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[playful piano music]
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[narrator] As a little kid,
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a single day can last forever.
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As a teenager, you can live
what feels like a whole lifetime
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in a single summer.
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Your twenties stretch on and on and on.
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And then suddenly,
you can't believe you're somehow 40.
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And the pace only picks up from there.
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Our time warps on small scales too.
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So, you might be aware of phrases like
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"Time flies when you're having fun."
"Time drags when you're bored."
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[narrator] Studies show marijuana
can slow down time,
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and alcohol and cocaine can speed it up.
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Music can do that too.
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That hold music might feel
like it's making every second torture.
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-[woman] Thank you for holding.
-[narrator] But silence…
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[no audio]
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…is worse.
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Now, what I was
particularly interested in was "Why?"
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[narrator] That's a great question.
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'Cause it seems like time passes
at a steady, relentless tick,
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but it also doesn't feel that way.
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It feels like the day after day gallops
and goes by so quickly.
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It's weekend to weekend, and there's
all this work happening all the time.
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My days do go by,
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seem to go by, quicker.
And I'm not sure why.
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[narrator] So why do we experience time
the way we do?
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And how can we take back some control?
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Tick, tock, tick, tock,
tick, tock, tick, tock.
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[man 1] To study time,
we must venture beyond the ordinary.
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And when we do,
it opens up a whole new realm.
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Time and space.
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[man 2] Just suppose
we could slow down time.
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Or speed it up.
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[man 3] To the question, "What is time?"
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there is no one answer.
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[Gordon-Levitt] In 1962,
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a young geologist went on an expedition
into the French Alps.
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He went with a team,
but Michel Siffre, just 23 years old,
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would face the real journey alone.
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Michel wanted to see what it would be like
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to live away from all people,
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all clocks, and even the rising
and setting of the sun,
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by living in a cave for two months.
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This was one of the first studies
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of the human sleep-wake cycle
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in the absence of any external signals
about the time of day.
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[Gordon-Levitt] As he described it
in an interview later,
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it was an existence beyond time.
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I was beyond time, without any time cues.
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No television, no radio. Nothing.
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No watch.
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Uh…
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You live following your mind.
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[Gordon-Levitt] Every time Michel woke up,
ate, and went to sleep,
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he'd call up his colleagues
stationed at the cave's entrance.
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Sometimes, he was awake for just six hours
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and went back to sleep.
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Or he could stay up for 27 hours in a row.
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But on average,
he fell into a sleep-wake cycle
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of roughly 24 hours.
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It was a key insight.
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Away from any external cues
about the time of day,
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his body kept track of it.
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Our most ancient clocks
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are inside of us.
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They're called circadian clocks.
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"Circa" meaning approximately,
and "dian" meaning day,
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because they tell time
on the scale of 24 hours.
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Interestingly, most cells in our body
have a circadian clock.
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[Gordon-Levitt] They make special proteins
specifically to tell time.
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And when they reach a certain limit…
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[Buonomano] That protein can turn off
the synthesis of itself.
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[Gordon-Levitt] And then
those proteins are destroyed,
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and the cell fires up again.
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And that cycle happens every 24 hours.
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Our bodies contain
billions of these tiny loops.
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[Buonomano] But there is a master clock
in the human brain,
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and that's located in the hypothalamus,
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in an area called
the suprachiasmatic nucleus.
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That's in charge in many ways
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of synchronizing all the other clocks
in our bodies.
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[Gordon-Levitt] Every mammal ever studied
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has a 24-hour internal clock.
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Every bird,
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and reptile,
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and fish,
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and insect.
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In fact, you don't even need a brain.
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Plants have a circadian clock,
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and even single-cell bacterium
have a circadian clock.
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[Gordon-Levitt] According to one theory,
billions of years ago,
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when the first glimmer of life emerged,
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cells that divided during the day
were damaged by the sun's UV rays.
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But the cells that learned
to divide at night
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survived.
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In other words, keeping time
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may have been fundamental
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to the evolution of life on Earth.
