(male narrator)
The end is coming. But which cosmic catastrophe
will deliver the death blow? Were the Vikings right
to fear the frozen apocalypse
of an endless winter? Did the Buddhists
correctly predict a fiery end
to life on Earth? Or will the thunderous
Christian vision of Armageddon come crashing down
from the stars? Which ancient prophesy
do scientists believe accurately foretells
our doom? And how close are we... To the end of the world? Ancient mysteries,
shrouded in the shadows of time. Now, can they finally be solved
by looking to the heavens? The truth is out there,
hidden among the stars in a place we call... It's the ultimate fear
for every human being on Earth and across time-- The end of the world. A time when death
is unescapable, delivered by fire... ice... or terrifying forces
from beyond our planet. Every civilization
has its own horrific vision. (Markley)
Every culture knows about death. Every culture has seen
major disasters. Destruction, death,
the ending of things really looks like
it's part of the natural order, so it shouldn't be
a surprise to us that every culture has
an Armageddon scenario. In a lot of mythologies, the world ends
by either cold or by fire, the real extremes
of weather on the Earth. (narrator)
But which vision of Armageddon
does modern science support? How exactly
will the world end? Could it be
the frozen apocalypse, feared by the Vikings? It's 535 A.D., and the people
of a Norse village, so used to harsh winters, have never seen
anything like this. Even the elders can't recall
such a brutal season. Spring should be here,
but the winter won't let go. Farmers can't plant crops.
Livestock is dying. What if winter never ends? This truly feels
like the beginning of the end of the world. It's winters like this
that probably inspired the Norse vision
of the apocalypse. They called it Ragnarok,
or the Twilight of the Gods. Even the doomed
pantheon of Norse deities was powerless to stop it. It meant the rise of monsters and the annihilation
of gods and men. It starts with Fimbulwinter, a killing cold worse than even
a hardened Viking could imagine. (Markley)
The Norse believed
that the end of the world would be heralded
by a three-year mighty winter, following which, the heavens and
the Earth would be destroyed. Perpetual winter--
that's the end. (narrator)
Could the end of everything
come in cold as the Norse predicted? Looking back
at our planet's history, it's not hard to imagine. Three times in the Earth's past,
glaciers may have spread to encase the entire planet
in ice and slush, like a giant snowball. Now scientists predict
something even more extreme, an icy apocalypse
that will put a deep freeze not just on Earth,
but the entire universe. And this frigid end
was set into motion at the very beginning... with the rapid expansion
of the universe after the Big Bang. (Johnson)
We've known for a long time
that the universe is expanding, and it's been cooling down
as it expands since the Big Bang,
13.8 billion years ago. (narrator)
Heat is energy, and the universe has
only so much of it to go around. As the universe expands,
the energy gets diluted, and everything starts
to cool. Scientists once believed that
the expansion of the universe would eventually slow down,
or even reverse as cosmic gravity
tapped the brakes. But then... they discovered that
some unseen, unexplained force was out-dueling gravity, accelerating us toward
a truly chilling Armageddon. (Johnson)
In the late '90s,
we discovered that the universe is actually
accelerating the expansion. This has put a new wrinkle
on the scenarios about how the universe
might end. (Alex Filippenko)
I was a member of both teams
that were studying the expansion history
of the universe, and when I saw the results, that the universe is
accelerating in its expansion, I was just
completely stunned. It was a shocking result. Essentially,
no one had expected this. (narrator)
What's out there,
stronger than gravity, that's pulling the universe
apart? Incredibly, nobody knows. Astronomers simply call it
dark energy. (Johnson)
We're still not sure
exactly what dark energy is. It may be an intrinsic energy
that space itself has that actually makes it
prefer to get larger. This rubber band has
what we call elasticity. If I pull on it
and make it larger, it actually tries
to pull back and restore its shape
to a smaller size. Imagine the reverse of that,
where instead, you have something
