0:00:06 > 0:00:08'Emergency, which service?'
0:00:08 > 0:00:10'Police. My husband's been attacked.'
0:00:15 > 0:00:19'There's still deadlock tonight between the United States and Iran
0:00:19 > 0:00:22'over the 60 American hostages held in their embassy in Tehran.
0:00:22 > 0:00:24'But the Muslim students did...'
0:00:26 > 0:00:30RADIO STATIC
0:00:38 > 0:00:44For decades, some have suspected there might be others out there.
0:00:46 > 0:00:48Beings capable of communicating with us,
0:00:48 > 0:00:51even visiting our world.
0:01:40 > 0:01:44HE SHOUTS
0:01:55 > 0:01:57It might sound like science fiction,
0:01:57 > 0:02:02but today, scientists from across the globe are scouring the universe
0:02:02 > 0:02:05for signs of extraterrestrial intelligence.
0:02:09 > 0:02:12My students showed me this signal that was so bright
0:02:12 > 0:02:14and apparently so far away
0:02:14 > 0:02:16that it was unlike anything we've ever seen before.
0:02:21 > 0:02:23Then we realised this is just impossible,
0:02:23 > 0:02:26unless a civilisation is way more advanced than we are.
0:02:29 > 0:02:30A Kardashev Type II civilisation
0:02:30 > 0:02:34would need to build a massive network of solar collectors
0:02:34 > 0:02:35that would orbit their star in space.
0:02:37 > 0:02:40Something we call a Dyson sphere or a Dyson structure.
0:02:41 > 0:02:47Some scientists believe advanced aliens really could exist.
0:02:48 > 0:02:52About 10,000 detectable civilisations
0:02:52 > 0:02:55at present in our galaxy, the Milky Way.
0:02:57 > 0:03:01And yet, no solid evidence has ever been found.
0:03:04 > 0:03:08But recent discoveries mean that could all be about to change.
0:03:10 > 0:03:13The data for the star looked nothing like any other star
0:03:13 > 0:03:15that we know of today.
0:03:20 > 0:03:25And so at last we might be close to answering the question
0:03:25 > 0:03:27of whether we are alone in the universe.
0:03:51 > 0:03:54One day my father happened to tell me, there are other worlds in space.
0:03:57 > 0:03:59And, to an eight-year-old kid,
0:03:59 > 0:04:02I thought that meant worlds just like mine.
0:04:04 > 0:04:08Just like the Earth, creatures just like myself and I wondered,
0:04:08 > 0:04:11what are they like? Are they really like that, or are they different?
0:04:13 > 0:04:16And I've wondered those same questions my whole life.
0:04:21 > 0:04:27The universe is thought to contain 700 million trillion rocky planets
0:04:27 > 0:04:28like our own.
0:04:31 > 0:04:34Countless worlds other intelligent beings might call home.
0:04:41 > 0:04:44And yet, in more than 50 years of searching,
0:04:44 > 0:04:46we're yet to find them.
0:04:48 > 0:04:53The deafening lack of any communication from extraterrestrials
0:04:53 > 0:04:56has become known as "the great silence".
0:05:00 > 0:05:04Oh, I believe very strongly that they're out there.
0:05:04 > 0:05:05The numbers support that.
0:05:05 > 0:05:08There's so many stars in the universe,
0:05:08 > 0:05:12numbers that are so large they make no sense to us.
0:05:12 > 0:05:15We can be very, very wrong and yet there will be
0:05:15 > 0:05:17many, many detectable civilisations.
0:05:39 > 0:05:41We met in Arecibo in Puerto Rico.
0:05:41 > 0:05:44There's a large radio telescope there.
0:05:44 > 0:05:47I used to work at the observatory as a staff scientist
0:05:47 > 0:05:50and you were a grad student at Cornell,
0:05:50 > 0:05:52and they used to send their students down from Cornell.
0:05:52 > 0:05:55We met at the observatory in the control room.
0:05:58 > 0:06:01Husband and wife Duncan Lorimer and Maura McLaughlin
0:06:01 > 0:06:03share a passion for astronomy.
0:06:07 > 0:06:11Boys, it's breakfast time!
0:06:11 > 0:06:14I was never, you know, the type of kid, when I was really young,
0:06:14 > 0:06:16that was super into astronomy.
0:06:16 > 0:06:19I still don't know, like, a single constellation.
0:06:19 > 0:06:24But when I was sort of 10, 11, 12, I started reading science fiction.
0:06:24 > 0:06:29So when I went to college I decided to take astronomy classes.
0:06:29 > 0:06:31I still wasn't sure what I wanted to do,
0:06:31 > 0:06:35but then I did research with a professor at Penn State
0:06:35 > 0:06:39that took me down to Arecibo and I observed pulsars.
0:06:39 > 0:06:40I was just so excited,
0:06:40 > 0:06:43and I just really enjoyed doing that and I thought,
0:06:43 > 0:06:45"OK, I think this is what I want to do",
0:06:45 > 0:06:48and I've just stuck with it ever since.
0:06:54 > 0:06:56- Nice day!- Yeah.
0:06:56 > 0:06:58What do you have today?
0:06:58 > 0:06:59- Gym.- Gym.
0:07:02 > 0:07:07I got into astronomy in a different way to Maura, I guess.
0:07:07 > 0:07:09I've always been fascinated with the night sky.
0:07:11 > 0:07:14When I was about 16, taking my A-levels,
0:07:14 > 0:07:17my physics teacher saw that myself and a few other students
0:07:17 > 0:07:19were interested in astronomy and said,
0:07:19 > 0:07:22"Here's the key to the school telescope. Go and fix it up."
0:07:23 > 0:07:26And it was this old telescope, this early 1900s telescope,
0:07:26 > 0:07:29and it had lots of things,
0:07:29 > 0:07:31lots of moving parts that were fascinating to us
0:07:31 > 0:07:33and we got the telescope going
0:07:33 > 0:07:36and we took a picture of a lunar eclipse,
0:07:36 > 0:07:39and we started a little astronomy club at school
0:07:39 > 0:07:43and I went to college after that and heard about neutron stars,
0:07:43 > 0:07:47and once I found out about those, I knew that's what I wanted to study.
0:07:47 > 0:07:49I would have had nothing to do with him
0:07:49 > 0:07:51if I'd met him like 30 years ago.
0:07:51 > 0:07:53- Yes.- That would have been it.
0:07:53 > 0:07:55Oh!
0:08:07 > 0:08:10We work here in the Department of Physics and Astronomy.
0:08:12 > 0:08:15We're next-door neighbours, aren't we?
0:08:15 > 0:08:17Yeah, our offices are right next door
0:08:17 > 0:08:19and it's typically really useful.
0:08:19 > 0:08:23We can just, you know, pop in and out, so it saves us a lot of time.
0:08:23 > 0:08:26- See you.- All right, then. - Have a good day.- You, too.
0:08:26 > 0:08:28Occasionally we have disputes.
0:08:28 > 0:08:32I'm in control of the temperature in both offices,
0:08:32 > 0:08:36and so I like it really warm, and Duncan likes it a lot colder.
