For more than a decade,
I've made programmes about the universe...
and our place within it.
There it is! There it is!
I can see the parachutes.
I've had some remarkable encounters...
I can't believe you can just stand next to a spacecraft.
Release.
memorable experiences...
They came down exactly the same.
Wow.
MUFFLED SHOUTING
and explained some beautiful science about how our planet works.
That really is the thin blue line that protects us.
Look at that!
Now I'm taking a new look at those past programmes.
It's surely as close as I'm going to get to being in space.
I think our knowledge really has moved on since we made these films.
So it's really interesting to revisit some fundamental
questions again.
Are we alone in the universe?
What really is gravity?
Where will the exploration of space take us?
And what is time?
BEEPING
Beeping's never good.
I'm back at the historic Royal Institution
to re-watch some of my previous films...
and explore one of the most profound questions we can ask...
are we alone in the universe?
Arthur C Clarke famously said,
"Two possibilities exist.
"Either we are alone in the universe,
"or we are not.
"Both are equally terrifying".
There are certain questions in science that,
if we can answer them, I think will have profound cultural ramifications
and the question, "Are we alone?" is one of them.
And to be able to answer that, I think
will change our view of our place in the universe in a very profound way.
It's one of the most common questions I get asked -
"Do you believe in UFOs?"
"Do you think there are aliens out there?"
People of my generation, certainly,
I think we'd all like ET to be real.
ET, by the way.
I don't really want Darth Vader coming down,
but I would like ET to arrive.
And as we send spacecraft to explore the solar system,
we're beginning the scientific search for alien life.
Just knowing that we are not alone,
that life exists elsewhere would, I think,
be one of the greatest discoveries in human history.
DRUMS AND SINGING
We have long sought to communicate with beings
out there amongst the stars.
DRUMS AND SINGING
In New Mexico, the Navajo tribe believe the stars
are home to another consciousness.
Once a year, they come together to communicate with this entity...
DRUMS AND SINGING
in a healing ceremony called Yeibichai.
It's a nine-day long festival of ritual and chanting...
the most sacred of which is the night chant,
performed by medicine men in private,
never filmed,
and recorded just once.
WINDING
MUSIC PLAYS
This recording was made by Willard Rhodes of Columbia University
in the early 19405...
SINGING
and he could not have imagined what was going to happen to it.
MUSIC CONTINUES
In 1977, the recording was transferred onto four golden records
and encased in these covers.
Today, only two of them remain on planet Earth.
The other two are bolted to the sides of two space probes -
Voyager 1 and Voyager 2 -
and are now travelling into deep space.
Accompanying the night chant are an eclectic mix of images
and sounds from Earth.
ARCHIVE: Shalom. Konnichiwa.
OPERATIC SINGING
The choice of images and sounds, music, is very important
because it's a snapshot of how we feel about ourselves.
It's what how would we like to represent ourselves
to alien civilisations out there?
What ideas do we want to communicate?
What music from Earth and sounds from Earth
and pictures would we like someone to find?
The Voyagers' primary mission
was to explore the outer planets of the solar system...
but adding the discs gave the spacecraft an extra purpose.
They've become Earth's emissaries,
carrying postcards to our alien neighbours,
if they exist.
I think the wonderful thing about the act of putting images
and sounds and the songs of Earth on this spacecraft
and sending it off into interstellar space
is that it speaks to our need, in a sense, not to be alone.
MUSIC: Johnny B Goode by Chuck Berry
♪ Deep down in Louisiana close to New Orleans
♪ Way back up in the woods among the evergreens
♪ There stood a log cabin made of earth and wood... ♪
The sounds of Earth may wash up on a distant shore.
♪ Who never ever learned to read or write so well
♪ But he could play a guitar just like a-ringin' a bell
♪ Go, go... ♪
The question is,
will there be anyone around to listen?
If you're going to look for life beyond Earth
out there in the universe,
you have to know what life is
and you have to know how to look for it.
And the best way to do that, by far,
in fact, the only way to do that
is to understand life here on Earth.
WAVES CRASH
Floating in the Sea of Cortez off the coast of Mexico is
the research vessel Atlantis -
the mothership for the exploration
of one of the most alien worlds we know.
But it's an alien world on our planet.
