All language subtitles for The universe S07E05 Microscopic Universe

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

As they try to unravel
the mysteries of the universe,

scientists are coming
to an astounding conclusion.

To make sense of outer space,

they need to understand
inner space,

the microscopic matter

that forms the foundation
of everything we see.

But shrinking down
billions of times,

into the realm of atoms
and subatomic particles,

takes us into a strange
unexplored world.

- When we descend
into the microscopic world,

we find that it's really weird,

and indeed downright bizarre
and unbelievable.

Narrator:
The stuff in this universe

is far smaller than anything
we can see with a microscope,

but it holds the key
to the cosmos.

- We can only understand
where we came from

if we understand
this crazy micro world.

Narrator: So let's go
on a fantastic voyage

into an uncharted world

known as
the microscopic universe.

[dramatic music]

♪ ♪

When people talk
about the universe,

they usually mean
the vast expanse of space

billions of light-years across

that they can see
with radio telescopes

and cosmic imaging.

- They think about stars
and galaxies and planets

and all the big stuff
out there.

- You have astronomical bodies

moving under the force
of gravity.

- There are laws of nature,

and you think
that the laws are right,

once and for all.

Narrator: However,
there is another universe,

an unseen world
that governs everything we see.

- When we go down in size
trillions of times smaller

to the microscopic world,

the rules are
much less intuitive

than the ones we're used to
from the large-scale world.

Narrator. The magic
of the microscopic universe

begins at about a ten-billionth
of a meter,

or the size of an atom.

Matter behaves so differently
at this level

that scientists have developed
an entirely new set of rules

to describe
what's going on.

They call it quantum theory.

And what it says
is extraordinary.

- This baseball represents
a subatomic particle,

like an electron
or a photon of light,

that routinely does all sorts
of weird, strange things

in the microscopic universe.

The subatomic version
of this baseball

can be invisible,

can go through solid objects
with ease,

can be in multiple places
at the same time,

and can seemingly
go backwards in time

and change the past.

This means I could throw
this microscopic baseball

to first base and to home plate
at the same time...

or change the seemingly
predetermined outcome of a play

while it's still going on.

Now this—this is the stuff
of science fiction.

But really,
we know it to be true,

or at least, it appears
to be true

in our quantum world.

We get all sorts
of weird things happening.

Narrator:
If scientists can understand

how these weird things work,

they'll be able
to put them to use

in our everyday world,

revolutionizing
modern computing,

and perhaps even allowing us

to communicate
across the cosmos instantly.

The key to making
these miracles come true

is a process called
quantum entanglement,

and scientists
are already harnessing

this astounding discovery

for both civilian
and military purposes.

- In quantum physics,

what happens to an object
over here

can instantly affect
an object over here,

and over here could be
millions of miles away.

Narrator: This is how it works.

When two subatomic particles
interact,

they can become entangled.

That means their spin, position,

or other properties
become linked

through a process
unknown to modern science.

- If you then make a measurement
of one of the particles,

then that instantaneously
determines

what the behavior
of the other particle should be.

And when the experiment is done,

it's found that, indeed,

the other particle's
quantum state

is exactly determined
once you've made a measurement

of the partner particle's
quantum state.

Narrator: That means

if a scientist observes
one entangled particle

and forces it to spin clockwise,

the other entangled particle

will immediately start spinning
in the opposite direction.

That seems intriguing,
but it's hardly earth-shattering

until you consider
that the two entangled particles

can be separated
by billions of light-years,

and still, the moment
you observe one particle's spin,

you've dictated
the other particle's spin.

- That's weird,
because it may suggest

that information
has traveled instantaneously,

faster than the speed of light,

from one particle to another.

I don't understand it.
I don't know that anyone does.

"Spooky action at a distance,"
as Einstein called it.

Narrator:
Quantum entanglement

is more than a curiosity
of the microscopic world

because the effects
of entangled particles

can be seen and felt
in our world.

If scientists can overcome
some fundamental obstacles,

quantum entanglement
could someday help humans

communicate across
vast distances instantly.

- People sometimes think
that quantum entanglement

will achieve the desired goal

of transferring information

at a speed
faster than that of light.

