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.
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.
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.
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.
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.
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.
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.
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.
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.
What's out there, stronger than gravity,
that's pulling the universe apart?
Incredibly, nobody knows.
Astronomers simply call it dark energy.
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.
One thing we do know
about the mysterious dark energy
is that it makes up around 70% of the universe.
That's crazy, that we don't know about most of the universe.
We're the weird things in the universe.
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.
When we look out in the universe,
we see that all galaxies appear to be moving away from us.
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?
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.
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.
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.
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.
It won't stop
until nothing's left to tear apart.
Scientists call this "the Big Rip."
If the Big Rip were to occur,
it would be the ultimate Armageddon.
Everything ripped apart.
Wow, doesn't get any worse than that.
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?
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!
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?
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.
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.
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.
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.
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.
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.
So what will drive the sun out of equilibrium?
And what will this mean for our planet?
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.
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.
That extra energy will push on the outer layers of the sun,
causing them to expand, becoming big.
We call this a red giant.
The core will keep contracting
while its outer layer grows bigger and brighter.
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.
The Earth will be incinerated,
lifeless, but still a planet after the sun gradually cools.
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.
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.
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.
The asteroid arrives unannounced...
leaving no time to react or take cover.
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.
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.
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.
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 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."
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.
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?
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.
With an asteroid impact, there's all kinds of other side effects.
The Earth could get increased vulcanism,
increased earthquakes, the ocean could acidify.
Anything not killed immediately
might die slowly.
The entire food chain would be disrupted.
Many or most species of life on Earth would perish...
A global mass extinction, a real Armageddon.
The sudden meteorite explosion in Chelyabinsk
put the world on notice.
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.
How do we know?
Earth's battered past is carved into the face of the moon.
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.
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.
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.
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.
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.
Spotting a threatening asteroid is one thing.
Heading off asteroid Armageddon is another.
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.
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.
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.
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.
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.
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.
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.
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.
What could cause these megablasts?
Gamma ray bursts are thought to be
hyper-energetic explosions of extremely massive stars.
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.
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.
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.
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.
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.
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.
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.
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.
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.
That's an ominous discovery
that makes our galaxy a bit more crowded, and maybe
a little more dangerous to our planet's survival.
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.
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.
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.
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.
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.
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.
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.
During the big crunch,
the universe would collapse...
and collapse... and collapse...
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.
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.
Toss it up again...
and again... and that's the Big Bounce.
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.
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.
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.
Sooner or later, things fail.
Sooner or later, people die.
Sooner or later, the world ends.