The Atlantis is the launch vessel for Alvin,
one of the world's most rugged submarines.
Built like a spacecraft, it's designed to explore
the deepest depths of the ocean...
and I'm lucky enough to have hitched a ride down
to the sea floor, 2km beneath the surface.
CHUCKLES
ARCHIVE: That has honestly got to be the closest thing
to going into space that you can do,
and given that I'm not going to go into space any time soon,
I think this is the next best thing.
See you in eight hours.
INDISTINCT INSTRUCTION
WINCH SQUEAKS
WATER BABBLES
The parallels to space flight are obvious.
As the tiny capsule descends,
we're leaving the familiar world of the surface of our planet
and entering a strange, hostile world.
MUFFLED SPEECH OVER COMMS
If anything goes wrong, we will be completely on our own.
It's very rare that you get to do something so challenging
and so alien,
and to be taken to that environment in the very deep ocean,
it's strange
and silent and unusual.
And it's tiny, as well.
Erm, so there's three people crammed into this little
titanium ball, which kind of creaks a bit as it goes down!
BEEPING
Beeping's never good!
BEEPING CONTINUES
BEEPING STOPS
MUFFLED SPEECH ON COMMS
At the Earth's surface, we're used to one atmosphere of pressure.
As we descend, the pressure increases by another
atmosphere every ten metres
and it soon adds up.
RADIO COMMS:
So we're just approaching a kilometre deep.
The pressure outside there is now, what, 100 atmospheres?
That's higher than the atmospheric pressure on the surface of Venus.
Without knowing,
if you're asked the question, "Could life exist down here?" -
100 atmospheres,
the cold, dark, no sign of sunlight at all,
it's pitch-black there -
you would say, "No".
Well, I would say, "No".
But the depths of the ocean are not lifeless.
Illuminated by Alvin's lights,
we find oases of life in the deserts of the ocean floor.
COMMS:
So we've landed, after about an hour of descent.
We've just stopped in the most incredible place.
This underwater city is one of the most bizarre
environments on our planet.
CAMERA WHIRS
It's built around a hydrothermal vent,
a volcanic opening in the Earth's crust
that pumps out clouds of sulphurous chemicals
and water heated to nearly 300 Celsius.
And somehow, life has found a way to thrive
in these most extreme conditions.
Look at that!
It's not only just bacterial blobs,
it's real complex organisms.
Alien - I want to say that word. Alien environment.
It really is alien to us.
For me, the fascinating thing about finding life down here
is that the conditions on the deep ocean floor
are more similar in many ways to the conditions
on worlds hundreds of millions of kilometres away
out there in the solar system
than they are to the conditions just 2km above my head
on the Earth's surface.
You know, it's incredibly dark.
There's no sunlight. There's a brutal mixture of hot and cold water
and just, well, rock and minerals,
so if life can not only survive
but even flourish in these conditions,
then you've got to feel that it's much more likely
that life can also survive and flourish
out there in the solar system.
One of the main benefits, I think,
in looking at life in extreme environments on Earth,
so-called extremophiles,
is that you get a wider view of what life is
and what chemical elements or compounds it produces.
And that is useful because, really,
if you think about life, subsurface on Mars, for example,
if it exists,
we really don't know how that life would behave.
BIRDSONG
This is the Cueva de Villa Luz in Tabasco, Mexico,
the Cave of the House of Light,
and it is the definition of a hostile environment
to me because it's full of hydrogen sulphide gas,
which is why I've got this gas mask in case it all gets too much.
Although the cave is a deathtrap for us,
that doesn't mean that nothing lives here.
In fact, it's teeming with life.
So you're looking for the chemistry.
You're looking for seeing how life behaves,
that almost alien chemistry to us, at least.
And that can tell us
what to look for when we're searching for life on other planets.
Well, these things are what I came deep underground to see.
These are snottites and you can see why they're called that.
They're really one of the most alien life forms that I can conceive of
on the Earth because they metabolise hydrogen sulphide.
So they metabolise this faintly
acidic and nasty gas that I'm just breathing
in now, you can almost feel it on your tongue, actually,
the acidity of it.
These guys breathe in hydrogen sulphide and oxygen
and produce sulphuric acid.
