0:00:03 > 0:00:05Stop for a moment and think of this.
0:00:06 > 0:00:09Are we alone in the universe?
0:00:09 > 0:00:12It's perhaps the biggest question we've ever asked.
0:00:12 > 0:00:16It's not crazy to imagine that some hugely super-human
0:00:16 > 0:00:18civilisation exists out there.
0:00:19 > 0:00:23They may have been watching the earth for millions of years.
0:00:25 > 0:00:27After a long and distinguished career
0:00:27 > 0:00:30at the forefront of cosmology,
0:00:30 > 0:00:34the Astronomer Royal, Martin Rees, has taken up
0:00:34 > 0:00:36the hunt for extraterrestrials.
0:00:39 > 0:00:42Absence of evidence is not evidence of absence.
0:00:45 > 0:00:48Now, with the help of the BBC's archive...
0:00:48 > 0:00:52We can't prove that bug-eyed monsters don't exist.
0:00:52 > 0:00:54..Martin's going to take us into his world.
0:00:56 > 0:01:00You might think hunting for aliens is just science fiction.
0:01:00 > 0:01:02You'd be wrong.
0:01:02 > 0:01:03Quite a sight, wasn't it, sir?
0:01:03 > 0:01:05A sight I'd rather not be seeing.
0:01:07 > 0:01:09It's a vibrant frontier of modern science...
0:01:15 > 0:01:17..where fierce debates rage.
0:01:18 > 0:01:23It's possible that we are a trillion-to-one fluke.
0:01:23 > 0:01:26I think that's an over-hasty conclusion.
0:01:26 > 0:01:29By exploring opposing views...
0:01:29 > 0:01:33A lot of sloppy thinking is quite accepted about alien intelligence
0:01:33 > 0:01:35and I think that is a problem.
0:01:35 > 0:01:39..we'll travel to the limits of our understanding about the universe
0:01:39 > 0:01:40and our place in it.
0:01:42 > 0:01:43It's a journey that, for Martin,
0:01:43 > 0:01:46leads to an extraordinary conclusion.
0:01:46 > 0:01:49Our idea of what an alien will be is all wrong.
0:01:50 > 0:01:54It's not organic beings we should be looking for.
0:01:54 > 0:01:55It's machines.
0:02:10 > 0:02:12On July 20th, 2015,
0:02:13 > 0:02:15Professor Martin Rees joined
0:02:15 > 0:02:18some of the greatest minds in science at the Royal Society.
0:02:20 > 0:02:25They were launching a £70 million research programme.
0:02:25 > 0:02:29The aim? Finding intelligent life in the universe.
0:02:29 > 0:02:31It's a huge gamble, of course.
0:02:31 > 0:02:35No-one would count on success, but the pay off would be so colossal.
0:02:36 > 0:02:40The team are using some of the world's biggest telescopes to hunt for a signal.
0:02:41 > 0:02:44It's our best chance yet of finding aliens.
0:02:45 > 0:02:49Stakes are so high, and that's why I think there's more interest
0:02:49 > 0:02:52and more focus - certainly among mainstream scientists -
0:02:52 > 0:02:56on this topic than there ever was in the past.
0:02:56 > 0:02:59And we are gradually edging closer to answers.
0:02:59 > 0:03:01'With at least two billion stars in our universe,
0:03:01 > 0:03:04'somewhere in deep space there are probably planets with
0:03:04 > 0:03:07'civilisations built by living creatures.'
0:03:07 > 0:03:10As our knowledge of the universe has increased...
0:03:12 > 0:03:17..so has our understanding of who or what might be living out there.
0:03:17 > 0:03:19Hello!
0:03:23 > 0:03:25Aliens have gone mainstream.
0:03:29 > 0:03:32That's why scientists like Martin -
0:03:32 > 0:03:36more famous for researching the big bang and black holes -
0:03:36 > 0:03:39have joined the hunt for extraterrestrials.
0:03:42 > 0:03:45Are we alone? Or is there life elsewhere?
0:03:45 > 0:03:47It's especially fascinating to us today,
0:03:47 > 0:03:51because, for the first time, we have a real chance of answering it,
0:03:51 > 0:03:53because of the advances in technology
0:03:53 > 0:03:55and in our understanding of life.
0:04:07 > 0:04:09But first, there's a problem.
0:04:09 > 0:04:13Before we can explore Martin's ideas on aliens,
0:04:13 > 0:04:17there's one question all those who look for ET must face.
0:04:18 > 0:04:22It's a question famously posed in the most unlikely of settings.
0:04:27 > 0:04:28Los Alamos.
0:04:30 > 0:04:31Birthplace of the bomb.
0:04:34 > 0:04:36The year is 1950...
0:04:37 > 0:04:41..and Enrico Fermi, one of the architects of the atomic age,
0:04:41 > 0:04:43is taking a break.
0:04:45 > 0:04:47Fermi was having lunch with some colleagues.
0:04:47 > 0:04:51They were talking about the existence or otherwise of aliens.
0:04:51 > 0:04:55And midway through the lunch, Fermi just stopped and said,
0:04:55 > 0:04:56"Where is everybody?"
0:04:58 > 0:05:00Where indeed.
0:05:00 > 0:05:04Fermi's point was that if there ARE lots of alien civilisations
0:05:04 > 0:05:06out there, why haven't we found any?
0:05:07 > 0:05:12It may seem a simple observation, but for physicist Stephen Webb,
0:05:12 > 0:05:16it casts doubt on the idea that we have any cosmic company at all.
0:05:17 > 0:05:21Because Fermi did more than just ask the question.
0:05:21 > 0:05:24Like all good scientists, he did a spot of maths.
0:05:25 > 0:05:29What he did was run through the numbers,
0:05:29 > 0:05:33looked at the number of stars in the galaxy, number of planets.
0:05:33 > 0:05:36He made an estimate of how many extraterrestrial civilisations
0:05:36 > 0:05:38should be out there.
0:05:38 > 0:05:40And he came to a large number.
0:05:42 > 0:05:46Given the huge scale of the galaxy, Fermi calculated that
0:05:46 > 0:05:50there should be loads of alien civilisations out there.
0:05:52 > 0:05:56What's more, he reasoned that many of them would
0:05:56 > 0:05:58be far more advanced than our own
0:06:05 > 0:06:11There are many stars which are quite a bit older than the earth.
0:06:11 > 0:06:16Indeed, in our galaxy there are stars two or three billion years older than the sun,
0:06:16 > 0:06:19which could perfectly well have evolved planets,
0:06:19 > 0:06:22rather like happened here on earth.
0:06:22 > 0:06:26And of course you then have to ask, if that were the case,
0:06:26 > 0:06:30then the life on those alien planets would have had a head start.
0:06:32 > 0:06:35Fermi's conclusion was that aliens should easily have colonised
0:06:35 > 0:06:38the galaxy by now - several times over.
0:06:39 > 0:06:45In short, there should be space-faring civilisations everywhere.
0:06:45 > 0:06:49So Fermi realised that there's something paradoxical about this.
0:06:49 > 0:06:52We expect to see them, and we don't.
0:06:54 > 0:06:58It's called...guess what? The Fermi Paradox.
0:06:58 > 0:07:02And for some, it leads to a stunning conclusion.
0:07:02 > 0:07:03It's a surprise to me.
0:07:03 > 0:07:06I would expect, if they exist, that we would see them.
0:07:06 > 0:07:08We would hear from them.
0:07:09 > 0:07:11They could build large structures,
0:07:11 > 0:07:14we could see exhaust from anti-matter rockets,
0:07:14 > 0:07:18we could see artificial lines in a star's spectrum
0:07:18 > 0:07:19that they've put there.
