[narrator] For thousands of years, mankind has questioned the existence
of extraterrestrial life in our universe. Sooner or later, we're going to see some
kind of signs of extraterrestrial life. We need to prepare. The chances that aliens exist
in some form is highly probable. It's entirely likely there's intelligent
life somewhere in the universe. Today, astronomers are already
sending messages into space. But what if these messages
are perceived as threats and aliens believe humans are the enemy? If they arrived as conquerors, it could be the end of
planet Earth as we know it. Is an invasion inevitable? [man] This is an alien attack! It would be like Godzilla meeting Bambi. I think there's almost 100% chance that there are alien forms of life
in the universe, other than our own. If extraterrestrials exist, they would
come from the far edges of the universe. Their vast spacecrafts may
already be en route to our world. And there is no way
to know when they will arrive. Many think that this scenario is possible,
including researcher Nick Pope, who has worked with the British Ministry
of Defence to investigate UFO sightings. There's no reason why
intelligent extraterrestrials couldn't already have
started their journey. It could be a year's time, it could be a month, it could be a week,
they could arrive later today. There's no way to determine
whether they would come in peace, or what their intentions would be. Extraterrestrial contact with our planet
would change life as we know it. Whoo! Nothing would ever be the same. The arrival of extraterrestrials could
mean extinction for the human race. It's impossible to know
exactly what would happen, but scientist Ben Moore thinks
it comes down to two basic principles. If alien life came here, they would be
coming because they were curious or because they were unfriendly. Our Earth is just a mere speck
in a massive universe. Statistically, scientists believe
that this must mean that there could be millions of
other civilizations like ours out there. The Earth orbits the Sun,
just like seven other planets. But our Sun is not unique. It is only one of more than 100
other billion bright stars in our galaxy, the Milky Way. And even the Milky Way is just one
of a trillion more galaxies. The universe is a very big place
and if you're talking something on the order of a trillion galaxies, each with half a trillion stars, it seems like a fairly silly notion to imagine that we're alone in the cosmos. Some scientists believe it's only a matter
of time before aliens finally reach Earth. They might be closer than ever before. Whoo! The most incredible guy on Earth. Beer! If there is life, intelligent life, other civilizations, in our small part
of the galaxy, we will find them in just half a dozen years or so. Does life exist in space? The answer might lie within Earth's
closest neighbor, the planet Mars. Located over 34 million miles from Earth, researchers speculate
that Mars is a planet that could support extraterrestrial life. In this infinite universe, the chances are
that the same chemical processes that gave rise to life will have arisen
many, many times elsewhere. One place that we might find life
is within our own solar system. There are suggestions, for example,
that there's microbial life on Mars. In 2003, ESA sent the Mars Express probe
to the red planet. Its mission - find water,
the basic substance of life on Earth. The images from the Mars camera
showed something remarkable - deep valleys that cut through
the Mars rock. At one point in time,
water must have flowed here. And in some Mars craters,
scientists have found frozen water. There are even entire glaciers capping
the Poles of Mars, but that's not all. We see images of riverbeds.
