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00:00The first exoplanet was confirmed in 1992. More than 5,000 others have been catalogued since,
00:07and many in a habitable zone. But the truth is, we know, even if we haven't yet confirmed,
00:13that there are billions of other planets out there, and the likelihood of alien life
00:18is almost certain. So, do you think that they might know about us?
00:25A new study published in the Astrophysical Journal in June 2020 has recontextualized
00:36the search for extraterrestrial life by taking a fresh look at the famous Drake Equation.
00:42The study, led by researchers at the University of Nottingham in the UK, guesstimates the
00:47number of CETI, or Communicating Extraterrestrial Intelligence Civilizations, that could be
00:54in our galaxy, putting the figure at somewhere between 4 and 211, but most likely a few dozen,
01:01or about 36. So, there's more than a few things to understand here. First, the civilizations
01:08that the team are proposing would all be able to send radio signals out into space, much
01:14like we can, which is what qualifies them as communicating. Next, and more significantly
01:20however, researchers reached this new number of potential alien societies by developing
01:26a calculation called the Astrobiological Copernican Limit, which is essentially a more specific
01:33alien probability analysis than the much more famous Drake Equation. The Drake Equation,
01:39devised by the astrophysicist Frank Drake in 1961, sets out to estimate the number of
01:46potential alien civilizations too, only it's infamously broad in its approach. The equation
01:52looks at seven criteria, none of which we conclusively know the answer to, including
01:58the rate of star creation and the possible lifetime of a communicating civilization.
02:04As a result, because of all the moving parts, the various attempts to solve the Drake Equation
02:10have generated wildly different outcomes down the years, alternately suggesting that there
02:15could be anything from zero other civilizations, for example, to tens of millions of them.
02:21The Astrobiological Copernican Limit calculation, however, significantly streamlines and tightens
02:27the method. Crucially, it works on the assumption that life on Earth develops scientifically
02:33rather than at random, and that intelligent life on an alien planet would therefore evolve
02:38in a similar way to how it has done on Earth. That is, it would take roughly five billion
02:44years to get to this point. It then takes into account the estimate number of planets
02:49within the habitable zones of their respective stars, in the Milky Way, and hey presto, it
02:56deems that there's potentially between four and two hundred and eleven communicating civilizations
03:02in our galaxy, or about thirty-six.
03:05Much like the Drake Equation, though, the Astrobiological Copernican Principle isn't
03:11without its fair share of problems. Again, we can't accurately know the correct figures
03:16to input into it, with estimates on the number of anything in the Milky Way tending to significantly
03:22differ from source to source. We simply don't know the exact number of stars, or exoplanets
03:29in the galaxy, and haven't yet even confidently observed an exomoon. So, while this new method
03:35is quicker, neater, more specialised, and arguably more authentic, it is by no means
03:42definitive. We're still very much at the stage of, there could be thirty-six alien
03:47civilizations in the Milky Way, but there also really couldn't be. There's also
03:52the fact that we're still not absolutely certain what caused intelligent life to evolve
03:57even on Earth itself, so the assumption that it even could happen, widely across the universe,
04:04under what might be deemed the right conditions, is still a vast, but in this case vital, leap.
04:10The whole estimating the lifespan of a communicating civilization thing is really tricky to do.
04:16We only have ourselves to measure against, and though humans have been on Earth for 200,000
04:22years or so, we've only been able to send radio signals for about a century. And we
04:27have no idea how long we'll survive as a radio-signalling, communicating species.
04:33This means our best guess at how long such a civilization could last has only one very
04:39modest data point to work from, of at least 100 years.
04:44While this latest method to count unseen aliens isn't infallible, however, it does prompt
04:50us to think about the search for extraterrestrial life from a range of other perspectives too,
04:56which is always fun. Another takeaway from this study, for example, is the calculated
05:02probable distance between us and the next civilization, with it suggesting that the
05:06closest alien group could be 17,000 light years away. This means that even if we knew,
05:13with 100% accuracy, that there really was an intelligent, communicating civilization
05:18that distance away from us, well, we'd be waiting some 34,000 years after sending a
05:24simple message to get a similarly simple response back. As for the prospects of conversing
05:30with such a society in depth, there aren't any.
05:33Not only that, but 17,000 years is obviously a long time, and more than enough time for
05:40a civilization – ours or theirs – to disappear for any number of reasons. Barring some sort
05:46of far-future immortality technique, at the very least anyone alive to blindly send the
05:52initial message would be long, long dead before the reply came through. What's even
05:57more disheartening, though, is that even if there is an alien civilization out there,
06:02or even 36 civilizations or more, how likely is it that they're sending out radio signals
06:08to try and communicate in the first place? Arguably, not very. Humankind has been sending
06:13radio messages into space for decades, the most famous of which being the Arecibo message
06:19in 1974, but it's not automatic that other species would do the same thing. While the
06:25astrobiological Copernican principle assumes that other life will have developed scientifically
06:30and somewhat similarly to ours, it could still be completely and fundamentally different
06:36to us, with zero use or knowledge of our communication methods. Nevertheless, there has been some
06:43cause for belief in recent decades, too, that perhaps an alien message would be receivable
06:49and decipherable for us. The most famous of all incoming signals was the WOW signal picked
06:55up by the Big Ear radio telescope at Ohio State University in 1977. When translated,
07:02it amounts to a string of six characters – 6EQUJ5 – and has been variably called the most
07:09likely candidate for a true alien communication. In 2012, we even sent a response to the signal
07:17from the Arecibo Observatory, in the form of 10,000 tweets all tagged with hashtag Chasing
07:24UFOs.
07:25More recently, notable radio signals from space were picked up by CHIME, the Canadian
07:31Hydrogen Intensity Mapping Experiment, a radio telescope, in 2018. CHIME detected what are
07:38known as FRBs – Fast Radio Bursts – coming from another galaxy 500 million light-years
07:45away, repeating at intervals of every 16 days. But could it be a sign of alien life, or could
07:52these interest-piquing FRBs instead be coming from a young neutron star or an incredibly
07:58bright supernova, as per other theories on what they really are? Either way, as they're
08:04from outside the Milky Way, they're not one of the 36 civilisations proposed by the
08:10Astrobiological Copernican Principle, and if CHIME's FRBs are alien in origin, it'd
08:16take us hundreds of millions of years to send a response with current technology – a significant
08:22portion of Earth's life so far.
08:25If anything, instances like the CHIME signal prove just how immense the task at hand really
08:30is. With a new calculation, the University of Nottingham team has devised a way to argue
08:36for multiple alien civilisations within the Milky Way. But the Milky Way is just one average-sized
08:42example in amongst billions more galaxies in the observable universe. So, while we may
08:48never be able to talk to distant aliens in our own galaxy or beyond, the belief that
08:53we're not alone isn't likely to disappear either. The Astrobiological Copernican Limit
08:59is one attempt amongst many to estimate how many intelligent species are out there, but
09:05until we have direct evidence that anything else exists, it's impossible to tell how
09:11accurate the calculations are. For now, we have to be content thinking that there might
09:16be 36 alien civilisations living in the Milky Way.
09:29What do you think? Is there anything we missed? Let us know in the comments, check out these
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