0:08:36 > 0:08:40So we have occasional arguments, but generally it's really useful
0:08:40 > 0:08:41being right next to each other.
0:08:41 > 0:08:43Sometimes you bang your feet on the wall
0:08:43 > 0:08:45and I have to tell you to stop.
0:08:45 > 0:08:47But generally it's really nice.
0:08:47 > 0:08:48- It's good.- We like it.
0:08:50 > 0:08:52In the summer of 2006,
0:08:52 > 0:08:56Duncan and Maura began a project searching historical data
0:08:56 > 0:08:58for the Park's radio telescope.
0:09:00 > 0:09:03So we'd just arrived at West Virginia University.
0:09:03 > 0:09:07We wanted to find some data that already existed to get working
0:09:07 > 0:09:08on a project straightaway.
0:09:08 > 0:09:12So we kind of like bandied around some ideas for good projects,
0:09:12 > 0:09:16and one of the things we thought of was re-analysing the data
0:09:16 > 0:09:19from an old survey taken, like, in the late 1990s,
0:09:19 > 0:09:23of the small Magellanic cloud and this large Magellanic cloud,
0:09:23 > 0:09:26to look for pulsars that had been missed before.
0:09:28 > 0:09:32The project involved painstakingly searching hundreds of data plots,
0:09:32 > 0:09:35work Duncan delegated to student.
0:09:37 > 0:09:41Every week my student would come to me with the results of his analysis
0:09:41 > 0:09:43from the previous week,
0:09:43 > 0:09:46and sometimes those would be known pulsars,
0:09:46 > 0:09:49sometimes we would see sources of interference or just noise.
0:09:49 > 0:09:52But one week, I remember it very clearly,
0:09:52 > 0:09:56he came to me and showed me this plot with a signal
0:09:56 > 0:09:59that was so bright and apparently so far away
0:09:59 > 0:10:03that it was completely unlike anything we'd ever seen before.
0:10:03 > 0:10:07So this is the plot that my student David brought to me,
0:10:07 > 0:10:11and you can see straightaway this is the pulse that he found.
0:10:11 > 0:10:13This big dark feature here.
0:10:13 > 0:10:17This is a graph of telescope time along the horizontal axis,
0:10:17 > 0:10:20so this is almost two hours of observation here.
0:10:20 > 0:10:22And on the vertical axis is basically distance.
0:10:22 > 0:10:26You can see the background of noise from the telescope and the sky,
0:10:26 > 0:10:28these little dots here.
0:10:28 > 0:10:30So this feature really stands out
0:10:30 > 0:10:35because it's so bright and so far up the plot here,
0:10:35 > 0:10:39which indicates that it's a bright source that's very, very far away.
0:10:39 > 0:10:42Quite frankly, it was unlike anything I'd ever seen before.
0:10:42 > 0:10:44Yet, it had all the hallmarks of a signal
0:10:44 > 0:10:46that was coming from deep space.
0:10:50 > 0:10:55The signal, or "fast radio burst" Duncan had discovered
0:10:55 > 0:10:58became affectionately known as the "Lorimer Burst".
0:11:01 > 0:11:04When people started calling it the Lorimer Burst,
0:11:04 > 0:11:06at first I just chuckled.
0:11:06 > 0:11:09Because it seemed just so funny
0:11:09 > 0:11:11to have something actually named after Dunc,
0:11:11 > 0:11:15and it was even funnier when people didn't realise I was married to him,
0:11:15 > 0:11:18we have different last names, so I got lots of questions,
0:11:18 > 0:11:21like, "What do you think about the Lorimer Burst, is it real or not?"
0:11:21 > 0:11:24So I kind of got a good chuckle out of it for a little bit,
0:11:24 > 0:11:27but then that kind of stuck and so we started using the name
0:11:27 > 0:11:31in proposals and things, which was kind of fun.
0:11:31 > 0:11:35To have something named after me like this was really a great honour.
0:11:35 > 0:11:39Yeah, not something I was expecting, but yeah, really nice.
0:11:43 > 0:11:47But the Lorimer Burst was so distant and yet so bright
0:11:47 > 0:11:49it didn't appear to have been produced
0:11:49 > 0:11:52by any naturally occurring phenomenon.
0:11:54 > 0:11:58I did think that it could be a signal from an extraterrestrial
0:11:58 > 0:12:02civilisation - we create signals like that on Earth,
0:12:02 > 0:12:05so it's not crazy to think that radio bursts
0:12:05 > 0:12:07could be created on another planet.
0:12:07 > 0:12:10Once we actually thought about it, and looked at the energetics,
0:12:10 > 0:12:13you'd need to harness almost a whole solar system's worth of energy
0:12:13 > 0:12:15to create something this bright.
0:12:15 > 0:12:17Then we realised this is just impossible
0:12:17 > 0:12:20unless the civilisation is way more advanced than we are.
0:12:20 > 0:12:23We couldn't think of how to make something this energetic.
0:12:33 > 0:12:36Scientists have been searching the cosmos for strange signals
0:12:36 > 0:12:39like the Lorimer Burst for more than 50 years.
0:12:40 > 0:12:43Ever since a secretive meeting took place
0:12:43 > 0:12:45in the foothills of the Appalachian Mountains.
0:12:48 > 0:12:51There have been, over the years,
0:12:51 > 0:12:55a lot of claims, of sightings of extraterrestrials,
0:12:55 > 0:12:57colonies on the moon.
0:12:59 > 0:13:02The subject had gotten to be treated with contempt, really.
0:13:03 > 0:13:06It was considered almost taboo.
0:13:09 > 0:13:11But, in 1961,
0:13:11 > 0:13:15Frank Drake held a conference behind closed doors in this room
0:13:15 > 0:13:17at the Green Bank Observatory.
0:13:21 > 0:13:23The National Academy of Sciences of the United States,
0:13:23 > 0:13:25a very eminent body,
0:13:25 > 0:13:30asked me to convene a meeting of all the people I knew in the world
0:13:30 > 0:13:33who were actually serious thinkers on the subject
0:13:33 > 0:13:34and I invited them all.
0:13:34 > 0:13:36All 12 of them.
0:13:38 > 0:13:42The group called themselves the Order of the Dolphin.
0:13:44 > 0:13:48I could talk about all of them at length but let me just mention a few
0:13:48 > 0:13:50just to give you a feel for who they were.
0:13:50 > 0:13:52There was Otto Stuber,
0:13:52 > 0:13:55director of the observatory here at Green Bank,
0:13:55 > 0:13:58and considered perhaps the most important astronomer
0:13:58 > 0:13:59of the 20th century.
0:13:59 > 0:14:01Besides being a great astronomer
0:14:01 > 0:14:05he was a very strong proponent of the idea that intelligent life,
0:14:05 > 0:14:09and life in general, was very common in the universe.
0:14:09 > 0:14:13And there was Carl Sagan, a familiar name,
0:14:13 > 0:14:16who was a great proponent of extraterrestrial intelligent life.
0:14:16 > 0:14:20He had popularised it, gotten support for it,
0:14:20 > 0:14:23both with the general public and the scientific world.
