All language subtitles for Through.the.Wormhole.S02E03.720p.HDTV.x264-DIVERGE.HI

Freeman: Time.

It's all around us.

[ Ticking ]

But is it what we think it is?

Time seems to flow forward...

...But can it run backward?

Do events unfold
one after another,

or do past, present, and future
exist side-by-side?

It's one of the most challenging
topics in science,

questioning our most basic
assumptions about reality.

Is time a fundamental part
of the Universe,

or could it be
that time doesn't really exist?

Space, time, life itself.

The secrets of the cosmos
lie through the wormhole.

♪ Through the Wormhole 2x03 ♪
Does Time Really Exist?
Original Air Date on June 22, 2011

== sync, corrected by elderman ==

What time is it?

I could tell you it's 9:02 p.m.,

but your time may vary,

depending on where and when
you are.

For most of us,

time was a set of numbers we use
to gauge our days.

We live our lives
by the clock --

waking up, racing to work,
going to bed, and on and on.

It wasn't always like that.

[ Birds chirping ]

When I was a kid,
summers were timeless.

I had no particular place to be,

no appointments to be kept.

My days were bounded
only by the position of the sun.

Time didn't matter so much
back then.

Now my life
is a race against time.

But what am I racing against?

Is time a real thing
built into the universe?

Or is it just an abstraction,

something we humans created

to keep our civilizations
running?

For the answer,

we have to ask
a deceptively simple question --

what is time?

Think about it.
Try to define it.

It's not easy.

Time is what keeps everything
from happening all at once,

and so time is
that part of the world

that orders events
in a certain way

so they happen sequentially,
from beginning to end.

[ Chuckles ]

What we're realizing
in neuroscience

is that time is not
what we thought it was.

Time is not something
you're passively tracking.

Instead, it's something

that you're actively
constructing with the brain.

And my brain and your brain
can be very different

in terms of how they see
the same event.

Time just does not exist.

What exists is

these distributions
of everything in the world,

these what I call "nows."

That's the real thing.

What I enjoy about time is
the recording of it.

Freeman:
To Roger Smith, time is money.

His custom-made watches sell

for hundreds of thousands
of dollars.

The hardest part of the job is

to get these jungles
of tiny gears and wheels ticking

at precisely spaced intervals.

To bring a watch to time,

it can be quite a lengthy
and complex process,

and this particular wheel
has to be perfectly balanced.

And if it isn't
perfectly balanced,

then your watch will keep
different rates,

different times
in different positions.

Freeman: Roger's goal is

to get his watches
to match Greenwich Mean Time,

the time that every clock
around the world uses

as its baseline.

It was named after this place --

Greenwich, England.

Time as we know it
was born here.

In 1884,

a world conference decided
that the Meridian Line

that passes through
the observatory at Greenwich

was to be
the initial meridian --

the master time
for planet Earth.

Greenwich Mean Time is
our best approximation of time

as described
by sir Isaac Newton --

a steady beat pounding

behind the scenes
of the Universe.

Newton believed the Universe
was like a giant clock

set into motion by God.

But Newton got it wrong.

Lee Smolin
is a theoretical physicist

trying to solve
the mysteries of time.

Newton's concept of time
was that it was absolute.

It was like a metronome,
which, as you said,

ticks on absolutely,
without regard

to whether anything is happening
in the Universe or not,

even if nothing is happening.

For example,
even if in our studio here,

no music is playing,

the metronome just kicks on
absolutely at the same rate,

no matter what is going on.

The problem with this is
that it's actually impossible

for any of us to detect
absolute time.

We don't detect absolute time.

We detect time as relationships
between things that happen,

and we can illustrate this

by asking the musicians
to start up the music.

One, two, three, four.

[ Band plays
mid-tempo jazz music ]

And they start to play,

and they develop time
between themselves,

a relational time
completely built

from the relationships between
the notes they're playing,

the events they're creating.

That's what time is really like.

So, we can turn
the metronome off.

In fact,
we can just get rid of it,

and the world keeps going on,

the music keeps going on
just as before.