Every time we think we know
what the envelope within which life can exist
is, every time we say, "Well, it's got to be at this temperature
"and it's got to have these gases
"and it's got to have these substances around",
then we tend to find somewhere that proves that we were wrong
and life is rather more ingenious than we thought.
But does that mean that life could exist anywhere in the cosmos?
We live in a vast universe, which is always an understatement.
It could well be infinite in all directions.
We cannot look everywhere for life.
So we have to try
and narrow it down and make an educated guess about what kind
of conditions might be prerequisites for the existence of life.
If there's one thing - it's probably the only thing that all biologists
agree on - it's that liquid water
is a prerequisite for life.
So in 2010, I visited the driest place on Earth.
If you want to see how important water is to life,
there's no better place to come than the Atacama Desert in Chile.
There's soil here
that's more sterile than a hospital operating theatre.
And in fact, scientists have looked for the most basic form of life
- bacteria - in some parts of the Atacama
and they found absolutely nothing.
All deserts are characterised by a lack of moisture,
but the Atacama takes that to the extremes.
The Sahara is 50 times wetter than the Atacama.
There are weather stations here that have measured one millimetre
of rainfall in ten years.
There are river valleys that have been dry for 120,000 years
and there are rocks that haven't seen rainfall for 20 million years.
It's this dryness that explains why nothing can survive here.
Even the most primitive form of life on Earth, the bacteria,
need water for their survival
and there are no exceptions
and this seemingly fundamental link between water and life
is driving the search for life out there in the solar system.
Since we filmed Wonders of the Solar System,
which is now over a decade ago, the science has moved on.
People have done research
and we have found bacteria in the driest parts of the Atacama.
However, they're dormant bacteria.
They are a bacteria that can survive without water,
in very arid conditions for long periods of time.
And then if you sprinkle some water on them, they are reanimated.
So if we accept that water is one of the prerequisites for life,
it is necessary for life anywhere in the universe,
then immediately you have a search strategy.
We want to look for signs that water was,
or maybe still is, present.
And fortunately, one of the places where that's certainly
a possibility and perhaps a probability, is Mars.
Mars is now the focus of Nasa's Mars 2020 mission,
the latest of many attempts to search for signs of life
on the planet.
In the 1940s and '50s,
serious astronomers thought that there may be liquid water
flowing on the surface, and even vegetation, because that's
sort of what it looks like when you look at it through a telescope.
But the first time we went to Mars, the results were quite shocking
to many people because what we saw was a world
that looked like the Moon, which is a barren,
lifeless world at first sight.
RADIO COMMS:
STUDIO: And there's the first piece of information coming in.
And later missions offered little encouragement.
So I think through the '70s, there was
a fairly negative view of certainly life existing today on Mars.
But as we've learned more about the geology of Mars
and the history of Mars, I think that sense has certainly changed.
And that's why we're sending increasingly complex robotic
explorers to Mars today to search for the conditions
necessary for life and ultimately to search for life itself.
In 2012, NASA attempted a new manoeuvre to land on Mars.
The payload was a one-tonne rover called Curiosity.
Its final descent has become known as the seven minutes of terror.
Curiosity touched down in Gale Crater,
a 150-kilometre-wide impact basin
thought to have been home to an ancient lake.
Then, 61 clays after landing,
Curiosity identified the perfect spot to begin its primary mission.
In a sandy area of the crater called "The Rock Nest"
the rover took its first scoops of Martian soil.
WHIRRING
Chemical analysis of the fine, dusty sand
revealed something quite unexpected.
Even though the surface of Mars appears completely dry,
2% of the soil is still made up of water.
Curiosity had found evidence of just how wet a planet
ancient Mars had been.
For hundreds of millions of years...
Mars was a water world.
THUNDER CRACKLES
Rains fell.
Rivers ran.
And in the Northern Hemisphere, water collected in a vast sea
that covered a fifth of the Martian surface.
The Red Planet was once blue.
On Mars around four billion years ago.
And the atmospheric pressure was at least that of Earth today,
perhaps even higher.
Temperatures were around 25 degrees.
So I could have sat on Mars all those years ago,
admittedly with a mask to breathe
because there was very little oxygen,
but I could have sat there and looked out over a view like that.
So you don't have to imagine what Mars was like in the past,
you can experience it.