0:07:19 > 0:07:23The conclusion that I would draw from that is that we are alone.
0:07:24 > 0:07:27And that's a really, really sad thought.
0:07:37 > 0:07:40I think that's an over-hasty conclusion...
0:07:43 > 0:07:47..because we've no idea what variety the life out there might take.
0:07:47 > 0:07:49If there are aliens out there,
0:07:49 > 0:07:52then they're likely to be extremely different from us, in my opinion,
0:07:52 > 0:07:55because there could be all kinds of intelligence which would not
0:07:55 > 0:07:58manifest itself in any way that we can yet detect.
0:07:59 > 0:08:04Indeed, Martin's not ruling out the possibility that we may
0:08:04 > 0:08:07someday find evidence that alien civilisations
0:08:07 > 0:08:09have visited our solar system.
0:08:11 > 0:08:14You could certainly imagine scenarios where some alien
0:08:14 > 0:08:19civilisation sent out lots of probes and some of them
0:08:19 > 0:08:21came to our solar system.
0:08:21 > 0:08:26And therefore we should keep our eyes open for any artefacts
0:08:26 > 0:08:30that we might come across orbiting in space or even on one of the planets,
0:08:30 > 0:08:35which could be evidence of some kind of external civilisation.
0:08:38 > 0:08:40It's an idea that's familiar
0:08:40 > 0:08:42from science fiction.
0:08:44 > 0:08:48In the film 2001: A Space Odyssey, alien artefacts
0:08:48 > 0:08:50were scattered in our solar system,
0:08:50 > 0:08:55left by higher civilisations, waiting to be discovered.
0:08:57 > 0:08:59It's a long shot, though.
0:08:59 > 0:09:02And in the absence of enigmatic monoliths,
0:09:02 > 0:09:05we need more solid foundations for our hunt.
0:09:07 > 0:09:10Which means starting with something much simpler.
0:09:10 > 0:09:13Because intelligence isn't everything.
0:09:15 > 0:09:19Consider bacteria. Simple single-celled organisms.
0:09:19 > 0:09:23Superficially, nothing special, but these humble life forms could
0:09:23 > 0:09:27hold the key to understanding how common life is in the universe.
0:09:29 > 0:09:33And if it's just alien bacteria we're looking for,
0:09:33 > 0:09:35it might be right under our noses.
0:09:45 > 0:09:48For centuries, Mars was the prime candidate for alien life
0:09:48 > 0:09:50in our solar system.
0:09:50 > 0:09:54In fact, in about 1900, a French foundation had set up
0:09:54 > 0:09:59a prize of 100,000 French Francs for the first detection
0:09:59 > 0:10:01of extraterrestrial intelligence.
0:10:01 > 0:10:04And in the rules for that prize, they excluded Mars
0:10:04 > 0:10:07because it was thought too easy to detect life on Mars.
0:10:11 > 0:10:14We've just had some amazing photographs sent back
0:10:14 > 0:10:16by the American Probe to Mars, Mariner 6.
0:10:16 > 0:10:20Nasa's Mariner probes first took us to Mars.
0:10:20 > 0:10:24First in 1965...then again in '69.
0:10:26 > 0:10:29You can see there some of the dark areas, which may be vegetation.
0:10:29 > 0:10:31And at the bottom, you can see the white polar cap,
0:10:31 > 0:10:35which has always been thought to be due to some sort of icy or frosty deposit.
0:10:35 > 0:10:39But close-up pictures revealed a barren world.
0:10:40 > 0:10:42Hopes of Martian life began to slip away.
0:10:45 > 0:10:48Well, primitive life, there may be. I don't even think so.
0:10:48 > 0:10:49Intelligent life? Certainly not.
0:10:49 > 0:10:52So, in other words, you think Mars is a dead planet?
0:10:52 > 0:10:53Absolutely dead as a dodo.
0:10:53 > 0:10:56It certainly looked as dead as a dodo.
0:10:59 > 0:11:03There's nothing. There's not even any desert scrub
0:11:03 > 0:11:06clinging to the edge of a cliff.
0:11:06 > 0:11:08There's nothing. It's completely bare.
0:11:21 > 0:11:23This is Professor Monica Grady.
0:11:23 > 0:11:27She's one of a growing number of scientists who believe that, despite appearances,
0:11:27 > 0:11:32our solar system may yet turn out to be home to alien life.
0:11:35 > 0:11:3915 or so years ago, you were regarded as, at best, fringe,
0:11:39 > 0:11:42at worst, lunatic,
0:11:42 > 0:11:45if you were going to study these sort of subjects.
0:11:46 > 0:11:49It's not hard to see why people were doubtful.
0:11:52 > 0:11:56As probe after probe visited the planets in turn,
0:11:56 > 0:11:59scientists had grown increasingly confident
0:11:59 > 0:12:01that Earth was unique in our solar system
0:12:01 > 0:12:03in being home to life.
0:12:06 > 0:12:10But for Professor Grady, this just doesn't make sense.
0:12:11 > 0:12:14The ingredients of life are really, really simple.
0:12:16 > 0:12:19Basically, hydrogen, carbon, oxygen and nitrogen.
0:12:19 > 0:12:23And they are the most abundant elements in the solar system.
0:12:23 > 0:12:26The most abundant elements in the universe.
0:12:26 > 0:12:32So there's no reason why life could not, should not
0:12:32 > 0:12:34have got going in places beyond the Earth.
0:12:34 > 0:12:36Because it's simply physics and chemistry.
0:12:38 > 0:12:39But that raises a big question.
0:12:41 > 0:12:43How did physics and chemistry...
0:12:45 > 0:12:47..turn into biology?
0:12:48 > 0:12:51How was life on Earth first created?
0:12:58 > 0:13:00We know that all life on Earth is related.
0:13:00 > 0:13:03We share DNA not just with monkeys,
0:13:03 > 0:13:05but with all the animals and plant life we see.
0:13:07 > 0:13:08Go back far enough
0:13:08 > 0:13:11and all living things share the same common ancestor.
0:13:13 > 0:13:14A single cell.
0:13:14 > 0:13:19What nobody knows yet is where that first cell came from.
0:13:21 > 0:13:24The origin of life, everyone has known for a century,
0:13:24 > 0:13:26is a key problem in science.
0:13:26 > 0:13:30At present, when we only know about life in one place,
0:13:30 > 0:13:32we can't rule out the possibility
0:13:32 > 0:13:35that the odds against life emerging are zillions to one.
0:13:37 > 0:13:41So, do we know anything about how easy it was for that first cell to form?
0:13:43 > 0:13:45Well, there is one thing.
0:13:45 > 0:13:48On our planet, it happened very early.
0:13:51 > 0:13:534.5 billion years ago, the Earth was formed
0:13:53 > 0:13:56from a collapsing cloud of gas and dust.
0:13:58 > 0:14:00It was a violent event.
0:14:02 > 0:14:04Volcanoes pumped out a toxic atmosphere.
0:14:06 > 0:14:09And the young planet was bombarded by asteroids.
0:14:14 > 0:14:17Yet in this literal hell on Earth,
0:14:17 > 0:14:19chemistry turned into biology.
0:14:22 > 0:14:26It was an event that Horizon investigated in 1974.
0:14:26 > 0:14:29At the University of California, Stanley Miller is re-creating
0:14:29 > 0:14:32the early Earth in a fourth-floor laboratory.
0:14:32 > 0:14:35The primitive atmosphere was very different than the one
0:14:35 > 0:14:37we have at the present time on the Earth.
0:14:37 > 0:14:39But the major difference was that there was no oxygen
0:14:39 > 0:14:42and there was an abundance of molecular hydrogen.
