Did you ever tell someone that they have no concept of time?
I mean, that's a little rude.
But, like, do humans have to have a concept of time?
Like, who was the first human to come up with the idea
that we, like, Frank, you are five decans late
for our meeting, you jerk.
The first humans to have a concept of time
were the Egyptians.
As early as 1500 BCE, or about 3,500 years ago,
they used sun dials and the stars
to divide daylight and night into parts.
Daytime was 12 parts, 10 hours for the day
and then one hour for dawn and one for dusk.
And then, night was 12 hours marked
by 36 decans, sometimes marked on the inside of coffins.
You know, so the dead could tell time in the afterlife.
The Egyptians, as you probably know, super into the afterlife.
And by the way, just as a little fun fact,
Cairo is about at the same latitude
as Tallahassee, Florida, Austin, Texas, New Orleans,
Louisiana in the United States.
So that means time is going to vary.
The number of daylight hours are going
to vary throughout the year, just like they
would in the American South.
So that would mean, because there are 10 hours for a day,
the length of hours would vary throughout the year
in the Egyptian clock.
But of course, they didn't have minutes.
So it didn't matter if the hours varied a little bit.
Because 3,500 years ago, there were
no trains arriving and leaving at, like, 3:42 PM on the dot.
There was no dot.
But the Egyptians did have 12 segments for day
and 12 segments for night, which is where we get
the basis for the 24-hour day.
Ba, ba, ba, ba, ba, ba, bingo.
So why 12?
Well, this one's pretty good.
Counting the number of knuckles on a finger, base 10,
you could use fingers.
Base 12, you can use finger knuckles and also, the number
of lunar cycles in a year.
That counter system is still used today.
It's worked for this long, so why not keep it up?
Other ancient cultures used other systems, too.
The ancient Chinese used stars.
And then they tried dividing the day into 100 chi--
I don't know how well that worked out.
With the Sumerians and then Babylonians,
like 4,000 years ago, used the stars to mark time as well.
But they divided time into base 60.
Think circles, 360 degrees.
That's part of base 60.
And so that continues today, but not necessarily in time,
except the 60-minute hour.
But there are different cultures that
use different measurements, of course, at different periods.
And the reason that this became the dominant one
was likely because of exploration, trade,
and religion.
There were a lot of European and Arabic scholars
who were exploring the world and spreading their time around.
Of course, it matters with some religions,
where prayers have to happen at specific times
and specific directions.
And over time, our measurement of time got better and better.
Because our astronomy got better and our mechanics got better.
And yet there were still no minutes.
But of course, half and quarter hours, but why would
you want minutes?
Why do you need to measure to the minute in 1509?
Michelangelo is not, like, I'm charging by the minute
to paint this Sistine ceiling.
You guys better figure that out.
Mechanical clocks came out in the 1600s.
And they were the first to put minutes on there.
And maybe, you know, it just looked blank without them.
It's, like, what do we do in between here and quarter hour?
And minutes only really mattered to some specific fields,
like scientists.
You know, nerds-- nerds, we always win.
First fantasy was nerdy.
And now it's everybody.
Computers were nerdy.
And now everybody has one in their pocket.
Comic books were nerdy.
It's literally the most highest grossing films ever
were from comic books.
Even the literal minute, y'all use it because nerds are
the best!
You're welcome!
Not that, of course, it matters.
Because like time, it isn't real anyway.
Right?
Let's kick into it.
Of course, time is real!
I was just testing you.
I was messing with you.
Of course, it's real.
Of course.
Time is real in that it's measurable.
Physical changes happen over time.
We talked about this earlier.
Anyway, let's not have a time crisis too here.
Let's go outside the clock a little bit.
In Dr. Stephen Hawking's book, A Brief History of Time,
he uses this graph.
The y-axis is distance.
And the x-axis is time.
This is a pretty common method of graphing time
in a two-dimensional space.
A lot of different cosmologists and astrophysicists use this.
And we know from observation that a mission to absorption
is important.
And if you think of it in light, time works great for that.
An event is something that happens
at a particular point in space and at a particular time.
So one can specify by four numbers or coordinates,
Hawking writes, x, y, and z for space,
and then, a coordinate for time.
That said, the coordinates are only
useful when referring to a similar phenomenon
in a similar region.
Because you can't use Earth hours, minutes,
and seconds for something that's happening on Mars.