I don't think this
will be achieved,

because to set up these systems,

you had to have
brought them there

at speeds slower
than the speed of light.

But then what do I know?

A hundred years ago,

they didn't think
that we'd be going to the Moon.

Narrator:
Quantum entanglement

is far more likely
to transform modern computing.

Scientists hope to use the magic
of the microscopic universe

to build powerful
new computers.

- We're going to see
what this baby can do.

Narrator: At the Massachusetts
Institute of Technology,

Professor Seth Lloyd

has helped create a prototype
of a quantum computer

which uses quantum bits

rather than traditional
computer bits

to perform its calculations.

- This lab has the world's best
superconducting quantum bit,

or Q-bit, in it.

And when we do quantum
computations with Q-bits,

we can have
the quantum computer

do multiple tasks
simultaneously.

It can do this,
it can do that

at the same time.

It can add two plus two,

it can add one plus three,

and it can add those two things
simultaneously.

Narrator:
The fact that a single Q-bit

can perform many calculations
at the same time

gives the quantum computer
the potential

to be far more powerful
than any computer ever imagined.

Like traditional computers
in the 1950s,

quantum computers
are in their infancy today.

The machines take up large rooms

and can do only
the most basic calculations.

But they hold great promise
for the future.

- Quantum physics
is notoriously weird,

strange,
and counter intuitive.

And so quantum computers use
this weirdness

to compute in ways
that classical computers can't.

Narrator:
The major stumbling block

is figuring out
how to effectively code

classical information—

The ones and zeros
that computers use—

In a way the microscopic
universe can process it

using entangled particles.

But when scientists
figure that out,

quantum computers
could transform the planet.

- Even if you have
a quantum computer

with not that very many bits,

you might still be able
to do things

like break all the codes

that people use
to communicate on the internet.

Or you could solve
very difficult problems

having gajillions of variables,

like try to figure out

what happened
at the big bang.

Narrator:
That may be hard to believe,

but the microscopic universe
gets even stranger.

In fact, the most famous
experiment in quantum physics

shows how one object can be
in two places at the same time,

a result that startled
the great Albert Einstein.

As scientists explore
the microscopic universe,

they find
it's governed by rules

that are often incomprehensible

to those of us
in the normal world.

At the smallest scales
imaginable,

not only does information

appear to travel faster
than the speed of light,

but human observation often
seems to decide what happens.

- It seems like the behavior
of quantum mechanical stuff

is different
when we're looking at it

than when we're
not looking at it.

Narrator:
This profound conclusion

comes from performing
the double-hole experiment.

Scientists first conducted
this experiment a century ago,

firing photons of light through
a metal plate with two slits.

The light that went
through the holes

hit a screen behind the plate.

- I'm going to demonstrate
the results

of this amazing experiment

with a bunch of baseballs

and a barrier
that we've set up

which has two holes in it.

Now, normally,
in the everyday world,

if I throw baseballs
through one hole or the other,

they'll form
a predictable pattern

on a screen that we've set up
behind home plate.

They'll be in one place
or the other.

Now, let's make that pattern
with a whole bunch of baseballs.

I'm going to use
this pitching machine.

Here's the first one.

Let's see what happens.

Now, you see?

The balls landed on the screen
in two bunches,

pretty much along a direct line
from each of the two holes.

That's natural.
That's what we expect.

But when we descend
into the microscopic universe

and use electrons,

which are 10 trillion times
smaller than baseballs,

we get a very different,
odd result

when we perform
this experiment...

A pattern that you would expect
if these were waves

going through both holes
at the same time

and interfering
with themselves.

Well, we usually think
of electrons

as being particles.

So how can they exhibit
wavelike properties?

Narrator: These test results
were confounding.

The electron was a particle

before it was fired
at the screen;

yet it formed a pattern
on the screen

as if this single electron

had gone through both holes
at the same time.

Does a microscopic particle

spontaneously clone itself
in midair?

After years of study,

scientists still don't know
exactly what's happening.

- Probably
the most magical thing

is that in quantum physics,

an object can be in more
than one place at the same time.

- It actually can sense
both slits

and actually go through

and quantum-mechanically
feel the structure

of both slits
in the experiment.

