Must we die?
Are there beings in the cosmos who live forever...
afloat on an endless journey down the river of time?
Our ancestors marked the passage of time by the moon and stars.
But it was the people who once lived here, around 5000 years ago...
who first started chopping up time into smaller bite-sized portions of hours...
and minutes. They call this place Uruk. We call it Iraq.
It's a part of Mesopotamia...
the land between the Tigris and the Euphrates rivers.
The city was invented here.
And one of humanity's greatest victories was won in the ceaseless battle against time.
It was here that we learned how to write.
Death could no longer silence us.
And writing gave us the power to reach across the millennia...
and speak inside the heads of the living.
No one had ever spoken across a longer stretch of time's river...
than this Akkadian princess, daughter of the first emperor in history...
and priestess of the moon. Enheduanna.
For not only did she write poetry...
but Enheduanna did something no one before her had ever done.
She signed her name to her work.
She's the first person for whom we can say we know who she was and what she dreamed.
She dreamt of stepping through the Gate of Wonder.
Here's a thought Enheduanna sent across more than 4000 years to you.
It's from her work entitled Lady of the Largest Heart.
Innana, the planet Venus, goddess of love...
will have a great destiny throughout the entire universe.
Throughout the entire universe.
And Uruk is also the place where the epic tale of the hero's journey was first written down.
Before Batman, Luke Skywalker, Odysseus, before them all...
there was a man named Gilgamesh who left home on a quest to vanquish time.
Gilgamesh was searching for immortality.
He looked everywhere, gained complete wisdom...
uncovered what was hidden.
He brought back a tale of times before the Great Flood.
He built the wall of Uruk, which no future king will ever match.
Read the story of that man, Gilgamesh, a hero born of Uruk...
who went through all kinds of sufferings...
who crossed the ocean, the broad seas...
as far as the sunrise...
who inspected the edges of the world, searching for eternal life.
On his travels, Gilgamesh encountered a wise man named Utnapishtim...
who told him the story of a flood that destroyed the world...
and how one of the gods instructed Utnapishtim...
to build an ark to rescue his family and the animals.
The earliest surviving account of the flood legend was written down in Mesopotamia...
a thousand years before it was retold as the story of Noah in the Old Testament.
So you could say Gilgamesh fulfilled his quest for immortality.
We still read the Epic of Gilgamesh, and with every reader...
he lives again.
And all those heroes and superheroes who have come since follow in the footsteps...
of the first hero's journey...
another kind of immortality.
A story sent from one civilization to another across thousands of years.
But life itself sends its own stories across billions of years.
It's a message that every one of us carries inside...
inscribed in all the cells of our bodies in a language that all life on Earth can read.
The genetic code is written in an alphabet consisting of only four letters.
Each letter is a molecule made of atoms. Each word is three letters long.
Every living thing is a masterpiece...
written by nature and edited by evolution.
The instructions for running...
and reproducing the intricate machinery of life.
The essential message of life has been copied...
and recopied for more than 3 billion years.
But where did that message come from?
Nobody knows.
Perhaps it began in a shallow, sunlit pool...
just like this.
Somehow, carbon-rich molecules began using energy to make crude copies of themselves.
Some varieties were better at making copies, and left more offspring.
The competing molecules became more elaborate.
Evolution and life itself was underway.
Or life could've started in the searing heat of a volcanic vent on the deep sea floor.
Or is it possible that life came to Earth as a hitchhiker?
Let me tell you a story about a traveler from another world.
The peace of the Egyptian village of Nakhla, near Alexandria...
was abruptly shattered on a June morning in 1911.
Written in this meteorite was a message from another planet.
But 70 years would pass before anyone could read it.
In 1976, NASA landed two Viking spacecraft on Mars.
Carl Sagan took us there on our original journey through the cosmos.
We found that the Martian air was less than 1 percent as dense as ours...
and made mostly of carbon dioxide.
There were smaller amounts of nitrogen, argon, water vapor and oxygen.
A few years later, when scientists thought to analyze the gasses...
trapped inside the Nakhla meteorite, and other members of its class...
they found a striking similarity.
The vast majority of meteorites are fragments of asteroids.
But the kind that hit Nakhla on Earth could only have come from one place.
Mars.
Welcome to Mars.
Over a billion years ago, a volcano erupted here...
and its lava cooled into solid rock.
Hundreds of millions of years later, this area was flooded with water.
And long after that flood, an asteroid the size of the Rock of Gibraltar...
crashed into the Martian surface, blasting out a huge crater.