Even the image of an ocean. So we do know that Mars
was once tropical, it was once lush. Scientists have been able to retrace
the entire history of Mars. Four billion years ago, a gigantic sea
covered a third of the planet. This water would have been enough
to support microorganisms. Except suddenly, the climate changed. For some reason, Mars lost
its atmosphere and cooled down. And the water evaporated or
became frozen within the surface soil. It may have had life in the past. But if just a small amount
of liquid water is still present, there is still hope for life on Mars. A recent promising sign -
strange grooves on the slopes of Mars. These features can occur
when water liquifies in the soil and rock slides back over it. Hiding under the barren surface
of this planet, there might still be liquid water,
water that could mean life. Except on Mars, temperatures can drop
as low as -121 degrees Fahrenheit. With no atmospheric protection, dangerous cosmic rays can
directly strike the planet's surface. Is it even possible for life
to survive in these conditions? To discover extraterrestrial life, to find out that we are
not alone in the cosmos, it would be one of the biggest, if not the single biggest
discovery of all time. Extraterrestrial arrival would be
a sudden and shocking event. No one would be ready. Our vulnerable planet could be
attacked by hostile invaders. If there was an alien spacecraft
coming into our solar system, we may only have a few days
or weeks warning. They are very hard to see. To answer the age-old question
of existence of life on Mars, scientists take a deeper look
at a continent on Earth that mimics Mars' icy climate, Antarctica. Researchers from
the German Aerospace Center are looking for extremophilic organisms, microorganisms that can handle
the harshest cold. They find cyanobacteria,
micro-fungi and lichens - tiny creatures that can
still survive at temperatures as low as negative 58 degrees. [he speaks German] [translation] These extremophilic
organisms clearly show us that life can exist in the most
unbelievable places. We find life in the most
extreme locations on our planet. So why shouldn't organisms also exist
on Mars, which is also an ice-cold desert? At his lab in Berlin, Jean-Pierre de Vera needs to test
whether these organisms from Antarctica can cope with even more
extreme conditions. He has designed a special
Mars simulation chamber to put the mosses
and bacteria to the test. [translation] This is our Mars chamber. We've made it as close as possible
to the condition of Mars. These temperatures go extremely low, negative 58 to negative
103 degrees Fahrenheit. To match the paper-thin
atmosphere on Mars, the pressure is dropped to six millibars. Air on Earth contains less than
1% carbon dioxide. The air in this chamber is
almost 96% carbon dioxide. Under these conditions, most earthly
creatures would immediately perish. But the extremophilic organisms
from Antarctica survive. [translation] So far, what I've
discovered in the Mars chamber has been very surprising.
Even under the Mars conditions, the fungi could form proteins
and bacteria still produced methane. These algae and lichen could still
be able to carry out photosynthesis even under Mars conditions. For this reason,
we want to take the next step. We need to do these
same tests in space. To assist with this study,
the International Space Station is called into action
for this unique experiment. With a risky setup outside, the astronauts
assemble an experimental lab on the external surface
of the space station. Several hundred samples, including
the bacteria, fungi and mosses, will be exposed to cosmic radiation,
orbiting the Earth for over a year. If these organisms can survive in space, they may have also managed
to survive on Mars. [translation] Life can exist on Mars. Based on the experiments we've done,
it's clear that today's Mars is a viable planet. I believe we need to seriously look for life on Mars. Proving simple life exists on Mars
would tremendously fuel the greater discussion
about intelligent life. Ours will be the generation that makes
this literally game-changing discovery, that alters everything we know about
ourselves and our place in the cosmos. But others in the cosmos
may be trying to find our world. There is no way to anticipate
where they would land. Their arrival would shock humans. Are they friendly or not? Who knows? I would hope they are friendly and that first contact would be
in a friendly fashion. Humans need to find proof
of extraterrestrial existence before they make contact. [man speaks Russian] March 14th, 2016. At the Russian Space Station in Baikonur, they are launching another new project
to find out even more about Mars. ExoMars is a joint project of
the European Space Agency, ESA, and the Russian Space Agency, Roskosmos. The mission is monitored via
ESA's control center in Darmstadt. Flight director Michel Denis makes sure
that the probe stays on course. [he speaks French] [translation] ExoMar's mission
is to find traces of life on Mars. That could be life that used to exist
or maybe even still exists today. Since on Earth, methane
is mostly produced by living things, the Trace Gas Orbiter is designed
to detect methane and then find the source of the gas. [translation] The methane on Mars
might be generated by volcanoes. We believe that those volcanoes
are now extinct. So it could be produced by minerals or
it could be created by living organisms. In the next phase of the mission,
a rover will land on Mars. Since cosmic radiation makes the surface
itself too hostile for lifeforms... the rover will search for life
in the ground. Protected from lethal radiation
under the surface, microbes could still be alive. This is the first time in history
that a Mars rover will drill two meters deep
into the planet. [translation] The deeper we drill,
the further we can go back in history, increasing the chances
that we will find life. The soil samples are examined
immediately at the site. A special set of instruments
on board the rover analyzes the drill-cores
for traces of life. But even after all this effort, there is still a chance that Mars
may actually be a dead planet. There are still other potentially
habitable worlds. The two moons orbiting Saturn -
Titan and Enceladus - could hold life in the ice
that covers them. Gas giant Jupiter also has its own
ice moons - Ganymede and Europa. Underneath their ice-crusts, they may have oceans of liquid saltwater
which could be teeming with life. [translation] Our next hot candidates
are still in our solar system. We definitely want to look for life
on the ice moons. One of these moons is very active and we can tell that it is
spurting out ocean material. That's exactly what we want to see. If something is coming out of the ocean,
there could be life in that material. Future missions could finally reveal
if there is life in our solar system. Unless highly developed extraterrestrials
discover us first. Scientists believe
they could reach our planet. A species that had evolved for
a million years longer than us would certainly have the capabilities
to send a starship here. [they speak French] Could these visitors be dangerous? What would such an advanced
species want from us? If aliens decided to conquer our Earth,
would we even stand a chance? Look at it! Look at it! -Look at what?