- Most physicists agree
that the math is quite solid

and leads to solutions
that are undeniable

and can be confirmed
with experimental measurements.

But exactly what is happening,
and how,

is a matter of debate.

Narrator: To try to grasp

this amazing
experimental result,

scientists decided to observe
how individual electrons behaved

when they went through
the double slit.

How exactly could a particle
go through both holes

at the same time?

- Scientists got
a front-row seat

to observe the strange behavior
of these electrons

or other subatomic particles
or even photons of light.

Doesn't really matter,
as long as they're small.

They didn't just look
at where they landed

on the screen back there;

they also watched the behavior
of the particles

as they went through the holes.

And then they saw
something amazing.

When scientists were watching
the holes,

the electrons behaved
like particles,

forming the baseball-like
pattern

on the screen back there.

But when the scientists
weren't watching,

then the electrons behaved
like waves.

They formed a pattern
that looked like

the interference pattern
produced by waves on a screen.

That's really strange.

What you see depends on whether
you're watching or not.

If you're watching,

you see the particle-like
behavior like baseballs.

If you're not watching,
you see a wavelike behavior.

But not both at the same time.

Narrator: This was nothing less
than astounding.

Observation seems to change

the nature
of subatomic particles.

- Mysteriously,
when we're not looking,

things are waves.

When we are looking,
they look like particles.

So even an electron,

which seems to us
like a particle,

has wavelike properties
when we're not looking at it.

- The fact
that when we don't look,

the electron appears
to go through both holes,

but when we do look,
we always see it

go through one hole
or the other

is what we call
the quantum enigma.

Narrator:
How could our decision

about whether
to observe something

change how that something acts?

There is
a technical explanation.

- To make an observation,

you somehow have to interact
with a system.

For example,
you have to shine light on it,

which then bounces off,
and you observe the light.

That's how we can tell that
a baseball is here or there:

we bounce light off of it.

Well, for macroscopic particles,

that doesn't disturb them
very much.

But for microscopic particles,

the act of bouncing the light
off of the particle

changes where it is
and how it's moving.

Narrator:
So in the microscopic universe,

where photons of light
are about the same size

as subatomic particles,

these photons have a big impact

when they illuminate
the particles

SO we can see them.

But this doesn't answer
the question

"Why doesn't the light

"simply change the direction
of the subatomic particles?

"Why does observation
actually change

the nature
of what is being observed?"

- The short answer is,
"We don't know."

This is the fundamental mystery
of quantum mechanics,

the reason why quantum mechanics
is difficult.

Mysteriously,
when we look at things,

we see particles.

Then when we're not looking,
things are waves.

- This is something

we scientists have argued
passionately about now

for almost a hundred years.

And there's still no consensus.

Narrator. When they were
first released a century ago,

these test results
were enough to unsettle

the brightest mind
in science.

- Einstein said,

"I don't believe
in quantum physics,

"because I believe
the Moon is there

even when I'm not
looking at it."

Einstein was of course referring

to the implications
of the theory

that the Moon
really isn't anywhere

until it's observed.

Narrator. However,
the double-hole experiment's

mind-boggling conclusions
don't end there.

In recent years, technology
has allowed scientists

to perform a fascinating
variation of the test.

Its results call into question
our perception of time itself.

- This is like
a high-tech version

of the double-hole experiment.

Electrons are being fired
toward a barrier

with two holes in it.

But the scientists
can delay their decision

about whether
to observe the electrons

until after they've passed
through the holes,

but before
they hit the screen.

It's as though
I'm on a baseball field

and there's a baseball
being pitched toward the barrier

with the holes in it.

But my eyes are closed,

so it goes through
and it behaves like a wave.

But then, at the last second
before it hits the screen,

I open my eyes
and decide to observe it.

Narrator: At that moment,

the electrons, in essence,
become particles

and seemingly
always were particles

from the time they left
the electron gun.

- So it's as though
they went back in time

to before they went
through the holes

and decided to go through
one or the other,

not through both,
as they would have,

had they been
behaving like waves.

That's really crazy!

- That's the enigma:

that our choice
of what experiment to do

determines the prior state
of the electron.