Much of the debris was ejected back out into space...
where it orbited the sun until a gravitational tug from its home planet, Mars...
diverted one of the boulders into a collision course with Earth. Its arrival...
shook up the little village of Nakhla. Meteorites...
of the type that hit Nakhla...
are the vehicles of a natural interplanetary transit system...
that sends rocks between the planets.
Such a meteorite can safely shelter microscopic cargo...
the seeds of life, an interplanetary ark.
Most rocks are porous, full of tiny nooks and crannies...
where life can stow away.
We know that some microbes can survive the hostile environment of space.
Take these guys, for instance.
These microbes spent a year and a half riding on the outside...
of the International Space Station, exposed to the extreme temperatures...
vacuum, and radiation of space.
And some of them were still alive and kicking when they were brought back to Earth.
Even more astonishing are these creatures...
awakened from a death-like sleep of 8 million years.
They were frozen in the Antarctic ice millions of years before our species even existed.
And they're still alive.
If life can withstand the hardships of space and endure for millennia...
then it could ride the natural interplanetary transit system from world to world.
It's a good bet that our microbial ancestors spent some time in space.
Why do we think so?
The Earth is 4 and a half billion years old.
For the first half of its lifetime...
large asteroids were bombarding the planet every few million years.
The most violent impacts vaporized the oceans and even melted the surface rock.
Each such collision would have completely sterilized the planet for thousands of years.
But we know from fossils in the rocks that bacteria were evolving on Earth...
during this formative period.
So how could life have survived such a lethal series of blows?
Whenever one of those big asteroids hit the Earth...
the explosion would blast out a crater, launching millions of boulders into space.
Many of those rocks carried living bacteria inside.
Some of the bugs would have survived in space...
while all those left behind on Earth would have been fried.
A few thousand years after each impact...
the Earth would have cooled down enough for water to condense into oceans.
The planet would again be habitable.
Meanwhile, most of the rocks launched into space would have been orbiting the sun.
Some of them would encounter the Earth again...
reenter the atmosphere as meteorites...
and deliver their precious cargo of life to re-seed the planet...
like Noah's ark.
What this means is that life doesn't have to start over again...
from scratch after each catastrophe.
It can pick up where it left off.
When the solar system was young...
Venus was probably more like Earth, with oceans and maybe even life.
Venus, Earth, and Mars were all exchanging rocks with each other...
due to asteroid impacts.
Does life on Earth carry any traces of interplanetary voyages...
made in the distant past?
Why is it that some microbes can survive the intense radiation and vacuum of space?
These conditions don't naturally exist on Earth.
Maybe those bugs are telling us that their ancestors survived...
those same conditions in space, a few billion years ago.
So we know that microbes can stow away in rocks and survive the voyage...
from planet to planet.
But what about a trip from star to star, an interstellar odyssey?
The dandelion.
Around 30 million years ago...
it evolved another way to send its own message of life through space and time.
Each seedling is a little paratrooper, floating on the wind...
risking everything for a safe place to land.
Updrafts can carry them higher into the air.
A dandelion can travel dozens...
possibly hundreds of kilometers...
even crossing over mountain ranges.
Evolution has shaped it into an exquisite flying machine.
The seed is another kind of ark...
ensuring the survival of its species by riding the currents of the atmosphere to safe harbors.
Each seed, in its DNA, carries a story...
the character and destiny of the next dandelion.
Life propagates by retelling its story.
Is it possible that life could survive the journey from star to star?
The stars are about a million times farther apart from each other than are the planets.
Space is so vast that it would take billions of years for a rock ejected from the Earth...
to collide with a planet circling another star.
Any stowaway microbes would never survive the cosmic radiation for that long.
But there's a plausible scenario for how life could spread from one solar system to another.
The stars of the Milky Way are drawn by gravity...
in their own enormous orbits around its center.
Our sun, for example...
takes some 225 million years to complete a single orbit.
During each revolution around the galaxy...
our solar system will pass through two or three gigantic interstellar clouds...
each of them many light-years across.
Galaxies are world-making machines.
Our Milky Way has more than 100 of these vast clouds...
places where gas and dust condense to form new stars and planets.
In its travels through the Milky Way...
our sun is accompanied not only by its planets...
but also by a trillion distant comets.
When our solar system passes through an interstellar cloud...
the gravity of the massive cloud stirs up the outermost comets.
Some comets will be hurled out into the space between the stars.
Others will plunge inward...
falling towards the sun.
And some of them may collide with the planets.
The high-speed impact of a comet with a rocky planet...
will launch boulders like rockets into space.