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But circadian clocks are pretty basic.
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They just keep
our bodily functions on a rhythm,
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telling us when to eat, sleep, wake up.
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A few other things.
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And it resets every day.
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Your ability to keep track
of time passing,
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day to day, month to month,
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year to year,
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is something else entirely.
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On September 14th,
Michel Siffre's team called him up
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to announce that his two months
in the cave were over.
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Siffre thought it was a joke.
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By his count, it was only August 20th.
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His body had kept track
of the days pretty well,
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but his mind had lost an entire month.
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Fast forward 60 years.
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Happy New Year, 2020.
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[Gordon-Levitt] And
the whole world experienced
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a kind of isolation experiment.
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When the UK first went into lockdown,
I had a six-month-old baby,
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and I also have a six-year-old
and an eight-year-old child.
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And my experience of time was
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that it was ridiculous
that there were 24 hours in the day.
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Time was dragging so slowly for me.
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I wondered, "Is this
a much more widespread phenomena?"
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[Gordon-Levitt] So she did a survey
of nearly 700 people across the UK.
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[Ogden] The majority of people experienced
a significant distortion to time.
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[Gordon-Levitt] 81% of them.
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And interestingly,
it was almost evenly split.
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Around half, like Ruth,
felt like time was dragging,
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and the other half
felt like time had sped up.
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[Ogden] So generally,
being bored, being sad,
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and being depressed are all associated
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with the slowing of the passage
of time during coronavirus.
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[Gordon-Levitt] Studies like this
in other countries
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have found similar results.
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In France, Italy, Argentina, and there are
currently studies going on in Iraq.
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So globally, it would seem that we have
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profound distortion to the passage
of time during coronavirus.
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During a pandemic, we know it's gonna
be over some day, but it's so far away
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that you have to consider
that this is now where you live,
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this is your life, this is your reality.
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[Gordon-Levitt] Scott Kelly was more
prepared than most for that experience.
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Back in 2015, he launched into space
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and stayed there a whole year,
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the longest manned mission
in NASA history,
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and he returned to Earth a national hero.
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Because a year
living in a high-tech aluminum can
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250 miles above Earth
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is a long time.
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I consciously tried
not to count the days I was in space,
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because I knew over the course of a year
that would get kind of irritating.
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[Gordon-Levitt] But then one day
near the end,
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the Russian cosmonaut
Mikhail Kornienko said to him…
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"Hey, Scott, do you know what day it is?"
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The day when we only have
ten days left in space.
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And then every day after that,
he asked how many days we had left.
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So he counted down from ten to zero.
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It drove me a little bit crazy
'cause it wasn't part of my plan.
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[Gordon-Levitt] And you don't need
to be an astronaut,
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or live through a pandemic,
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to know that stress
can make things drag out.
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We know that emotion is one of the things
that really distorts our sense of time.
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[Gordon-Levitt] It doesn't really affect
our circadian clocks,
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but it seems like there's some
other kind of clock in our brains,
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something like a stopwatch
that consciously tracks the time for us.
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But the stopwatch in this case
isn't a machine.
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It's more like a human.
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When it's bored or lonely,
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it obsessively counts every beat.
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And when it's really stressed,
it might even count some twice.
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And then on the flip side,
when we're busy, relaxed, and social,
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our minds are doing other stuff,
and we skip a lot of beats,
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and time seems to whiz by.
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I really like this idea,
because it makes sense
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that we have some sort
of clock-like system in the brain.
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But the problem with this idea is
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that we've really struggled
to locate where this clock is.
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[Gordon-Levitt] We've tried to find it,
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putting people in MRIs
and asking them to count time passing.
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And there isn't one area
that consistently lights up.
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Our sense of time
seems to be embedded across our brain.
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So we talk about our sense of time,
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but, of course, we don't have
an organ that detects time.
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[Gordon-Levitt] We can't see or hear
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or smell or touch it.
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We have no direct way to sense it at all.
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So in many ways, our sense of time
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is a creation, a construct,
of the human mind.