0:14:23 > 0:14:28Then there was John Lilly, not an astronomer,
0:14:28 > 0:14:31a neurologist who had studied the human brain,
0:14:31 > 0:14:33and then the brains of dolphins,
0:14:33 > 0:14:38and was convinced that dolphins were close in intelligence to us,
0:14:38 > 0:14:42and, in studying the brain, he was trying to make the case
0:14:42 > 0:14:47that intelligence is inevitable in the course of evolution,
0:14:47 > 0:14:50and therefore it should be very common in the universe.
0:14:50 > 0:14:52Then there was Melvin Calvin,
0:14:52 > 0:14:57a chemist who had successfully understood how chlorophyll works
0:14:57 > 0:15:01to produce food and plants and makes life on earth thrive.
0:15:01 > 0:15:05And in fact had been awarded the Nobel Prize for it.
0:15:05 > 0:15:08In fact, that prize was given to him right in the middle of this meeting,
0:15:08 > 0:15:11which was pretty disruptive, I have to tell you.
0:15:14 > 0:15:18The purpose of the meeting was to estimate how many extraterrestrial
0:15:18 > 0:15:21civilisations might be out there
0:15:21 > 0:15:24using what's become known as the Drake Equation.
0:15:27 > 0:15:31So, we start out with the rate of star formation,
0:15:31 > 0:15:33which you write R star,
0:15:33 > 0:15:36and of course the more stars more planets there will be,
0:15:36 > 0:15:38the more possibilities for life.
0:15:38 > 0:15:43We multiply that by the fraction of stars which actually have planets
0:15:43 > 0:15:49and then again by the number of habitable planets in each system.
0:15:49 > 0:15:53We then multiply this by the fraction on which life develops.
0:15:54 > 0:15:58And then by the fraction by which intelligence appears.
0:15:58 > 0:16:01And then by the fraction of those
0:16:01 > 0:16:05which actually give a detectable technology,
0:16:05 > 0:16:10one we might detect across the great distances between the stars.
0:16:10 > 0:16:15What we have now in these six factors is the rate of production
0:16:15 > 0:16:17of detectable civilisations.
0:16:17 > 0:16:19Well, how many are there?
0:16:20 > 0:16:23This rate times the average time
0:16:23 > 0:16:26that these civilisations remain detectable.
0:16:26 > 0:16:30'United States maintains its determination...'
0:16:30 > 0:16:33For two days, the group worked out best guess values
0:16:33 > 0:16:35for each term in Frank's equation.
0:16:39 > 0:16:42The answer we came to for the value of N
0:16:42 > 0:16:50was N equals about 10,000 detectable civilisations at present
0:16:50 > 0:16:54in our galaxy, the Milky Way.
0:16:58 > 0:17:01It became clear to us that it was very likely
0:17:01 > 0:17:04that there were radio signals from other worlds
0:17:04 > 0:17:06passing through the room in which we were sitting
0:17:06 > 0:17:10and which we could detect if we but pointed our telescopes
0:17:10 > 0:17:13in the right direction and tuned to the right frequency.
0:17:16 > 0:17:18At the time of the meeting,
0:17:18 > 0:17:21Frank thought he knew exactly what channel to listen into.
0:17:23 > 0:17:26What we needed was a special place in the universe
0:17:26 > 0:17:31where civilisations might contact, and we realised it wasn't a place,
0:17:31 > 0:17:33but it was a radio channel.
0:17:35 > 0:17:39The most common element in the universe is hydrogen.
0:17:39 > 0:17:43It happens to transmit a very beautiful signal
0:17:43 > 0:17:47at a certain frequency when it's in its lowest energy state.
0:17:48 > 0:17:52And we decided that might be the place you meet your friends
0:17:52 > 0:17:55when you can't arrange in advance where to meet.
0:17:55 > 0:17:59So we decided to search the hydrogen wavelength.
0:18:15 > 0:18:19My father served in the Army, and when I was in high school he really
0:18:19 > 0:18:22encouraged me to join the Service, so that's what I did.
0:18:22 > 0:18:24I joined the military as an intelligence officer
0:18:24 > 0:18:27and after seven years I transferred to the Department of Defence.
0:18:30 > 0:18:33I was in the cold case unit for four years
0:18:33 > 0:18:36and during that time I would look through cases that were
0:18:36 > 0:18:3920, 30 or 40 years old, and the intent for that
0:18:39 > 0:18:42was to capture spies that slipped through our fingers.
0:18:44 > 0:18:47The Department of Defence was just a chapter in my life,
0:18:47 > 0:18:50but as a kid I always wanted be an astronomer,
0:18:50 > 0:18:53so I went to school, received my degrees and I became a scientist.
0:18:58 > 0:19:00Since leaving the agency,
0:19:00 > 0:19:04Antonio has become obsessed with the most famous cold case
0:19:04 > 0:19:06in the search for extraterrestrials.
0:19:13 > 0:19:15On August 15, 1977,
0:19:15 > 0:19:18astronomers at the Big Ear radio telescope in Ohio
0:19:18 > 0:19:23were listening to the night sky and, at about 23:00 hours local time,
0:19:23 > 0:19:26they detected a radio signal from space.
0:19:26 > 0:19:28The single was strong, about 72 seconds,
0:19:28 > 0:19:32but more importantly, it was detected in something known as
0:19:32 > 0:19:33the hydrogen line.
0:19:33 > 0:19:36That was significant because at the time,
0:19:36 > 0:19:39astronomers thought that if extraterrestrials did exist
0:19:39 > 0:19:41they would use that frequency.
0:19:43 > 0:19:46The astronomer Jerry Ehman and was so excited
0:19:46 > 0:19:49that he actually wrote the term "Wow!" on the printout.
0:19:52 > 0:19:54But what exactly caused the Wow! signal?
0:19:55 > 0:19:58It's a mystery that has endured for decades.
0:20:01 > 0:20:04I approached the Wow! signal just like any cold case at the Pentagon.
0:20:04 > 0:20:06I had multiple facts.
0:20:06 > 0:20:09I had a crime scene, and in this case
0:20:09 > 0:20:12we know that the crime scene is the constellation Sagittarius.
0:20:12 > 0:20:17I have a time of the crime, which was at 23:17 local,
0:20:17 > 0:20:21and the date of the event which was on August 15, 1977.
0:20:21 > 0:20:24More importantly, we have a fingerprint of the suspect,
0:20:24 > 0:20:26and that's hydrogen.
0:20:26 > 0:20:28So I went back to the NASA databases
0:20:28 > 0:20:31and I plugged in the date and time of the event,
0:20:31 > 0:20:35and what I learned was there were two comets in the very same area
0:20:35 > 0:20:39at the same time that the Wow! signal was detected.
0:20:39 > 0:20:42Comets are giant rocks of ice, dust and carbon.
0:20:42 > 0:20:46And, as they get closer to the sun, they begin to melt
0:20:46 > 0:20:49and as they melt they give off a massive envelope of hydrogen,
0:20:49 > 0:20:52that can be millions of kilometres across.