0:14:42 > 0:14:44But nobody had ever tried an experiment
0:14:44 > 0:14:48to see what would happen in such an atmosphere.
0:14:49 > 0:14:53So, at the age of just 23, Stanley Miller decided to do just that.
0:14:53 > 0:14:55It was a famous experiment
0:14:55 > 0:14:58in our understanding of the origins of life.
0:14:58 > 0:15:01So the experiment was to construct the model ocean,
0:15:01 > 0:15:03which is the small flask here,
0:15:03 > 0:15:07a model atmosphere, which is the large flask
0:15:07 > 0:15:10containing the gases of the primitive atmosphere.
0:15:10 > 0:15:12So he boiled up the model ocean,
0:15:12 > 0:15:15added lightning and sat back to wait.
0:15:16 > 0:15:19His flask contained nothing organic at all.
0:15:21 > 0:15:24But after just a week, the miniature ocean within it
0:15:24 > 0:15:26had turned muddy brown.
0:15:28 > 0:15:31He'd created his very own primordial soup,
0:15:31 > 0:15:33full of organic compounds.
0:15:33 > 0:15:35The building blocks of life.
0:15:38 > 0:15:41In fact, the major group of organic compounds
0:15:41 > 0:15:44produced by the spark were amino acids.
0:15:44 > 0:15:48And one had no right, really, to expect such a result.
0:15:51 > 0:15:55Miller had shown just how easily the building blocks of life can form.
0:15:57 > 0:16:00We still don't know how those organic chemicals
0:16:00 > 0:16:01turned into a living organism.
0:16:03 > 0:16:08But we do know that almost as soon as the planet had a solid crust,
0:16:08 > 0:16:09life began.
0:16:12 > 0:16:17I suspect that we will find that simple life in some form
0:16:17 > 0:16:21is something which can form fairly readily,
0:16:21 > 0:16:24given the amount of space and time on a young planet.
0:16:28 > 0:16:31Biology's early emergence on Earth offers hope
0:16:31 > 0:16:35that life might have formed elsewhere in our solar system.
0:16:36 > 0:16:40And possibly not too far away.
0:16:40 > 0:16:44Because our next-door neighbour had a remarkably similar early life.
0:16:47 > 0:16:50Mars was made at the same time as the Earth was made -
0:16:50 > 0:16:53so, roughly 4.5 billion years ago.
0:16:53 > 0:16:56Made from the same materials, by the same processes.
0:17:00 > 0:17:05It did have active volcanoes, it had rain, it had water,
0:17:05 > 0:17:07water flowing over its surface.
0:17:07 > 0:17:13So for the first billion years of its life, it was like the Earth.
0:17:13 > 0:17:17And in the first billion years of Earth, life got going.
0:17:20 > 0:17:22But if life did get going on Mars,
0:17:22 > 0:17:25it would have soon found it tough-going.
0:17:26 > 0:17:28Mars cooled down fast.
0:17:28 > 0:17:32Its small size meant it couldn't retain its internal heat.
0:17:33 > 0:17:37And with no magnetic field, much of its atmosphere was lost to space.
0:17:39 > 0:17:41Could life still be there now?
0:17:42 > 0:17:46Until recently, most people would have said no.
0:17:46 > 0:17:49But the more we learn about simple bacterial life
0:17:49 > 0:17:51of the kind that might have formed on Mars,
0:17:51 > 0:17:56the more we realise it's more robust than we ever thought possible.
0:17:57 > 0:18:01If you think of the range of environments in which people can survive - you know,
0:18:01 > 0:18:05some of us get really sunburnt if we go out into the garden
0:18:05 > 0:18:09and the temperature's above about 25 degrees C.
0:18:09 > 0:18:14But bacteria is everywhere. I mean, you know, absolutely everywhere -
0:18:14 > 0:18:18deep inside nuclear reactors, deep below the surface of the Earth,
0:18:18 > 0:18:20in boiling-hot water,
0:18:20 > 0:18:24frozen in Antarctica - it's all over the place.
0:18:24 > 0:18:27These sorts of microorganisms are called extremophiles.
0:18:27 > 0:18:29They love being at these extremes.
0:18:31 > 0:18:35In fact, they're so hardy, scientists decided to test them
0:18:35 > 0:18:37in the ultimate extreme environment.
0:18:39 > 0:18:40Space.
0:18:44 > 0:18:48Minus ten, nine, eight. Go from eight and just start. Seven, six...
0:18:48 > 0:18:53On February 7th, 2008, the Space Shuttle Atlantis blasted off
0:18:53 > 0:18:55with a surprising payload onboard.
0:18:55 > 0:18:57..Space Shuttle Atlantis.
0:18:57 > 0:19:01Bacteria, taken from the cliffs of Devon.
0:19:03 > 0:19:06..A voyage of science to the Space Station.
0:19:06 > 0:19:09Devon may be a holiday spot for us,
0:19:09 > 0:19:13but for bacteria, these cliffs are a surprisingly harsh place.
0:19:13 > 0:19:16When they're not being hit with a hammer,
0:19:16 > 0:19:19they're being blasted by sun and salty water.
0:19:21 > 0:19:23So a sample of these hardy bacteria
0:19:23 > 0:19:26spent 553 days
0:19:26 > 0:19:29outside the International Space Station.
0:19:31 > 0:19:33Scorched by cosmic rays
0:19:33 > 0:19:37and subjected to extreme shifts in temperatures.
0:19:38 > 0:19:42When they returned, something was still alive.
0:19:42 > 0:19:45Bacteria called OU-20.
0:19:45 > 0:19:49Life could survive in space.
0:19:49 > 0:19:53Study of extremophiles has shown that it can exist
0:19:53 > 0:19:55over a wider range of conditions
0:19:55 > 0:19:57than people had thought previously.
0:19:57 > 0:20:00And that, of course, is something which is good news
0:20:00 > 0:20:04in the sense that it widens the range of possible locations for life,
0:20:04 > 0:20:06if we think about the wider galaxy.
0:20:07 > 0:20:12And for Monica Grady, these hardy organisms raise a startling possibility.
0:20:13 > 0:20:17If bacteria did form on Mars, as they did on Earth,
0:20:17 > 0:20:19then maybe they're still there today.
0:20:25 > 0:20:28If you look at Antarctica from the air,
0:20:28 > 0:20:30you see a barren and desolate place.
0:20:30 > 0:20:33You don't see any trees or vegetation.
0:20:33 > 0:20:37When you get up close to some of the rocks and break them open,
0:20:37 > 0:20:41you can see that there is a colony in there.
0:20:41 > 0:20:45A colony of microorganisms called cryptoendoliths
0:20:45 > 0:20:46hidden inside the rock.
0:20:46 > 0:20:49Maybe they're there on Mars.
0:20:51 > 0:20:55And we might not be too far off finding out if it's true.
0:20:58 > 0:21:01Right now, the European ExoMars probe
0:21:01 > 0:21:03is en route to the red planet...
0:21:06 > 0:21:09..where it will scan for biological signatures.
0:21:18 > 0:21:21It's then hoped a rover will follow in 2019,
0:21:21 > 0:21:24drilling for signs of life in the Martian soil.
0:21:27 > 0:21:31And if we find Mars has, at any time, played host to bacteria...
0:21:32 > 0:21:34..it will be a game-changer.
0:21:36 > 0:21:43As soon as we find a trace of some sort of biology,
0:21:43 > 0:21:47we can be almost certain,
0:21:47 > 0:21:50almost absolutely 100% certain maybe...
0:21:50 > 0:21:53SHE LAUGHS
0:21:53 > 0:21:56..that there is going to be physics turning to chemistry,
0:21:56 > 0:22:01turning to biology on planets around stars in our own galaxy
0:22:01 > 0:22:04and in many, many, many other galaxies.
