TYSON: We inhabit a cosmos of undiscovered dimensions
and paradoxical realities.
We live on one level of perception,
but there are others.
Every once in a while, a searcher happens upon
the doorway to one of these other levels.
One of them discovered a paradox about reality that
proved to be so profound, we have yet to understand
how it could be possible.
The universe, or perhaps we should say,
universes have never been the same.
♪ ♪
[theme music plays]
♪ ♪
Nature writes her most intimate secrets in light.
The light from our star that powers all life on this world.
The light that plants eat to make sugar.
The light that is the yardstick of the universe,
stitching diamonds into the fabric of space and time.
The imprisoned light that defines black holes.
The absence of light that prevents us from knowing
what dark matter and dark energy are.
"Seeing the light" usually refers to a religious epiphany,
but no one is more light-obsessed than astronomers.
And as soon as they began studying light,
it challenged even the very best of them.
Take Isaac Newton, for example.
He was so desperate to understand the nature of light and colors,
he was willing to stick needles in his eyes.
No, I mean literally.
Newton was only in his mid-20s,
but he had already laid the foundations of a new branch of mathematics called "calculus,"
and he was conducting a series
of experiments that led him to conclude that color was an aspect of light.
Newton wanted to find out which of the things we see
are properties of light and which are caused by our nerves.
Was color hiding inside the light?
Or was it in our eyes?
With a burning desire to know,
he took a needle called a bodkin and
Newton carefully noted that if he conducted
the experiment in a room filled with light,
even with his eyes shut, some light would pass through
his eyelids and he would see a great, broad blue-ish circle.
It may not sound like much of a result considering the pain,
but it was with simple homemade experiments such
as this one that Isaac Newton became the first person to explain rainbows,
and how white light hides a whole
palette of colors inside itself.
Most people thought of the events Newton studied as
being just the way things were.
The way an apple falls.
The way a ray of light shines through a window.
Newton's greatness stemmed from his questioning of the
"why" and "how" of ordinary things.
Newton asked, what was light made of?
If you could break light apart into its tiniest components,
what would you see?
Newton noticed that light moved in straight lines.
How else to explain the edges of shadows?
Or the straightness of the inspiring rays of sunlight
that poke through a cloud?
Or the darkness that resulted from a total solar eclipse?
From these observations, Newton reasoned that light
must consist of a stream of particles,
or corpuscles as he called them,
that a ray of light was like a stream of bullets striking
the retina of the eye.
But there was one man over in Holland,
who vigorously disagreed with Newton's particle theory of light.
Christiaan Huygens shared Isaac Newton's insatiable curiosity,
and when it came to changing the world,
he was no slouch himself.
Despite a lifelong struggle with depression,
he managed to get a lot done.
While looking through a telescope that he designed and built himself,
he discovered Saturn's moon, Titan.
Huygens invented the pendulum clock.
He worked out the mathematical formulas necessary to create
a pendulum with an arc that would accurately and
consistently measure out uniform increments of time.
Huygens sketched a prototype for a new machine
that he thought might have some promise.
It was what he called a "magic lantern."
A few hundred years would pass before it evolved into
a working motion picture projector.
But back in the 17th century,
Christiaan Huygens already had an idea for a movie,
possibly influenced by his gloomy disposition.
Huygens, like Newton,
also invented his own new branch of mathematics,
a predictive theory of the outcomes of games of chance,
probability theory.
A way to call heads or tails.
And like Newton, Christiaan Huygens had his own theory of light,
but it was very different.
He didn't think light consisted of particles like
bullets firing along a single path.
Huygens saw light as a wave,
spreading out in all directions.
[speaking in native language].
TYSON: It was already known in that time that sound must travel as a wave.
How?
Because a voice could be heard around a door when it was slightly ajar,
so sound must travel around the door as water would,
like a wave.
[speaking in native language].
TYSON: Huygens thought that light moved the same way sound did,
spreading out as waves.
♪ ♪
So, which genius was right?
The answer to that question of whether light was a particle
or a wave would prove to be complicated.
Now enter Thomas Young.
The man who exposed the enigma at the heart of light
and unraveled the fabric of the cosmos that we thought we knew.
Come with me to one of the greatest mysteries in the history of science.
It's a story about a man who could do just about anything,
and Thomas Young did.
For 1500 years, no one had been able to decipher Egyptian hieroglyphics.