-Behind you! If they arrived as conquerors, it could be
the end of planet Earth as we know it. If extraterrestrials arrive,
they will have traveled a great distance, from a planet that is very far
from our solar system. How do we identify
where they will come from? One man is getting closer to the answer. Swiss astronomer Michel Mayor is
on his way to an observatory in France. It was here in 1995 that he
made a breakthrough discovery. [he speaks French] [translation] We have come here
to the Observatory of Haute Provence to measure as many stars
as possible in the clear sky. In just his first week, Mayor was able to pinpoint 142 stars and there something very peculiar
about one of them. Star 51 Pegasi seemed to be moving, a small strange wobble that made him think
that it could have a planet in its orbit. [translation] Looking at them from Earth, most stars appear to have
a steady, even speed. But we have noticed that 51 Pegasi actually changed its speed
in a very specific way. Mayor has a theory - the gravitational
pull of this star holds onto a planet. But the planet itself is tugging back, causing the star to
also make a small movement. Astronomers call this
a "change in the radial velocity", which causes a shift in the way the light
of the star reaches us back on Earth. As it moves forward, it is seen as bluish. As it moves back, it is perceived as red. Mayor checks these tiny deviations in
the light spectrum with his spectrograph. Mayor is positive,
51 Pegasi must have a planet. [translation] This was our proof that
there was a planet orbiting the star. For the first time ever,
an exoplanet has been identified. A planet outside our solar system. The newly discovered planet
is located in the constellation Pegasus, 50 light-years away from the Earth and
it's been given a name, 51 Pegasi b. [translation] This was the first time
that we found a star, other than our Sun, that actually has a planet. The discovery of 51 Pegasi b is
a major milestone in space exploration. We now know for certain that
exoplanets exist outside our solar system. The discovery also is another reason
why many scientists are convinced extraterrestrials exist, including well-known
theoretical physicist Michio Kaku. I think the probability is near 100% that we will find intelligent life
in the universe. Do any planets have the potential
to support not just simple lifeforms, but the development
of whole civilizations? Could there be a second Earth - a planet exists with the same
characteristics as our own? [mission control]
Three, two. Engines start. One, zero and lift-off
of the Delta II rocket with Kepler. In 2009, the Kepler telescope
was launched into space. The telescope's main task - fly through
space to search for new exoplanets. Kepler has spotted over 2,000 exoplanets and the telescope keeps making
new discoveries every day. The Kepler satellite has giving us
a census of the Milky Way galaxy. We know that between 50 to a 100%
of the stars you see at night have planets going around them. And so the chances that we are
the only planet with intelligent life I think is very close to zero. To this day, almost 4,000
exoplanets have been discovered. Like Corot 7b. 490 light-years away, this planet,
likely, is primarily made up of hot lava. At first glance, planet HD 189733b
actually looks like Earth. But it has its blue color
for another reason, not water, but hazardous glass particles
in the atmosphere. With brutal winds of 5,000 miles per hour, it may even rain molten glass
on this planet. 55 Cancri e may actually possess
a diamond core. The surface is a scorching
3,600 degrees Fahrenheit, and the atmosphere of this exoplanet contains high amounts
of a toxic prussic acid. Life as we know it on Earth
could not exist here. A shadow Earth or Earth 2.0,
I think, that's what we'll be looking at. Alien invaders may come from a place
much like a second Earth. Then why would they need to come to ours? [tires screech] If they truly come to wage war,
humans would have no hope. Military experts believe that facing