Somehow or other
we've had an influence on it

which appears to travel
backwards in time.

Narrator: Scientists
are only beginning to grasp

what these microscopic mysteries
mean for time travel

and changing the past
in our everyday world.

But one thing is clear.

The rules that govern
this subatomic world

hint at a universe
that's just as mysterious

as science fiction.

In fact, quantum physics
may suggest

that reality is simply
a figment of our imagination.

After discovering mysteries
in the microscopic universe,

scientists wanted
to quickly unravel,

study, and solve them.

But as they tried to figure out
exactly what was going on

in this strange
subatomic realm,

they found something
completely unexpected.

Nature refused to tell them.

- When we descend
into the microscopic world,

we find that there's
a fundamental uncertainty

in essentially all quantities
that we wish to measure.

And it's not a problem
with the measurement process.

It's that nature herself
does not know.

Narrator: Scientists call this
the uncertainty principle.

And as strange as it is,

it may be
the most profound concept

to emerge
from the microscopic universe.

We simply cannot know anything
with absolute certainty.

- In our everyday world,

we think we know a lot
about the things around us.

We can actually locate,
for example,

the position of this cue ball

and strike it
at a certain speed,

which we know,

and we can use that
to collide it into other balls,

and go ahead
and play a game of pool.

But what actually happens

if we shrink everything down
trillions of times?

In that world,
these pool balls

are now actually
like subatomic particles.

Narrator:
In this microscopic realm,

quantum physicists have found

they simply cannot determine
with any precision

where these particles
are located

because of their
wavelike qualities.

And what's even stranger:

if scientists try
to box in a particle,

it will always generate
enough energy

to break out of the box

before its position and speed
have been determined.

The uncertainty principle says

nature will not allow
its fundamental elements

to be boxed in.

- So because
in the microscopic world—

Because particles will interact

with a completely different
set of rules,

the rules of quantum physics,

microscopic pool will be
a completely different game.

Narrator: The uncertainty
of the microscopic universe

extends far beyond
the location of particles.

It applies to everything,
including a particle's energy.

And this gives rise
to a stunning phenomenon

called quantum tunneling.

- In classical physics,

if you throw a ball
at a wall

and you don't throw it
hard enough,

it won't go through the wall;
it will bounce back.

But if it's an electron

and you don't throw it
hard enough

to go through the wall,

it might go through anyway.

We call that quantum tunneling.

Narrator:
How can this be possible?

It may sound bizarre,

but one way to explain
quantum tunneling

is that the uncertainty
of the microscopic universe

allows a particle
to borrow energy

from the future
to breach the barrier

and then pay it back

after it gets
to the other side.

- The electron actually
already is

on the other side of the wall,

and therefore,
it can go through it

and appear on the other side
of the wall.

Narrator:
Ever since these wonders

of the microscopic world
were discovered a century ago,

people have asked
if quantum tunneling—

Being in multiple places
at the same time

and what appears to be
traveling backwards in time—

Can be achieved
in our everyday world.

Some scientists say
we'll never be able

to throw a baseball
through a solid barrier.

- A baseball is a huge number
of particles.

You would need all of them

to collectively suddenly appear
in another place

for the baseball, as a whole,
to appear in another place.

And that's just
extraordinarily unlikely.

A single electron
or a single proton can do this.

But the bigger your particle,

or the bigger
the collection of particles,

the more difficult
that process of tunneling is.

Narrator. However,
a growing number of physicists

are developing
a more outrageous theory

for what's going on.

- We know that
these tiny particles

can be in two places
at the same time.

But, hey, I'm made
of these kinds of particles.

So if they can be
in two places at once, so can I.

Narrator: Scientists call this

the many-worlds interpretation
of quantum physics.

They say, just like the electron
in the double-hole experiment,

human beings are all in multiple
places at the same time.

They say anytime
anyone makes a decision,

we don't actually choose
one option over another.

Instead, we do them both,

in slightly different versions
of reality.

- What happens when you use
your mind

and your will
to decide things is,

you end up actually
making many choices at once,

and all of them become realized
in different parallel universes.

- The many-worlds hypothesis
of quantum physics

says that when
I throw a curve ball,

I do so
only in this universe.