By identifying six major sounds that the hieroglyphics represented,
he was able to decrypt six of the symbols,
which led to the complete translation of the ancient
Egyptian language by others.
He was the first to chart the family tree of the Indo-European languages.
As a physician, he identified a deformity in the shape of the eye,
the defective vision he named astigmatism.
But it was Young's design of an experiment that sent
physics down the rabbit hole we still live in.
It looks simple, right?
How could three sheets of cardboard set such a catastrophe in motion?
A green glass shade like this one will only allow the green light through,
so that only a single color,
or frequency of light will pass through the slits.
Why was that important?
Because he assumed that the many overlapping colors would
result in the same light wave that Huygens imagined,
called an interference pattern.
He forced that single color of light to travel through
two separate slits to see what kind of pattern the light
would make on that last piece of cardboard.
If light was a particle, you'd expect to see two distinct
clumps of light on the opposite wall,
where the individual particles of light ended up
after they passed through the slits.
But that's not what happened.
Instead, a completely unexpected pattern.
The one that two waves would make when they overlapped,
or interfered with each other.
That's why they're called an interference pattern.
Young had demonstrated that light was actually a wave.
That Newton, the greatest genius in the history of science was half wrong.
That light was not a particle as he confidently proclaimed.
There's a reason that arguments from authority
hold little weight in science.
Nature and nature only settles the argument.
And she has so many tricks up her sleeve,
only a fool would ever consider our understanding of nature complete.
Newton had missed something fundamental.
Surprising, but we haven't gotten to the really disturbing part yet.
TYSON: Thomas Young left a time bomb with a long fuse.
One that took 100 years to burn down before it exploded.
It wasn't until the end of the 19th century that science
developed the necessary tools to find an opening to a hidden universe,
a realm of deeper mystery.
You can hear the discoverer's astonishment in his own account.
THOMSON: Could anything, at first sight,
seem more impractical than a body which is so small that
its mass is an insignificant fraction of the mass of an atom of hydrogen?
Which itself is so small that
the crowd of these atoms equal
in number to the population of the whole world would be too small
to have been detected by any means then known to science.
TYSON: That voice, that particular organization of
sound waves frozen in time nearly 100 years ago,
belongs to J.J. Thomson.
He's remembering his discovery of the electron in his cathode ray experiment.
He had heated up a metal electrode until it spit out an electron.
And another, and another.
For the first time, an elementary particle of
the atom was made visible.
Science was breaking into nature's vault where she had
kept her most closely held secrets,
and that's when things got really crazy.
If even the smallest units of matter, atoms say,
had even smaller components, such as an electron,
then could the same thing be true of light?
Scientists, in their never-ending fascination with light,
set out to devise ways of isolating smaller
and smaller units of it.
It proved to be the passage way through the looking glass.
It was the crossing of a threshold into a wonderland
where the known rules of physics do not apply.
For the first time, they were able to isolate the tiniest unit of light,
a single photon.
And to perform Young's double slit experiment on a whole new level,
tracing its precise path either through the right slit or the left slit.
We'll pull over to the side of the road for the best possible view of which slit,
the right or the left,
the photon passes through to get to the far wall.
Left slit, right slit.
Another right slit.
Left slit.
If we watched them all day long,
the pattern would be random.
About half would go through either slit.
Wait a second.
Where are the waves?
Where is Young's interference pattern?
This is where the weird begins.
I cannot explain to you what you're about to see.
That's because no one on earth understands it yet.
If you can't live with that,
then you're not gonna be happy with what lies up ahead.
On the smallest possible scale that we've ever discovered,
the quantum universe, the mere act of observation changes reality.
Okay, photons, keep on coming, and this time we promise not to look.
You're not gonna believe this, but we can change the pattern
on the far wall simply by not watching which slit the
photons pass through.
I know it sounds crazy, but in every trial ever conducted,
the outcome depends on whether or not the experiment was observed.
So, the reason we didn't get the interference pattern
earlier wasn't because we chopped up the light into single photons,
it was because we were observing which slit
the photons passed through,
but how can a photon know if someone is watching?
A photon doesn't have eyes.
A photon doesn't have a brain.
How could it know it was being watched?
You might reasonably conclude that a single photon is such
a tiny thing that it's very hard to see without using complex technology.
This machinery does violence to the delicate photon.
It changes it, but that doesn't explain why photons
behave like particles when we're watching but waves when we're not.
If light is fundamentally a particle,
then it should never create a wave pattern,
whether we're observing it or not.