that likes to increase its size. That's the sort of physics
that might underlie dark energy, where it actually is driving
the acceleration of the whole expansion
of the universe. (narrator)
One thing we do know about the mysterious
dark energy is that it makes up
around 70% of the universe. (Howell)
That's crazy, that we don't know
about most of the universe. We're the weird things
in the universe. (narrator)
So how will dark energy drive us toward a frigid
cosmic Armageddon? Little by little,
but faster and faster, it will move everything
away from everything else. And as clusters of galaxies
spread, the expanding universe
will get colder. (Danly)
When we look
out in the universe, we see that all galaxies appear
to be moving away from us. (narrator)
If we could view the universe
from a different galaxy, we'd see the same thing. How can all the galaxies
be moving away from all the other
galaxies? (Danly)
One way to think
about the expanding universe is to think about an expanding
loaf of raisin bread. The raisins are galaxies,
and the dough is the universe. The raisin bread
is expanding because the baking soda
in the bread is causing it to expand,
kind of like dark energy. (narrator)
The baking soda
is expanding the dough and spreading the raisins, just like dark energy
is expanding the universe and moving all the galaxies
farther and farther apart. As the universe expands,
its energy gets diluted. There won't be enough to build
new stars as old ones die. With no stars to generate heat
and no new stars being born, the universe marches
toward a bitterly cold end, an ice age that affects
not just one planet, but the entire universe. In a universe that's
expanding eternally, it's getting colder and colder
with time. It's as though you're entering
a long, extended-- Indeed, eternal winter. (narrator)
A Nordic nightmare, the mighty winter
that heralds Armageddon. But is that truly the end? Or does dark energy
have the power to do something
even more destructive? It's possible
that the mysterious force could grow stronger
over time. (Filippenko)
In that case, eventually, clusters of galaxies
will get ripped apart, then galaxies
will be ripped apart, then planetary systems
will be ripped apart, planets, us, and even
the atoms of which we are made. (narrator)
It won't stop until nothing's left
to tear apart. Scientists call this
"the Big Rip." (Filippenko)
If the Big Rip were to occur, it would be
the ultimate Armageddon. Everything ripped apart. Wow, doesn't get
any worse than that. (narrator)
The Big Rip is one vision
of Armageddon on a universal scale. But even if the universe
is fated to end in bitter cold, is the Earth itself destined
to die much sooner, not in cold, but fire? (narrator)
Ancient prophesies
foretell Armageddon, but few agree
how it will come to pass. The ancient Norse predicted
the beginning of the end in bone-cracking cold, a prophecy
that our expanding universe might make happen. The Norse weren't the only ones
to fear a wintery Armageddon. It's the 16th century,
in what is now Mexico. A prisoner captured
from a recent battle is dragged out
and held down on a slab. The Aztec priest
raises an obsidian knife and slices open
the prisoner's chest... Aah! (narrator)
Ripping out
the still-beating heart and raising it triumphantly
to the sun. He holds the fate of the planet
in his bloodstained hands. The Aztecs believed
they had a duty to feed the sun
through blood sacrifice, giving it the strength
to make its daily journey across the sky. If they failed to feed it, they believed
it would disappear. But what would
really happen if one dark morning,
the sun vanished? (Filippenko)
If the sun were to suddenly
disappear from the universe, then there'd be no gravity
pulling the Earth toward the sun anymore,
and that means that the Earth would go
flying off in space in a straight line along the direction
it was moving at the instant
that the sun disappeared. (narrator)
This would doom the Earth
to a frozen Armageddon that recalls
the deadly Norse winter. Fortunately for us,
our sun won't magically vanish, but what it will do
is evolve. (narrator)
Evolve...and then die. Will this mean a cold,
dark death for the Earth, or something more like the ancient Buddhists
envisioned? In the Buddhist
apocalypse, seven suns will blaze
across the sky. When the sixth sun rises, it will bake the Earth
like pottery. Then, according to the prophesy,
"A seventh sun appears. "The mountains
fire and blaze, "and of this great earth,
