All language subtitles for Explained.S01E09.Extraterrestrial.Life.720p.NF.WEB-DL

[narrator] Fifty years ago,

astronomers picked up
this radio signal coming from deep space.

The signal repeated so regularly,

it kept time better than an atomic clock.

[imitates signal] What could that be?
That couldn't be natural.

[narrator] They thought it might be
an alien transmission,

so they nicknamed the signal LGM-1,
for Little Green Men.

It turned out to be a pulsar,

radio waves from a neutron star
collapsing 5.5 million years ago.

A lot of us put aliens
in the same category as ghosts

or the Loch Ness Monster,
a subject for science fiction.

Or left to the cranks, kooks
and conspiracy theorists.

[man] Immediately, I was just lifted
from the ground,

to about the height
that they were off the ground.

That's when I first saw this thing coming
straight down, just like an elevator.

This is a center for the distribution
of information

coming through me telepathically
from the space people.

[narrator] But time and again,

serious scientists
have thought they've found evidence

of extraterrestrial life.

[man] Are these really canals on Mars?
Are the polar caps frozen water?

[narrator] As recently as 2016,

astronomers proposed that
never-before-seen dimming patterns

from a star could be evidence
of gigantic structures built

by an advanced civilization
to harness the star's energy.

It turned out to be dust.

Scientists feel confident
that there is biology beyond Earth.

Not because we've found it,
we haven't found it.

The reason that we think
that they're out there is simply, if not,

then Earth is some sort of miracle.

[narrator] For most scientists
who study the universe,

searching for aliens isn't crazy.

What's crazy is that
we haven't found them.

In a universe so vast, where is everybody?

[Stephen Hawking] It is important to us
to know if we are alone in the dark.

Unidentified objects that
sound warning klaxons around the world.

[man] Oh, my gosh, look at that thing.
It's resting!

[Ronald Reagan]
How quickly our differences would vanish

if we were facing an alien threat
from outside this world.

Out there is a million other
civilizations.

They all look fabulously ugly.

And they're all a lot smarter than us.

[theme music playing]

Trash cans been vanishing
from city sidewalks in alarming numbers.

[narrator] Stolen trash cans are
a time-honored public nuisance.

You may have seen local news reports
about it.

The New Yorker magazine even published
a cartoon about it back in 1950,

blaming mischievous aliens.

That silly joke inspired one
of the most profound insights

in modern scientific history.

Because the physicist Enrico Fermi
saw that cartoon,

and the story goes, blurted out,
"Where is everybody?"

The fact that we haven't found
any evidence of aliens

became known as the Fermi Paradox.

There are about ten
to the power of 22 total stars.

That's about 10,000 stars
for every grain of sand on Earth.

A conservative scientific estimate says 5%

of those stars are similar
to our sun,

which means 500 billion billion suns
in the universe.

Many scientists are more confident
than ever that aliens exist

because of some game changing discoveries
in the last few decades.

Nobody could say for sure
if there were any planets

outside of our solar system,
until the 1990s.

Now, scientists think one in five
sun-like stars is a planet...

similar to our own.

When I get asked what are the chances
there's life out there,

I always answer 100%.

Just because there's
so many stars and planets...

we think pretty much every star
has planets.

[narrator] We've also discovered
life on Earth

in environments where nobody
expected to find it.

We see life all the way deep
in the sub-surface of the planet,

miles down, in like, gold mines.

We see life near volcanic calderas.

We see life on nuclear reactors.

We see life in the most extremes.

That actually gives us lot of hope
for the search for life elsewhere,

'cause we can't necessarily expect
that all planets

will have just the same conditions
as Earth.

[narrator] Estimates of how many
Earth-like planets will develop life vary.

So, let's say even with this new
scientific confidence,

it's just one out of every thousand.

That means every tenth grain of sand
on Earth

represents a planet with life on it.

And if just one out of every thousand
of those planets develop intelligent life,

that's a quadrillion intelligent alien
civilizations in the universe.

10,000 just in our galaxy.

Extraterrestrial life also has time
on its side.

Earth is only about a third
as old as the universe.

And so there's been plenty of time

for life to evolve
to advanced civilizations and for these civilizations to spread
across the galaxy.

[narrator] With all that time and space,
the math seems pretty clear.

We should've found aliens by now,
or they should have found us.

There's one popular explanation for
why we haven't found evidence of aliens.

We have found it.

Governments have just covered it up.

I believe that the flying saucers seen
by veteran airline and Air Force pilots

are objects from another planet.

Our critics continually charge

that the United States Air Force
is withholding information

from the general public on this subject.

This is absolutely untrue.

[narrator] Every so often,

something comes out
that gives this theory new life,

like the revelation in 2017 that
the US government had spent millions

on a secret program
to investigate UFO sightings.

[narrator] But as almost any scientist
will tell you,

looking into UFOs isn't the same
as searching for extraterrestrial life.