And how can individual photons know where to take their places,
so that as a group they create the interference patterns of waves?
This is a maddening conundrum at the heart of quantum physics.
Isaac Newton and Christiaan Huygens were both
equally right and equally wrong.
Light is both a wave and a particle, and neither.
Until we make an observation,
the photon exists in a state of uncertainty,
governed by laws of probability.
And when we do observe it,
it becomes something completely different.
We would be lost in the quantum universe without Christiaan Huygens.
His probability theory provides, even now,
the only key we have to grasping the laws of quantum reality.
Every particle is at the mercy of random chance
and shifting probabilities.
Thinking about it is like looking at an optical illusion,
you can only grab hold of it for moments at
a time before it pops back into something else.
In the quantum universe, there's an undiscovered
frontier where the laws of our world give way to the ones
that apply on the tiniest scale we know.
They're divorced from our everyday experience.
How can you think about a world that has different rules than ours?
It's not easy.
That's why I want to take you to this place where it's not
only possible to make such a leap, it's mandatory.
It's a world very much like our own,
except in one respect.
It just happens to be missing a spatial dimension,
the third one.
TYSON: In order to venture into the quantum cosmos,
we have to be able to imagine another dimension.
That's very hard to do.
It's much easier to wrap your mind around a world that's
missing one of the three dimensions that we take for granted.
The beings of the world we're about to enter have only two.
This world was first imagined by a man named Edwin Abbott.
Everyone and everything here and everyone they know
and love is flat.
Their houses are flat.
Some are squares, others are triangles.
Some have more complex shapes, say octagons.
But all are completely flat.
They scurry about on foot or in little vehicles,
in and out of their flat buildings,
busy with their flat lives.
Everyone on this world has width and length,
but no height whatsoever.
These Flatworlders know about left-right and forward-back,
but have no hint, not an inkling, about up-down,
except for one tiny group,
the mathematicians, who imagine something more.
The mathematicians dream of a world in three dimensions,
but it's too hard for most of the Flatworlders to think about.
The mathematician says,
"Listen, it's really very easy.
We all know left-right.
We all know forward-back.
So let's just imagine another dimension at right-angles to the other two."
But the Flatworlders say,
"What are you talking about?
At right angles to the other two?
Everybody knows that there can only be two dimensions.
Go ahead, wise guy, show us that third dimension.
Where is it?"
So the mathematician draws a picture.
Poor teacher.
Nobody listens to mathematicians.
Every creature on flatworld sees its fellows as merely short lines,
which are the nearest sides of their oblong bodies.
But the insides of a Flatworlder are forever mysterious,
unless exposed by some terrible accident or autopsy.
And then one day, we came along.
Hello? How are you?
Hi, I'm a visitor from the third dimension.
Hello? I feel sorry for the little guy.
To him, it appears that my greeting is emanating from his own flat body,
an alien voice from within.
That's because nothing can come from above.
There is no above in this world.
A three-dimensional creature like me can only exist
on Flatworld where my feet touch the surface of the plane.
Sorry, little guy.
I know how weird this must be for you.
Don't worry.
You'll have a perfectly safe trip to the third dimension.
Nothing's gonna harm you.
But this is your chance to see a whole new perspective
on where you live.
At first, our Flatworlder can make no sense of what is happening.
It's utterly outside the realm of Flatworld experience.
But eventually he realizes that he's viewing Flatworld
from a totally new vantage point above.
Now, he can see into closed rooms.
He can see into his flat fellows.
This unprecedented three-dimensional view of
his two-dimensional universe is devastating.
Traveling to another dimension provides as an incidental benefit,
a kind of X-ray vision.
Just as the Flatworld houses can have no roofs,
their inhabitants can have no sky,
because that sky could only exist in a third-dimension.
Little guy's suffered enough.
Better put him down.
From the point of view of its spouse,
this Flatworlder has distressingly disappeared,
then unaccountably materialized from out of nowhere.
It's easier to imagine the universe in fewer dimensions
than our comfort zone of three.
A zero-dimensional universe is just a point.
A dot with no dimension at all.
Or a one-dimensional universe where everyone is a line segment.
Or the two-dimensional Flatworld.
Or 3D, where we all live.
We can laugh at the cluelessness of
two-dimensional creatures.
Unable to imagine a three-dimensional world.
But, when it comes to quantum reality, that inability,
resembles the problems we have.