when consumed, neither ashes nor soot
remains." Although there aren't
multiple suns in our future, were the Buddhists right
that Earth will die by fire? Will we be burned into oblivion
by our dying sun? At 5 billion years old,
the sun has reached middle age and its days are numbered. Scientists have a clear idea
of how it will die, and it's all driven
by pressure. The heat of nuclear fusion
in the core creates enormous
outward pressure that should
blow the sun apart, but instead,
it's countered by the equal force
of gravity pushing in. Balancing inward
and outward pressure is something every diver
stakes his life on. (Howell)
The reason we
have life on earth is because the sun is burning
through its nuclear fuel. it's an equilibrium. It's a balance between gravity
trying to crush it down and pressure holding it up. (narrator)
So what happens
when equilibrium is lost? On the surface of the Earth, human beings are in equilibrium,
just like the sun. The atmosphere presses on us
at 15 pounds per square inch, or one atmosphere. We don't feel it
because the air inside us is pushing out
at the same pressure. But take an object designed
to be in equilibrium on the surface,
and bring it underwater, and you start to see
what happens when equilibrium is lost. (Howell)
I want to demonstrate what a small amount
of atmospheric pressure can do to this metal can. As we're descending, we're already seeing
effects of this can. Check it out. The can is starting to bend,
and we're only at 15 feet. I'm pretty surprised
that we're starting to see the effects of pressure
at only 15 feet. I dive 15 feet all the time,
and I didn't know I was exerting these kinds
of forces on my body. Now we're finally
at 33 feet. That's double
atmospheric pressure. We totally crushed our can. It's pretty obvious
that when you have twice the amount of pressure
on the outside of the can, what's on the inside, our can,
just can't survive. (narrator)
So what will drive the sun
out of equilibrium? And what will this mean
for our planet? (Lucianne Walkowicz)
The sun's lifetime
is mostly governed by how much fuel
it has in its core versus the force of gravity
of its own matter pushing inward. Over time,
stars like our sun, which fuse hydrogen into helium
in their cores, eventually start
to run out of fuel, and enter a period of time where they
go through these death throes. (narrator)
As the sun runs out of fuel, gravity will keep pulling
the core tighter. But as the core shrinks, it will heat
the surrounding layers of gas, causing hydrogen and helium
to fuse even faster than before. The extra energy released
will increase the pressure on the outer layer
of the sun. (Filippenko)
That extra energy will push
on the outer layers of the sun, causing them to expand,
becoming big. We call this a red giant. (narrator)
The core will keep contracting while its outer layer
grows bigger and brighter. (Filippenko)
The sun will become so bright
and so big that the Earth might actually
find itself inside the sun for a while. That would be Armageddon. (narrator)
The Earth will be incinerated, lifeless, but still a planet
after the sun gradually cools. (Filippenko)
The sun will fade away, and then the Earth
will just keep on orbiting a very dim, ever dimmer lump
that remains from today's sun. (narrator)
The dying sun will trigger
our own infernal Armageddon, a blazing, Buddhist finale
before eternal Aztec winter. Or life on Earth
could be finished long before that happens, and much, much sooner
than we expect. (narrator)
Ancient visions predict that Armageddon is inevitable
some distant day. But what if
our day of reckoning... Is today? Chelyabinsk, Russia,
February, 2013. Residents see a fireball blaze across the sky,
seconds before it detonates. [boom] [glass breaking
and car alarms blaring] The asteroid arrives
unannounced... leaving no time to react
or take cover. [boom] (Howell)
It exploded in the atmosphere with a force
about 20 times greater than the atomic bomb
dropped on Hiroshima. Luckily, it was high enough
in the atmosphere that the atmosphere absorbed
most of the energy. [boom] (Filippenko)
That object was only
about 20 yards in diameter. That was a small rock, yet the explosion caused
widespread damage, lots of imploding glass
that actually hurt 1,500 people, many buildings damaged. (narrator)
A larger asteroid or comet could cause
mass extinction on Earth... leaving the planet intact,
but lifeless. The idea of an Earth
devoid of people is something