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[Gordon-Levitt] For centuries, we assumed
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that time had to be out there,
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ticking away
just like it existed in our heads.
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It's hard to even imagine another option.
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But now, many scientists believe
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we only experience a tiny sliver
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of what time really is.
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And that the reality of time
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is something much bigger.
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Something more like
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space.
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We already sort of think of time
like it's space,
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although it depends on your culture,
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or rather, your writing tradition.
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In you live in the West,
you imagine time moving left to right,
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like words on a page.
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In Israel, the past is on the right
and the future on the left,
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'cause that's the way you write Hebrew.
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And in Mandarin, you write vertically,
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which is why the past is up
and the future is down.
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But everywhere we think of time
as having a direction,
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as coordinates on a map.
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It's like putting a grid, right?
You put a grid on space.
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This is so many grid marks this way,
so many grid marks that way,
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and so many grid marks going up.
Then you can attach a time to it.
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You are at this grid position
at this time,
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and that grid position at that time.
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[Gordon-Levitt] So if space
has three dimensions,
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you can think of time as the fourth.
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Four dimensions is hard to imagine.
Also, time is weird.
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But anyway, you put these four dimensions
together, and you call it space-time.
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[Gordon-Levitt] Where space and time
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are woven together
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in a single, stretchy fabric.
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And that fabric
is warped all over the place.
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[Balasubramanian]
Matter and energy can bend space.
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And, even more dramatically,
can bend time.
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[Gordon-Levitt] So on Earth,
time ticks a bit more slowly
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than it does out in space.
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And time on the Sun
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ticks even more slowly than that.
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And time also slows down
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at really fast speeds.
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This all happens at a scale
too big for us tiny humans
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to ever feel.
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But by the 1970s,
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we had invented atomic clocks
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that were precise enough to test it.
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We put them on a plane
and flew them around the world.
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And sure enough,
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those clocks said that less time
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had passed.
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And if time moves
more slowly at faster speeds,
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that means a person
would age more slowly too.
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For example, if you're an astronaut
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who's spent a lot of time
zooming around Earth,
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while your twin brother,
who's also an astronaut,
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stayed on the ground.
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00:13:10,122 --> 00:13:12,666
I am now, like, three milliseconds younger
248
00:13:13,375 --> 00:13:15,211
than him.
249
00:13:15,294 --> 00:13:18,547
I used to be, like, six minutes younger,
approximately,
250
00:13:18,631 --> 00:13:21,884
and now I am six minutes
and three milliseconds younger,
251
00:13:21,967 --> 00:13:24,470
so I got that going for me, I guess.
252
00:13:25,137 --> 00:13:28,724
[Gordon-Levitt] But if time is
a dimension, just like space,
253
00:13:29,558 --> 00:13:32,937
that raises a pretty huge question.
254
00:13:33,562 --> 00:13:37,650
Clearly, you can move to the right
or the left in any spatial direction.
255
00:13:37,733 --> 00:13:40,194
So why can't I move up or down in time,
256
00:13:40,277 --> 00:13:42,655
or to the later times
and the earlier times?
257
00:13:42,738 --> 00:13:46,033
This is a really complicated
and interesting question.
258
00:13:46,116 --> 00:13:47,576
Because to the best of our knowledge,
259
00:13:47,660 --> 00:13:49,829
it's not possible
to move backward in time.
260
00:13:49,912 --> 00:13:52,331
[Gordon-Levitt] But if all
the space around us,
261
00:13:52,414 --> 00:13:54,208
forwards and backwards,
262
00:13:54,291 --> 00:13:57,878
is just as real as where we're sitting,
263
00:13:57,962 --> 00:13:59,839
then the past and the future
264
00:13:59,922 --> 00:14:02,800
should be just as real as the present.
265
00:14:03,509 --> 00:14:06,804
As if it's all already recorded.
266
00:14:07,596 --> 00:14:09,265
The stuff that already happened.
267
00:14:09,348 --> 00:14:11,058
Time flies when you're having fun.