0:22:04 > 0:22:07I would say that finding evidence for life elsewhere
0:22:07 > 0:22:10of independent origin would be a huge discovery -
0:22:10 > 0:22:12one of the great discoveries of the century, if it happened.
0:22:12 > 0:22:15Because it would have these implications about
0:22:15 > 0:22:20the likelihood of life existing throughout the entire universe.
0:22:23 > 0:22:26These days, most scientists think it's likely
0:22:26 > 0:22:29that we do live in a universe teeming with simple life.
0:22:32 > 0:22:34But a few cells in a Petri dish
0:22:34 > 0:22:37aren't what most people think of when they imagine ET.
0:22:43 > 0:22:45So here's the next big question.
0:22:45 > 0:22:47If there is primitive life out there,
0:22:47 > 0:22:51what are the chances it could have evolved into something
0:22:51 > 0:22:53we might truly call an alien?
0:23:06 > 0:23:08Again, our Earth offers
0:23:08 > 0:23:12the only example of evolution that we can use as evidence.
0:23:13 > 0:23:16But this time, things don't look so hopeful.
0:23:17 > 0:23:20All we know from the history of life on Earth
0:23:20 > 0:23:23is that it took a long time
0:23:23 > 0:23:25to get from single-celled life
0:23:25 > 0:23:27to the next stage - a multi-cellular one.
0:23:27 > 0:23:31And that, of course, suggests that that might involve
0:23:31 > 0:23:33some rather improbable change.
0:23:36 > 0:23:38For two billion years,
0:23:38 > 0:23:43the Earth was home only to simple organisms, like bacteria.
0:23:43 > 0:23:45In short, slime.
0:23:47 > 0:23:50But then, something happened.
0:23:52 > 0:23:55It's thought one primitive cell swallowed another
0:23:55 > 0:23:58and the two began working together.
0:24:00 > 0:24:04It was the first step on the path to more and more complex organisms
0:24:04 > 0:24:06and the huge diversity we see today.
0:24:08 > 0:24:13What we don't know is how many of the specific features of the Earth
0:24:13 > 0:24:16were crucial in order to allow life
0:24:16 > 0:24:19to proceed through its stages of emerging complexity.
0:24:19 > 0:24:23And that, therefore, means we don't know for sure
0:24:23 > 0:24:24how likely it would be
0:24:24 > 0:24:27that life would develop complexity on other planets.
0:24:27 > 0:24:29This is a big debate.
0:24:31 > 0:24:34For some, the late emergence of complex life on Earth
0:24:34 > 0:24:37points to it being a very rare event indeed.
0:24:42 > 0:24:46There's a hypothesis - it's called the Rare Earth hypothesis -
0:24:46 > 0:24:50that suggests that there's something special about Earth.
0:24:52 > 0:24:56This Rare Earth hypothesis claims that an extraordinary
0:24:56 > 0:24:59once-in-a-galaxy run of good luck
0:24:59 > 0:25:02led to the evolution of our planet's rich and diverse life.
0:25:14 > 0:25:18If true, other worlds wouldn't make it past slime.
0:25:20 > 0:25:23And slime isn't well suited to interstellar travel.
0:25:29 > 0:25:32Some conditions that are part of the Rare Earth hypothesis
0:25:32 > 0:25:34don't sound too rare.
0:25:34 > 0:25:38We're looking for a star that's been stable for billions of years
0:25:38 > 0:25:42and we're looking for a rocky planet with water on there.
0:25:44 > 0:25:46But some are trickier.
0:25:47 > 0:25:51One in particular takes us back once again
0:25:51 > 0:25:53to our Earth's violent formation.
0:25:54 > 0:25:58And a day that was responsible for much of what makes Earth so special.
0:25:59 > 0:26:01And yet it was just a chance event.
0:26:03 > 0:26:05It's believed the Earth once had a twin.
0:26:06 > 0:26:09A Mars-sized planet named Theia.
0:26:09 > 0:26:11Born in a similar orbit.
0:26:12 > 0:26:14The result?
0:26:16 > 0:26:18Well, be grateful you weren't there.
0:26:23 > 0:26:25Theia was destroyed in the collision.
0:26:28 > 0:26:33But the debris coalesced, forming our planet's travelling companion.
0:26:33 > 0:26:35The moon.
0:26:39 > 0:26:41It's true, moons aren't rare,
0:26:41 > 0:26:44but our moon is huge compared to the Earth.
0:26:44 > 0:26:47And this may have been vital for complex life.
0:26:50 > 0:26:53Because our moon doesn't just give us tides.
0:26:55 > 0:27:02The moon plays a key role in stabilising the Earth's axial tilt,
0:27:02 > 0:27:07which gives rise to the nice, pleasant seasons that we enjoy.
0:27:07 > 0:27:10There's the possibility that the existence of the moon
0:27:10 > 0:27:16has helped a long, four-billion-year period of clement weather.
0:27:22 > 0:27:26Without the moon, some believe our planet's tilt would have been unstable.
0:27:27 > 0:27:31Some years, our seasons would be unbearably hot and long.
0:27:31 > 0:27:34Other years wouldn't have seasons at all.
0:27:35 > 0:27:38Such an unstable climate might have meant
0:27:38 > 0:27:41that complex life never got out of the starting blocks.
0:27:44 > 0:27:48Because evolution relies on small changes from one generation to the next.
0:27:48 > 0:27:53If that change is useful, the creature is more likely to survive.
0:27:55 > 0:27:58But if there were extreme swings in climate -
0:27:58 > 0:28:02so extreme that, at times, there was no liquid water -
0:28:02 > 0:28:06an adaptation that's useful one year may be wiped out the next.
0:28:08 > 0:28:11No long-term stability, no natural selection.
0:28:14 > 0:28:16And it's not just the moon.
0:28:17 > 0:28:20There are many other examples of our planet's apparent good fortune.
0:28:22 > 0:28:25Earth has a system of plate tectonics.
0:28:25 > 0:28:31Plate tectonics is important for stabilising Earth's temperature.
0:28:32 > 0:28:34The movements of the vast network of rigid plates
0:28:34 > 0:28:37that make up our planet's surface...
0:28:39 > 0:28:41..create massive volcanic eruptions,
0:28:41 > 0:28:44recycling carbon dioxide into the atmosphere.
0:28:47 > 0:28:50Today, we think of it as a nasty greenhouse gas.
0:28:50 > 0:28:52But throughout the Earth's long history,
0:28:52 > 0:28:57carbon dioxide has helped regulate our planet's temperature,
0:28:57 > 0:28:59so complex life can survive.
0:29:06 > 0:29:08The Rare Earth hypothesis also suggests
0:29:08 > 0:29:11that we've a lot to thank Jupiter for.
0:29:11 > 0:29:15The gas giant's huge gravitational pull might capture asteroids
0:29:15 > 0:29:19that would otherwise be on a collision course with Earth.
0:29:22 > 0:29:24It's hard to evolve if icy rocks
0:29:24 > 0:29:26constantly rain down on you from above.
0:29:31 > 0:29:35The special conditions that led to complex life on Earth go on and on.
0:29:36 > 0:29:40And maybe there's only one conclusion.
0:29:41 > 0:29:47It's possible that we are a trillion-to-one fluke.
0:29:47 > 0:29:51That there's some combination of factors that make Earth special.
0:29:56 > 0:30:01My view is that these ideas of a so-called very rare Earth are rather oversold
0:30:01 > 0:30:06and that we've learnt that life can exist in a variety of contexts in the Earth.
0:30:06 > 0:30:08And our observations are limited,
0:30:08 > 0:30:10our imaginations are even more limited.