It was pretty much like this.
Perseverance, the rover for Nasa's current mission to Mars,
landed in February 2021.
Manoeuvre has started.
Tango delta.
Touchdown confirmed.
Perseverance is safely on the surface of Mars
ready to begin seeking...
So Perseverance is going to prepare samples of Martian soil
from below the surface, where there may be evidence
that life existed or could possibly still exist.
And then we're going to send another spacecraft there
to take those samples prepared by that rover
and bring them back to Earth.
We wouldn't do that if we didn't think there was a chance
that life had existed, and may still exist, on Mars today.
But life needs more than just water to exist.
When Earth formed, there was no life.
So there had to be a genesis.
Life had to emerge somehow from the geology of a lifeless planet.
And discovering how life emerged here
gives us vital clues in our search for alien life.
This is Lake Taal.
Despite its sleepy, languid appearance,
this landscape has been violently transformed.
When I think of a volcano, I usually think of a pointy, fiery mountain
with a little crater in the top.
Probably a bit like that one.
But actually, this entire lake is the flooded crater
of a giant volcano.
It began erupting only about 140,000 years ago.
This crater is 30km across and in places, 150 metres deep,
and that's a cube of rock,
5km by 5km by 5km,
just blown away.
Taal Lake is testament to the immense power
locked within the Earth at the time of its formation.
Since the lake was created, a series of further eruptions
formed the island in the centre.
And at its heart is a place where you can glimpse
the turmoil of the inner Earth,
where energy from the core
still bubbles up to the surface...
producing conditions similar to those that may have provided
the very first spark of life.
The volcano transforms heat from the inner Earth
into chemical energy and stores it
as a reservoir of protons in the lake.
This reservoir of positively charged particles is a natural battery.
These bottles contain a weak acid
and are connected by a semipermeable membrane.
Passing an electric current through them has a similar effect
to the volcano's energy bubbling up into the lake.
It causes protons to build up in one of the bottles.
You can think of it, I suppose, like a waterfall where the protons
are up here waiting to flow down, and all you have to do
to release that energy and do something useful with it
is complete the circuit, which I can do
by just connecting a motor to it.
There you go.
Look at that.
That's the protons cascading down the waterfall
and driving the motor around.
It actually works!
Quite remarkable, actually!
Proton cascades once occurred naturally at openings in the
Earth's crust called alkaline vents,
deep in the primordial oceans.
This could be where your distant ancestors come from.
Places like these could be the places where life on Earth began.
The first living things might have started out
as part of the rock that created them.
Simple organisms that exploited energy
from the naturally occurring proton gradients in the vents.
And today, this same flow of energy,
this waterfall of protons,
is found in the cells of every living creature on this planet,
from a single bacterium cell, to you and me.
We are now, as we speak,
recreating the conditions
that were present in a primordial ocean of ancient Earth,
3.8 billion years ago
in the deep oceans close to hydrothermal vents.
Why? Well, the theory is because that's where we come from.
That was our home.
If life emerged in this way from the energy of our planet,
this allows us to narrow down the search
and send space probes to hunt for places with similar geology.
And, in recent years,
we've found these conditions in some unexpected locations.
I think one of the great revelations
and surprises in the exploration of the solar system
has been the richness in the geology
and geochemistry of moons.
I think before we went,
before we flew out into the outer solar system
to look at the moons of Jupiter and Saturn in particular,
when you said, "moon", the image conjured is that of our Moon,
which is, as Buzz Aldrin said, "magnificent desolation",
but essentially an arid rock, a lifeless rock,
geologically inactive.
We're not going to find life on the Moon, right?
But as is always the case,
what we found when we flew to the moons of the outer solar system
with spacecraft, is that the moons are more interesting and varied
and fascinating than we could possibly have imagined.
Jupiter's moon, Europa, has more salt water in its ocean
below its icy surface than in all the oceans of the Earth combined.
And we have found evidence of, um,
perhaps, fountains of ice
rising up from the surface.
So geological activity below the surface, perhaps.
And if you have energy, geological activity and you have water,
then perhaps you have life.
Jupiter's frozen moon, Europa, is echoed in this spectacular
ice cave in the Vatnajokull glacier in Iceland.