And in fact, the coordinates for time and location on Mars
are not relevant when you're talking about where the nearest
Dunkin' Donuts is, right?
So instead, it's important to remember
that time is only relevant to an observer on a local frame.
Hawking also writes Newton's Laws of Motion
put an end to the idea of absolute position in space.
The theory of relativity got rid of the absolute time.
And that might require a little bit of unpacking.
So before Isaac Newton's time in the 1600s,
the universe was considered static.
Think of it like everything existed inside
of a snow globe or a shoe box or a mechanical clock.
It's unchanging.
Yes, it's in motion.
But it doesn't change over time.
An object at rest was completely still,
staying at rest like a donut on a plate.
And it only moved when I acted upon it.
And this is Newton's Laws of Motion.
It stays at rest until something acts upon it.
But it's not actually true, right?
The donut is on a plate.
The plate is on the Earth.
The Earth is spinning.
And the Earth is going around the sun.
The universe is moving and changing
and expanding and shifting.
So even though the Laws of Motion
threw away the concept of a static universe,
and threw away the concept of absolute position
in the universe, they did start to explore
the movements of planets and the relative forces
acting upon them.
And while the Laws of Motion that Newton came up
with in Newton's laws would be able to define things that
are small, like this coffee mug, they're
not going to be so great for things like stars and galaxies.
We could calculate forces that are small.
But they're endemic to that thing.
Now imagine that donut in another galaxy, light years
away, sitting on another plate.
We cannot know anything about what is happening with that
donut.
We don't know about the plate it's sitting on.
We don't know if it's on a table, or a train,
or if it's floating in space.
We have no absolute position for that donut.
Now apply that thinking to time.
We have a future and a past.
And that would look like this.
This is a Minkowski spacetime light cone diagram.
It kind of looks like an hourglass.
It's pretty funny.
The hypersurface is the imaginary now.
And that event is at the middle, where the hypersurface meets
the light cone.
That is not Earth in the middle.
That is just an event.
Sure, maybe that is the donut, any fried dough.
You want it eclair style?
You want it churro?
Awesome.
Whatever.
All donuts have different time cones.
That's what's that's called, or light cones.
They're different calculations.
Don't try and calculate them all, because you would
shatter an iPhone 5, my friend.
There is no such thing as absolute position.
Because we can't know everything about everything.
And there's no such thing as absolute time
for the same reason.
My time is not the same as this donut's time.
And this donut's time is not the same
as the time of a SpaceX satellite, or Mars.
Time is about perception, not in a psychological way,
but based on the illusion of place of our event.
We know this is true because of space exploration.
Einstein's special relativity says
that the faster something moves, the slower time
is going to move for that thing.
It is not an illusion.
It's physically slower.
Astronauts age slower.
It's not super measurable, because they're not moving
that much faster than we are.
You know, Scott doesn't feel younger
when I talk to him or anything like that.
GPS satellites, though, they have atomic clocks
on them, super accurate clocks.
And those super accurate clocks need correcting.
Because they are moving faster than the atomic
clocks on the ground.
Time actually moves slower for satellites providing
you GPS than it does for the person actually
using the signals, you know, relatively speaking.
[LAUGHS]
Pardon the pun.
And if you think about it that way, our planet is also moving.
And so our sense of time is warped in that way.
And yet there's no way to measure time without moving.
It's all relative to where we are.
If you could somehow find a way to be completely still
within an expanding universe that is inflating as we speak,
it would be a different time frame than the Earth
as it flew by.
And on a universe scale, it's a bit easier to explain.
Because time does go into the same direction all the time.
Oh, gosh.
I've said time so many times.
[LAUGHS]
You've probably seen one of the many videos
on the Second Law of Thermodynamics.
So I'm not going to be as great as Henry
or the other scicommers that have all covered this.
I've even covered it myself.
I'll just say this, the Second Law of Thermodynamics--
which if you want to know more, go look it up--
says that entropy will increase in a closed system, period.
I mean, it can be more complicated than that.
But that is what it's saying.
And what we think of as time is connected to that entropy.
Entropy, in all the existence of all the universe,
has never decreased.
So time will continue to flow, called the Arrow of Time,
from past into the future.
Think about that documentary, at the historical documents
of Galaxy Quest.
And they use the thing called the Omega 13.