If that planet should happen to be inhabited...
many of those rocks will carry passengers...
living microbes.
After thousands of years...
fragments of the rocks ejected from Earth can fall as meteors...
into the atmospheres of newborn planets in the interstellar cloud.
If the stowaway microbes should happen to come in contact with liquid water...
they can revive and reproduce.
This may be how life comes barreling into the barren places.
The sun emerges from the cloud...
having scattered the seeds of life among the newborn worlds of other stars.
Those new worlds, now touched by life...
will then leave their birth cloud and go their separate ways.
Eventually, their stars will carry them through other interstellar clouds...
where they may seed still more new worlds.
Imagine this process repeated from world to world...
each one bringing life to others.
Life would then propagate, like a slow chain reaction...
through the entire galaxy.
This could be how life came to Earth.
We do not know for sure.
Are there any beings out there like us?
Do they ask the same questions? Do they share our fears?
Do they have heroes and adventurers?
If they do exist, where are they?
How might they make their presence known?
How did we first announce our presence to the galaxy?
It was 1946, the year after the Second World War ended.
The imaginations of H. G. Wells and Buck Rogers never cooked up...
a more fantastic experience...
than the Army engineers at their laboratory in Belmar, New Jersey.
It opens up unlimited possibilities for interstellar experiment.
American engineers bounced a beam of radio waves off the moon...
and were able to detect its echo.
They called this experiment Project Diana.
It was the first interstellar message ever sent by our species.
An eerie tolling bell.
If one allows the imagination free rein...
many future possibilities appear.
Spaceships, carrying passengers at thousands of miles per hour...
can be controlled...
and communication established with their passengers.
For we now know that the Earth's atmosphere can be penetrated.
Traveling at the speed of light...
it takes just over one second for a radio wave to reach the lunar surface.
But the expanding wave front is much bigger than the moon.
Most of the wave passes right by it...
but the central part gets bounced back.
After a round-trip travel time of two and a half seconds, it hits our planet.
Project Diana transmitted a series of powerful radio waves...
one every four seconds, to ping the moon.
The parts that missed the moon are traveling still.
It was just the beginning.
After World War II...
television stations cropped up all over the United States...
and other parts of the world.
The Project Diana message...
and the FM radio, television and radar signals of the 20th century...
all move outward at the speed of light.
These transmissions make up a vast sphere of radio waves...
expanding away from the Earth in all directions.
You could say that our world is radiating stories.
Our ancestors etched the story of Gilgamesh into clay tablets...
sending that epic tale into the future.
We've encoded our stories in radio waves and beamed them into space.
They cover one light-year of distance...
that's 6 trillion miles, for every year of time since they were sent.
We've been sending our stories into space for over 70 years.
The leading edge of these signals has already washed over...
thousands of planets of other stars.
If any of these worlds are home to a civilization with radio telescopes...
they could already know that we're here.
What if other worlds are sending their stories into space?
Since 1960, we've been listening for extraterrestrial radio signals...
without hearing so much as a tolling bell.
But our search has been sporadic and limited to certain parts of the sky.
For all we know, we may have just missed an alien signal...
looking in the wrong place at the wrong time.
We've only listened to a miniscule fraction of the stars in our galaxy.
And there may be another problem.
We are, to some extent, prisoners of our own moment in time...
and the limits of our technology.
Radio and television broadcasting...
may be only a brief passing phase in our technological development.
When we imagine alien civilizations broadcasting signals with radio telescopes...
are we any different from earlier generations...
who imagined riding cannon shells to the moon?
Civilizations even slightly more advanced than ours...
may have already moved on to some other mode of communication...
one that we have yet to discover or even imagine.
Their messages could be swirling all around us at this very moment...
but we lack the means to perceive them...
just as all of our ancestors, up to a little more than a century ago...
would have been oblivious to the most urgent radio signal from another world.
But there's another, more troubling possibility.
Civilizations, like other living things...
may only live so long before perishing due to natural causes...
or violence, or self-inflicted wounds.
Whether or not we ever make contact with intelligent alien life...
may depend on a critical question:
What is the life expectancy of a civilization?
By the time of Enheduanna, the first person to ever get a writing credit...
civilization was already more than 1000 years old.
But today, her glorious city is a barren wasteland.
What went wrong?
One problem was the almost ceaseless warfare between the cities of Mesopotamia...
which continually destroyed their achievements.
They glorified military conquest, and ultimately...
became its victims.
Another cause of decline was that...
their technical know-how overran their understanding of nature.