The word UFO is
"unidentified flying object."

It's unidentified.

So, by definition, we have to
leave it open.

It doesn't mean it's been identified
as an alien spacecraft.

[narrator] Scientists have their own
favorite theories about

why we haven't found aliens.

It could be that they came here,

didn't like what they found and moved on.

Imagine for a moment, you get
an infestation of ants in your house.

It happens.

Now let's say you wanna
have a conversation with those ants.

Say, "Excuse me, can you please leave?"
How would you even do that?

I like that theory, that we're
just so dumb right now.

We're not even at the level where
if they wanted to talk to us,

these so-called intelligent creatures out
there could even communicate with us.

It could be that they've got better things
to do

than just waft around the galaxy.

They've seen our planet,

they just don't wanna interfere with us

until we get to this point
of technological or societal advancement

where we're ready to be interacted with.

Maybe the galaxy is colonized,

maybe it's heavily colonized,

but just not where we are.

In other words,
the fact that we seem to be alone

may be only that we're in a backwater.

[narrator] But it's important to remember
that when Fermi calculated the odds

that alien life is out there,

it was just an educated guess.

With so many stars and planets,

he bet at least some of them
will develop life,

which would evolve and spread out.

The trouble with this bet is
there's a lot we don't know about life.

The great filter theory helps us think
about what we don't know.

Imagine the evolution of life
as a series of hurdles.

First, molecules
start replicating themselves,

which evolves into single-cell life,
then multi-cell life

and then animals with large brains
that can use tools,

and then smarter animals
that create even better tools. That's us.

And finally, animals that can figure out
how to colonize the galaxy.

Given the size and age of the universe,

it seems like a lot of alien species
should have beat us to that last stage,

unless one of those stages
is much harder than we think.

[Paul Davies]
The view seems to be that

given the right conditions,
life will obligingly pop up,

but the truth is, nobody has a clue.

We have no idea how non-life
turns into life.

We know how life structures itself,
but our gaps are in the major transitions.

[narrator] We know what the major hurdles
are in the evolution of life.

Just not how hard they are to get past.

Another example of life would help us
understand life better.

But so far, no aliens have contacted us.

So, it's up to us to find them.

[man] Listen to the sound of the sun
and the stars.

[Jill Tarter] I've spent my career
at the SETI Institute, S-E-T-I.

Search for Extraterrestrial Intelligence,
that's the acronym.

But in fact, we don't know how
to detect intelligence directly.

[narrator] When scientists look
for intelligent aliens,

they look for what are called
technosignatures...

evidence of alien technology.

We want to find
extraterrestrial intelligence,

by finding something that's engineered,
something that's artificial,

something that nature can't produce.

If I find technology...

I'm going to presume,
at least at some time...

the existence
of an intelligent technologist.

[narrator] From up close,

Earth has technosignatures
in the form of city lights.

From further out, aliens might notice
the satellites

and space stations orbiting our planet.

From even further,
they might pick up radio signals

or stumble across the Voyager probes

that are hurtling
across interstellar space.

Sometimes the things we think
are technosignatures

turn out to be natural phenomena,
like that pulsar.

But since radio signals are still
our most promising leads,

scientists do a lot of listening
to the sky.

[Tarter] If you've seen the movie Contact,

there's Jodie Foster on the hood
of the car with the earphones on.

It's a bit ridiculous. Because in fact,

the computer back
in the observatory control room

is doing the signal processing.

They're analyzing the equivalent of
the Encyclopedia Britannica every second.

[narrator] Jill Tarter would know.
Jodie Foster's character was based on her.

Holy shit!

She gets to say, "Holy shit!," you know?

We hope to some day have that moment.

[narrator] But that's just one way
to search for extraterrestrial life.

There are also biosignatures.

Biosignatures are indications

that life existed or once did exist
in any given environment.

[narrator] If aliens came to Earth looking
for life after we were long gone,

they would find biosignatures
in the form of fossils

and chemical evidence of life processes.

My favorite line to say with kids
is that all life poops.

So we know that all life takes in energy
and releases waste products.

[narrator]
If aliens were observing us from afar,

they would see biosignatures
in the form of water

and the gases in our atmosphere.

Oxygen is so reactive

that it can only be in our atmosphere
if it's being continuously produced.

Without life, Earth's atmosphere
would have no oxygen,

so we're trying to look for gases
that don't belong,

that might be attributed to life,
and we call them biosignature gases.

[narrator] Searching for biosignatures
on other planets is really hard.

We can't even see planets
outside our solar system. Stars are so much brighter than planets.

It's like trying to see a firefly
in a spotlight.

Today, we have a planet finding technique
called the transit technique.

When a planet goes in front of its star,
the starlight drops by a tiny amount.

[narrator]
These drops in light give scientists clues

about whether a planet might have life
on it.

Like the distance from its star.