[ Music continues ]

This was the great insight
of Einstein,

and it was the basis of his
general Theory of Relativity --

that time is created
by the relationships

of the changes that happen
in the Universe,

and nothing else.

Freeman: Even today,

some people have
a hard time accepting

Albert Einstein's
relational time

over Isaac Newton's
absolute time.

But the better we get
at telling time,

the more we can see
that Einstein was right.

This is the aluminum ion
experimental clock

at the National Institute
of Standards and Technology

in Boulder, Colorado,

America's official timekeepers.

It's the world's
most accurate clock,

measuring the oscillations
of supercooled atoms.

It keeps time

to within one second
every 3.7 billion years.

In 2010, Boulder's time lords

took two ion clocks side by side
in perfect synchronization,

then moved one of the clocks
up 12 inches.

The higher clock
went out of sync.

It beat just a tiny bit faster
than the lower clock,

because the higher clock is
just a tiny bit farther away

from the gravitational pull
of the Earth,

which slows things down.

Einstein predicted
this would happen

back at the dawn
of the 20th century,

and he was just getting started.

If we perceived the Universe
as Einstein pictured it,

life would not have to flow
in a smooth, linear progression.

A simple act could be cut up
and rearranged

with no logical direction
backward or forward,

no beginning or end.

This is how the Universe
would look

if we were physically unstuck
in time.

Sean Carroll is a physicist

at the California Institute
of Technology.

We live in space.

All around us, there are
three dimensions of space.

What Einstein realized is
that time is also a dimension.

In fact, time and space are
one thing called space-time,

which is four-dimensional.

That's what we live in.

That's what we move in
and live our lives through.

Einstein furthermore realized

that gravity is a manifestation
of the curvature of space-time.

You have stuff
in the Universe --

you know, a planet
or a black hole

or some kind of mass
or energy --

it warps the space and time
around it,

and that's what we see
as gravity.

And it really is the space-time
that gets warped.

It's time as well as space.

So, if you travel close
to a strong gravitational field,

you feel the flow of time
differently than in outer space.

Freeman: The relativity of time
causes a lot of strange effects,

such as time running faster
for astronauts

than people on Earth.

But Einstein's solution
to the mystery of time

opens up an even more
challenging notion.

If we look around,

we see that all of space exists
right here, right now.

So, doesn't it follow
that all of time --

past, present, and future --
already exists, as well?

Could it be that the future
is already here?

Physics says
that all the moments of time

are equally real,

and that tempts us into saying

that they all exist
simultaneously,

they all exist now,
but that's not what it's like.

Different moments of time

are really like different places
in space.

They're not here.

They exist,
but they're somewhere else.

The difference is
that, unlike space,

we can't help
but experience time

one moment after the other.

We can't go back
to moments in the past,

and we can't, right now,
talk to moments in the future.

Freeman: This sort
of temporal dislocation

seems to contradict the laws
of physics and human experience.

Or does it?

Maybe not.

This man would argue

that the world is filled with
people who are unstuck in time

and that time itself
may be all in our heads.

Is time the steady beat
behind the Universe?

Or is time
something that changes

from place to place
and person to person?

The older we get,

the faster the currents of time
seem to carry us along.

Our relationship to time
changes as we age.

Studies show
that the passage of time

seems to increase
by the square root of your age.

So, if at 10 years old,
it's 1:1,

when you're 20, it's 1:1.4.

And by the time you're 60,
it's 1:2.44,

about 2½ times faster.

We all experience time
at one second per second,

but it doesn't feel that way.

David Eagleman of
the Baylor College of Medicine

has spent much of his career

puzzling out
how humans perceive time.

He's found
that our perception of time

is governed by biological
and psychological states.

Many people will wake up
just before their alarm clock,

because as their body's
circadian rhythm

is moving along,

the signals in their body
tell them...

[ Clicks tongue ]

...This is the time to wake up,
and then they pop awake.

Freeman: Our time sense
can also be altered

by things
such as sensory deprivation,

overstimulation,

and altered states
of consciousness.