the ancients feared. (Markley)
When they talk
about Armageddon scenarios, it's wiping away
the living organisms that are here now
and starting again. At least that's
the usual scenario. So the world will still be here,
the heavens will still be there. We won't. (narrator)
But the Ancients had
different visions of how humanity
would be wiped out. Muslim writings foresaw
the end of the world, signaled by landslides and a cloud of smoke... engulfing the planet. The Romans envisioned Armageddon
by fire or flood--or both-- when the time comes
to cleanse the Earth. The Roman philosopher Seneca
wrote, "Water and fire
bring about creation, "they bring about
destruction, "so when the world
decides to change, "it sends the sea
crashing down on us, or causes extinction
by heat and fire." (Markley)
This sounds a lot like
the kind of thing you would get when you got a meteorite
slamming into the oceans, a global tsunami,
nuclear winter, the end of the world. (narrator)
Perhaps the most frightening
vision of Armageddon comes from Christianity. The Book of Revelation describes
all manner of destruction raining down on Earth. "And there were voices,
and thunders, and lightnings; "and there was
a great earthquake, "not seen
since men were upon the Earth. "He maketh fire
come down from heaven, and the sun became black,
and the moon became as blood." It's a terrifying vision, but can such a global cataclysm
really happen? (Markley)
The Christian scenario
for the end of the world involves raging seas, famine,
pestilence, fire, earthquakes. These are all
of the kind of things that you could have if you were
suffering multiple impacts. Perhaps multiple meteorites,
a comet that's fragmented and slammed into the Earth. This kind of thing could easily
happen in real life. (Howell)
With an asteroid impact, there's
all kinds of other side effects. The Earth could get
increased vulcanism, increased earthquakes,
the ocean could acidify. (narrator)
Anything not killed immediately might die slowly. (Filippenko)
The entire food chain
would be disrupted. Many or most species of life
on Earth would perish-- a global mass extinction,
a real Armageddon. (narrator)
The sudden meteorite explosion
in Chelyabinsk put the world on notice. (Filippenko)
There are a lot of asteroids
and other big rocks in the solar system
just kind of flying around, and most of them are between
the orbits of Mars and Jupiter, but some of them
cross Earth's orbit, and so eventually,
they can slam into the Earth. [huge explosion] (narrator)
How do we know? Earth's battered past is carved
into the face of the moon. (Howell)
Over the Earth's history,
it's been bombarded by meteors, and one way we can tell
is just by looking at the moon. There are craters everywhere,
and they aren't eroded by the water and the air
like they are on the Earth, so you can look up
and see a fossil record of all of the impacts
near Earth. (narrator)
Most scientists believe
that an asteroid or comet measuring 6 miles across killed off the dinosaurs
65 million years ago, but few people realize
that wasn't the biggest impact to ever strike the Earth. In what is now South Africa,
an asteroid slams into the Earth at around
33,000 miles per hour, blowing out a crater
almost the size of Connecticut. 2 billion years later, the Vredefort Impact Crater
remains to tell the tale. Luckily, that happened
billions of years ago, but if one were to happen today,
it would end all life on Earth. (narrator)
Is there another large rock
out there, hurtling through space with Armageddon
written all over it? Probably. And if an asteroid
doesn't get us, we might find ourselves
in the crosshairs of a deep-space death beam. (narrator)
The Christian vision
of Armageddon foretells a worldwide apocalypse
delivered in thunder, earthquakes, fire,
and brimstone. And frighteningly,
modern science thinks this kind of global cataclysm could actually be
in Earth's future, delivered by a single event-- the impact
of a near-earth asteroid. (Walkowicz)
The discovery
of near Earth asteroids is a major priority-- not only for scientists,
but also for our government-- where we'd like to know
how many are out there, how big they are, and how likely
they are to impact Earth. (narrator)
Spotting a threatening asteroid
is one thing. Heading off asteroid Armageddon
is another. (Filippenko)
Detecting an asteroid
days or hours before it hits doesn't give us many choices
for deflecting it. We need a long time scale.