You see, the laws of nature
are universal and that may not only
apply to the laws of physics, but also to the laws of biology as well.
If that's the case, then what we find in these ice caves of Iceland
may tell us something about what we could expect to find
below the frozen surface of Europa.
Now, it's hard to describe this place.
I mean, it's absolutely magnificent.
Visually, the quality of the ice,
it's just completely transparent and clear.
You can see straight through it.
It's what astrobiologists find in this ice that makes us think
that Europa could be teeming with life.
FAINT HAMMERING
NASA scientist, Richard Hoover,
has spent his career
looking for life in unlikely places.
Well, that went very well.
OK. So will any organisms that you find in that ice
be living in a sense that I would understand it, like, they're
actually alive now and metabolising?
For a long time, it was thought that ice microorganisms
were present only in a state of what is called deep antibiosis -
suspended animation.
It's now becoming quite clear that that isn't necessarily
the case for all the microorganisms.
There may be others that are actually actively living in the ice.
That's quite incredible.
So in this glacier, the whole place, this whole cave,
may be populated by actual living things, not frozen things,
but things existing, living, cell dividing, reproducing,
all those things.
Cell dividing, reproducing. All of this.
It's this prospect of finding things living in solid ice
that has had the greatest impact on our ideas of where life could
survive in the solar system.
We're at lowest magnification.
That's 100,000 millionths of a metre? Yeah. Yeah.
We have bacteria.
HE CHUCKLES
Look, I'm really interested there
because we found these living things in the ice.
Tremendous.
So these are organisms that have been trapped in that glacier for...
Yes... thousands of years?
Look at this, beautiful.
You're seeing life in ice. So, that's amazing.
We now know that some microorganisms are capable
of actually causing the ice to melt
because they generate essentially antifreeze proteins.
So what are the implications of these discoveries,
the fact that you've got living bacteria inside ice on Earth?
What are the implications for Europa?
You can clearly have bacteria like this in the frozen ice
near the surface crust.
I've learned this lesson all the way through making these programmes
over the years. Every time you send a spacecraft somewhere new,
it discovers new stuff.
And when NASA sent space probe Cassini to Saturn,
it stumbled upon another surprising potential home for alien life.
Enceladus, Saturn's moon, is one of the great discoveries,
and I think it's widely accepted now,
it strongly suggests that there's both liquid water
and geological activity below the surface of that tiny moon.
If you force me to guess,
then I would guess that we may find
evidence of bacterial life,
single-cell life, simple life,
somewhere in the solar system beyond Earth. That would be my guess.
But I am as certain as I can be
that we won't find complex life.
There won't be fish in the oceans of Europa.
But this begs the question -
is there intelligent life beyond our solar system?
And really, that's a different question
that we want to know the answer to.
When we talk about aliens,
we talk about the search for extra-terrestrial life.
We kind of mean ET, don't we?
We mean something that we can talk to.
This desire to know if there are other civilisations
out there in the universe
has inspired decades of scientific research.
Right now, as we speak,
there are telescopes searching the skies for signals, for hints,
for a sign of civilisations
or even the signals from starships moving
through the sky, you know, whatever it is, that we're looking for that.
Every hour of every day,
some among us scan the skies listening for alien civilisations.
They call themselves SETI -
the Search for Extraterrestrial Intelligence.
This is the Allen Array in Northern California,
and it's SETl's most ambitious instrument to date.
This collection of 42 radio telescopes is optimised
to detect signals from extra-terrestrial civilisations.
And it's exquisitely sensitive.
If a signal would beam to us,
with the sort of power that we can generate using our
current technology, from any one of the million or so sun-like stars
within a thousand light years of Earth, then this would hear it.
This experiment has yet to detect a call from ET.
But they live in hope
because SETI did once pick up a tantalising signal.
PIERCING TONE
On August the 15th, 1977, a radio telescope called a Big Ear detected
a radio signal from somewhere in the vicinity
of the constellation Sagittarius.
And this is the printout from that night.
You can see that somewhere around 10.15pm,
Eastern Standard Time, a very bright radio signal pulsed in.
It looks something like this.
I can sketch it out.
It was a pulse...
with a width of around 72 seconds
and the peak intensity,
the peak brightness, was over 30 times the brightness of
the background radio emission from the galaxy, so it's fascinating.