So, for example,
when people smoke marijuana,

they sometimes feel like, "Wow,
I've been standing here forever.

How long have I been here?"

And it's as though their passage
of time is going slowly,

but it's not exactly about
slow time perception.

I believe it's about their
inability to nail down a memory,

a landmark
of when they arrived there.

And without that landmark,

it feels like they've been there
for a very long time.

Freeman: If you've ever been
in an accident,

you might have experienced
the strange feeling

that the whole event
was playing in slow motion.

But unlike a narcotic haze,

you recall everything
in vivid detail.

This is another case
of memory warping time.

What happens during
a really high-intensity event is

you have an emergency control
center in your brain

that kicks into gear

and lays down very dense
memories during that event.

So, it seems like
it must have taken a long time.

Freeman:
At any given moment,

the brain processes
and synchronizes

an enormous amount
of information.

Simple acts are
actually small miracles

of the mind's speed and power.

When you snap your fingers,
it looks like it's simultaneous.

It looks like
the sight and the sound

are happening at the same time.

But in fact,
what's happening is...

...Your auditory system
is able to take information

coming in through the ears
and process that very quickly,

whereas your visual system
is much slower.

So, what happens is
your brain hears the sound,

and then it sees the sight,

and somehow it has to
take both of those

and stitch them together
and serve up...

[Clicks tongue]

...A single story, which is
that they were simultaneous,

even though the signals
are arriving at the brain

at different times.

This whole thing
is really smeared out in time,

and yet it doesn't feel
that way to us.

It feels as though
the whole thing is simultaneous.

Freeman: It takes
a few millionths of a second

for your brain
to put together information

and serve it up
to your consciousness,

which means that we're all
living a tiny bit in the past.

This time delay is the tradeoff
our brains make

to give us the best story
of what happened.

But when the brain
doesn't get the story right,

it can change
your relationship with time.

Your personal time
becomes different from others',

and that can have
very bad consequences.

Medical journals tell
of the strange case

of the man who went for a drive

and noticed that the trees
and buildings by the road

were speeding by

as if he were driving
at 200 miles per hour.

He eased up on the accelerator,

but the cityscape
continued to whiz by.

This man perceived the world
as having accelerated.

In reality, he had slowed down.

He walked and talked
in slow motion.

He had become unstuck in time.

It turned out
that his time sickness

was caused by a brain tumor.

Whatever time is,
it's deeply wired into us.

We are all clocks
with our own internal time.

David Eagleman suspects

that going even slightly out
of sync with the flow of time

can lead
to serious mental illness.

I think that schizophrenia
might fundamentally be

a disorder of time perception.

So, imagine if there were some
deficit in your time perception

where you didn't know
if your own actions were coming

before or after
the sensory consequences.

What would happen is

you would have
a very fragmented cognition.

You wouldn't know
which things you caused

and which things
you didn't cause.

Freeman: To show how flexible
our personal time can be,

David devised an experiment

that subtly warps a test
subject's perception of time.

Eagleman: So, imagine that
I have you press a button

and that causes
a flash of light.

Now I inject a very small delay,

so that when you hit the button,
the flash of light comes,

let's say,
1/10 of a second later.

What happens is your brain
gets used to that delay.

It starts understanding
that when it puts out this act,

the sensory feedback is a little
bit slower than it expected.

So, it starts adjusting to that,

and it starts to seem
simultaneous to you.

Now, if I remove the delay --

so now you hit the button and
the flash happens immediately --

you will believe

that the flash happened
before you pressed the button.

This is exactly what happens
in schizophrenia.

Somebody will make an act
and say, "It wasn't me.

I don't feel like
I was the one who caused that."

Freeman: Time seems to vary
from person to person,

and the elastic nature
of our subjective time

has caused David to wonder
whether time is, in fact, real.

Eagleman:
I think that time might be

the most stubborn psychological
filter that we have,

and that when we start really
reaching down below that,

when we start
really figuring out

how time is constructed
by the brain,

we're going to have to
go back to physics

and rejig
all of the equations there.

Freeman: Is it possible
to eliminate the human factor

and pull time completely out

of our physical description
of the Universe?