0:30:10 > 0:30:14So my view is that we should not be put off
0:30:14 > 0:30:16and not take too seriously
0:30:16 > 0:30:20the fact that our particular evolutionary track here on Earth
0:30:20 > 0:30:22depended on some special conditions.
0:30:29 > 0:30:31There's another, more practical reason
0:30:31 > 0:30:34that the Rare Earth hypothesis might be overplayed.
0:30:37 > 0:30:41Perhaps it underestimates the sheer number and variety
0:30:41 > 0:30:43of other worlds in our galaxy.
0:30:45 > 0:30:48We've learnt, actually, just in the last few years,
0:30:48 > 0:30:50a great deal about our universe
0:30:50 > 0:30:53that makes the night sky far more interesting.
0:30:53 > 0:30:56100 years ago, people thought that planets were very rare
0:30:56 > 0:30:58around other stars.
0:30:58 > 0:31:04No-one had found any direct evidence for a planet until 20 years ago.
0:31:06 > 0:31:09It was once thought that detecting planets around other stars
0:31:09 > 0:31:11would be impossible.
0:31:14 > 0:31:17They were just too small and too far away.
0:31:20 > 0:31:23But in 1995, the impossible happened.
0:31:30 > 0:31:34Two Swiss scientists - Didier Queloz and Michel Mayor -
0:31:34 > 0:31:37were monitoring the positions of some 140 stars.
0:31:39 > 0:31:41But one of these stars was a puzzle.
0:31:42 > 0:31:44On closer inspection, they realised
0:31:44 > 0:31:49the sun-like star, 51 Pegasi, was on the move.
0:31:52 > 0:31:55In fact, the first reaction that you have at that time is,
0:31:55 > 0:31:57"Oh, something is wrong with the experiment".
0:31:57 > 0:32:00And you observe it again the day after and the day after
0:32:00 > 0:32:03and then it was more and more awful
0:32:03 > 0:32:06because it was moving every day.
0:32:06 > 0:32:09And you say, "There is really a big problem with the experiment".
0:32:09 > 0:32:14Each time they looked, the movement had changed.
0:32:14 > 0:32:16Gradually, a pattern emerged.
0:32:18 > 0:32:21The star was wobbling around a point.
0:32:24 > 0:32:27This could mean only one thing.
0:32:27 > 0:32:2951 Peg was not alone.
0:32:31 > 0:32:33It was being pushed and pulled by the gravity
0:32:33 > 0:32:35of a smaller body we couldn't see.
0:32:38 > 0:32:41This was the first planet we'd found orbiting another star.
0:32:41 > 0:32:46A huge moment in our hunt for worlds aliens might call home.
0:32:48 > 0:32:54It was a completely crazy time, with calls from papers,
0:32:54 > 0:32:59from television, from radio, from...from all the world.
0:32:59 > 0:33:03And, er...e-mail - 100 email per day, or something like this.
0:33:03 > 0:33:06It was absolutely, completely a time
0:33:06 > 0:33:08where we had no possibility to work at all.
0:33:11 > 0:33:15This planet was too large and too hot to be home to life.
0:33:16 > 0:33:19But we've got better at this planet-hunting lark.
0:33:21 > 0:33:24Over time, we've found smaller planets,
0:33:24 > 0:33:26further out from their parent stars.
0:33:29 > 0:33:33Until eventually, in April 2007,
0:33:33 > 0:33:36Gliese 581c was discovered.
0:33:36 > 0:33:42And scientists thought it just might be capable of supporting life.
0:33:42 > 0:33:46European astronomers have spotted a new planet outside our solar system
0:33:46 > 0:33:48which closely resembles the planet Earth.
0:33:50 > 0:33:52Every time somebody finds an Earth-like planet,
0:33:52 > 0:33:54the probability that there is life
0:33:54 > 0:33:57somewhere else in the universe goes up a bit.
0:33:57 > 0:34:01This latest find has set the world of astronomy alight.
0:34:02 > 0:34:06In the last few years, more and more planets have been found.
0:34:06 > 0:34:08Many in the so-called Goldilocks Zone -
0:34:08 > 0:34:11not too hot and not too cold for liquid water.
0:34:16 > 0:34:18The more we look, the more we realise
0:34:18 > 0:34:21that Earth-like planets are all over the place.
0:34:23 > 0:34:26The universe which we now perceive
0:34:26 > 0:34:31is far vaster than it was perceived to be in earlier centuries.
0:34:31 > 0:34:33In our galaxy, there are probably
0:34:33 > 0:34:36literally a billion planets like the Earth.
0:34:38 > 0:34:42We've seen that it's possible simple life is common in the universe.
0:34:45 > 0:34:47Complex life could be trickier.
0:34:50 > 0:34:52Conditions need to be just right.
0:34:56 > 0:35:00But the sheer number of planets we've discovered in our own galaxy
0:35:00 > 0:35:04suggests that such conditions could be surprisingly common.
0:35:07 > 0:35:09But there's one further leap that needs to happen
0:35:09 > 0:35:12before we can hope to make contact with aliens -
0:35:12 > 0:35:15the leap to intelligence.
0:35:17 > 0:35:20We're not talking about the ability to bash a few rocks together.
0:35:20 > 0:35:24We need civilisations that can communicate
0:35:24 > 0:35:26across the vastness of space.
0:35:46 > 0:35:47So, is it possible to predict
0:35:47 > 0:35:51how common intelligent civilisations are in the galaxy?
0:35:57 > 0:36:00Fortunately, thanks to astronomer Frank Drake,
0:36:00 > 0:36:04we have an equation designed to tell us just that.
0:36:04 > 0:36:07And, in, fact this is our number N.
0:36:07 > 0:36:10The number of technical civilisations in the galaxy.
0:36:12 > 0:36:15The challenge is to give each term a number
0:36:15 > 0:36:17and simply multiply them together.
0:36:19 > 0:36:21Into the now famous - or infamous - Drake equation
0:36:21 > 0:36:25goes everything from astrophysics, through evolutionary biology
0:36:25 > 0:36:27to whatever it is that governs
0:36:27 > 0:36:30the lifetime of a detectable civilisation.
0:36:30 > 0:36:34Not surprisingly, no-one's solved it yet, but anyone can have a go.
0:36:34 > 0:36:37It's almost a game the whole family could play.
0:36:37 > 0:36:40Get the numbers right, and, bingo!
0:36:40 > 0:36:44You know how many communicating civilisations are likely to be out there.
0:36:47 > 0:36:52So, in 1981, BBC Horizon locked some of the brightest minds in Nasa
0:36:52 > 0:36:56in a room together and asked them to come up with a solution.
0:36:58 > 0:37:00Team captain today is John Wolfe.
0:37:00 > 0:37:03I think it was Frank Drake himself who said that
0:37:03 > 0:37:05this is a rather nice way of fitting
0:37:05 > 0:37:08a great deal of ignorance into a very small space.
0:37:08 > 0:37:12Some of Drake's variables we know reasonably well.
0:37:12 > 0:37:15We know how often stars form.
0:37:15 > 0:37:17And these days, we can have a good stab at
0:37:17 > 0:37:20how many stars have planets.
0:37:20 > 0:37:22- Seem to have more consensus... - That was easy!
0:37:22 > 0:37:24..more consensus there than anywhere. Quickly.
0:37:24 > 0:37:28This may reflect the fact that we're moving to the area we know least about.
0:37:28 > 0:37:31It's the later terms we know less well.
0:37:32 > 0:37:36But scientists don't mind guesswork, provided it's educated guesswork.