PIERCING TONE
And it came in on a wavelength that SETI believes an intelligent
civilisation might choose.
The wavelength was 21 centimetres.
That's the wavelength of light,
of radio waves emitted from hydrogen atoms.
So the whole sky glows at that wavelength,
and back in the 1950s,
radio astronomers speculated that if an alien civilisation
wanted to communicate with us, then they might well
choose that very special, natural wavelength to send their message.
So surprising was this that when it was spotted a few clays
later by an astronomer called Jerry Ehman,
he circled that pulse,
that 72-second flash of radio waves, and wrote, "Wow" next to it.
So this has become known as the Wow! signal.
RUMBLING
Today, over 35 years after the Wow! signal was detected,
there's still no satisfactory explanation.
It doesn't seem to have been local, a military signal or a satellite,
and indeed, nobody's supposed to transmit
at the hydrogen line frequency.
It's reserved for radio astronomy,
Since the Wow! signal, we've heard nothing.
We've searched in more detail with better telescopes,
more systematically, by no means exhaustively,
by the way, I think we can do much more,
but we've searched and we've heard nothing.
So the name that astronomers give it,
the rather ominous name - The Great Silence - still applies, right,
we listen and we look out into the universe
for signs of others and we see no sign.
A possible reason for that can be found in the biology
of complex organisms here on Earth.
The story of life on this planet shows that the transition
from single-celled life to complex life may not have been inevitable.
Life had to overcome a significant bottleneck.
Everything we would call a complex living thing today
shares the same basic structure.
It's built out of cells called eukaryotic cells.
They're, roughly speaking, the same in every tree,
every blade of grass, every fish, every insect, even in every
piece of skin in my knee. Every cell in my body is a eukaryotic cell.
And they're extremely different to the simple cells,
the bacteria.
So how did those cells come to exist?
One popular theory is that it was two simple cells merging together
that formed what we'd recognise today
as the complex cells in your body.
Somehow, the invader managed to survive the host cell's defences.
And when the cells reproduced,
they reproduced together.
We still struggle to understand how this happened
because it's incredibly unusual.
Here's the point - because every complex animal
and plant shares that same basic building block,
we are very confident that it only happened once,
somewhere in the oceans of the primordial Earth.
And biologists call this merger
the Fateful Encounter Hypothesis for a good reason.
It seems that that kind of merger between two simpler life
forms may be extremely rare.
The idea that one organism can get inside another and doesn't kill it,
that they both survived to produce something that's actually capable
of doing magnificent things - things that are far more complicated
and wonderful than the two simple building blocks can manage
on their own - seems to be... it seems to be unlikely,
a fateful encounter.
Now, if that's the case, then that may suggest that complex life,
that intelligent life, is extremely rare indeed in the universe.
But that possible rarity hasn't stopped us
searching for signals from intelligent civilisations.
Now, here's Frank Drake.
And this was a tremendous privilege to me
cos I'd grown up with that name.
I mean, if you're interested in astronomy and SETI -
the Search for Extraterrestrial Intelligence -
you know the name Frank Drake.
When you meet someone like that, one of your heroes,
it's a special moment.
And he did not disappoint.
So if I'd have asked you, back in the 1960s,
"By the 21st century, do you expect to have seen a signal?",
what would you have said?
I would have said,
"Yes, I expect to succeed",
because we were doing a lot of searching then.
Does that make you disappointed?
I'm disappointed, yes, but not surprised.
What we've learned over the years is the searching has to be much
more comprehensive than we'd realised 50 years ago. Hm.
But we know it's still doable.
It just takes much more time than we imagined.
Let me show you something.
This is an orchid...
a very peculiar and beautiful orchid, it's very fragrant...
which actually only blooms two days a year.
If you would have been here two days ago, you wouldn't have seen this
orchid and you might have thought that this plant never blooms.
Well, so it is with SETl.
We've learned that we must search over and over and over through
the years till we are in the right place at the right time
to make the discovery.
What are they called?
This is called a Stanhopea.
It has hope in its name and we have hope that
someday we'll be in the right place, at the right time in SETI.
Frank Drake makes the argument that
if there are civilisations out there, then you might imagine
that the radio waves that they send out
are passing through the galaxy...
and so they would be passing through this room now.