268
00:14:11,141 --> 00:14:12,893
The stuff that hasn't happened yet.
269
00:14:12,977 --> 00:14:14,937
I think the best holiday
is New Year's Eve.
270
00:14:15,020 --> 00:14:17,314
[Gordon-Levitt] You can't say
it's all happening now,
271
00:14:17,398 --> 00:14:19,358
because only now is now.
272
00:14:20,401 --> 00:14:24,113
We don't even exactly know
the vocabulary to use.
273
00:14:24,780 --> 00:14:26,282
[Gordon-Levitt] But you could say,
274
00:14:26,365 --> 00:14:30,160
just like everything that's happening
now is happening somewhere,
275
00:14:31,161 --> 00:14:34,331
everything in the past and future
could be happening
276
00:14:35,165 --> 00:14:36,709
"somewhen."
277
00:14:40,504 --> 00:14:42,089
An eccentric young man,
278
00:14:42,172 --> 00:14:43,841
Albert Einstein,
279
00:14:43,924 --> 00:14:46,969
first came up
with these theories back in 1905.
280
00:14:48,387 --> 00:14:49,972
And 50 years later,
281
00:14:50,055 --> 00:14:52,766
when his lifelong collaborator
and close friend
282
00:14:52,850 --> 00:14:55,144
Michele Besso passed away,
283
00:14:55,227 --> 00:14:57,563
Einstein wrote a letter to his family.
284
00:14:58,689 --> 00:15:01,775
"Now he has departed
from this strange world
285
00:15:01,859 --> 00:15:03,277
a little ahead of me."
286
00:15:04,069 --> 00:15:05,571
"That means nothing."
287
00:15:06,572 --> 00:15:09,241
"People like us, who believe in physics,
288
00:15:09,325 --> 00:15:12,745
know that the distinction
between past, present, and future
289
00:15:13,662 --> 00:15:17,374
is only a stubbornly persistent illusion."
290
00:15:21,086 --> 00:15:23,088
Now, this idea of time
291
00:15:23,172 --> 00:15:25,841
is hard to swallow for a few reasons.
292
00:15:26,592 --> 00:15:29,929
First, there's the small issue
of free will.
293
00:15:31,388 --> 00:15:33,390
If the future is already written,
294
00:15:34,266 --> 00:15:36,935
that means whatever we do,
295
00:15:37,019 --> 00:15:38,854
it's not up to us.
296
00:15:38,938 --> 00:15:42,066
The recording knew
it was going to happen anyway.
297
00:15:43,275 --> 00:15:45,235
So that's pretty spirit-crushing.
298
00:15:46,570 --> 00:15:49,323
And while we can put clocks on planes
299
00:15:49,406 --> 00:15:51,575
and prove that time warps,
300
00:15:51,659 --> 00:15:54,745
we can't send those planes
into the past or into the future,
301
00:15:54,828 --> 00:16:00,125
so we can never really prove
that the past or the future is real.
302
00:16:00,209 --> 00:16:03,295
In fact, we can hardly imagine
what that even means.
303
00:16:04,463 --> 00:16:06,715
There are a lot of videos
and documentaries that have tried
304
00:16:06,799 --> 00:16:08,550
to help us make sense of it,
305
00:16:08,634 --> 00:16:10,552
using all kinds of metaphors,
306
00:16:10,636 --> 00:16:12,179
like a DVD record,
307
00:16:12,972 --> 00:16:15,641
or a vinyl record, or…
308
00:16:15,724 --> 00:16:17,184
A loaf of bread.
309
00:16:17,267 --> 00:16:21,063
[Gordon-Levitt] But it's actually pretty
useless to try to imagine this.
310
00:16:21,146 --> 00:16:24,274
We evolved
from those single-cell organisms
311
00:16:24,358 --> 00:16:26,568
that learned to tell day from night.