This man says "yes."

He's rejigged
Einstein's equations,

and he's found
that time may not exist at all.

Declaring that time
is an illusion

may sound radical,

but the denial of time
is an old idea --

2,500 years old.

In 500 B.C.,
the philosopher Parmenides

declared that motion
is impossible

because for an object to move
any distance,

it would have to pass through

an infinite series
of fractional steps

to get from one place
to another,

and no one
can take infinite steps.

And if motion is impossible,
then change is also impossible.

So, therefore,
time must be an illusion.

No one knew
quite what to make of this.

Surely, motion is real.

Things do change
and time does pass, right?

Maybe not.

In an ancient village
in the English countryside,

this man thinks that the laws
of quantum physics prove

that Parmenides was right.

His name is Julian Barbour.

Decades ago, he began carefully
laying out a mathematical case

that the universe
doesn't need time,

which is a bit odd,
as he's surrounded by the past.

We're standing in the town,
which is a very ancient street,

and behind me is my home,
built 1659.

Newton was 17 then,

just seriously beginning
to think about time and motion.

Freeman:
If time doesn't exist,

what's all this?

To Julian, everything we see
is an archaeological dig.

Things are there first,

and time is deduced from it
afterwards.

He believes
this 1,000-year-old church

and these
14th-century wall paintings

are proof that the whole of time
exists in slices of space.

Barbour:
Our past is just another world,

or it's another possible
configuration of the Universe.

It's another now.

[ Bell tolls ]

And this is literally true.

The instant is not in time.
Time is in the instant.

Freeman:
Julian's radical view of time

grows out of
the Wheeler-DeWitt equation,

a mathematical exercise
from the 1960s

that sought to reconcile
Einstein's relativity

with quantum mechanics.

A strange thing happens
when you do this.

You're left with an equation
that has no "T" for time.

Since this runs counter
to observable reality,

most saw the equation
as further proof

that quantum physics
and relativity theory

don't play well together.

[ Bell tolls ]

But to Julian,
it was a revelation.

There is no unique history
in quantum mechanics.

And if the evidence

from the attempts to combine
quantum mechanics

with Einstein's
general relativity is right,

there is no time at all.

Freeman: So at the deepest level
of reality,

time doesn't exist.

What matters is
how objects relate to each other

in freeze frames of space.

My view of the Universe --

it's just like a huge collection
of snapshots

which are immensely,
richly structured.

They're not in any communication
with each other.

They're worlds unto themselves.

But each world is so rich

that it's, so to speak,
part of this world.

It's snapshots within snapshots.

This is really what
our life is about.

Freeman: Our brains assemble
these frozen moments

and play them in our minds

the same way
that still photographs

played at 24 frames per second

make the images you're watching
now seem to move.

But nothing is moving.

What we call "time"
is an illusion.

Barbour:
In some very deep sense,

the Universe,
the quantum universe,

is just static.

Nothing changes.

Freeman:
And according to Julian,

all of these snapshots
of the Universe

exist simultaneously.

If I were to say that
my yesterday no longer exists,

it would be like the number 13
saying that 11 has died.

Mathematicians would regard that
as ridiculous.

This instant is so vital
and so alive,

but in a way, it's eternal.

This when you translate that
into mathematics,

it's eternal.

Julian Barbour's view of time
may sound radical,

but it's taken very seriously
by the physics community,

which doesn't mean
everyone agrees with him.

Far from it.

Julian's close friend Lee Smolin

is also one of
his biggest critics.

Smolin:
Time is not an illusion.

Time is not a construction.

Time is not emergent.

Time really is real.

The idea
that time is an illusion

has ignited a civil war
in physics --

a war that pits friend
against friend.

Is time an illusion we create
to make sense of the Universe?

Neurologists and physicists say
it might be so.

But there's another camp
that says we can't ignore

what our senses and observations
tell us,

that time really does exist.

In this view,

we experience the world
as a flow of moments

because that's the way
nature is.

Passage of time is a basic truth

and, in fact, may be the one
true thing in the Universe.