So if only you had a sensitive enough detector,
then maybe you could pick up the signals.
And he's right.
The point he's making, as a scientist,
is that the only way you're going to know is to look.
And he doesn't think we've looked closely enough.
And I agree with him.
But Frank wasn't content just to hang on the line,
waiting for ET's call.
In 1961, he devised what remains a useful scientific
framework for considering how likely it is that we share
the galaxy with others.
The Drake Equation has become famous
because it gives us a tool to continue the search.
It dares us to answer a series of provocative scientific questions.
On the left-hand side, there's the number we want to measure,
the number of intelligent civilisations
in the galaxy that we can communicate with,
and then there's this group of terms that really ask questions
about ourselves - how likely is it for life to arise on a planet?
How special is the Earth? How special is the Sun?
How special is the solar system?
How special is intelligence?
And then there's this last term, L, which perhaps speaks to us
most profoundly of all -
the lifetime of intelligent civilisations.
Do civilisations live for a long or short time?
And if it's short, what is it that destroys them?
Is it a natural disaster?
We do after all live in a violent universe.
Or, are they condemned to destroy themselves?
When Frank first thought about it, sort of 50 years ago,
for example, the number of planets around distant stars -
how likely is it, what's the probability,
that a star will have planets around it?
We didn't know, we hadn't detected any.
It's not till the 1990s that we have the evidence for planets
around distant stars.
Now we have dedicated missions to go and look for them.
And these missions are revealing a universe full of possibilities.
Within the constellation of Pegasus,
around a sun-like star, there's a planet called Osiris.
It's way closer to its parent star than Mercury is to our Sun.
But it's a massive gas giant, a hotjupiter,
and by measuring the light that shines through its atmosphere,
we found that the atmosphere's full of hydrogen and methane... and water.
And just 24 light-years away, in the constellation of Scorpius,
there's a small, rocky world, one of the most Earth-like worlds we know.
It orbits around a red dwarf star,
which is one of three stars in the system -
a planet with three suns in the sky.
So now we can say with confidence that virtually every star
has a planetary system and we can put numbers on the number
of potentially Earth-like planets in a galaxy like ours.
We think it's something like 20 billion.
So probably one in ten stars
has an Earth-like planet
potentially around it.
We're on the verge of being able to analyse
the atmospheres of those planets.
We can very slightly now.
We have the capability to do it and look for signs of life
and look for signs of civilisation.
Given the importance of the question,
"Are we alone in the universe?",
it is inconceivable to me that we would not
continue to look as hard as we can
for evidence of life beyond Earth.
But are we likely to find it?
Or are we, in fact, alone?
I would guess that simple life is reasonably common,
but complex life is far less common.
And if we're talking about aliens, I mean, what do we really mean?
Going back to my ten-year-old self watching Star Wars,
aliens means Chewbacca
and spaceships and lasers!
Civilisations, right?
I think that my guess is there are very few of those.
And it's my working assumption that there may be, on average,
a handful, maybe one civilisation per galaxy at any given time.
If there is only one civilisation per galaxy,
a simple message to our nearest alien neighbours
could take millions of years to reach them,
making it inconceivable that we'll ever establish contact.
So we may be, for all intents and purposes,
alone.
Just think about what that means for a moment.
If indeed we are the only civilisation currently
present in our galaxy of 200 billion stars,
then I think that that means that, notwithstanding the fact that we
are physically insignificant, a speck of sand,
a grain of dust in this galaxy,
we are in a very real sense, extremely valuable.
And so that, to me, is why this question is so interesting
and so profoundly important,
because the more we hear silence,
right, the more we detect nothing,
the more we begin to think,
in my view, about our value in this universe.
I'd be delighted if we found anything that you could call
alive anywhere beyond Earth.
I don't care, at one level, if it's a little microscopic organism.
But I'd be even happier
if someone sent me
the Encyclopaedia Galactica,
do you know, by radio waves,
and I knew that there were other civilisations out there
because I'd have loads of questions for them.
Look at that!
Gravity...
Release!
the mysterious force of nature...
I've got to say, this is one of the most exciting things I've ever done.
that's challenging our understanding of reality.
Holy mackerel!