We call the "Goldilocks zone"
the distance from the star,

where the planet, as heated by the star,
is not too hot,

not too cold, but just right for life.

[narrator] Researchers have been able to
surmise some amazing things about planets

just from these light patterns.

Scientists think they found a super Earth
with really intense gravity.

A planetary system with seven planets
all crammed into the Goldilocks zone.

And even a planet that could have
red vegetation,

from the different wavelengths
of light it receives.

We now know of over 3,500 planets
outside of our solar system.

Most of them were discovered
in just the last five years.

And tools are only getting better.

The next generation of space telescopes
will be able to see more distant galaxies.

A newly launched satellite will survey
the entire sky for possible planets,

rather than just small sections.

And astronomers are developing
new technologies

that would let them see
distant planets directly.

The line between what is considered
completely crazy

and what is mainstream
is constantly shifting.

[narrator] For all the exciting new ways
to search for life in deep space,

scientists are also searching
a lot closer to home.

-[man] We have landed.
-[man 2] Roger.

[narrator] In the 1970s,
we sent two landers to Mars

to test the soil for evidence of life.

The first and only time we've ever tried.

One of the experiments came back negative.

But another came back positive
for evidence of a process

that we only associate with living things.

When some of the experiments
came back positive,

and the others came back negative,
it was controversial,

because it was ambiguous.

So it was hard to say,
did we actually really find life?

[narrator] The contradiction could mean
an unknown chemical reaction occurred

that only looked like a living
thing consuming energy.

But since the '70s, we've learned
that life in extreme environments

uses energy differently and leaves
different markers on its environment.

The experiments that were designed

were designed based on life as we knew it
back then,

which was a very limited view
of life just here on Earth.

We need to go back to Mars
and do the experiment again.

[narrator]
The Mars 2020 mission is our next shot.

Unlike the Viking experiments,
it won't test for currently living things,

but it will look for signs that life once
did exist in certain Martian environments.

A mission is also in the works
to look for biosignatures

in the frozen oceans
of Jupiter's moon Europa.

In the search for intelligent life,

scientists are also trying to expand
their thinking and their search.

Now, the only example we have
of intelligent life is indeed us.

You know... [laughs]

in Star Trek, I guess it was the doctor
on board, Bones,

who'd occasionally say,
"It's life, Jim, but not as we know it."

[narrator]
Actually, this is a common misquote.

The line is a lyric in the song
"Star Trekkin" by The Firm

and was never said in the show.

It's life, Jim, but not as we know it. [narrator]
Spock, however, said something similar

in Season One, episode 29.

It's not life as we know or understand it.

It is obviously alive. It exists.

[narrator] Advances in our own technology
give us new ideas

about what intelligent aliens
might be like.

One thing that we're doing in this century

and certainly in the first half
of this century, it seems,

is to develop artificial intelligence
that does more

than just play a good game of chess.

Humans are the best known reference
for intelligence.

What a great standard
to try to live up to.

We think of the aliens as being
like a soft and squishy biology,

whereas in fact the majority
of the intelligence in the universe

could very well be synthetic intelligence.

One good thing in terms of helping us
to think about what we don't know

is to read science fiction.

Actually, Arrival was one
of my favorite movies.

Just because of the concept
that the aliens could be so different

from intelligent humanoids.

I really think that's
how it's gonna end up being.

[narrator] Science fiction has shaped
our space programs

from the very beginning.

[Kennda Lynch] The Martian Chronicles,
War of the Worlds, many senior scientists

were inspired by those early,
early novels,

and they've actually created
the science reality of Mars exploration

that we have today.

[Sara Seager]
It's a multi-generational search.

We're just starting now.

We're just kind of planting the seeds
for a really long endeavor.

[man] Velocity build up
in feet per second.

[man 2] Okay.

[Tarter] Consider the volume
of all the Earth's oceans.

All right, and let's say,
that's the volume of search space,

where we might find a signal.

Well, in 50 years,
how much of that ocean have we searched?

It's a pretty disappointing
one glass of water.

[narrator] Whether we find
extraterrestrial life

or learn that we are alone,

it will tell us a lot
about our civilization

and what our future might be.

Think back to that great filter theory.

It could be even life rarely gets started

or that the universe is teeming with life,
but none of it...

as smart as us.

That is good news
for the future of our civilization.

It means that we are maybe
the only planet in the galaxy

that got as far as intelligent life,

and there's no reason
we can't be set fair

for thousands or millions of years
in the future.

[narrator] Or maybe the hardest stage
is ahead of us.

And some unknown challenge
awaits humanity.

If life on Earth is typical
and we are typical,

but the typical thing is
you don't survive very long then,

that doesn't say much about our future.

The importance for the search
for life elsewhere in the universe

is kind of the search
in understanding ourselves.

It's important to understanding
how did we as a planet come here.

And how rare are we
or how rare are we not?

And for humans, it's an understanding of,
you know,

what's the next big step for us.