312
00:16:27,236 --> 00:16:30,656
And somewhere along the line,
we developed our particular sense of time,
313
00:16:30,739 --> 00:16:33,951
because that helped us survive too,
314
00:16:34,034 --> 00:16:37,246
and it's the only window into time
we'll ever have.
315
00:16:38,747 --> 00:16:40,499
And it isn't just one window,
316
00:16:40,582 --> 00:16:43,252
because we also have
an awareness of the past.
317
00:16:44,128 --> 00:16:46,130
Which is a whole other sense of time.
318
00:16:46,839 --> 00:16:49,675
In many ways, the brain's main function
319
00:16:49,758 --> 00:16:51,969
is to use the past
320
00:16:52,052 --> 00:16:53,762
to predict the future.
321
00:16:53,846 --> 00:16:56,724
So the evolutionary advantage of that
322
00:16:56,807 --> 00:16:58,934
is, of course, very, very profound.
323
00:17:00,978 --> 00:17:03,981
[Gordon-Levitt] Revisiting the past
to imagine the future.
324
00:17:04,815 --> 00:17:09,194
It's how we first realized that stars
in the sky moved in predictable ways.
325
00:17:10,487 --> 00:17:13,323
And developed clocks and calendars
to track them.
326
00:17:14,408 --> 00:17:16,952
It's what allowed us to organize,
327
00:17:17,661 --> 00:17:19,538
coordinate with each other,
328
00:17:19,621 --> 00:17:21,415
and build civilizations.
329
00:17:22,166 --> 00:17:26,420
The ability to engage in mental time
travel is what makes Homo sapiens sapien.
330
00:17:27,296 --> 00:17:31,008
[Gordon-Levitt] And the fact that time
is a sense that's easily warped,
331
00:17:31,091 --> 00:17:32,634
in some ways, it's a gift,
332
00:17:32,718 --> 00:17:36,138
because we have the power
to speed it up, or slow it down,
333
00:17:36,221 --> 00:17:39,016
depending on how we choose to spend it.
334
00:17:39,099 --> 00:17:40,642
We search our memory,
335
00:17:40,726 --> 00:17:44,313
and the more memories that we've
accumulated during a period of time,
336
00:17:44,396 --> 00:17:47,733
the longer we believe
that period of time to have lasted for.
337
00:17:48,400 --> 00:17:49,651
[Gordon-Levitt] Michel Siffre
338
00:17:49,735 --> 00:17:52,946
felt like he only spent
one month in a cave
339
00:17:53,030 --> 00:17:56,200
because he had
fewer memories worth storing.
340
00:17:57,076 --> 00:17:59,161
He said in an interview later,
341
00:17:59,244 --> 00:18:03,415
"When you're surrounded by night,
your memory doesn't capture time."
342
00:18:03,499 --> 00:18:05,000
"You forget."
343
00:18:05,084 --> 00:18:09,004
And as you get older and busier,
and settle into a routine,
344
00:18:09,922 --> 00:18:11,298
you can also forget.
345
00:18:11,381 --> 00:18:14,510
Just the emails
will sort of keep you busy forever.
346
00:18:14,593 --> 00:18:16,553
So that boom, boom, boom
347
00:18:16,637 --> 00:18:19,640
makes it feel like the time
has gotten very compressed.
348
00:18:21,100 --> 00:18:22,976
[Gordon-Levitt] But for many people,
349
00:18:23,060 --> 00:18:25,979
childhood felt like it lasted the longest.
350
00:18:26,688 --> 00:18:30,275
If you think when you're a child,
you're learning lots of new skills.
351
00:18:30,359 --> 00:18:32,945
You're learning how to socialize
and how to play,
352
00:18:33,028 --> 00:18:35,989
and you're taking on lots
of educational knowledge from school.
353
00:18:36,073 --> 00:18:39,451
And I think the perception
of whether it's moving fast or slow
354
00:18:39,535 --> 00:18:41,829
has something to do with what you notice.
355
00:18:41,912 --> 00:18:44,748
Children notice everything.
They're very much in the present.
