One gene revs up the other, which then puts the brakes on the first gene, creating a swinging
06:02rhythm.
06:03During the day, when the sun's up, a photoreceptor tells certain parts of the loop to relax.
06:09There's a whole complex network of molecules and neurons making sure everything ticks just
06:14right.
06:15Every living thing's got its own circadian clock, with its own set of clock genes doing
06:20the work.
06:21Besides light, other stuff, like temperature and food, helps sync up an organism's clock
06:26with the outside world.
06:31If you're feeling adventurous and want to try cave isolation yourself, how about the
06:35deepest one on our planet – Varyovkina Cave?
06:39It only got this title in early 2018.
06:42It was explored step by step, deeper and deeper.
06:45The first expedition to this cave in the West Caucasus only explored around 5% of it, but
06:51it was already nearly 400 feet.
06:54It was obvious there was much more to this cave, with a small entrance diving into the
06:58limestone of Earth's crust.
07:01Expeditions from all over the world went back there until they finally reached the bottom.
07:06The world's second, third, and fourth deepest caves are all nearby, hiding deep in the mountains
07:11of the Arabica Massif.
07:13It is one of the largest karst massifs on Earth, but it's still not well-explored
07:18because it's really tricky to get to this area.
07:21It's only accessible up to 4 months of the year because of weather conditions.
07:26Going all the way down there is really tricky and takes several days.
07:30There are underwater waterfalls with near-freezing water, flooding, obstructed entrances, and
07:35other surprise dangers.
07:40So if you aren't ready for the deepest of them, you could go with the longest one.
07:44Mammoth Cave in Kentucky has over 400 miles of limestone labyrinths already explored and
07:50probably around 600 miles still to discover.
07:54Over half a million people visit the cave every year as part of organized tours.
07:59You can choose between a classical and more extreme version, learn about the cave's
08:04cultural history, or attend a concert within its stone walls.
08:08You can also enjoy meeting over 100 wildlife species living there.
08:12One of the most famous and unusual of them is the eyeless cave fish.
08:17It has adapted to the environment without light by no longer growing eyes.
08:22That's it for today!
08:24So hey, if you pacified your curiosity, then give the video a like and share it with your
08:29friends!
08:30Or if you want more, just click on these videos and stay on the Bright Side!
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