And it rearranged matter.
But it had to do it for all matter
and energy in the whole universe instantly.
Wow, is that thing way more powerful
than you thought, right?
By Grafdar's hammer, whoa!
You know?
And it would take that matter and energy
and restore it to a slightly lower entropic state.
Easy, 13 seconds of whatever, the amount of energy
required for that, again, astonishing,
truly astronomical, but interesting to think about.
I don't want to be accused of telling time tales outside
of time school.
So I'm not the only one thinking about this, obviously.
We can look at theoretical physicist
Carlo Rovelli's assertion that time doesn't exist.
It's not real.
Because, quote, "There is no time variable
in the fundamental equations that describe our world."
So there is no entropic clock that started at zero
and counts up to make the Arrow of Time.
Instead, we use our biology and our experiences to tell time.
And we can infer it from the changes happening around us.
We try and force the universe into
our puny brain-time framework.
And instead, take Hawking's events like donuts.
Even though you see a donut, the donut
is actually changing over time.
It's not a rock.
It's not some kind of imaginary object,
like a box that never changes.
Everything changes over time, stars, space, rocks,
everything.
They're all in flux.
We only experience it as slowly changing because
of our perception of time.
It's imperceptible to us with our puny brain holes.
But we link cause and effect along this timeline.
Yeah.
It's a lot.
I feel like I've been going and going.
And I want to make sure everybody
follows what's happening.
There's no such thing as absolute time.
Time is relevant only for the observer,
whether that observer is a GPS satellite, a donut on a plate,
or Alpha Centauri.
All of those experience time differently.
And that's fine.
Relativity takes care of that.
So we take this idea of individual time,
or you know, no universal time, no absolute time.
We take that perception into a whole new place.
Because what we're trying to do when we explain
time is fit nature into a perfect box.
What the Egyptians were trying to do
when they took the 12-hour day and 12-hour night
was to understand how the Earth was moving in such a way
that you could make a clock or make a way to talk about it.
But it's, again, nature that you're trying
to put in a perfect little box.
And nature doesn't do that.
Even cesium clocks, atomic clocks
that are supposedly so, so accurate
will lose a second every 10,000 years.
Which to you and me, whatever.
To the Earth, 10,000 years, nothing.
Based on timeframe, it's important.
So time that we have now is good for humans, bad for geology,
worse for astrophysics.
There was an ancient Chinese philosophy of time
by somebody named Yi Xing.
And they talked about it as multiple timelines.
There's no such thing as a privileged present.
This was ancient China.
And they're talking about the same thing
we were talking about earlier.
There's no such thing as now.
Time are relationships between events and situations.
Change doesn't happen "over time."
Time and change are the same.
Right?
Weird.
It's not the best system.
It's still flawed.
Why?
Because time doesn't matter.
So if you're still with me, and you're not in the comments
talking about how I'm a crazy person,
time is a relationship between an event and a situation.
Just like Yi Xing said.
So it is, in fact, still flawed.
Because time is only important for the observer.
And Einstein said the dividing line between the past, present
and future is an illusion.
There is no such thing as the past, present and future.
Mathematically, the equations work both ways.
You can move forward or backward with this mathematical equation
in time.
Time is only relevant to the event, the observer.
And this brings us to the idea that it's easier
to quantify the universe, it's easier
to put it on paper with a graph or a diagram,
like, for example, a block universe.
The block universe is everything that has ever happened,
everything that will happen.
And it's all within the block universe.
Even you and me right now and also then and tomorrow,
the block universe is everything everywhere
that has ever happened.
And we know it has.
So thank you for joining Nebula.
Because you already have, right?
I mean, we're still on the Arrow of Time thing.
So let me explain.
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Plus this is episode 3 of 5 of this series.
But you could have watched the whole series already
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So episode 1 through 5 on Nebula from day 1.
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So thanks.
But let's keep going on this time series.
Huh?
So for more on the block universe, come back on Monday.
I know.
I'm such a tease.
Subscribe.
More time explanation tomorrow.
It's going to be so crazy my brain hurts.
I'm running out of coffee.
I don't know what to do.
Share this with a friend whose brain
doesn't hurt or bothers you because they were late that one
time.
And you can be all, like, time is relative, Carl.
Doesn't really matter.
Anyway, thanks for watching.
I'm Trace.
And I will see you in the future.