0:37:36 > 0:37:38And when it comes to asking if life
0:37:38 > 0:37:41would eventually evolve intelligence,
0:37:41 > 0:37:45the Nasa scientists were actually quite confident.
0:37:45 > 0:37:47It's very natural, I think, to argue that intelligence
0:37:47 > 0:37:51with the survival capability that's inherent in it will also follow.
0:37:51 > 0:37:54I think that's the usual argument for it being an unity.
0:37:55 > 0:37:59In fact, the first guy to get smart is the one that dominates the planet.
0:37:59 > 0:38:03- That's right. - Thank God we were first.
0:38:03 > 0:38:06They were equally confident that intelligent life
0:38:06 > 0:38:10would go on to develop the ability to communicate across space.
0:38:13 > 0:38:15Put it up there, that's good enough. Wait until we get to L.
0:38:15 > 0:38:17THEY LAUGH
0:38:17 > 0:38:22You might think this would mean that intelligent civilisations are ten a penny.
0:38:22 > 0:38:26But the final term, L, causes the team some problems.
0:38:28 > 0:38:32It asks us to estimate the lifetime of communicating civilisations.
0:38:34 > 0:38:37It soon emerges they're going to chicken out of reaching a conclusion.
0:38:37 > 0:38:42So if we were to take that lower value of 100, that says that N is, er...
0:38:42 > 0:38:45The average lifetime lies somewhere between a few hundred years
0:38:45 > 0:38:46and a few billion.
0:38:46 > 0:38:49So the number of civilisations in the galaxy now
0:38:49 > 0:38:52is somewhere between a few tens and a few hundred million.
0:38:52 > 0:38:55A few tens to a few hundred million
0:38:55 > 0:38:57isn't the most exact solution.
0:39:00 > 0:39:03The term L is so hard to estimate
0:39:03 > 0:39:06because it forces us to ask a very difficult
0:39:06 > 0:39:08and rather uncomfortable question.
0:39:10 > 0:39:15How long do intelligent civilisations like ours last?
0:39:16 > 0:39:19Of course, we know that here on Earth, the amount of time
0:39:19 > 0:39:24we've had any kind of civilisation is a few thousand years,
0:39:24 > 0:39:28and that is only one millionth of the age of the Earth.
0:39:28 > 0:39:30So it's just a sliver.
0:39:30 > 0:39:33And we don't know how long it'll last in future.
0:39:36 > 0:39:39If civilisations last for only a few hundred years,
0:39:39 > 0:39:43then the window of communication is impossibly small.
0:39:45 > 0:39:47There are actually people trying to figure out
0:39:47 > 0:39:50just how long advanced civilisations might last.
0:39:52 > 0:39:56Dr Anders Sandberg works at the Future of Humanity Institute
0:39:56 > 0:39:58in Oxford University.
0:39:59 > 0:40:02It's his job to think about the myriad ways
0:40:02 > 0:40:04a society could destroy itself.
0:40:06 > 0:40:09So we humans have mastered this planet,
0:40:09 > 0:40:10but in the process, of course,
0:40:10 > 0:40:12we caused a lot of extinctions of animals,
0:40:12 > 0:40:16and now we're changing the climate and we're developing bioweapons
0:40:16 > 0:40:18in the lab that could kill a lot of people.
0:40:18 > 0:40:20So we're obviously a danger to ourselves.
0:40:20 > 0:40:23So it might be that sufficiently-powerful technologies
0:40:23 > 0:40:26mean that a civilisation will start blowing itself up,
0:40:26 > 0:40:30or poisoning itself in a very effective way.
0:40:36 > 0:40:40And let's not forget, advanced aliens
0:40:40 > 0:40:44might have technologies that we haven't even dreamt of yet.
0:40:46 > 0:40:50The basic problem here is that powerful technology is dangerous.
0:40:52 > 0:40:56And advanced civilisations will have a lot of powerful technologies at their disposal.
0:40:57 > 0:40:59Quite a sight, wasn't it, sir?
0:40:59 > 0:41:01A sight I'd rather not be seeing.
0:41:05 > 0:41:08The truth is, we don't know whether intelligence
0:41:08 > 0:41:09might ultimately be fatal.
0:41:11 > 0:41:14So we can't know how many civilisations out there
0:41:14 > 0:41:17could hold up their end of the conversation.
0:41:17 > 0:41:20And this makes our hunt all the more important.
0:41:22 > 0:41:26Because if we find advanced aliens, we'll know for certain
0:41:26 > 0:41:30that societies can survive their own powerful technologies.
0:41:33 > 0:41:36So, how do you go about finding extraterrestrial intelligence?
0:41:47 > 0:41:49What we know is that here on Earth,
0:41:49 > 0:41:52life has evolved to a kind of intelligence
0:41:52 > 0:41:55that can develop a technological civilisation
0:41:55 > 0:41:59which would make our activities detectable in principle
0:41:59 > 0:42:01to an alien with a big telescope.
0:42:01 > 0:42:05So we've learnt that we have become more conspicuous
0:42:05 > 0:42:07and that an alien watching the Earth
0:42:07 > 0:42:09would realise that something special had happened
0:42:09 > 0:42:11in the last few centuries.
0:42:12 > 0:42:16Humans have existed for about 200,000 years.
0:42:16 > 0:42:20But for most of this time, alien astronomers looking at the Earth
0:42:20 > 0:42:24would see little to suggest there's anything intelligent down here.
0:42:24 > 0:42:26INSTRUMENTAL
0:42:32 > 0:42:35In fact, it wasn't until 80 years ago
0:42:35 > 0:42:38that we really screamed our presence to the galaxy.
0:42:41 > 0:42:44When we began leaking radio and television signals into space.
0:42:48 > 0:42:50So if the Earth's first sign of intelligence
0:42:50 > 0:42:53was our making a racket in the radio spectrum,
0:42:53 > 0:42:56it's only natural to wonder whether intelligent aliens
0:42:56 > 0:42:58would be doing the same.
0:42:59 > 0:43:02- Listen... - CRACKLING
0:43:04 > 0:43:08Sound picked up from outer space by radio telescope
0:43:08 > 0:43:11for some earthly usage still unknown.
0:43:17 > 0:43:22The '50s and '60s saw the construction of radio telescopes
0:43:22 > 0:43:25so sensitive, they could tune into signals
0:43:25 > 0:43:27from the other side of the galaxy.
0:43:28 > 0:43:30The hunt was on.
0:43:34 > 0:43:36Into such a dish one day could come a signal
0:43:36 > 0:43:39that would reveal the existence of other creatures
0:43:39 > 0:43:41unimaginably more intelligent than we are.
0:43:43 > 0:43:46It was the radio astronomers who were the first to talk about
0:43:46 > 0:43:50doing serious searches for artificial signals.
0:43:50 > 0:43:55And the first effort to do this was pioneered by Frank Drake,
0:43:55 > 0:43:58who is one of the pioneers of this subject
0:43:58 > 0:44:01and is still one of the leaders of it today.
0:44:06 > 0:44:08Before he wrote his frustrating equation,
0:44:08 > 0:44:11Frank Drake gave birth to Seti -
0:44:11 > 0:44:14the Search for Extraterrestrial Intelligence.
0:44:17 > 0:44:19We used the 85-foot telescope there
0:44:19 > 0:44:21and a special, very sensitive receiver
0:44:21 > 0:44:25which was especially designed to detect intelligent signals
0:44:25 > 0:44:29rather than the natural emissions radio astronomers normally study.
0:44:29 > 0:44:32For the first time, man made a serious attempt
0:44:32 > 0:44:35to determine whether he was alone in the universe.
0:44:35 > 0:44:37We searched for two months
0:44:37 > 0:44:40and studied the two nearest stars which are like the sun.