356
00:18:44,832 --> 00:18:47,626
And having that process
where every moment counts
357
00:18:47,709 --> 00:18:49,169
I think gives you the sense
358
00:18:49,253 --> 00:18:51,421
of a longer period of time
that slows everything down.
359
00:18:52,256 --> 00:18:55,843
[Gordon-Levitt] In fact,
studies show just being in nature
360
00:18:57,094 --> 00:18:59,054
makes time pass more slowly.
361
00:19:04,518 --> 00:19:07,437
Being social, on the other hand,
can make time fly by.
362
00:19:07,521 --> 00:19:10,274
One of the things
I really wanted to capture in my study
363
00:19:10,357 --> 00:19:14,820
was the thing that had really changed
in the UK as a result of COVID.
364
00:19:14,903 --> 00:19:17,489
We couldn't go out and socialize
with friends and family.
365
00:19:17,573 --> 00:19:19,241
We couldn't meet people in the park.
366
00:19:19,324 --> 00:19:22,369
So perhaps the most interesting variable
that I also studied
367
00:19:22,452 --> 00:19:25,581
was how satisfied they were
with social interaction,
368
00:19:25,664 --> 00:19:28,458
because it didn't matter
how many people you lived with.
369
00:19:29,501 --> 00:19:33,338
[Gordon-Levitt] What mattered was
how socially satisfied you felt.
370
00:19:35,299 --> 00:19:39,052
And all the celebrations
people missed in the pandemic.
371
00:19:40,470 --> 00:19:43,599
The ones we use to mark the years
372
00:19:43,682 --> 00:19:46,101
may make time whiz by in the moment,
373
00:19:47,352 --> 00:19:50,522
but they also force us
to notice time passing
374
00:19:51,648 --> 00:19:54,067
and create landmarks in our memories.
375
00:19:56,195 --> 00:19:58,405
Making them one of the best ways
376
00:19:58,488 --> 00:20:01,658
to live a long life in retrospect.
377
00:20:03,744 --> 00:20:05,621
You know, birthdays are great in space.
378
00:20:05,704 --> 00:20:08,373
What's really, I think, the best holiday
is New Year's Eve,
379
00:20:08,457 --> 00:20:12,711
because New Year's is something that
everyone celebrates from every culture.
380
00:20:14,171 --> 00:20:16,256
[Gordon-Levitt]
On the very same day every year,
381
00:20:16,340 --> 00:20:19,176
the entire world comes together
382
00:20:19,259 --> 00:20:22,179
to mark another spin
of our planet around the sun.
383
00:20:22,846 --> 00:20:26,099
Counting the beats
of time's steady march forward
384
00:20:26,975 --> 00:20:29,311
as the future rushes into the present
385
00:20:30,020 --> 00:20:32,481
and after a fleeting moment of now…
386
00:20:32,564 --> 00:20:35,108
[crowd] Three, two, one…
387
00:20:35,192 --> 00:20:37,903
[cheering]
388
00:20:37,986 --> 00:20:39,863
[Gordon-Levitt] …vanishes into the past.
389
00:20:41,990 --> 00:20:45,285
That young geologist Michel Siffre
390
00:20:45,369 --> 00:20:47,871
was a 60-year-old man in 1999
391
00:20:48,538 --> 00:20:51,541
when he took off his watch
with a familiar gesture,
392
00:20:52,125 --> 00:20:54,962
waved goodbye to a crowd of reporters,
393
00:20:55,045 --> 00:20:58,590
and disappeared into a cave
for another isolation experiment.
394
00:20:59,591 --> 00:21:01,927
Siffre greeted the new millennium
395
00:21:02,010 --> 00:21:04,638
some 3,000 feet below ground,
396
00:21:04,721 --> 00:21:06,765
with champagne and foie gras.
397
00:21:08,267 --> 00:21:12,437
And there was no one there to tell him
that, in fact, in the world above ground,
398
00:21:13,563 --> 00:21:15,565
it was already January 4th.
399
00:21:21,363 --> 00:21:25,158
[closing theme music playing]