aliens in combat would be devastating. If an alien civilization has the ability
to cross interstellar space to reach Earth, they undoubtedly
have advanced technology. If their civilizations are
more advanced than our own, how can we prepare for contact? Another scientist is also
scouring the skies to find a planet where life is possible. Heike Rauer is an astrophysicist
at the German Aerospace Center. [she speaks German] [translation] The big goal we have
is to find planets similar to our Earth. Habitable ones where
we might be able to find life. Heike Rauer knows the key is to find
planets with a solid surface and water, the two attributes that
seem to go hand in hand with the existence of intelligent life. [translation] If I pushed the Earth closer
to the Sun, it would get hotter. Some of our oceans would evaporate,
and then we would have a planet that was not inhabitable and if I pushed
the Earth farther away from the Sun, it would be so cold
that the water would freeze and we would just have an ice planet. Our planet wouldn't be habitable
then either. So there's a specific
ideal distance from the Sun. We call this area the "habitable zone". This habitable zone is the only place
where life can develop. But for that to happen,
the planet also needs an atmosphere... like the thin gas layer,
which also surrounds our Earth, protecting life
from the lethal UV radiation emanating from stars,
including our own Sun. [translation]
The atmosphere is also crucial, of course, because we breathe and we need
the oxygen from our atmosphere to live. So a planet must also have
the right kind of atmosphere. She uses a trick to quickly find
habitable planets. Whenever a planet flies past its star, at this precise moment
the star darkens slightly. Using this strategy, researchers
like Heike Rauer now have detected more than 30 planets in the habitable
zone that could be full of life. One planet looks particularly promising
to researchers - Kepler 452b, a planet 1,400 light-years away
in the constellation Cygnus. This planet is amazingly
similar to Earth. Its star has a similar size
and temperature to our Sun. For a round trip around the star
it takes 385 days, just a little longer
than our Earth's orbit. And the distance to the star
is just right. We're getting closer and closer to
finding a world very much like our own. I think it's only a matter of time now and I think it could be
staggeringly close. A new European telescope has the means
to finally find this second Earth. This advanced device is called the
European Extremely Large Telescope, E-ELT for short. By 2024, the telescope will be
stationed in the Chilean desert. It will be the largest
of its kind in the world. At the assembly hall of
the European Southern Observatory, technicians test the parts that will later
become the telescope's main mirror. So what we have here
is the very first prototype of the primary mirror of the ELT. So we need a very large mirror which is impossible to build today
in a monolithic piece. Close to 800 individual hexagonal mirrors will be put together to create
the telescope's 40 meter massive mirror. Up to now we've been building
telescopes up to eight to ten meters. But now we have the technology to build
something which is extremely large. 40 meters in diameter is as big
as the Allianz Arena nearly and it's enormous. The scientists hope
that the telescope's power will finally prove that there is life
on an exoplanet. They want to use the telescope
to examine the planet's atmosphere. As soon as the planet moves
in front of its star, using the color, scientists can determine
what kinds of molecules it contains. The ultimate proof is to identify
some specific markers, some ozone, for example,
some specific elements in the atmosphere of this planet that can only be produced by life. By plants, by little creatures in...
in the ecosystem. With the new telescope, researchers
are aiming to find proof of life within the next 30 years. So it's definitely in our lifetime.