0:44:40 > 0:44:43The stars Tau Ceti and Epsilon Eridani.
0:44:46 > 0:44:51For all we knew then, every star had intelligent civilisations in orbit,
0:44:51 > 0:44:53pumping out radio waves.
0:44:53 > 0:44:55And just a few days into the search,
0:44:55 > 0:44:58it looked like that might be the case.
0:44:58 > 0:45:01At one point, we had a very exciting recording on our tape recorder.
0:45:04 > 0:45:07The telescope picked up a short, but clearly artificial signal
0:45:07 > 0:45:10on a frequency protected for radio astronomy.
0:45:14 > 0:45:16The news leaked out.
0:45:16 > 0:45:18Journalists started to call up,
0:45:18 > 0:45:22asking if Drake had found an alien civilisation on his first go.
0:45:23 > 0:45:25Could it really be so easy?
0:45:27 > 0:45:30Ten days later and the signal came again.
0:45:30 > 0:45:33Only this time, the source was clear.
0:45:34 > 0:45:38Analysis of this and further study of the signal
0:45:38 > 0:45:41showed it had come not from space,
0:45:41 > 0:45:43but rather from a radio station on Earth.
0:45:44 > 0:45:49What Drake had discovered was a top-secret U2 spy plane
0:45:49 > 0:45:50flying at high altitude.
0:45:50 > 0:45:53# I'm sorry...#
0:45:53 > 0:45:56Not quite the distant signal they were hoping for.
0:45:57 > 0:46:02# That I was such a fool...#
0:46:02 > 0:46:04After 300 hours of searching,
0:46:04 > 0:46:07we concluded that our two target stars,
0:46:07 > 0:46:09Tau Ceti and Epsilon Eridani,
0:46:09 > 0:46:13had produced no evidence whatsoever for extraterrestrial radio signals.
0:46:17 > 0:46:20It was an inauspicious start to our search.
0:46:20 > 0:46:23No aliens, and a false signal.
0:46:23 > 0:46:25But Frank had paved the way.
0:46:25 > 0:46:28Systematic searches were now possible.
0:46:29 > 0:46:34More followed. This time, scanning thousands of stars.
0:46:34 > 0:46:37- I see two glitches on this one. - Yeah, yeah.
0:46:37 > 0:46:39Probably a car going by,
0:46:39 > 0:46:42or the equipment's screwed up, or something like that.
0:46:43 > 0:46:45Still nothing.
0:46:45 > 0:46:47But maybe we don't hear anything
0:46:47 > 0:46:50because we're going about the search all wrong.
0:46:50 > 0:46:54A lot of sloppy thinking is quite accepted about alien intelligence.
0:46:54 > 0:46:56And I think that is a problem.
0:46:56 > 0:46:59A lot of people, for example, just make bland assumptions
0:46:59 > 0:47:02that aliens must, of course, be like us.
0:47:05 > 0:47:08Radio signals of the type we churn out
0:47:08 > 0:47:11may have been ditched long ago by alien civilisations.
0:47:14 > 0:47:18Who knows what technologies they're on to now?
0:47:18 > 0:47:20But if they're super-advanced,
0:47:20 > 0:47:22they'll probably be doing things on a big scale.
0:47:22 > 0:47:25Maybe big enough for us to detect.
0:47:26 > 0:47:29Maybe we should look for the side effects of activities.
0:47:29 > 0:47:32A super civilisation might be sending off all sorts of radiation,
0:47:32 > 0:47:35not because they want to tell us, "We're here,"
0:47:35 > 0:47:38but because that's a side effect of what they're actually doing.
0:47:41 > 0:47:43It comes down to energy.
0:47:43 > 0:47:46As humanity has advanced, we've needed more and more of it.
0:47:48 > 0:47:51Fossil fuels may not be the best solution,
0:47:51 > 0:47:54so we're turning to wind power, tidal power...
0:47:56 > 0:47:58..and the light emitted from our star.
0:48:01 > 0:48:04And advanced aliens might have to go to even further lengths
0:48:04 > 0:48:06to quench their thirst for energy.
0:48:07 > 0:48:11You can get even more energy if you put solar panels in space.
0:48:11 > 0:48:15It's day all the time, and there is no atmosphere blocking it.
0:48:15 > 0:48:17So the logical endpoint would be
0:48:17 > 0:48:21to put solar panels around the entire sun.
0:48:21 > 0:48:23Who knows what such a structure would look like?
0:48:23 > 0:48:27Indeed, who knows what other strange, supersized technologies
0:48:27 > 0:48:29aliens might develop?
0:48:29 > 0:48:33But it's likely that from Earth, such megastructures would appear
0:48:33 > 0:48:36like nothing we've ever seen before.
0:48:36 > 0:48:39And maybe this is how an alien civilisation will reveal itself.
0:48:40 > 0:48:43I think we look in every way we can.
0:48:43 > 0:48:46Traditionally, we've looked for radio signals.
0:48:46 > 0:48:50We should look for optical flashes, we should look for artefacts,
0:48:50 > 0:48:52we should look for structures in space
0:48:52 > 0:48:54that look manifestly artificial.
0:48:56 > 0:48:59Whilst we wait for first contact,
0:48:59 > 0:49:01we have time to consider another question.
0:49:03 > 0:49:06If any aliens out there are more advanced than we are...
0:49:08 > 0:49:11..is it a good idea for us to track them down?
0:49:18 > 0:49:20The dangers of alien encounters have certainly
0:49:20 > 0:49:23inspired their share of sci-fi films.
0:49:26 > 0:49:29Whether they're galactic colonialists,
0:49:29 > 0:49:32as in The War Of The Worlds,
0:49:32 > 0:49:34taking over our lives one at a time...
0:49:34 > 0:49:36You fools! You're in danger!
0:49:36 > 0:49:40..like in the classic Invasion Of The Body Snatchers...
0:49:40 > 0:49:43They're after all of us! My wife, my children, everyone!
0:49:43 > 0:49:47..or simply mindless predators, like in Alien.
0:49:49 > 0:49:50SCREAMING
0:49:50 > 0:49:53And maybe science fiction wasn't too wide of the mark.
0:49:53 > 0:49:58Even top scientists have their concerns.
0:49:58 > 0:50:02If aliens decided to visit us, then the outcome might be similar
0:50:02 > 0:50:06to when Europeans arrived in the Americas.
0:50:06 > 0:50:10That did not turn out well for the Native Americans.
0:50:11 > 0:50:14So should we be worried about advertising
0:50:14 > 0:50:16our existence to the galaxy?
0:50:16 > 0:50:18Martin's not convinced.
0:50:18 > 0:50:21I would guess that if there are any aliens out there,
0:50:21 > 0:50:26then, if they were advanced, they would know we're here already.
0:50:26 > 0:50:30They may have been watching the Earth for millions of years,
0:50:30 > 0:50:32realising it's a place where something interesting
0:50:32 > 0:50:33might be happening.
0:50:33 > 0:50:36So, for that reason, I find it hard to take seriously people
0:50:36 > 0:50:40who are worried about sending out some sort of message.
0:50:40 > 0:50:43And, anyway, it's already too late.
0:50:43 > 0:50:46As soon as we started leaking waves into space,
0:50:46 > 0:50:49we said to the galaxy, "We're here."
0:50:51 > 0:50:54So what type of entities might be out there, tuning in to our signals?
0:50:56 > 0:51:00Who, or indeed what, might we make contact with?
0:51:14 > 0:51:17We think we'd know an alien if we saw one.
0:51:17 > 0:51:19The classic is ET.
0:51:21 > 0:51:26I'll be right here.