In another universe,
I might be throwing a fastball.

And in still another one,
I throw a knuckle ball

for the first time
in my life.

And in yet another universe,

I heave this ball
to the outfield.

In the many-worlds hypothesis,

all of these choices
are outcomes

that occur in universes
that are parallel to our own—

Just not in ours,
but in parallel universes.

That's what the many-worlds
hypothesis tells us.

Narrator: This may sound
far-fetched,

but an impressive array
of theoretical physicists

believe it's the way
the microscopic world works.

If it's true, the implications
of this startling theory

go far beyond
the baseball diamond.

In essence,
it suggests there are universes

parallel to our own
in which

the Nazis won World War I will.

And in another,
the American government

foiled the 9/11 hijackers.

So the world trade center
still stands in Manhattan.

- If you take quantum mechanics
absolutely at face value,

it says that every time
you observe

something quantum-mechanical,

you become two different copies
of yourself.

There's the copy
that got one answer

and a copy
that got another answer.

It just implies
there's a huge number

of other copies of you

that saw slightly different
things happen

in the universe.

- These days,
it's completely accepted

that the micro world is weird.

Many people had hoped
that this weirdness

could be confined
to the micro world

so that big things like us
would be immune to it

and always be
in a single place.

But it's become clear now
that that hope...

[laughs]
Was naive.

The weirdness can't be confined.

Narrator:
The fascinating debate

about the many-worlds
interpretation

of quantum physics

will rage until physicists
finally solve

the mysteries
of the microscopic universe.

However, some astronomers
are concluding

that we will never
be able to fully explain

any of these mysteries,

because, according
to their calculations,

the vast majority of matter
holding the universe together

exists in a higher dimension
that we can never explore.

If there's anything
in the microscopic universe

stranger than quantum particles,

it's the mysterious matter
that scientists have never seen

but that plays a crucial role
in the formation of planets,

solar systems, and galaxies.

- Astronomers know that there's
all sorts of matter out there

that exerts
a gravitational influence

but that we can't see.

We call that dark matter.

- I wouldn't exist
if it weren't for dark matter,

because dark matter
has this nurturing force

of bringing things together
to form structure,

to form galaxies,

which are absolutely necessary
for life.

Narrator: Dark matter makes up
a staggering 85%

of the gravitationally
attractive stuff

in the universe.

- If the dark matter
is some kind of particle,

then typically, millions
of dark matter particles

will pass through me
every second.

Narrator: But even though
they know dark matter exists,

astronomers have been confounded
by a microscopic mystery:

what is it?

At first, they thought
it was ordinary matter that,

for some reason,
they couldn't see.

- But what happened was,

astronomers went
and took an inventory.

We know how much ordinary matter
there is in the universe.

By "ordinary matter,"
we basically mean atoms,

things that are made
out of protons,

neutrons, and electrons,

the elementary particles
that go into making you, me,

everything on Earth.

And it just doesn't measure up.

There's not nearly enough
ordinary matter

in the universe
to make up the total.

Narrator:
This conclusion was bizarre.

How could most of the matter
in the microscopic universe

not be made of protons,
neutrons, and electrons?

- It's been quite shocking
to discover

that these atoms
actually make up

just a small minority of all
the stuff in the universe.

There's six times more

of an altogether
different substance

which is invisible to us.

- It's interesting to think
that science has brought us

to the point where we realize

not only are we not
the center of the universe;

we're not even made
of the same stuff

as the universe is made of,
for the most part.

Most of the stuff
in the universe

is this dark matter,

and it's some small particle

beyond the reach
of our direct detection.

Narrator:
Some theoretical physicists

speculated that dark matter
might be made of neutrinos—

Tiny particles

a thousand times smaller
than an electron

that fit many of the known
characteristics of dark matter.

- We know neutrinos exist.

And they have mass.

They contribute weight,
so maybe we're done.

But now it's turned out
that they're not neutrinos.

- Most of the dark matter is
probably not normal neutrinos,

because they travel
very, very quickly.

And they wipe out the formation

of what's called
large-scale structure,

the clumping of material
on the scale of galaxies,

early in the universe's history.