So in the next decade, we will be able, with E-ELT, to really understand if there
is life, potential life, or not. Is it possible that extraterrestrials
are already also watching us? Are they planning a visit
and for what purpose? Sooner or later, we're going
to see some kind of signs of extraterrestrial life. We need to prepare. An extraterrestrial attack would be the
greatest catastrophe in human history. [they speak French] Is life out there like on Earth? It probably shares some of those
characteristics that life on Earth has. Is there any way to predict
what the invaders will look like? Some researchers believe that aliens
might be extremely similar to us. I think there's a great chance that some extraterrestrials
would look exactly like us. So, for example, eyes are very useful. Legs are very useful for mobility. Those things may be present
elsewhere in the universe. So I would not rule out
some extraterrestrials being indistinguishable
from human beings. Different environmental conditions
could mean that life from other planets would look drastically different. These organisms would need to endure
extreme heat or extreme cold. If they came from a planet
with stronger gravitational forces, extraterrestrials may have adapted
and developed massive muscle to fight against gravity's pull. Small, compact creatures would have
the advantage on this type of planet. Or a planet with less gravity, aliens would need much less muscle
to move around. Their planet could be populated
by thin giants. All life on Earth is made up
of carbon and water, but in another world
it's possible that life developed from entirely different
chemical elements. On Saturn's moon, for example,
there may be no liquid water, but there are still other building blocks
that could be combined to form life. So creatures on Titan could use ethane
or methane as a liquid instead of water. Then the building block would
probably be silicon instead of carbon. And those creatures might breath
in hydrogen instead of oxygen. So life could be very alien
on that world. There's also the possibility that
the visitors will not be actually alive. Aliens could potentially send their own
intelligent machines into space. When we actually meet them in person they may already have bioengineering
and artificial intelligence. So don't be shocked to find that
they're part robotic and part biological. Many scientists think
that it's entirely plausible that aliens have developed advanced
spacecraft capable of reaching Earth. Yes, it's perfectly possible
to do interstellar travel. It just takes a lot of effort and a lot
of money to develop such a spacecraft. A journey through the stars
is already within reach. Russian millionaire Yuri Milner
has invested $100 million into the US Breakthrough Initiatives
project. And others are on board,
including astronaut Frank Drake and even star physicist Stephen Hawking. It's time to commit to finding the answer
to search for life beyond Earth. It is important for us to know
if we are alone in the dark. The plan is to visit our neighboring
star system, Alpha Centauri, only 4.2 light-years away from Earth. Scientists have discovered that
in this system, the red dwarf star Proxima Centauri
is orbited by an Earth-like planet. Proxima b sits perfectly
in the habitable zone, making the planet a prime candidate
for harboring extraterrestrial life. But it would take an unmanned probe
32,000 years to reach Proxima b. Milner and Hawking believe we need
a mini-probe, which will be able to make
the journey in only 20 years. If the probe weighed only a few grams,
it could be equipped with a sail. Extremely powerful lasers on Earth
would then be aimed at the sail and in just ten minutes, the probe
would be pushed by the lasers at a quarter of the speed of light. For the first time in human history we can
do more than just gaze at the stars, We can actually reach them. Traveling at a speed
of 46,000 miles per second, it would only take
the ultra-light spaceship 20 years to reach Alpha Centauri. If sentient life is based upon expansion
and based upon exploration, then it's entirely likely
that other sentient species are also engaging
in interstellar exploration. Advanced civilizations could have
developed entirely different technology. Some researchers believe
that the most progressive aliens can tap the energy of entire stars
to create wormholes that they then use
to travel through space and time. We have come from horse and cart to Stealth fighter and space rocket
in 200 years. Now imagine a civilization
with a million-year head start, which is not difficult to conceive of
in a universe 14 billion years old. So let's not rule out the fact that
if there are civilizations out there, they may come knocking on our door. Invasion by a higher-tech civilization
poses a serious threat to the human race. In an attack, we would
barely stand a chance. Humans would need to find shelter
and safety as soon as possible. If this crisis would come to fruition,
everyone would be caught off guard. I think it's important to consider
the possibility of interstellar species approaching the Earth
that might be hostile and consider what resources
we might have at our disposal to allow us to defend ourselves. And time may be running out. Aliens may already be heading
towards their target - Earth. But some alien hunters
are more optimistic. One of the most famous hunters
believes that aliens will be peaceful. Seth Shostak has devoted 50 years
of his life to SETI research, the search for extraterrestrial
intelligence. The American astronomer is convinced
that his body of work will pay off. There are a trillion, so that's a million
million, planets just in our galaxy. It's like you bought
a trillion lottery tickets. You know, a couple of them
are gonna be winners. So it strikes me as inevitable that there
is other intelligent life out there. Someday we may be able
to actually communicate with extraterrestrial civilizations. But are they already
trying to get in touch with us? To find out, SETI researchers
use radio telescopes, like the Allen telescope array
in California. These telescopes can receive
acoustic radio signals from deep within the universe. We point them in the
direction of nearby stars, which we think might have planets,
which might have life, which might have intelligent life. And we just look for signals that
are coming from those directions. Signals that at one spot
on the radio dial would tell us, "Hey! You know,
I don't know what they are saying, I don't know what they look like,
but they've built a radio transmitter." And once upon a time, a signal
just like this one reached Earth. 1977, the Big Ear radio telescope
of the Ohio State University has its antennas
aimed directly into space. Using these antennas,
the telescope could capture every radio wave lying in its orbit. And suddenly it received
a strange signal from space. Astrophysicist Jerry Ehman was working
on the Big Ear telescope. He could hardly believe it when
he analyzed the recorded data. In those days, all the data was just
printed out as numbers on a big printer and he would just go through and
see if there was anything interesting that had happened the night before.