0:20:52 > 0:20:54So when we put two and two together,
0:20:54 > 0:20:58what we have here is a suspect that matches the fingerprint
0:20:58 > 0:21:00of the Wow! signal.
0:21:02 > 0:21:05But not everyone is convinced by Antonio's detective work.
0:21:06 > 0:21:10Few believe that comets produce enough hydrogen
0:21:10 > 0:21:12to emit such a strong signal.
0:21:15 > 0:21:18If my theory proves wrong, then I won't be upset.
0:21:18 > 0:21:20There are no emotions in science.
0:21:20 > 0:21:23What I'll do is what any other scientist would do,
0:21:23 > 0:21:25and that's move onto the next suspect.
0:21:31 > 0:21:33As Antonio continues his hunt,
0:21:33 > 0:21:36many believe the answer lies far closer to home.
0:21:38 > 0:21:40Rather than coming from deep space,
0:21:40 > 0:21:45the most likely source of the Wow! signal is thought to be interference
0:21:45 > 0:21:48from passing satellites, or aircraft here on Earth.
0:22:09 > 0:22:11Four years following its discovery,
0:22:11 > 0:22:15people were beginning to have doubts about the Lorimer Burst, too.
0:22:16 > 0:22:18Let's get to the bus stop.
0:22:18 > 0:22:21Because only one had ever been detected.
0:22:21 > 0:22:23So, did you bring your book?
0:22:24 > 0:22:27- Yes.- What was your favourite part of that?
0:22:27 > 0:22:28When he chewed gum.
0:22:29 > 0:22:31I knew you were going to say that.
0:22:34 > 0:22:35So, around 2010,
0:22:35 > 0:22:38people were actively looking for these bursts in other datasets
0:22:38 > 0:22:43and then one day I got a call that the first few were found.
0:22:43 > 0:22:47This might sound exciting, but it really wasn't because these bursts
0:22:47 > 0:22:50were a lot like the Lorimer Burst, the original burst.
0:22:50 > 0:22:54But they had a couple of different characteristics
0:22:54 > 0:22:57which indicated that they definitely were not extragalactic,
0:22:57 > 0:22:59and that they were from some source,
0:22:59 > 0:23:04either on the Earth, or maybe just right in our local atmosphere.
0:23:06 > 0:23:10When I got that call, my heart really did sink and I thought,
0:23:10 > 0:23:13"Oh, the original burst is probably a similar thing."
0:23:15 > 0:23:17Just a locally generated signal.
0:23:17 > 0:23:20So it was very, very depressing.
0:23:23 > 0:23:27There was also something deeply suspicious about the new bursts.
0:23:29 > 0:23:31They were far more common in winter
0:23:31 > 0:23:34and always appeared around lunch time.
0:23:35 > 0:23:39It was eventually discovered they weren't coming from space at all.
0:23:40 > 0:23:44They were being generated by the observatory's microwave.
0:23:47 > 0:23:49So I think it was a hard time for him
0:23:49 > 0:23:54because he felt like his original paper was discredited.
0:23:54 > 0:23:57It made it harder that everyone had been calling it the Lorimer Burst
0:23:57 > 0:23:59because then it felt very personal.
0:23:59 > 0:24:03When I first saw the data and I compared their properties
0:24:03 > 0:24:05with the Lorimer Burst properties,
0:24:05 > 0:24:09they looked really similar and I thought it too much of a coincidence
0:24:09 > 0:24:12for them not to be coming from the same source.
0:24:12 > 0:24:16My initial conclusion was that the Lorimer Burst probably wasn't real.
0:24:24 > 0:24:27But Duncan wasn't prepared to give up on his discovery so easily.
0:24:30 > 0:24:34So what we're looking at here is the original burst from 2007,
0:24:34 > 0:24:38and then one of the detections that was coming out in 2010,
0:24:38 > 0:24:41so you can see that they have quite a lot of similarities.
0:24:41 > 0:24:43Both pulses are about the same width.
0:24:43 > 0:24:47But if you look at them in terms of their frequency versus time,
0:24:47 > 0:24:50you'll see that they have an overall slope.
0:24:50 > 0:24:52They both have the same slope,
0:24:52 > 0:24:56but the structure within the pulse is quite different.
0:24:56 > 0:24:59One of the new signals has this very blotchy appearance,
0:24:59 > 0:25:04whereas our original signal had a smoother, continuous appearance.
0:25:04 > 0:25:07And that was the thing that was really giving me hope
0:25:07 > 0:25:08that this was still real.
0:25:12 > 0:25:14But for the scientific community,
0:25:14 > 0:25:17the most likely explanation for the Lorimer Burst
0:25:17 > 0:25:19was still interference.
0:25:23 > 0:25:26For now, at least, the great silence persists.
0:25:55 > 0:25:56In 1989,
0:25:56 > 0:25:59the International Academy of Astronautics
0:25:59 > 0:26:02approved a post-detection protocol.
0:26:09 > 0:26:12A code of practice to be put into play by governments
0:26:12 > 0:26:14should we detect an alien transmission.
0:26:26 > 0:26:31The document detailed how to control the dissemination of information
0:26:31 > 0:26:33and coordinate a unilateral response.
0:26:41 > 0:26:45One reason scientists believe such a protocol was required...
0:26:47 > 0:26:49..is because in the mid-'70s,
0:26:49 > 0:26:53we tried to make contact with aliens ourselves.
0:27:06 > 0:27:10There were two purposes to the Arecibo message.
0:27:10 > 0:27:14One was to demonstrate that it was possible to send a message
0:27:14 > 0:27:16across the interstellar space
0:27:16 > 0:27:21that would be detectable and decodable, understandable.
0:27:22 > 0:27:26The other was simply to show that we had in fact reached the stage
0:27:26 > 0:27:28where we ourselves could do this sort of thing.
0:27:31 > 0:27:35There were like probably 200 people, they're sitting in chairs
0:27:35 > 0:27:38on the edge of the big giant dish,
0:27:38 > 0:27:41and we tell them we're about ready to send,
0:27:41 > 0:27:46and they steer the telescope, that whole great big thing starts moving.
0:27:47 > 0:27:50Which is in itself very impressive.
0:27:51 > 0:27:53This giant thing is moving,
0:27:53 > 0:27:58and you just have the sense that something spectacular is going on.
0:28:01 > 0:28:03I will play the tape for you.
0:28:06 > 0:28:09This is a recording made in the control room
0:28:09 > 0:28:14of the Arecibo radio telescope at the time, in November 1974,
0:28:14 > 0:28:17when we sent a message to the stars.
0:28:17 > 0:28:21LONG, LOW TONE
0:28:21 > 0:28:25That steady tone is the sound of the transmitter being turned on,
0:28:25 > 0:28:29it's simply sending out a signal without any information on it.
0:28:30 > 0:28:32To call attention to itself,
0:28:32 > 0:28:36so that people who capture this will know that something is coming
0:28:36 > 0:28:37and here it comes.
0:28:37 > 0:28:42That sort of warbling sound you hear is actually a sequence
0:28:42 > 0:28:47of 10 characters per second, being sent out with those characters
0:28:47 > 0:28:50being on two slightly different radio frequencies.