So it would be much harder
to produce galaxies

if the universe is filled

with lots and lots
of neutrinos zooming around.

- So the dark matter
is not ordinary matter.

It's not neutrinos.

It's some wholly new
kind of particle

that we haven't detected yet.

- It has to be some sort
of weird subatomic particle

left over from the big bang,

when the universe
was very hot and dense.

A whole zoo of particles
was created.

Most of them annihilated
or decayed into other particles.

But some were left over,

and they are what are thought
to be the dark matter.

Narrator: But what could this
exotic microscopic particle be?

Since it's nothing known
to science,

astronomers proposed
an entirely new particle

that embodied all of
dark matter's characteristics

and then began
searching the universe for it.

They call it a WIMP,

a Weakly Interacting
Massive Particle.

- One of the problems
with the WIMP hypothesis

is that we've never actually
detected a WIMP in a laboratory.

- In fact,
there's several experiments

going on right this minute

to look for WIMPS
in underground laboratories.

And you'd also like to make them
in particle accelerators,

like the Large Hadron Collider
in Geneva.

So there's a multi pronged attack
to detect WIMPs directly

if they're the right answer.

Narrator: If scientists find
evidence of dark matter,

will they also find evidence
of another world

of dark planets...

dark life-forms...

and a dark matter
table of elements?

- I don't think
they are like us,

in that
the dark matter particles

can form planets
and so on,

because if they could,
then we would expect

most of the planets
in our solar system

to actually
be made of dark matter.

But I think
it's much more likely

that the dark sector

is many different kinds
of particles

that are much more complex
than just one.

Narrator:
However, modern science

still has not found evidence

of this mysterious
microscopic material.

And a growing number
of scientists argue

that's because
it's not something else;

it's somewhere else,

like other dimensions.

- People have taken
very seriously

the idea that the dark matter
comes from other dimensions,

or represents ordinary particles

that are actually moving
in the other dimensions.

The thing
about other dimensions are,

we don't see them,

we don't interact with them
very strongly,

so they're a natural place
to put the dark matter.

- It's conceivable that
the gravitational influence

in galaxies
and clusters of galaxies

that we attribute to dark matter
in our own universe,

is actually caused
by concentrations of matter

in other dimensions

that are felt
within our dimensions

but will never be discovered
within our dimensions

because they're actually
somewhere else.

Narrator:
Whatever or wherever it is,

many physicists are confident

they'll eventually discover
a complete solution

to the dark matter mystery...

unless, they say,
it simply exists

at an incredibly small size,

far smaller than humans
have ever been able to explore.

That raises the question:

"What does exist
at the smallest scales

of the microscopic universe?"

That's what viewer Jason L.
from Houston, Texas,

wanted to...

- Jason, I'm glad you asked
that question.

The smallest things
in the universe

are the fundamental
subatomic particles,

like electrons

or the quarks that make up
protons and neutrons

or neutrinos.

Now, all these particles
are thought to be

different vibrational modes

of a little tiny entity
called a string,

a little tiny package
of energy.

And that, then,
is the smallest thing

from which
everything else is made.

Narrator:
Scientists have just started

trying to explore strings,

and other incredibly small stuff
in the microscopic universe.

And what they found
offers tantalizing clues

to a world beyond.

As they delve
into smaller and smaller spaces

in the microscopic universe,

scientists have successfully
looked inside atoms.

But what exists if we continue
our fantastic voyage

still deeper
into this subatomic netherworld?

- Even scales that are smaller
than the electron

are really a vast
unexplored territory,

more so than solar systems
or galaxies

or even the universe,

because we can make observations
of planets and stars

and galaxies and the universe,

but it's hard
to conduct experiments

that allow us
to directly explore

tiny scales
in time and space.

- Essentially,
what you need to examine

the microscopic world
is a sharper and sharper tool,

something that actually
allows you

to distinguish the details
down at that very small level.

Narrator: But as scientists

try to probe spaces
smaller than the atom,

they cannot possibly
focus enough light

to illuminate them.

They need something
more powerful.

- To look more finely,
you need more energy.

We can go
to incredibly small details

using high-energy devices
of various kinds.

Now, the state of the art

are actually
particle accelerators.