The ingenious irrigation system...
that was the basis for the great civilizations of Mesopotamia...
had an unintended consequence.
The water channeled into their farmlands every year...
evaporated and left its salt behind.
Over generations, the salt accumulated and began to kill the crops.
And then, about 2200 B. C...
not long after the time of Enheduanna, disaster struck.
A drought of truly epic proportions, lasting for many decades.
The rains stopped, crops withered, there was famine and anarchy.
Barbarians invaded.
The streets of many cities were littered with dead.
There could be only one explanation.
Enlil, the supreme god, was angry...
because one of his temples had been destroyed.
The people of Mesopotamia could not know...
that the same drought was crushing the dawning civilizations of Egypt...
Greece, India, Pakistan and China.
All the gods of the Earth must have been really angry about something.
For all their brilliance...
the people of those civilizations had no inkling...
they were experiencing abrupt climate change.
Three thousand years later...
the climate would change abruptly for another glorious civilization...
this one in Central America.
At its peak, the Mayan civilization perished...
wiped out by a series of severe droughts over the course of a century.
We still carry within us the echoes of these extinct civilizations, in our languages...
and our myths.
Today, we have a single global civilization.
How long will it live?
There are so many ways for a civilization to die.
Let's start with the ones that we wouldn't be able to do much about.
That supernova is 1000 light-years away.
If it were much closer, say less than 30 light-years from Earth...
its cosmic radiation would shred the atmosphere's protective ozone layer...
and destroy our civilization.
Lucky for us, none of the stars close enough to harm us...
are likely to go supernova any time in the next few hundred million years.
Every million years or so, a supervolcano erupts somewhere on Earth.
The last time it happened was 74,000 years ago...
on the island of Sumatra in what is now Indonesia.
It spewed hundreds of times more rock, ash and toxic gas...
than any single volcano in recorded history.
The molten rock that erupted from Earth's crust left this caldera...
100 kilometers long, now filled with a lake.
The Toba volcano sent more than 600 cubic miles...
of pulverized rock soaring skyward.
The westward wind carried the volcanic ash over India...
where it fell out in a smothering blanket over the subcontinent.
The eruption loaded the upper atmosphere with sulfur gases.
The result was a global haze that blocked most of the sunlight...
from reaching the surface for at least five years.
It was like one five-year-long cloudy day.
This so-called volcanic winter resembled a nuclear winter...
but without the radiation.
Temperatures fell everywhere.
Plants and animals froze, even in the tropics...
dying in enormous numbers.
But life is hardy. Only a few species were driven to extinction.
One of our ancestors in central India sharpened this stone blade...
in the years before the Toba eruption.
And this blade was one of dozens that were found in the soil layer...
above the volcanic fallout.
This tells us that some toolmakers...
even in the area directly affected by the volcano...
managed to survive the cataclysm.
But the global human population must have plummeted before rebounding.
If an eruption like this were to happen tomorrow...
our civilization would be brought to its knees...
although the human species would survive.
I can imagine that our technology of a few hundred years from now...
would allow us to siphon off the energy of a threatening supervolcano...
before it explodes.
We could then use that energy for our own purposes.
About once every million years, a small asteroid collides with the Earth...
causing a similar amount of devastation.
With our science and technology...
we already know how to prevent an asteroid impact.
We would see it coming years in advance...
and could send a spacecraft there to deflect it into a harmless orbit.
With the technology of a thousand years from now...
we might even be able to mitigate the deadly effects of a nearby supernova...
on Earth's atmosphere.
But what happens when the danger to a civilization is invisible?
When no one can see it coming?
Beginning with Columbus, the European invaders of the Americas...
had a secret weapon that even they knew nothing about.
They were carrying bacteria and viruses for deadly diseases, such as smallpox...
that the original Americans had never been exposed to.
The Europeans like to believe that it was their valor and superior weapons and culture...
that won them the New World.
The real conquistadors were the armies of the pathogens...
that raced on ahead to infect and kill nine out of 10...
of all the Indians of North, Central and South America.
The great civilizations of the New World crumbled...
under the onslaught of invading microbes.
Without his invisible army...
Cortez and those who followed might never have stood a chance.
But what about civilizations that self-destruct?
Our economic systems were formed when the planet and its air...
rivers, oceans, lands, all seemed infinite.
They evolved long before we first saw the Earth...
as the tiny organism that it actually is.
They're all alike in one respect.
They're profit-driven, and therefore, focused on short-term gain.
The prevailing economic systems, no matter what their ideologies...
have no built-in mechanisms for protecting our descendants...
of even 100 years from now, let alone 100,000.
