Hey, smart people.

Joe here.

Every 23 hours, 56 minutes, and 4 seconds, our planet makes one rotation on its axis.

Time is always passing for all of us all the time at a constant rate of one second per second in this constantly evolving instant that we call now between a past that we can remember and a future that we cannot.

But if time is this unchanging thing, flowing constantly in one direction, then why does it feel like it's happening so slow sometimes?

Like, come on already.

And other times, whoosh, times passes right out of our grasp so fast.

I mean, what's going on here?

How can the same sum total of solar orbits and lunar phases, terrestrial rotations, or transitions of a Cesium-133 atom be so constant, yet feel so different in our minds?

I mean, these days people are just having a hard time remembering what day it is.

If you're not at work today or you're working from home, you may be wondering, "What day is it?"

It's Monday.

What is it about COVID-19 that makes March feel like it was approximately 4.7 years ago?

What makes time feel fast and slow?

[light music] This is a stopwatch, and when you hear the bell, it's going to start.

I want you to close your eyes, count off seven seconds in your head, now.

Open your eyes.

How close were you?

Well, some of you probably cheated and didn't do it, but those of you who did, you probably weren't that far off, which is amazing!

Unlike touch, taste, or smell, our bodies don't have a sensory organ for time.

We do have an internal biological clock, but your body's timekeeping is tuned to circadian rhythms, the broad patterns of day and night.

And like other animals, we also rely on astronomical cues and biological hormones to notice the passage of months, seasons, even years.

But you have no internal timekeeping device that can accurately sense the passage of seconds, minutes, or hours.

That still doesn't explain the constant, ever-present ticking sound, which I'm sure is a totally normal thing, right?

Well, although there is no actual clock inside your brain, we now know that how we perceive the passage of time can be stretched or slowed.

And scientists once tested this by dropping people off a 15-story building.

[Morty yells] Let me explain.

Have you ever heard someone say that a car accident or some other life or death situation felt like it happened in slow motion?

It makes you wonder if our brains are able to suddenly reach in and stretch out a second to give us conscious access to smaller windows or slices of time, like milliseconds, when we're super freaked out.

Experiencing bullet time, like in "The Matrix," when we're scared, might let us react better or escape to safety.

So to test this, scientists dropped people from 150 feet up.

They had harnesses and a safety net.

Doesn't feel very realistic to me, but you gotta be "safe," I guess.

During the free fall, each person was asked to look at a display with flashing numbers, only these numbers were flashing by too quickly to be read under normal circumstances.

If a state of fright actually altered their time perception, they should be able to read the numbers while falling.

So what happened when they were dropped?

Well, no one could read the numbers.

In scary times, our brains do not stretch time itself and allow us to perceive smaller moments.

But still, the study subjects reported that their own fall lasted longer than when they simply observed someone else falling.

Their memory of the fall was slowed down.

So why does this happen?

Well, one theory suggests it has something to do with a specific region of the brain.

During stressful or negative situations, this region kicks into high gear, causing more of the brain's resources to be directed at making memories of that moment.

These memories are richer in detail, and when they're replayed in our minds, they give us the sensation that they lasted longer than other low-resolution memories.

This is even true in cases like PTSD, where people would rather the memories weren't so strong.

Our emotions can also influence our perception of time.

During the COVID-19 pandemic, people who say they're feeling nervous or stressed reported that time seemed to pass more slowly in any given moment, while those who felt happy, well, they tend to experience time passing more quickly.

So yeah, that vacation really did go by fast.

At least in your mind.

What's a vacation again?

But something interesting happens when we look back on these memories later.

How is it September already?

March feels like yesterday.

We've all experienced that in some way, right?

Even though time feels like it's passing more slowly in the moment, day after day of routines where nothing new is happening, our memory of the time period just seems to fly by.

We can see this in action through something called the Oddball Effect.

When you're exposed to the same image over and over and over, a new or different image seems to last longer, even when its displayed for the same period of time.

This might also explain why time seems to pass slower when we're young.

When we're kids, everything is new.

We were seeing everything for the first time.

Creating memories of this never-before-seen information makes our brain work harder and makes time seem slower.

But as we age, we have more routines, fewer new experiences filling our days, so time seems to flow by more quickly.

It's almost like memories are the landmarks along the river of time, and the fewer that we have, the faster it feels like we're going.

Thanks to COVID, many of us are bored, forced into routines where we experience less newness, and we're stressed, unhappy, or even frightened.

So time is going by really slow in the moment and really fast in the long run.

These emotional connections to the perception of time seem to be universal among humans.

But the way we think about our physical place in time is not.

We all experience time and space together.

As you travel faster, or if you find yourself in the vicinity of a higher source of gravity, time ticks more slowly for you than it does for other-- Not now, Neil deGrasse Tyson.

Listen, we all live on Earth.

None of us are near a black hole or approaching the speed of light, so I'm not talking about the effects of relativity on whether time actually passes fast or slow sometimes.

Okay?

Thank you.

Now, where was I?

Take your finger and point to the past.

Go ahead!

If you're from a culture anything like mine, then you probably pointed back there.

Or did you point somewhere else?

All human cultures seem to interpret time through spatial metaphors, as if there was a you standing in a physical location in time, with you either moving through it or it flowing past you.

But have you ever really thought about how your daily perception of time is influenced by things like culture or history or language?

For me, a person who lives in the United States and grew up speaking English, the past is behind me.

You gotta put your behind in your past.

No, no, no.

That's why we say things like, "closing a door to the past," or, "this week flew by me," or, "knowing something ahead of time."

When I think about the timeline, the literal line of time, it goes this way.

How would you arrange these images?

Speakers of languages written left to right will order them like this, while speakers of languages written right to left, like Hebrew, often arrange chronological events in space like this... And people who speak Mandarin Chinese, typically written top to bottom, sometimes refer to the past as above and the future as below.

In Vietnamese and some South American cultures, the past, the before time, which is known to us and seen clearly in our memories, is in front of us, and the future, obscured and unknown, is what's behind.

The Yupno people of Papua New Guinea orient their place in time with the contours of the land.

The future is uphill, and the past downhill.

Other cultures align with the cardinal directions, mimicking the path of the sun.

Look at these dots.

The length of time between the flashes is actually the same.

But this larger space makes it seem like the third dot takes more time to show up.

No matter how we do it, or even if we realize it, we all make some link between space and time, and this can vary depending on where we're from.

There is still a lot that we don't know about the connection between time passing in the physical world and time passing in the brain.

But we're all living through a massive, global human experiment right now, in this pandemic, about how our perception of time can change based on our experience in the world.

In the eyes of physics, the difference between the past, present, and future, might just be an illusion.

But for us, a conscious animal with a mind, the journey through the past, present, and the future is remembered and experienced in ways that even Einstein would find mysterious.

Stay curious.