We use elementary particles

to actually probe the structure
of other elementary particles

by colliding them together,

letting them interact
with each other

and then seeing what comes out
at various energy scales.

So we can continue this process

of examining
smaller and smaller distances

in space and time

by actually going
to higher and higher energy

with collider experiments.

[explosion]

Narrator: However,

the world's largest
particle accelerators

have not yet generated
enough energy to probe things

much smaller than the elementary
particles inside atoms.

Even so, scientists believe
something exists

at even smaller scales,

at a size so tiny,
the human mind

cannot possibly
comprehend it.

- Physicists are now trying
to understand

what's called
the Planck length,

10 to the minus 33-power
centimeters.

That's 20 factors of 10—

20 orders of magnitude
smaller than an electron.

Now, an electron is yea big,
and I exaggerate a lot.

So the Planck length is just
almost unimaginably smaller

than any objects
we can actually measure.

Nevertheless,
physicists are trying

to deal with these scales.

And that's what string theory
is all about.

- String theory says
that everything

that we think of as a particle

is actually a tiny
vibrating loop of string.

To get an idea
of how tiny it is,

I have here an eyedropper.

We're going to put out
one drop of water.

That has about
a trillion trillion atoms

of hydrogen and oxygen.

Now imagine taking
one hydrogen atom

and blowing it up
by 10 billion times.

It becomes
about 1/2 a meter across.

And you might say,

"Can we now see
the individual strings

inside that hydrogen atom?"

But the answer is no.

We can continue
to make it bigger,

make one hydrogen atom
the size of the solar system.

The strings are still
too small to be seen.

It's only when we make that atom

the size
of our observable universe,

that a string becomes
macroscopically large.

If one hydrogen atom is as big

as the whole observable
universe,

how big is a string?

Only about the size
of one of these trees.

The amazing thing
is that we human beings

can even talk sensibly

about what exists
at this microscopic scale.

Narrator. Not only can
scientists talk sensibly;

they've also formulated theories
about what happens down there.

- This is really
one of the holy grails

of all of science.

- We think that
ordinary space and time

cease to exist
at the Planck length.

What we don't know
is what takes their place.

We need to replace our idea
of space itself

by something
more fundamental,

something that might involve
different numbers of dimensions

or just a different concept
entirely.

Narrator: One possibility is
that space at the Planck length

resembles the grid
on a football field.

The yard lines are the fabric
of our universe,

and there's simply nothing
in between.

- It could be that time jumps

from one discrete point
to another,

and there are no steps
in between.

- And, like,
little quantum mechanical ants

could tunnel
from one spot on the grid

to another spot on the grid

without ever going

into the intervening space
in between.

Why?

"Cause there isn't any
intervening space in between.

Narrator: Whatever exists
at this incredibly small scale,

most scientists believe that
the concepts of space and time

segue into another kind
of universe

where shrinking smaller
is a meaningless concept.

- It could be that
time and space

are what we call
emergent properties

of the universe,

but that if you go
to very small spatial scales,

or very small intervals of time,

the concepts of time and space
break down.

They don't make sense.

Narrator. Scientists say the
conditions at the Planck length

may be very similar
to those that existed

before the big bang,

when everything
in our universe

was probably concentrated
in a microscopic pinpoint.

- Maybe the same answers
to the question

about what happens
to the universe

at the very smallest scales

may also be connected
to knowing,

what was the universe like
before the big bang?

Did it just come into being
at the big bang,

or was there something different

which then turned into
the universe

that we're familiar with
at the big bang?

These are all questions
we don't know the answer to

but are all connected
to the issue

of what's going on
at the Planck scale.

- You might think that
these tiny Planck-scale things

have nothing to do with us,
who are much bigger.

But actually, it has everything
to do with us.

It's our origins.

Our entire universe,
if we extrapolate backwards,

would have been smaller
than the Planck length.

Narrator: Whatever exists
at the smallest scales

of the subatomic world,
and however these things behave,

scientists say
they must make sense of it all

before they can possibly
comprehend the cosmos above,

human behavior,

and what might have existed
before the big bang.

It's a mind-boggling amount
of information

tucked inside
an unimaginably small space

of our microscopic universe.