Tim Maudlin
is a philosopher of physics

at Rutgers University.

To say that the passage of time
is really an illusion

suggests that it's not really,
really the case

that I'm getting older
all the time,

that I should be worried
that my death is, every day,

one day closer to me and so on.

But I just can't believe that.

As hard as I try,
I can't believe it,

and it doesn't fit
with the world I live in.

Freeman: For Tim,

it is just common sense
that time exists.

So, why do some physicists
deny it?

Tim thinks
it's an occupational hazard

of working with math.

Our representations in physics
are all mathematical,

and mathematical objects
are not in time.

Mathematical objects
don't change.

So, if you work too much
with numbers

and numbers don't change

and you're using that
to represent the world,

it might seem hard to see

how the world itself
can really be changing.

People seem to be stuck
on the idea

that the world has the features

of the mathematics
that they use to represent it.

That allowed people

to get carried away
with their mathematics

and lose sight
of the physical world.

Freeman:
Julian Barbour believes

space is all there is
and time is an illusion.

Tim says
Julian has got it all wrong.

We need time,
but we don't need space.

Maudlin: We can make space
not fundamental,

but time remains fundamental.

There doesn't have to be
anything more than time,

and you can't do it
the other way around.

You have to start with space
and then get time.

So, time is
at the very bottom level.

I think even this is
what the physics is telling us,

although we haven't been
paying enough attention to it.

Freeman:
Did space come first...

Or did time come first?

This argument
leads all the way back

to the explosive birth
of our Universe --

the Big Bang.

Physicists agree
that the Big Bang created space.

They don't agree
on whether it also created time.

[ Mid-tempo jazz music plays ]

Smolin: There's a lot of people
in physics and philosophy

who think
that time is an illusion,

that what's really true

at the deepest, deepest level
is timeless,

is outside of time.

And I don't believe that.

I used to believe that,

but I've come to believe

that time is really,
really real.

Freeman:
Lee Smolin believes

that time is older
than the Universe --

it was here before the Big Bang,

and it will be here
after the Universe ends.

And he thinks he can prove it

by looking closely at
how particles of light behave

over long distances.

One of the core laws
of physics states

that light travels
at 186,282 miles per second.

If time is an illusion,

then this will be true
everywhere in the Universe,

no matter where we look.

But if time is real,

it's possible that
the laws of physics have changed

as the Universe has aged.

If a basic law of physics
such as the speed of light

doesn't hold true out in
the oldest part of the Universe,

we'll know
that physics has evolved

since the Universe was born,

so time can't be an illusion.

There should be some experiments

where, if you look
very sensitively,

maybe the speed of light
is not Universal.

And there are such experiments
which are being done.

[ Beeping ]

Freeman:
The Fermi Space Telescope

is one such experiment.

Fermi records
gamma-ray bursts --

strange blasts of energy

from the farthest reaches
of the Universe.

These bursts give us the chance
to check out the laws of physics

as they were
13 billion years ago.

Imagine two photons
race out of a gamma-ray burst

10 billion light-years away.

One photon bursts
with more energy than the other.

In our part of the Universe,

both photons will travel
at exactly the same speed.

But if the physics of light
are different

in an older part
of the Universe,

Lee believes
the higher-energy photon

should fall slightly behind.

Smolin: It would break down
at the point where,

after 10 billion years,

one of them would be a second
or two or three seconds ahead,

but that's enough
to be detected.

Even one second worth
over 10 billion years --

we can detect that.

Freeman: The gamma-ray burst
data from Fermi

will come in
over the next few years.

Lee may soon have his proof

that the now
of 13 billion years ago

is truly different from our now,

and therefore,
time must be real.

Conclusive proof that the laws
of physics change over time

would settle the debate

over whether time is real
or an illusion.

But it still leaves
a big question unanswered --

why is there time?

In theory, physics
doesn't seem to need time,

and yet we feel ourselves
moving through it.

If time wasn't born
in our minds,

then where did it come from?

Sean Carroll
thinks he has the answer.

But it takes
an evil-twin Universe

with backward-flowing time
to make it all work.