0:28:56 > 0:28:59When you listen to the sound, you had the impression
0:28:59 > 0:29:02that there was a story being told here.
0:29:09 > 0:29:13And when it finally ends, everybody was crying...
0:29:15 > 0:29:17..on the actual occasion.
0:29:26 > 0:29:29It was just the, um...
0:29:29 > 0:29:35sense that this great big machine was talking to another world.
0:29:37 > 0:29:40The message goes to 300,000 stars, so there's a good chance, actually.
0:29:47 > 0:29:54The recipient of the Arecibo message is a galaxy 25,000 light years away.
0:29:56 > 0:29:59But the 50,000 years it would take for a message to get there,
0:29:59 > 0:30:03and for any reply to journey back to Earth,
0:30:03 > 0:30:06is far beyond the lifespan of any single human.
0:30:09 > 0:30:12Perhaps even the lifespan of civilisation itself.
0:30:47 > 0:30:50Human civilisation is thousands of years old,
0:30:50 > 0:30:54but we've only been sending strong signals into space
0:30:54 > 0:30:56for really about 60 years.
0:30:58 > 0:31:02The truth is, we don't know how long we'll continue to send the signals
0:31:02 > 0:31:03out into space
0:31:03 > 0:31:07because we don't know longa technological civilisation like ours
0:31:07 > 0:31:08typically lasts.
0:31:15 > 0:31:19When we look into space, searching for extraterrestrial intelligence,
0:31:19 > 0:31:22in a way we're looking for a glimpse of our own future
0:31:22 > 0:31:26and potentially a glimpse of how our civilisation might come to an end.
0:31:29 > 0:31:31And one of the biggest dangers we face
0:31:31 > 0:31:34is the threat we pose to ourselves.
0:31:35 > 0:31:39In the Cold War, we were worried about nuclear annihilation.
0:31:39 > 0:31:41Nowadays we worry more about climate change,
0:31:41 > 0:31:45and in the future we might worry about things such as nanotechnology
0:31:45 > 0:31:47or artificial intelligence.
0:31:47 > 0:31:50These are all serious risks that we have to be very careful about.
0:31:51 > 0:31:53As we become more advanced,
0:31:53 > 0:31:56the threat we pose to ourselves increases
0:31:56 > 0:32:00because we have improved ability to harness large amounts of energy
0:32:00 > 0:32:02and manipulate the environment to a greater degree.
0:32:06 > 0:32:08When those processes go wrong,
0:32:08 > 0:32:11the damage we can inflict on ourselves and on the planet
0:32:11 > 0:32:13becomes substantial.
0:32:18 > 0:32:20Faced with these dangers,
0:32:20 > 0:32:23advanced civilisations could be relatively short-lived.
0:32:27 > 0:32:31It might be that in the 13.5 billion year history of the universe,
0:32:31 > 0:32:34many have risen,
0:32:34 > 0:32:38but today, nothing but ruins remain.
0:32:41 > 0:32:45So if we don't find anything, that could be quite a disturbing thought
0:32:45 > 0:32:48because it could mean that the reason we don't see anything
0:32:48 > 0:32:50is that civilisations don't last very long,
0:32:50 > 0:32:53and that the signals they produce suddenly disappear.
0:32:53 > 0:32:57MUSIC: It's Not Unusual by Tom Jones
0:33:04 > 0:33:08# It's not unusual to be loved by anyone... #
0:33:08 > 0:33:11But if they haven't destroyed themselves,
0:33:11 > 0:33:14a technologically advanced civilisation
0:33:14 > 0:33:17might provide us with another way of detecting them.
0:33:17 > 0:33:21Because all technology needs energy.
0:33:25 > 0:33:30In 1994, Las Vegas consumed 1300 megawatts of power.
0:33:30 > 0:33:35Today that figure has nearly doubled to 2400 megawatts.
0:33:35 > 0:33:38That's the same trend that we see all over the world.
0:33:38 > 0:33:41For the last century, every few decades,
0:33:41 > 0:33:43humanity's power consumption has doubled.
0:33:43 > 0:33:47As our technology has increased, so too has our need for power.
0:33:50 > 0:33:51And, as demand increases,
0:33:51 > 0:33:55civilisations must look beyond their home world.
0:33:55 > 0:33:57Every star, just like our sun,
0:33:57 > 0:34:00is basically a giant nuclear furnace,
0:34:00 > 0:34:04fusing hydrogen into helium and producing energy.
0:34:04 > 0:34:08The ultimate limit to the amount of energy available to any civilisation
0:34:08 > 0:34:11is just the amount of energy that they can harvest
0:34:11 > 0:34:12from that parent star.
0:34:29 > 0:34:31Deep in the Mojave Desert,
0:34:31 > 0:34:34halfway between Las Vegas and Reno...
0:34:38 > 0:34:40..it's possible to glimpse the future.
0:35:15 > 0:35:18So, this is the Crescent Dunes Solar Facility.
0:35:18 > 0:35:21There are 10,347 of these mirrors.
0:35:21 > 0:35:24They all reflect the sun's energy up to that tower.
0:35:24 > 0:35:27The heat's a reservoir of molten salt,
0:35:27 > 0:35:29that's then used to turn water into steam,
0:35:29 > 0:35:32turning turbines, and generating electricity.
0:35:36 > 0:35:39Crescent Dunes is one of the world's largest solar power plants,
0:35:39 > 0:35:41but even this gigantic facility
0:35:41 > 0:35:44can only collect a small fraction of the sun's energy.
0:35:47 > 0:35:50In the future, we might build thousands more of these facilities,
0:35:50 > 0:35:52collecting even more of the sun's energy.
0:35:58 > 0:36:02The amount of energy a civilisation can harness from their star
0:36:02 > 0:36:05provides an indication of their technological advancement.
0:36:09 > 0:36:12And it's measured on what's known as the Kardashev scale.
0:36:16 > 0:36:18A Kardashev Type I civilisation
0:36:18 > 0:36:22is a civilisation that's capable of harnessing all of the energy
0:36:22 > 0:36:24that falls on their planet from their parent star.
0:36:26 > 0:36:31Human civilisation only consumes about 20 terawatts of power.
0:36:31 > 0:36:34That's about 1000th of the amount of energy that falls on our planet
0:36:34 > 0:36:35from our sun.
0:36:38 > 0:36:40But the amount of sunlight that hits the Earth
0:36:40 > 0:36:44is only a tiny fraction of the light that leaves the sun.
0:36:46 > 0:36:50Our sun's power is 400 billion terawatts.
0:36:50 > 0:36:55That's 10 million times as much energy in just one second
0:36:55 > 0:36:58as the entire United States consumes over the course of the year.
0:37:00 > 0:37:04Any civilisation capable of harnessing all the energy
0:37:04 > 0:37:09emitted by its star would have achieved Kardashev Type II status.
0:37:12 > 0:37:14But to do it
0:37:14 > 0:37:18would require engineering on a truly astronomical scale.
0:37:20 > 0:37:22A Kardashev Type II civilisation
0:37:22 > 0:37:25would need to build a massive network of solar collectors
0:37:25 > 0:37:27that would orbit their star in space.