One morning, he finds a big signal and he gets so excited about it,
he writes "Wow!" next to it. This "wow!" signal came
from the constellation Sagittarius, 200 light-years away from Earth. With a 30-fold standard deviation, the signal was strong enough to be heard
over the background noise of the universe, and it may have been sent out
by another civilization. But the "wow!" signal was
never detected again. To this day, it is unclear if it is
the result of something natural, or if it was caused
by something else. If extraterrestrials are
sending signals to us, what would happen if they
personally paid us a visit? People would respond
in many, many different ways. Some people would
literally panic in the streets. OK, nobody knows what's going on.
People are freaking out... Hey! Chaos and violence would
strike the cities of Earth. Or world as we know it would collapse. Here's somebody. Come on. -Is he dead?
-Let's get out of here. Just go! Fear, shock, panic, anger. It's entirely likely that humans
would be terrified. At the SETI Institute in California, Seth Shostak and his colleagues
are still looking for recent signals. The astronomers evaluate data from
radio telescopes all over the world. To date, they have not found any evidence
proving that extraterrestrials exist. Therefore, many scientists
criticize SETI's search methods. We looked for radio signals
from intelligent planets but that's looking at the wrong frequency. Why should they use
old-fashioned radio to communicate? The alien hunters have not given up. To finally get in touch
with extraterrestrials, some SETI researchers think that we should
play a more active role in communication. Instead of listening to distant signals, our own messages
should be sent into space. If you send to some nearby stars
that are not terribly far away - ten light-years, 20 light-years -
then maybe you get a response while you are still alive
and can enjoy a response. It would not be the first time
that astronomers have sent a message to aliens. In 1977, the Voyager 1 probe
made its way into space. Since then, it has reliably sent back data
and images from our solar system. Precious cargo is stored on board. The "golden record" - a copper disk that holds music,
images and sounds from the Earth. [dog barks] Greetings recorded
in 55 different languages. A way to kindly introduce
ourselves to foreign civilizations. [American boy] Hello from
the children of planet Earth. [German woman]
Herzliche Grüße an alle. [French woman]
Bonjour tout le monde. [Japanese woman]
Kon'nichiwa? Ogenkidesuka? [Spanish man]
Hola y saludos a todos. [narrator] In 2012, Voyager 1 became
the first probe to leave our solar system. It has flown further into space than
any man-made object ever before. This cosmic message-in-a-bottle
will travel even deeper into interstellar space. By 2025, the probe will
run out of its energy supply and continue into the cosmos,
uncontrolled. Will the aliens ever find
these spacecraft? I don't think so. They're about the size
of a Volkswagen Beetle, right, and they're dark and their transmitters
won't be working then. So how are you ever going
to find these guys? It's like looking for, I don't know, a little bit of flotsam
on the Pacific Ocean. [laughs]
You're probably never gonna find it! Acoustic signals are already
being sent out into space. [signal oscillating] The most famous signal was
the Arecibo Message in 1974. The message created by astronomer
Frank Drake used binary code to provide information about human
biology, the population on the Earth and tell the recipient exactly
where the signal originated. So far, we haven't received
a reply from aliens. Seth Shostak thinks
we need to be thinking bigger. In fact, he wants to offer
big data to the aliens. The more information they receive,
the better they will understand us. I would send the internet, actually.