Theories abound
about how time works,

in the Universe
and in our minds.

But it's a rare physicist
who asks the question,

"Why is there time?"

If time isn't something
we humans invented,

then where did it come from?

Sean Carroll thinks he knows.

Sean is a theoretical physicist

at the California Institute
of Technology.

Time is real.

We use it every day.
The evidence is all around us.

But as scientists,

the more we think about
what time really means,

the more mysterious it becomes.

Freeman: Sean accepts
the common-sense idea

that time moves forward
from the past to the future,

like an arrow.

But why does time have
a direction?

Sean believes
the answer is closely tied

to something called entropy.

What makes time special
is a law of physics,

the second law
of thermodynamics.

The second law essentially says

that as time goes on,
entropy increases.

Entropy is telling us
how messy things are,

how disorderly, how chaotic
things are in the Universe.

So in the past,

if you go all the way back
to the early Universe,

it was very organized.

It was like this delicately
arranged configuration

of billiard balls.

As time goes on,
it's like we're playing pool --

the first thing we do...

...Is we increase
the chaos of the Universe.

As time goes on in the Universe
as a whole,

disorderliness, entropy goes up.

Freeman: Since the explosive
birth of the Universe,

the increase of entropy
is the reason

why the past is different
from the future...

Why there is an arrow of time...

Why we remember the past...

Why we grow older...

Why evolution happens
the way it does.

It's all because
of this increase of entropy.

So, where's the mystery?
Entropy goes up as time goes on.

But interestingly,

in the fundamental
laws of physics

underlying everything around us,

there is no difference
between the past and the future.

The laws handed down to us
by Isaac Newton,

Albert Einstein,
even in quantum mechanics,

you have no distinction

between one direction of time
and the other.

So, if you have
a very simple physical system,

like just two billiard balls,

when you knock one
into the other...

...There is no difference

between one direction of time
and the other.

You could play
that movie backwards,

it would look perfectly normal.

It's only when we get to
complicated, macroscopic systems

that there's a difference
between the past and the future.

When we have lots of balls
on the billiard table,

things happen
in one direction of time

but not the other.

Or when all hell breaks loose
in the pool hall.

[ Both grunting ]

So, now we have noise,

breaking glass,
blood splattering.

These are all processes

that increase the entropy
of the Universe.

Together, all of these increases
of entropy

define the arrow of time.

The question is,

why was the entropy so low
to begin with?

Our Universe seems to be
out of balance.

The far, far future

is going to be
a very, very disorganized place,

but the far, far past
was highly organized.

As physicists, this kind
of imbalance really bugs us.

Freeman:
Sean looked for an explanation

of this imbalance of time,

and he found it
in the multiverse.

According to this theory,
the Universe we see

could be one of an infinite
number of Universes.

Carroll:
Imagine a mommy Universe.

So, this mommy Universe

can essentially give birth
to baby Universes.

A little quantum fluctuation

can make a bubble of space that
starts small and then grows --

starts with low entropy
and then increases in entropy,

just like our Universe does.

Freeman:
So, a mother Universe

gives birth
to a Universe like ours --

a Universe where
the arrow of time moves forward.

But to stay in balance,

it also has to give birth
to a mirror-image Universe,

where time moves backward.

This means that
in some other dimension,

our Universe has an evil twin.

Every bubble is its own Universe
with its own arrow of time.

Within each bubble,
the arrow of time seems fine,

but if you compare different
bubbles to each other,

the arrows will be pointing
in opposite directions.

Freeman:
Sean's multiverse theory

has attracted a lot of attention
since it was introduced.

But will it prove to be
the ultimate solution

to the mystery of time?

Well, part of making progress
in physics is saying,

"What if this is true?
What if that is true?"

And sometimes
when you say "What if?"

You realize, "Oh,
making that hypothetical leap

really helps us with all these
problems we're having."

Other times,
it just gets you in a mess.

Quantum mechanics
and the multiverse theory

give us interesting ways to
grapple with the riddle of time.

What happens when we add
string theory into the mix?