0:37:27 > 0:37:30Something we call a Dyson sphere, or a Dyson structure.
0:37:33 > 0:37:37A Dyson structure is very much like the solar power plant here,
0:37:37 > 0:37:41but billions of times larger, in space, orbiting an entire star.
0:37:43 > 0:37:46But they needn't be a solid surface.
0:37:46 > 0:37:49It could be a swarm of individual solar panels,
0:37:49 > 0:37:53all interconnected, as long as they occluded a large fraction
0:37:53 > 0:37:55of the light that came from the star.
0:37:57 > 0:38:00To construct a Dyson sphere that enveloped the sun
0:38:00 > 0:38:04would require all the matter in all the planets in the solar system.
0:38:06 > 0:38:08And so until recently,
0:38:08 > 0:38:11Dyson spheres were thought to be purely theoretical.
0:38:40 > 0:38:41Then, in 2013,
0:38:41 > 0:38:46some deeply strange observations from NASA's Kepler space telescope
0:38:46 > 0:38:51fell onto the desk of astronomer Tabetha Boyajian.
0:38:58 > 0:39:02Kepler looked at over 150,000 stars in our galaxy,
0:39:02 > 0:39:06and the data for this star looked nothing like any of the stars,
0:39:06 > 0:39:09and nothing like any other star that we know of today.
0:39:13 > 0:39:16For four years, the telescope scoured the Milky Way,
0:39:16 > 0:39:20hunting for evidence of exoplanets.
0:39:21 > 0:39:24Meticulously measuring the brightness of stars
0:39:24 > 0:39:26in search of the tell-tale dimming in light
0:39:26 > 0:39:29produced as a planet passes in front of them.
0:39:36 > 0:39:40So, this is what an exoplanet transit looks like.
0:39:40 > 0:39:42On the left-hand side you have the amount of light,
0:39:42 > 0:39:44and on the bottom you have time,
0:39:44 > 0:39:48and when a Jupiter-like planet transits in front of a star,
0:39:48 > 0:39:52you have this clean U-shaped dip in the star's light.
0:39:52 > 0:39:54And this dip this about 1%.
0:39:56 > 0:40:01So this is the Kepler data for KIC 8462852.
0:40:01 > 0:40:05And it shows four years of Kepler photometry of the star.
0:40:05 > 0:40:09And, as you can see, for most of the time it's pretty flat.
0:40:09 > 0:40:10Nothing is going on.
0:40:10 > 0:40:14But then in May 2009, you had this dip that on face value,
0:40:14 > 0:40:18appears to look like what a transiting planet would look like.
0:40:18 > 0:40:19But if you take a closer look,
0:40:19 > 0:40:23then you actually see that the transit lasts for almost a week,
0:40:23 > 0:40:25compared to a planet-sized object,
0:40:25 > 0:40:28which would just last for a couple of hours.
0:40:28 > 0:40:31It was also very asymmetric in shape,
0:40:31 > 0:40:34meaning that, instead of having that cleanly U-shaped dip,
0:40:34 > 0:40:38it had this strange slope over here on the left-hand side.
0:40:38 > 0:40:40This seemed to indicate that whatever was crossing
0:40:40 > 0:40:43in front of the star was not circular like a planet.
0:40:48 > 0:40:50Things are pretty quiet for a couple of years,
0:40:50 > 0:40:56and then in March of 2011 we have this very dramatic feature
0:40:56 > 0:41:00where the star's brightness drops by 15%.
0:41:02 > 0:41:06And this drop is also very asymmetric.
0:41:06 > 0:41:09It gradually decreases in brightness for about a week
0:41:09 > 0:41:13and it then snaps right back up to normal in just a few days.
0:41:13 > 0:41:17Now, after this nothing happens again for a couple of years
0:41:17 > 0:41:19until February of 2013,
0:41:19 > 0:41:25when you have this huge complex of dips that last almost for 100 days.
0:41:25 > 0:41:27Each of these dips have a different structure,
0:41:27 > 0:41:30some are very shallow, some are very sharp,
0:41:30 > 0:41:35and the deepest one here drops by over 20%.
0:41:35 > 0:41:39And so it seems to indicate that there is some swarm of objects
0:41:39 > 0:41:43with different sizes and shapes that were passing in front of the star.
0:41:46 > 0:41:50At first, no one had any idea what those objects could be.
0:41:52 > 0:41:53Then somebody came along and said,
0:41:53 > 0:41:57"What if there was a giant swarm of comets that was
0:41:57 > 0:42:00"swooping down towards the star and blocking out the star light?"
0:42:00 > 0:42:05And this seemed to be consistent with the observations that we had,
0:42:05 > 0:42:09but it seemed a little bit contrived because it would take, you know,
0:42:09 > 0:42:13hundreds if not thousands of comets to block out the star's light.
0:42:13 > 0:42:18But nevertheless this was kind of the best idea, theory,
0:42:18 > 0:42:20that we had to explain the data.
0:42:25 > 0:42:26But there was another possibility.
0:42:28 > 0:42:31That Tabby had detected the deep shadows
0:42:31 > 0:42:34cast by a Dyson sphere constructed around the star.
0:42:38 > 0:42:41The scale of these things is kind of hard to imagine,
0:42:41 > 0:42:42but you can think of it this way.
0:42:42 > 0:42:46So the Earth-Moon distance is about a quarter of a million miles
0:42:46 > 0:42:51and the simplest element in one of these would be 100 times this size.
0:42:52 > 0:42:55Now, imagine these in orbit around the star,
0:42:55 > 0:42:58and you can see how it would produce anomalies
0:42:58 > 0:42:59in the data that we detect.
0:43:02 > 0:43:04Scientists are still trying to determine
0:43:04 > 0:43:06the precise cause of the dimming.
0:43:08 > 0:43:10But they have at least settled on a name.
0:43:11 > 0:43:14Star KIC 8462852
0:43:14 > 0:43:19has become known as Tabby's Star.
0:43:35 > 0:43:37- See you, bye!- OK, bye.
0:43:47 > 0:43:51Along with the potential discovery of alien mega structures,
0:43:51 > 0:43:562013 also brought good news for Duncan Lorimer.
0:44:00 > 0:44:02A group at Manchester University
0:44:02 > 0:44:04announced the discovery of four more bursts.
0:44:05 > 0:44:08There were coming from all over the sky and they were clearly real,
0:44:08 > 0:44:10so it was a breakthrough moment.
0:44:10 > 0:44:14It meant the Lorimer Burst was real, which was just great news.
0:44:14 > 0:44:18And it also meant that we could learn a lot about these bursts
0:44:18 > 0:44:20that we couldn't before - we'd be able to study the population
0:44:20 > 0:44:24and the energetics and try to figure out exactly what's causing them.
0:44:24 > 0:44:27I think up until that moment when the confirmation came through,
0:44:27 > 0:44:30I certainly every now and again, would begin to doubt myself
0:44:30 > 0:44:33and think, is it really just some bizarre form of interference
0:44:33 > 0:44:35that causes that one object?