I'd just send everything on the internet. I mean, if you walk down to the beach
and you find a message in a bottle and it's one sentence, you may never
figure out what that message was about. But if it was a thousand books,
you might figure out a lot more. But others think that these
well-meaning messages would make us incalculably more vulnerable. Enemy aliens might leverage
these communication efforts into a full-scale attack. I think it's a rather
silly idea to send out powerful beamed messages
indicating our presence. Who knows what's out there
in our galaxy? It's like being a four-year-old in the middle of a dark forest. Does she explore and learn the situation, or does she go running screaming
through the forest saying, "Monsters, hello! Everybody, I'm here"? Critics say that stopping these messages is the only way to prevent
a human catastrophe. Before proceeding, there needs
to be a greater scientific discourse about what these messages should contain
and who is allowed to send them. I think we should hold discussions, serious scientific investigations
and discussions of the pros and cons before we beam messages into space. Early projects, like Yuri Milner's,
are already under way. For the best message that
could be sent to extraterrestrials, a reward of $1 million is up for grabs. Though he previously also warned
against sending messages, Stephen Hawking now supports the endeavor. It is time to open our eyes, our ears
and our minds to the cosmos. If extraterrestrials
received our signals long ago, now it's too late for us to hide. Any society that could do that, any society that could come here
and threaten you, they've got bigger antennas than we do,
they can already pick up our television, our airport radars, all sorts of stuff, so
we're already telling them we're here. Pandora's Box might already be open. At this very moment,
aliens could be en route to Earth. [man speaks German on radio] If there are more intelligent,
more powerful and therefore more
dangerous civilizations out there, we should be very careful
about contacting them. These fears are not unfounded. In the history of mankind, when
a new country or continent is discovered, it has always ended tragically
for those who are conquered. The less technologically
advanced culture experienced pain, in some cases death and extinction,
in some cases slavery. An invasion of militant aliens
could end the human species. If the battle begins, those who could hide
in time would be the only survivors. Aliens would need a motive to fight Earth. It is possible to conceive of other
civilizations who are at war in the cosmos and
who are perhaps desperate for new territories or new resources. They may look at the Earth and say,
"This could be our new home." Would universal war
with extraterrestrial life be plausible solely for our resources? With so many planets out there orbiting
stars that will have water and carbon and all the elements that are on Earth, there's no reason to come
to a planet filled with life. This is an alien attack! Our planet is home
to seven billion people. To aliens, the most
interesting resources on Earth might actually be its inhabitants. -[thrusters whooshing]
-Run! If they are warlike, it would be like
Godzilla meeting Bambi. It would be no contest whatsoever. Is there any way to prepare
for this kind of disaster? Space agencies have emergency procedures to respond to dangers
like meteorite impacts. Do they also have a plan
in case of an alien attack? Scientists and military experts
have already thought through what would really happen
in an attack situation. An alien civilization approaching Earth
as a potential target for conquest is going to first try to eliminate
any kind of resistance. The simplest thing they can do
to neutralize our weapons is to use the electromagnetic pulse. Without warning, all energy supplies
would be shut off. Electronic devices,
cars and telephones would be useless and humans would be suddenly powerless. You would essentially drive human
civilization back into the 19th century. Earth's largest cities would be
targeted first in an invasion and most would not survive the brutal war. I'm sure that many of the nations of Earth
would use nuclear weapons, even on their own soil as a last resort to try to stop some form
of alien invasion. Using weapons of mass destruction
would destroy our own planet. Luckily, there is also another strategy. The first objective would
actually just be survival. The second priority would be the capture
of enemy technology. And reverse engineer them,
it may be possible for us to produce them in significant quantities. Even if aliens haven't planned
a deadly invasion, it could still turn into war
if we get in their way. Even if the aliens
don't want to conquer us, even if the aliens
don't want to eat us, even if the aliens don't want
to plunder our natural resources, we might get in the way because maybe
they have different intentions toward us. Humans would have no way to escape. We still don't know what's going on.
We have hidden ourselves underground. If an enemy arrives that
has such a massive disparity in their technological capabilities
that you have no means of potentially fighting back, then perhaps your best
opportunity to survive is to accept the changing
nature of your civilization. If they came here with friendship,
as explorers, that's great. We would hold out the hand
of friendship ourselves. If they came as conquerors, I think
we would simply have to surrender. This would be a war we could not win. Only one thing is for certain - extraterrestrials arrival would
change our world forever. The only hope is that if they do come,
they will come in peace.