We need early detection. That's the key. (narrator)
If we can intercept the asteroid in time,
we might be able to gently nudge it
out of the way with rockets, or, as some suggest,
sunbeams... and a well-aimed paintball. Just as dark rooftops in the sun
get hotter than light ones, changing an asteroid's color
can change its temperature and its direction. (Filippenko)
By painting it either with white
or silver paint or with a very dark black paint,
that changes the degree to which light from the sun
is either reflected or absorbed. That will
ever so slightly change the trajectory
of the asteroid. Whenever you reflect light
or absorb light, that changes
the motion of the object that's reflecting
or absorbing the light. (narrator)
With vigilance and technology, we might be able
to avert Armageddon, at least for a while. But asteroids aren't
the only threat that can destroy the planet
without warning. (narrator)
On April 27, 2013, scientists at observatories
around the world are shocked
when NASA's Swift satellite detects a monstrous dagger
of deadly radiation hurtling through space
near the speed of light. It's a gamma ray burst, a death beam
for anything in its path, and this one
was closer to the Earth than anyone had ever seen. All light,
whether it's lamp light, infrared light,
radio waves, or X-rays, are part
of the electromagnetic spectrum. Gamma rays are a kind
of high-energy light that's much, much stronger
than X-rays. (Filippenko)
Gamma ray bursts are thought
to release more energy than any other single events
in the universe other than the Big Bang, the birth of the universe
itself. They release
gargantuan amounts of energy. (Johnson)
It's interesting to speculate
about what must be happening to any habitable planets
that are in the neighborhood of such gamma ray bursts. They must be bathed in a huge
amount of gamma radiation, which means that probably
it would be somewhat cataclysmic for life
neighboring such an event. (narrator)
So far, it appears the Earth
has been mainly spared, or at least
dodged the worst of it. (Howell)
We see gamma ray bursts
at a rate of about one a day in the universe, and sometimes,
they're so powerful, they even affect
the Earth's atmosphere. (Filippenko)
They can be seen easily from billions of light years
away, and if the jet is pointing
toward Earth and the gamma ray burst
is sufficiently nearby, then that can spell doom
for much of life on Earth. (narrator)
What could cause
these megablasts? (Filippenko)
Gamma ray bursts
are thought to be hyper-energetic explosions
of extremely massive stars. (narrator)
When these massive, spinning
stars suddenly collapse, their last gasp
is a gamma ray burst. Gamma ray bursts get
their enormous energy ultimately from gravity. A gravity well like this one
can help us understand what's happening on the inside
of massive stars when they die. The shape
of this gravity well illustrates
the strength of gravity around the central mass
of a star. When material falls
into a collapsing, massive star, it spirals around
until it finally falls into the center,
forming a black hole. As it does this,
enormous jets of energy are released
as a gamma ray burst. (narrator)
Where that gamma beam points is
like a game of Russian roulette, and if the beam strikes Earth,
it's game over. It might be the most agonizing
Armageddon of them all. (narrator)
The ancients have foreseen
Armageddon in all its terrible guises-- by fire or water, by ice...
or cataclysm. But gamma ray bursts defy
even their vivid imaginations. The deep space death beam can strike the Earth
without warning. When a massive star explodes
as a gamma ray burst, a lot of the energy
gets channeled along the axis of rotation
of that spinning star. Now, the axis can point
in any random direction, but if it happens to point
toward the Earth, then the energetic
charged particles and the electromagnetic
radiation blast into the Earth, causing potentially
damaging effects. (narrator)
Driving in our cars, walking in the park, we probably
wouldn't hear a thing when the gamma ray
strikes our atmosphere and annihilates it. But once the Earth's
protective ozone layer is gone, so are we, as death spreads
slowly over the globe. (Filippenko)
The side of the Earth
facing the gamma ray burst would have
a radiation blast that could kill
animals and plants, and over the long run, the loss or severe depletion
of the ozone layer could let in a lot of the ultraviolet
radiation from the sun, leading to damaging effects
and loss of life. (narrator)
The more scientists
search the skies, the more they locate hazards
that could fulfill-- or surpass--ancient visions
of Armageddon. From stars that explode... to objects like this-- rogue planets
careening through space. We used to think that
all planets circled stars, which kept them bound to
a particular spot in the galaxy. It was reassuring,
but wrong. Scientists have recently started
discovering rogue planets, wandering aimlessly
through space, unleashed from any star's
gravitational field. There are more out there
than we ever imagined, hiding in plain sight. (Walkowicz)
We know that there's
a population of planets out there that exist
without orbiting a parent star. Because there's no light