0:51:26 > 0:51:28He might have a bigger head, short little legs
0:51:28 > 0:51:31and long, thin fingers, but the basic body shape
0:51:31 > 0:51:33is much like our own.
0:51:37 > 0:51:40But Martin thinks this is about as far from what an actual alien
0:51:40 > 0:51:42might look like as it could be.
0:51:44 > 0:51:49A clue to what we might find, lies in our own species' future.
0:51:49 > 0:51:53It's taken us a few hundred years to evolve
0:51:53 > 0:51:55our technological civilisation.
0:51:55 > 0:51:56It's changing very fast,
0:51:56 > 0:52:00and if we think of what's going to happen in the next century,
0:52:00 > 0:52:05one scenario is that intelligence of the organic kind
0:52:05 > 0:52:08may be near its limit with humans.
0:52:09 > 0:52:12We like to think we're a pretty smart species.
0:52:13 > 0:52:17As evidence, we might point to our technological achievements.
0:52:18 > 0:52:21Our computers and sophisticated artificial intelligence, perhaps?
0:52:23 > 0:52:28But maybe they're getting so good that our robot servants
0:52:28 > 0:52:30will soon be our robot masters.
0:52:32 > 0:52:35The future intelligence in our solar system may lie
0:52:35 > 0:52:38not with organic life on Earth, but with these entities which are
0:52:38 > 0:52:41electronic, rather than chemical,
0:52:41 > 0:52:43like what goes on in our human skulls.
0:52:44 > 0:52:47Martin's point is that it looks like it won't be long
0:52:47 > 0:52:51before the robots here on Earth are much smarter than we are.
0:52:52 > 0:52:54And if this happens,
0:52:54 > 0:52:57it's likely that THEIR culture will dominate ours.
0:53:03 > 0:53:06But what does this have to do with aliens?
0:53:06 > 0:53:10Well, if it does turn out that humanity's role is to act
0:53:10 > 0:53:14as the midwives to a new robotic super species,
0:53:14 > 0:53:17there's no reason other worlds won't have followed a similar path.
0:53:19 > 0:53:24If there were another planet on which evolution had tracked
0:53:24 > 0:53:28what happens on Earth, then there are two options.
0:53:28 > 0:53:30Either it hasn't yet got to
0:53:30 > 0:53:34the stage of emergent intelligence - we see no signal from it -
0:53:34 > 0:53:38or it's got to the stage when the machines have taken over.
0:53:39 > 0:53:44What is most unlikely is that we would find another planet
0:53:44 > 0:53:47whose evolution was so synchronised with ours
0:53:47 > 0:53:52that we would observe it in just the few centuries
0:53:52 > 0:53:57when the dominant feature is organic intelligent civilisation.
0:53:59 > 0:54:02If Martin's right, in our first encounter with aliens
0:54:02 > 0:54:05we might be dealing not with organisms,
0:54:05 > 0:54:08but with super-advanced artificial intelligences.
0:54:10 > 0:54:13And this might give us cause for concern.
0:54:13 > 0:54:15After all, in films like The Terminator,
0:54:15 > 0:54:19when the machines took control, it didn't turn out well for the humans.
0:54:21 > 0:54:25And, actually, maybe they underestimated the dangers.
0:54:25 > 0:54:27It might all depend
0:54:27 > 0:54:30on why the robots were built in the first place.
0:54:30 > 0:54:35So you might want to use an autonomous weapon for warfare.
0:54:35 > 0:54:38And it's very convenient if it can build more of itself.
0:54:38 > 0:54:40And you could programme it to attack your enemies.
0:54:40 > 0:54:44So what if you let them loose and they attacked everybody else,
0:54:44 > 0:54:45and then you went extinct?
0:54:45 > 0:54:48So now you have these mindless machines
0:54:48 > 0:54:51going around killing off young civilisations.
0:54:52 > 0:54:56The idea that self-replicating killer robots roam throughout space
0:54:56 > 0:55:02is called the Berserker Hypothesis, after the novels by Fred Saberhagen.
0:55:03 > 0:55:07If true, maybe we should turn off our transmitters
0:55:07 > 0:55:10and sit in the dark with our fingers crossed, hoping the machines
0:55:10 > 0:55:14have been too busy causing destruction elsewhere to notice us.
0:55:18 > 0:55:21And even if the robots aren't programmed killers,
0:55:21 > 0:55:23we could still be in trouble.
0:55:23 > 0:55:26And this might not be deliberate at all.
0:55:26 > 0:55:29The software is really smart and you give it an order
0:55:29 > 0:55:31and it implements the order faultlessly,
0:55:31 > 0:55:34except that it wasn't in the way you wanted.
0:55:34 > 0:55:36And it converts the planet into paperclips,
0:55:36 > 0:55:39and then the rest of the galaxy into paperclips,
0:55:39 > 0:55:42because that was the order - "Make more paperclips."
0:55:43 > 0:55:46Whilst we can't do anything about how aliens may create
0:55:46 > 0:55:51their AI, Martin thinks that we at least should proceed with caution.
0:55:52 > 0:55:56We've got to ensure that the way in which innovation leads
0:55:56 > 0:56:01from the limited-capacity artificial intelligence we have today,
0:56:01 > 0:56:06to the more powerful ones, is moderated and regulated,
0:56:06 > 0:56:08just like we already have to moderate and regulate
0:56:08 > 0:56:10the way biotech is used.
0:56:11 > 0:56:15Whether benevolent or not, one thing's for sure -
0:56:15 > 0:56:18if we encounter such beings,
0:56:18 > 0:56:21they would be unlike anything we've ever seen before.
0:56:23 > 0:56:28We are thinking about the possibility of entities who may
0:56:28 > 0:56:33be able to grasp concepts which are as far beyond the human mind
0:56:33 > 0:56:36as quantum theory is beyond a monkey's mind.
0:56:38 > 0:56:40So, are these entities out there?
0:56:43 > 0:56:45We've seen how scientists think our universe
0:56:45 > 0:56:47might be teeming with life.
0:56:49 > 0:56:52And perhaps somewhere it's evolved,
0:56:52 > 0:56:55and gone on to do things that dwarf our own achievements.
0:56:59 > 0:57:03But we've also seen that there are an awful lot of barriers
0:57:03 > 0:57:04to intelligent civilisations.
0:57:05 > 0:57:08It feels like we're on the brink.
0:57:11 > 0:57:13There is a huge truth to discover.
0:57:14 > 0:57:19A truth that tells us not just what's out there,
0:57:19 > 0:57:23but what might lie ahead for us down here on Earth.
0:57:24 > 0:57:28Whatever we find, one thing is certain -
0:57:28 > 0:57:30the answer will change our understanding
0:57:30 > 0:57:33of our place in the universe for ever.
0:57:34 > 0:57:37Were it the case that the origin of life,
0:57:37 > 0:57:41or the origin of intelligent life, were an extremely rare phenomenon
0:57:41 > 0:57:45so that we were, in a sense, unique, or unique in our galaxy,
0:57:45 > 0:57:48then our fate matters not just to us,
0:57:48 > 0:57:51but maybe in a sense of cosmic importance,
0:57:51 > 0:57:55and the greening of the galaxy could then start with us.
0:57:58 > 0:58:03But, of course, if there were life everywhere in our galaxy -
0:58:03 > 0:58:05as there may well be -
0:58:05 > 0:58:08it would, in a sense, force us to be somewhat more cosmically modest.
0:58:11 > 0:58:13But the upside would be that,
0:58:13 > 0:58:15instead of there just being lifeless planets and stars
0:58:15 > 0:58:18orbiting around in the galaxy,
0:58:18 > 0:58:21we would realise that we were in a far more interesting cosmos
0:58:21 > 0:58:24than one in which life is limited to one place.