The best we can do for now is to imagine this
three-dimensional cube as a four-dimensional hypercube.
We're living in our own Flatworld,
just like the 19th Century writer, Edwin Abbott,
in his book Flatland, was trying.
TYSON: It's the rarest of events,
when a searcher happens on a hole in the curtain
that hides the matrix.
It was not until Isaac Newton that we began to understand
the motions of the worlds.
The variety of living things always astonished us,
but Charles Darwin discovered how time and the environment
sculpted these forms, including us,
from life's first living cell.
We had no idea that the quantum universe even existed
until Albert Einstein revealed it.
The mysterious laws of this paradoxical cosmos deeply disturbed him.
And we have yet to understand them ourselves.
At its heart, was a relationship that seemed
to violate the speed of light.
The backbone of modern physics and reality itself.
That blue photon, a quantum packet of light,
will divide into two.
Splitting its energy and emerging as a pair of red photons.
These new red photons are married in the most profound physical sense or,
as quantum physicists say, entangled.
And no matter how far they wander from each other,
in space and in time, the bond between them will endure.
It's a little like Plato's Ancient Greek explanation of love.
A single being splits into two and separates.
For the rest of their existence,
each remains the one and only soul mate of the other.
Exquisitely attuned to the inner life of its partner.
Even if they are separated from each other by a whole universe.
Observe the spin of one photon and you will instantly know
the spin of its entangled partner.
It's not something special about these particular photons.
As far as we know, it's the rule.
This kind of long distance relationship has been going
on for the whole history of the universe.
Two photons born in the early universe nearly 14 billion years ago,
separate and head in opposite directions.
They could end up tens of billions of light-years apart and yet,
over all that time and across all that space,
the bond between them endures.
What is it about a photon or an electron or any other
elementary particle, once entangled,
that makes them capable of such lasting fidelity?
And to me, an even stranger fact,
is that all it takes to sever that awesome commitment,
is the simple act of measurement.
All I have to do is measure the spin of one of them.
How can it be that only one seemingly innocuous act
by a third party can forever sever such a deep and enduring bond?
There she is.
Half of our cosmic couple.
Somewhere, at this very moment,
many billions of light-years away from us,
her soul mate is suddenly feeling something different.
The thrill is gone.
The bond has been broken.
They are no long entangled with each other.
Our simple act of observing one of them has ruined
a marriage that has lasted since the beginning of time.
But, how could that be?
And that's not the only crazy thing about this.
How could one photon, a cosmos away from its partner,
send a break-up message across the universe and have
the other photon receive it instantaneously?
Faster than the speed of light could possibly carry
such a message between them.
These are two of the greatest unanswered questions in science.
So, don't worry if they bother you.
These questions haunted a mind as great as Einstein's for the rest of his life.
There's nothing more intriguing to a scientist than a paradox.
If light, the fastest thing there can be,
has a cosmic speed limit, then it would be impossible
for one photon to communicate with another instantly across such vastness.
Einstein found it almost unbearable to live in this kind of universe.
Where what he called, "spooky" action at a distance was possible.
Remember those particles in the double slit experiment?
Taking either the left or the right slit?
Those choices amounted to nothing more than random chance,
but even random chance must follow certain rules.
That's the basis for Huygens's probability theory and
for calculating the odds in flipping a coin or throwing dice.
When Einstein applied probability theory to the
problem of entangled protons, he was deeply disturbed.
If these photons could brazenly violate the speed of light,
then the universe and all of creation was nothing
more than a casino where the laws of nature can be broken.
Einstein dealt with his discomfort by clinging to the
idea that the dice was somehow loaded in a way we didn't yet understand.
We had passed this way before.
More than 100,000 years ago, our ancestors domesticated fire.
They didn't know what fire was,
but they used it anyway to build a civilization.
And so it was with quantum physics.
We didn't need to understand it to exploit its countless
practical applications, scientific and technological.
Much as our ancestors used fire without understanding how it worked,
we lived with this mystery for decades.
We have entered a territory beyond the reach of classical physics.
Where the elementary particles that make up everything,
including us, respond to events they can't possibly know about.
In the outlaw casino of the quantum universe,
there is no objective reality.
And that's where we're headed next.
TYSON: We are made of atoms.
The bizarre quantum universe is inside us,
tugged on by undiscovered moons.
Performing its impossible magic on every level of life and experience.
What is this?
A smattering of stars or something else?
We are sending an image made of light to your eyes.