from the parent star, and we can't use the parent star
to indirectly detect these planets, that makes them
very difficult to find. (narrator)
Maybe we need
to look harder. As a rogue planet wanders
into our solar system, its gravitational pull
could disrupt the Earth's orbit, slowing it down, speeding it up,
or changing its shape. That could affect
the seasons and the climate, endangering life on Earth. (Filippenko)
We now think that
there could easily be as many rogue planets
in our Milky Way Galaxy as there are stars, and perhaps many, many more
rogue planets, ten or hundred
or a thousand times as many rogue planets
as there are stars. (narrator)
That's an ominous discovery that makes our galaxy
a bit more crowded, and maybe a little more dangerous
to our planet's survival. (Filippenko)
If there are
way more rogue planets than there are stars
in our galaxy, then the chances
that they will come and gravitationally interact
with our solar system are greater. (Walkowicz)
Fortunately for us, the galaxy is still
very, very sparsely populated. Everything
is very far apart, and so it's almost
diminishingly small chances that you would have
one of these dark planets entering
our solar system. (narrator)
But in 2014, just on the edge
of our solar system, the closest rogue planet
was found to date. It's out there, 80 times further
from the sun than we are, which isn't very far
at all. That's the bad news. The good news,
if you can think of it that way, is that another, much larger
and more distant rogue planet is holding it safely
in its gravitational grip. Knowing the apocalypse
probably won't be tripped by a rogue planet
is only slightly reassuring. The ancients
and modern scientists agree, there is no escape. Somehow, someday,
the end is coming, and the final vision
of Armageddon is the strangest of all. (narrator)
We've seen Armageddon
rain down on us by Nordic ice
and Buddhist fire, Aztec darkness, killer meteorites
of Biblical proportions, and deep space
death beams, but maybe there's hope. What if the end...isn't? The biggest recycling project
in the universe might be
the universe itself, and according
to Ancient Hindu philosophy, every Armageddon
marks a new beginning. (Markley)
Hindu belief for the end
of the world involves cycles. The end of the world was also
the beginning of the world, which in due course
would live out its life span, and it too would end
and once more be reborn, in constant cycles. (narrator)
Could this view of Armageddon
really come to pass? Not if dark energy continues
to expand the universe eternally, extinguishing it
in a Big Chill. But the mysteries of dark energy
leave open the possibility that instead of a Big Chill,
there will be a Big Crunch, a universe that reverses course
and collapses back in on itself. (Filippenko)
It's conceivable
that the dark energy could change sign
in the future. Right now, it's repulsive,
but what if someday, it becomes
gravitationally attractive? We don't know
what dark energy is, so it's possible. (narrator)
During the big crunch, the universe
would collapse... and collapse...
and collapse... (Filippenko)
Everything becomes so dense,
so compressed, that we call this a singularity,
a big crunch, a "gnab gib,"
which is "Big Bang" backwards. It's conceivable
that there will be a rebirth, a new expansion,
a new big bang, if you will. (narrator)
Scientists call that
the Big Bounce. It's very much like what happens if you take a ball
and throw it up into the air. You give it that initial push,
that would be like the Big Bang, it expands out,
it goes up into the air, and then the gravity
of the Earth eventually turns it round and brings it
back down to your hand. (narrator)
Toss it up again... and again...
and that's the Big Bounce. (Howell)
That's what's called
the cyclic model in cosmology. The universe is born, dies,
and then is reborn again, and this process could go
over and over. It's akin
to Hindu mythology. (narrator)
If the universe does in fact
crunch and bounce back, as the Ancient Hindus
believed, then we might have been
down this road many times before. Or maybe there isn't
just one universe after all. We now think that there
may well be other universes popping into existence
with their own big bangs and their own expansion
and their own stars and perhaps even
their own life, and that process can lead
to a progression of universes that is never-ending. (narrator)
That's good news for universes,
if not necessarily for us. If the Earth can dodge
asteroid strikes and gamma ray bursts
and rogue planet invasions, we can expect our sun
to expand before burning out
5 billion years from now, incinerating the planet
as the Buddhists envision. If dark energy
can be trusted, the universe will
continue to expand, freezing to death
in the process, as the Norse predicted. Or maybe another universe
will spring to life from the corpse of the old one,
as some Hindus suggest. Whether we look
to the ancient lore of the Aztecs,
the Norse, the Hindus,
the Buddhists, the Romans, or to modern science,
the answer is the same-- We are doomed. (Markley)
Sooner or later, things fail. Sooner or later,
people die. Sooner or later,
the world ends.