In one respect, we're ahead of the people of Ancient Mesopotamia.
Unlike them, we understand what's happening to our world.
For example, we're pumping greenhouse gases into our atmosphere...
at a rate not seen on Earth for a million years.
And the scientific consensus that we're destabilizing our climate.
Yet, our civilization seems to be in the grip of denial...
a kind of paralysis.
There's a disconnect between what we know and what we do.
Being able to adapt our behavior to challenges...
is as good a definition of intelligence as any I know.
If our greater intelligence is the hallmark of our species...
then we should use it, as all other beings use their advantages...
to help ensure that their offspring prosper, and their heredity is passed on...
and that the fabric of nature that sustains us is protected.
Human intelligence is imperfect, surely, and newly arisen.
The ease with which it can be sweet-talked, overwhelmed, or subverted...
by other hard-wired tendencies...
sometimes themselves disguised as the light of reason, is worrisome.
But if our intelligence is the only edge, we must learn to use it better.
To sharpen it. To understand its limitations and deficiencies.
To use it, as cats use stealth before pouncing.
As walking sticks use camouflage.
To make it the tool of our survival.
If we do this...
we can solve almost any problem we are likely to confront...
in the next 100,000 years.
And now we've arrived at the place where our ancient dreams of immortality...
and modern astrophysics converge. Giant elliptical galaxies...
are something like Florida...
where the oldest stars in the universe may be found.
This is a red dwarf star, smaller and fainter than our sun.
Red dwarfs are by far the most plentiful stars in the cosmos.
Unlike the sun, which is halfway through its 10-billion-year lifetime...
red dwarfs will continue to provide light and warmth to their planets...
for trillions of years.
That's hundreds of times longer than the present age of the universe.
What would intelligent beings do...
if they had an eternity to develop their understanding of the universe?
Perhaps they would learn how to open shortcuts in the fabric of space-time...
to travel between galaxies faster than the speed of light.
Maybe they would create whole new universes...
as artistic or scientific experiments.
Of course no one, or at least nobody on Earth...
knows what the immortals might do.
If one allows the imagination free rein...
But what about us?
What is our own future?
What would the cosmic calendar of the next 14 billion years look like?
If the original cosmic calendar includes all of the time...
from the birth of the universe until this very moment...
what would the cosmic calendar look like for the next 14 billion years?
Just as with the cosmic calendar of the past...
every month on the future calendar equals about a billion years...
every day, some 40 million.
Science makes it possible for us to foretell...
certain astronomical events in the unimaginably distant future.
The death of the sun, for example.
In some 5 billion years...
our star will have exhausted its hydrogen, the nuclear fuel that powers it...
becoming a red giant.
I know that sounds depressing, but if we apply our intelligence...
our descendants of that distant future...
will have long departed from the lost worlds of the sun.
Who knows?
Human events entail too many variables, too many uncertainties...
to make scientific statements about our future.
But we can still dream.
The next golden age of human achievement begins here and now.
New Year's Day of the next cosmic year.
In the first tenth of a second...
we take the vision of the pale blue dot to heart...
and learn how to share this tiny world with each other.
The last internal combustion engine is placed in a museum...
as the effects of climate change reverse and diminish.
A fifth of a second into this future...
people will stop dying from the effects of poverty.
The planet is now a completely self-sustaining, intercommunicating organism.
A half-second from now...
the polar ice caps are restored to the way they were in the 19th century...
and the forecast is mild and pleasant for the next cosmic minute and a half...
40,000 years.
By the time we are ready to settle even the nearest other planetary systems...
we will have changed.
The simple passage of so many generations will have changed us.
Necessity will have changed us.
We are an adaptable species.
It will not be we who reach Alpha Centauri...
and the other nearby star systems on our interstellar arks.
It will be a species very like us...
but with more of our strengths and fewer of our weaknesses.
More confident, far-seeing, capable and wise.
For all our failings, despite our flaws and limitations...
we humans are capable of greatness.
What new wonders, undreamt of in our time...
will we have accomplished in another generation...
and another?
How far will our nomadic species have wandered...
by the end of the next century and the next millennium?
Our remote descendants...
safely arrayed on many worlds throughout the solar system and beyond...
will be unified by their common heritage...
by their regard for their home planet...
and by the knowledge that whatever other life there may be...
the only humans in all the universe came from Earth.
They will gaze up and strain to find the blue dot in their skies.
They will marvel at how vulnerable the repository of all our potential once was...
how perilous our infancy, how humble our beginnings.
How many rivers we had to cross...
before we found our way.