It's arriving at your retina at this very moment.
The cells in your retina are changing chemically right
now because we are stimulating some of them with photons.
Your retina stores these changes for a fraction of a second.
Now, it's erasing them in readiness for the next barrage of photons.
Your retina doesn't detect all of them, it can't.
It picks up on only a small percentage of photons that come your way.
It's impossible to predict which particular cell in your
retina will catch a photon.
Even when it comes to something as vital as our vision,
all we have is our probabilities.
Now, we're shooting many more photons at you.
More like, half a million.
What are you looking at?
The surface of some planet orbiting another star?
We need still more of those photons to know for sure.
Say, a couple of million or more.
Only when we send all of those photons your way,
tens of millions of them,
does reality begin to take shape.
Over time, probabilities become likelihoods and eventually,
likelihoods become certainties.
But is there really any such thing as certainty.
If everything, even our own vision,
is governed by probabilities,
can there be any absolute reality?
Is there any hope of rescuing our classical idea
of reality in the quantum universe?
Scientists have come up with one way to preserve our
traditional understanding of cause and effect called
"The Many Worlds Hypothesis."
That's a misnomer because it can't be tested scientifically,
but it goes like this.
Every probability that can happen does happen in
some parallel cosmos that is foreclosed to us.
An infinite number of ever branching realities.
Unfolding at every possible juncture.
Every probability that can happen does happen
in some parallel cosmos...
♪ MAN: Oh, we need the funk ♪
♪ Gotta have that funk ♪
♪ Oh, we want the funk ♪♪♪
TYSON: Or is probability just an illusion itself?
A phantom of our ignorance?
It is, if we live in a universe where every single
event was already foreordained at the beginning of time.
What is called, superdeterminism.
In a superdeterministic universe,
the catastrophic failure of treaties, a sneeze.
The asteroid that wiped out the dinosaurs,
one particular bee pollinating one particular flower.
You listening to me right now, all of these events were set
in lockstep motion at the moment the universe began.
When it was all no larger than a marble.
Superdeterminism has an additional virtue.
It can explain mystery of entanglement.
The ability of entangled particles to communicate across the vastness,
apparently violating the speed limit of light.
In a superdeterministic cosmos,
entangled partners separated by whole galaxies,
don't need to hear from each other to change their spin.
They were always destined to do so at that precise moment.
And so were their partners.
And so was the intruder,
who severed their bond by observing one of them.
Think of it.
All these events and trillions of others,
inscribed in the potential of the first moment of the universe.
Since everything in the universe is made of those
same elementary particles, including us,
we are subject to the same laws as those that rule
the quantum universe.
And so it is, for what will happen next.
And what will happen after that.
The good news is superdeterminism gives us
a solution to the mystery of entanglement,
the bad news is,
it seems to rob us of all agency.
Are we just going through the motions,
acting out a script that was written for us nearly
14 billion years ago?
All the while,
telling ourselves how clever we were in that argument.
How selfish, how brave.
If you could only change that one little thing about yourself.
In a universe devoid of free will,
are we nothing more than deterministic robots?
[church bells ringing]
We have found a way to hitch a ride on the uncertainties.
To forge technologies that would otherwise be unattainable.
We have built a quantum clock.
One that you never have to wind.
It will only lose a single second in the next 15 billion years.
A three-dimensional lattice of laser light keeps isolated
atoms of the element strontium,
suspended in space.
For all we know, we may be near collections
of preprogrammed particles in a deterministic universe.
But I say, let's not live like we are.
Besides, we have no way of knowing if that's true.
And to think that, in some sense,
our freedom to explore the quantum realm begins
with Thomas Young.
Remember, it was Young who also found the key to
decrypting the lost language of the ancient Egyptians.
With quantum encryption, we are creating codes that
vanish the moment someone tries to hack into them.
The key to the code, can be sent via entangled photons.
The observer effect is our insurance policy that no
spy can decipher the message without causing the
entanglement to break apart.
Rendering the message unintelligible.
We still don't know how a photon can be both a particle
and a wave at the same time.
What I love about science, is that it demands of us,
a tolerance for ambiguity.
It requires us to live with humility regarding our ignorance,
withholding judgement until the evidence comes in.
That needn't prevent us from using the little we do know
to search for and decrypt new languages of reality.
In this vast cosmos, we are all Flatworlders.
Science is the struggle to imagine and find above.
Captioned by Cotter Captioning Services.