0:44:35 > 0:44:38But as soon as you get those other objects,
0:44:38 > 0:44:43all of those doubts go away and it's a very, very liberating feeling.
0:44:43 > 0:44:46Duncan was very, very excited when these other bursts were announced
0:44:46 > 0:44:48because, yeah, he felt vindicated.
0:44:48 > 0:44:53He was very self-satisfied and had a little bit of a high and mighty air
0:44:53 > 0:44:56for a few weeks because I'd sort of started to doubt
0:44:56 > 0:44:59that the Lorimer Burst was real, and he had never given up.
0:44:59 > 0:45:02He always said it was real, so he'd won the argument.
0:45:02 > 0:45:05And he made it well-known that he was right.
0:45:07 > 0:45:11I think I told her something like, "I told you so!"
0:45:15 > 0:45:17By the end of 2013,
0:45:17 > 0:45:21there had been six confirmed detections of fast radio bursts.
0:45:23 > 0:45:26But what was causing them was still unknown.
0:45:28 > 0:45:30Now that fast radio bursts are real,
0:45:30 > 0:45:33it comes back to the idea of whether they could be caused by aliens.
0:45:33 > 0:45:36And I've never really subscribed to that.
0:45:36 > 0:45:39If I were looking for a signal from an extraterrestrial civilisation,
0:45:39 > 0:45:41I'd be looking for it coming from a single point in the sky.
0:45:41 > 0:45:44We have a population of sources all over the sky
0:45:44 > 0:45:46which implies that the aliens are all over the place,
0:45:46 > 0:45:49all over the universe, and that just seems highly unlikely to me.
0:45:54 > 0:45:57But then, mathematical analysis of the known signals
0:45:57 > 0:46:01seemed to show they were all placed at regularly spaced distances.
0:46:06 > 0:46:10Maybe, whatever was responsible for the fast radio bursts
0:46:10 > 0:46:13were put there by extraterrestrials,
0:46:13 > 0:46:16perhaps even ones on the next level of the Kardashev scale.
0:46:18 > 0:46:22Communication beacons placed across the Milky Way
0:46:22 > 0:46:24by a Type III civilisation.
0:46:25 > 0:46:30One with the ability to harness the power of an entire galaxy.
0:46:41 > 0:46:45But, if the Milky Way were home to a Type III civilisation,
0:46:45 > 0:46:48its presence should be written across the sky.
0:46:52 > 0:46:56We know from thermodynamics that any energy usage that does useful work
0:46:56 > 0:46:57produces waste heat.
0:46:57 > 0:46:59Our car engines produce waste heat,
0:46:59 > 0:47:02our laptop batteries produce waste heat,
0:47:02 > 0:47:04so too does any energy usage by any technology,
0:47:04 > 0:47:08whether it's human technology, or an extraterrestrial technology.
0:47:10 > 0:47:13If there were a civilisation in our galaxy that was using the energy
0:47:13 > 0:47:15of millions or billions of stars,
0:47:15 > 0:47:19we would see evidence of that energy usage in the form of waste heat.
0:47:21 > 0:47:24As more fast radio bursts were discovered,
0:47:24 > 0:47:27so the regular pattern disappeared.
0:47:28 > 0:47:32And nothing like the heat produced by a Type III civilisation
0:47:32 > 0:47:34has ever been seen in our galaxy.
0:47:38 > 0:47:41There are hundreds of billions of galaxies in our universe
0:47:41 > 0:47:43so there's certainly still room for these very,
0:47:43 > 0:47:46very advanced civilisations to exist somewhere in our universe.
0:47:54 > 0:47:57But, wherever those civilisations might be,
0:47:57 > 0:47:59for as long as we have been looking...
0:48:01 > 0:48:03..they have remained elusive.
0:48:23 > 0:48:25In the spring of 1960,
0:48:25 > 0:48:27Frank Drake arrived in Green Bank
0:48:27 > 0:48:31to fulfil the dream he'd had since childhood.
0:48:42 > 0:48:47I had been waiting for many, many years for this opportunity
0:48:47 > 0:48:51to answer that question, are there other civilisations out there?
0:48:54 > 0:48:57It was very exciting, because at that time, for all we knew,
0:48:57 > 0:49:01every star had a planet that was sending intelligent signals.
0:49:01 > 0:49:03We might succeed the first day, in the first hour.
0:49:05 > 0:49:08It was here that Frank conducted Project Ozma,
0:49:08 > 0:49:12the first scientific search for extraterrestrials.
0:49:12 > 0:49:17We did in fact attach a loudspeaker just in case a miracle happened
0:49:17 > 0:49:20and we actually heard someone talking to us.
0:49:20 > 0:49:22It was not out of the question.
0:49:22 > 0:49:25We had a tape recorder that was recording everything coming in.
0:49:25 > 0:49:27So when we first turned it on,
0:49:27 > 0:49:30of course everybody was wondering, what are we going to hear?
0:49:30 > 0:49:33What we heard was noise.
0:49:33 > 0:49:35Static, nothing.
0:49:37 > 0:49:41Project Ozma heard no alien communications.
0:49:43 > 0:49:48And it's been the same story for every subsequent search.
0:49:50 > 0:49:54We've done a great deal of searching in the last 50-plus years,
0:49:54 > 0:49:57and we've learned that we're going to have to search
0:49:57 > 0:50:00perhaps a million stars and countless frequency channels
0:50:00 > 0:50:02before we have a good chance of success.
0:50:05 > 0:50:08But, after more than half a century,
0:50:08 > 0:50:12Frank's own search is drawing to a close.
0:50:14 > 0:50:17If I had this to do all over, I would still do it.
0:50:17 > 0:50:20In fact, probably put more time into it because I've come to realise
0:50:20 > 0:50:22that's what's required to succeed.
0:50:22 > 0:50:26And to me that time is not time wasted.
0:50:26 > 0:50:32Because the eventual discovery is of such importance that it justifies
0:50:32 > 0:50:37not just one human life being dedicated to succeeding, but many.
0:50:44 > 0:50:45Are we alone?
0:50:47 > 0:50:49If we are, then that tells us something
0:50:49 > 0:50:52about the preciousness of life on Earth.
0:50:56 > 0:50:58And if we're not alone...
0:50:59 > 0:51:02..then what discovery could possibly be more important?
0:51:19 > 0:51:21Come with us.
0:51:24 > 0:51:29Breakthrough Listen takes the search for intelligent life in the universe
0:51:29 > 0:51:31to a completely new level.
0:51:33 > 0:51:37In 2015, Russian billionaire Yuri Milner
0:51:37 > 0:51:40put down 100 million of his own money
0:51:40 > 0:51:43to conduct the most comprehensive search for extraterrestrials
0:51:43 > 0:51:45ever undertaken.
0:51:47 > 0:51:49This was once a dream,
0:51:49 > 0:51:52it is now a truly scientific quest.
0:51:52 > 0:51:54The 20th century...
0:51:55 > 0:51:59..we stepped out from our planet to space,
0:51:59 > 0:52:02to the moon,
0:52:02 > 0:52:03to the solar system.
0:52:03 > 0:52:08In the 21st century, we'll find out about life on a galactic scale.