[ Blink! ]

[ Distorted voice ]
Serious weirdness.

[ Slump! ]

The mystery of time
has many possible solutions --

time is absolute
or it is relative;

time is an illusion

or it is the very real product
of entropy.

But there is
one other possibility --

an idea that challenges
our assumptions

about yesterday, today,
and tomorrow.

To us, time seems to flow
from left to right,

but what if it also goes
up and down?

What if time, like space,
has more than one dimension --

a hidden dimension
that we can't see?

Steve Weinstein, a scientist
at the Perimeter Institute,

thinks it could be true

and that it may solve
another great mystery --

the riddle
of quantum uncertainty.

Steve is a physicist,
philosopher,

and professional musician.

His view of time grows out of

one of the most mathematically
dense ideas in science --

string theory.

String theorists believe

that space has more than
the three dimensions we see.

This got Steve to thinking

that the same idea
could be applied to time.

Weinstein:
I thought, "well,

"Why do we multiply
spatial dimensions so freely,

"but not time?

"And, you know,
is there any good reason?"

So there was
a sort of curiosity there.

Freeman:
Steve set to work.

Time has always been treated
as a line --

a one-dimensional thing.

But if time has two dimensions,
then time isn't a line.

It's a shape.

Weinstein: If you look at
this guitar cable from far away,

it looks like
a one-dimensional object.

It just looks like a line.

If you get up close,

you can see
that it has another dimension,

which has to do with
the circumference of the cable.

It's like a cylinder.

Our world
looks three-dimensional

in the same way
that this cable from far away

looks one-dimensional.

Freeman: According to Steve,
if time has an extra dimension,

then fundamental particles
like electrons and photons

are smeared across time.

So, an ordinary way
of describing a particle

would be to talk about
its position

at any moment in time.

So the particle, or the pick,
could be here or here

or here or here or here or here.

So, if I were to graph that

and I had the time
as a vertical axis,

I would just draw that.

Now, if you have
an extra time dimension,

you might visualize
the time dimension

perpendicular
to the guitar neck,

in this direction.

The particle could be --

it might be here,

and it might be here,
and it might be over here.

Freeman:
To put it another way,

quantum theory tells us
that subatomic particles

don't have definite addresses
in space.

We can only guess
where they probably live.

Steve suspects
they do have addresses,

but those addresses
are spread out

across an extra dimension
of time

that we can't detect.

If true,
this revolutionizes physics.

The fuzzy quantum world
suddenly snaps into focus.

But unfortunately,

proving two-dimensional time
is real

may be next to impossible.

For one thing,
it's not easy to understand,

even for other physicists.

The math required
to describe a Universe

with two dimensions of time
is difficult.

Add in the nine spatial
dimensions of string theory,

and people's heads explode.

[ Crash! Cuckoo! Cuckoo! ]

It's very challenging
conceptually.

It's the hardest problem
I've ever worked on,

and I think this is why
more people don't do it.

It's very hard
to think in these terms --

what would an extra time mean?

[ Guitar playing ]

Freeman: Nonetheless,

Steve thinks
it's worth the effort.

Weinstein:
Multiple times is one way,

possibly the wrong way,
but it's a different way of --

and a radically different way --

of conceptualizing
the physical world.

Freeman: The physicists
exploring the mystery of time

have very different ways
of looking at the Universe,

but they all agree on
one thing --

we'll never solve the mystery

if we don't do
the detective work.

Smolin:
You have to work really hard,

and you have to be prepared
to fail over and over again

and to make mistakes
over and over again.

But I think that
that wisdom also applies

to the whole community
of science.

That is, we have to experiment
with every stupid, wrong idea

before we get
onto the right one.

Time may be real

or it may be an illusion.

But from our perspective,

the past is gone forever,

and the future
is yet to be written.

Whether or not we discover

there are physical aspects
of time we can't perceive,

our human experience

of the endless cycle
of life and death won't change.

The golden summers
of my childhood

are gone forever.

But there are
new summers ahead --

summers rich with the potential
of things yet to come.

== sync, corrected by elderman ==