0:52:10 > 0:52:13And the search begins with Tabby's Star.
0:52:16 > 0:52:20KIC 8462852 is one of the best targets we've had in a long time
0:52:20 > 0:52:22for study searches.
0:52:24 > 0:52:27We're going to be using the 100-metre Green Bank telescope,
0:52:27 > 0:52:30the largest fully steerable radio telescope on the planet,
0:52:30 > 0:52:33paired with a brand-new set of instrumentation we've installed
0:52:33 > 0:52:35as part of the Breakthrough Listen project.
0:52:35 > 0:52:39This instrumentation allows us to conduct a very sensitive search
0:52:39 > 0:52:41over a huge amount of the radio spectrum.
0:52:42 > 0:52:46Now, if Tabby's Star does indeed have a Dyson sphere around it,
0:52:46 > 0:52:49and it is inhabited by a very advanced civilisation,
0:52:49 > 0:52:53perhaps that civilisation might have technology like we use on Earth,
0:52:53 > 0:52:54perhaps radio technology.
0:52:54 > 0:52:57And if they do, we could detect it with this telescope.
0:53:00 > 0:53:04Tonight represents perhaps the best chance humanity has ever had
0:53:04 > 0:53:07to make contact with extraterrestrials.
0:53:13 > 0:53:15Hey, Dave.
0:53:15 > 0:53:17Could you put Vegas back in mode one?
0:53:17 > 0:53:20This evening is a very exciting night.
0:53:20 > 0:53:21Turned back on and then...
0:53:23 > 0:53:25We've been waiting for it for over a year,
0:53:25 > 0:53:29so, yeah, I think we're all pretty excited about what's happening.
0:53:29 > 0:53:31What's next? Is Tabby's Star next?
0:53:31 > 0:53:32Tabby's Star is next, yes.
0:53:32 > 0:53:35All right, time for you to push the button!
0:53:39 > 0:53:41Right, here we go.
0:53:43 > 0:53:45- We're off.- Here we go.
0:53:45 > 0:53:47MOTOR WHIRS
0:53:52 > 0:53:54Once it's moved into position,
0:53:54 > 0:53:57the telescope begins to gather radio waves
0:53:57 > 0:54:01that just might contain messages from an alien civilisation.
0:54:05 > 0:54:07- There you go. It's coming in.- Right!
0:54:10 > 0:54:14For six hours, the giant dish tracks the star across the sky,
0:54:14 > 0:54:18scanning billions of radio channels simultaneously.
0:54:24 > 0:54:27By 3:30am, the observations are complete.
0:54:28 > 0:54:32These four plots represent about 800 megahertz of the radio spectrum
0:54:32 > 0:54:36and this is only about one quarter of the amount of the radio spectrum
0:54:36 > 0:54:37that we're observing.
0:54:37 > 0:54:40So this plot shows the shape of the radio spectrum
0:54:40 > 0:54:42as a function of frequency.
0:54:42 > 0:54:45And here we see the radio spectrum as a function of time.
0:54:45 > 0:54:48If there was evidence of technology in these data,
0:54:48 > 0:54:51what we would expect to see is a spike in one of these plots,
0:54:51 > 0:54:53a lot of electromagnetic energy in just one channel.
0:54:53 > 0:54:56Now we don't see that yet, but in the coming days,
0:54:56 > 0:54:59weeks and months, we're going to be looking at the data
0:54:59 > 0:55:02in many different ways with much higher resolution,
0:55:02 > 0:55:05that will allow us to be much more sensitive to evidence of technology.
0:55:09 > 0:55:14For tonight at least, Tabby's Star is holding onto its secrets.
0:55:16 > 0:55:18For the Breakthrough team,
0:55:18 > 0:55:21the search for extraterrestrials is only just beginning.
0:55:24 > 0:55:26I don't know if they're out there or not.
0:55:26 > 0:55:28As a scientist I have to admit that.
0:55:28 > 0:55:32But I think that it would be a pretty strange universe
0:55:32 > 0:55:36in which life only arose once, and intelligence only arose once.
0:55:37 > 0:55:40I think, to me, the most interesting property of the universe
0:55:40 > 0:55:42is the fact that intelligence exists at all,
0:55:42 > 0:55:46that somehow the universe has evolved a capacity to know itself,
0:55:46 > 0:55:48to ask questions about itself,
0:55:48 > 0:55:52and ultimately I think, until we answer this question,
0:55:52 > 0:55:54we won't really understand the universe at all.
0:56:13 > 0:56:18Since 2013, many more fast radio bursts have been discovered.
0:56:20 > 0:56:24Duncan and Maura now have a theory for what might be producing them.
0:56:26 > 0:56:30So whatever it is that is causing FRBs must be both very compact
0:56:30 > 0:56:32and very energetic.
0:56:32 > 0:56:36It must be compact because the width of the pulses is very narrow,
0:56:36 > 0:56:38and they must be very energetic
0:56:38 > 0:56:41because the distances that we infer are very far away.
0:56:43 > 0:56:46It's thought, in fact, the bursts could be created
0:56:46 > 0:56:50during the explosive collisions of neutron stars,
0:56:50 > 0:56:54some of the densest, most energetic objects in the universe.
0:56:57 > 0:57:00We observe binary systems of two neutron stars
0:57:00 > 0:57:02that are in orbit around each other,
0:57:02 > 0:57:05and when we observe these systems, we see them getting closer
0:57:05 > 0:57:07and closer together all the time.
0:57:07 > 0:57:10So what will happen eventually is that they're going to collide.
0:57:13 > 0:57:14And when they merge,
0:57:14 > 0:57:18the neutron stars will be completely destroyed and form a black hole.
0:57:19 > 0:57:23As they annihilate, the two stars release in an instant
0:57:23 > 0:57:28the same energy the sun produces in an entire month.
0:57:30 > 0:57:36A blinding flash visible to our telescopes as a fast radio burst.
0:57:37 > 0:57:40This theory perhaps solves the mystery
0:57:40 > 0:57:43of these strange signals from space.
0:57:44 > 0:57:47When you look at the energetics of these events,
0:57:47 > 0:57:50you can easily explain the FRB energies with them.
0:57:50 > 0:57:53You can also explain the durations of the FRB pulses
0:57:53 > 0:57:56with the expected durations of these merger events.
0:57:56 > 0:57:58So it's quite a plausible explanation.
0:58:05 > 0:58:09Then, in 2016, a new burst was detected.
0:58:10 > 0:58:12The distinctive pulse of radio waves
0:58:12 > 0:58:16released as the neutron stars collided and were destroyed.
0:58:18 > 0:58:20Followed by nothing.
0:58:20 > 0:58:21Silence.
0:58:23 > 0:58:25Just as the astronomers expected.
0:58:30 > 0:58:32But then, when they looked again...
0:58:36 > 0:58:37..the signal came back.
0:59:03 > 0:59:07# It's not unusual to be loved by anyone
0:59:08 > 0:59:12# It's not unusual to have fun with anyone
0:59:14 > 0:59:17# But when I see you hanging about with anyone
0:59:19 > 0:59:22# It's not unusual to see me cry. #