Hello, I'm David. Oh, hi. Would you like to talk about...Jesus? Uhhhhh... Jesus Christ. Uh, yeah, sorry... Yes. No, sorry. Oh, no, I understand. Would you like this? Uh, yeah, ok. Thanks then! My song! You haven't heard my song! Something about the city... ...something about the Jesus. And... and that's it? Yes. Ok, thanks then. Ohhh... one final question! Wow! Although probably shouldn't be that surprised. I mean the odds are, that
out there in the vastness of space that there's other intelligent life, are pretty high. I mean, out of the 200 billion stars in our galaxy, 20 billion of those are like our Sun. And, it's reckoned that one in five of those has at least one planet in its Goldilocks zone. Which is the distance where the
planet doesn't fry, or freeze. And, if only 0.1% of those planets have life on... Then there would be a million planets with life in our galaxy. Of course, not all of them would harbour intelligent life... ...they might only have bacteria. But, there should be at least some that are capable of saying hello. The famous astronomer and astrophysicist Frank Drake devised this equation to estimate
the number of communicative, extraterrestrial civilisations in our galaxy. And he reckoned there could be as many as 50,000! Although, it really is
only an estimate. You see, the equation contains some variables that we have a pretty good idea about... Like the average rate of star formation. But it also contains variables that aren't known. Like the fraction of planets that can
support life, all the way to... ...the fraction of civilisations that would have developed technology detectable from space. And for these ones we have no definitive proof so you just kind of have to guess. Which means that you could
get an answer 50,000 or even just 50. But, we are getting better at guessing all
the time as we discover new exoplanets and learn more about the universe in
general. Slowly refining those variables so we get a better estimation of
intelligent life forms. Although, who's to say that they're intelligent anyway? Well, firstly, I think it would be pretty big headed to think that we're the best thing going. The universe is 13.8 billion years old... ...which means life has had an incredible amount of time to arise and and evolve. The earth is 4.5 billion years old, but planets were forming long before that. Some emerged after just 1 to 2 billion years. But, to get a better sense of these timescales... ...let's represent the
age of the universe by a single year. And if we do that, the Earth arose in early September... ...with Homo sapiens only arising at twelve minutes to midnight ...on the 31st of December. Now imagine a planet somewhere else in the galaxy that have formed before Earth... ...with an alien civilisation that arose in August on our cosmic timeline. And let's say that they were technologically advanced enough to make self-replicating probes. Not too inconceivable based on our own
technological progress. If one August day, just after midnight they launched the first probes... ...then before breakfast that same day they could have colonised the galaxy. So if the maths tells us that there
should be thousands of other civilisations out there and they've had, potentially, so long to develop the technology to explore the vast reaches of space... ...then well, where are they all? Well, maybe there's more to it than just
time. It might not be as easy as just waiting for intelligent life to evolve. It might be that there are just too many
hurdles for life to overcome before it's able to communicate with other civilisations. Hurdles like those outlined in The Great Filter Theory, A universal checklist that has to be completed first. And it can be simplified into four basic tick boxes. The first box to tick isn't life though. It starts way before that. Firstly you need a habitable world. A planet orbiting a star at just the right distance for water to exist. But it's far more nuanced than just that. For example, one of the reasons that life has flourished on Earth is due to its relatively stable climate... ...which some believe is, in part, owed to our moon. One study showed that if the moon were just a few kilometres bigger... ...the Earth's spin in axis would wander chaotically, causing episodes of rapid climate change... ...which would be bad for life. After you have a habitable world, you need abiogenesis. The creation of life from non-life. The basic building blocks of life aren't
unique to Earth. Amino acids have been found in comets and complex organic molecules in interstellar dust clouds... ...and water in exoplanetary systems. The ingredients are there, we just don't know how they combine to create life. The development of technological civilisation is the third checkbox. And even with intelligent creatures that still might not be that easy. There are a few other clever species on our own planet... ...dolphins, whales, elephants and octopuses are among them. And yet, despite the huge variety of life
on Earth, only one species has developed... ...lasers, the internet and this YouTube channel. Like and subscribe! The final check box is colonisation and
communication across space. And despite what you might think, it's not just a technological hurdle. Aliens might choose to remain quiet for a number of reasons. For example, it might just be deemed to just be too dangerous to contact other worlds... ...for the risk of coming across a more advanced and hostile species. According to The Great Filter hypothesis, at least one of these checkboxes must be improbable. Otherwise, surely, we'd some evidence of life elsewhere in the galaxy. But, no-one knows which checkboxes are easy, and which ones are hard. We can only hope that the hard ones are the ones we've already overcome... ...or the future for human colonisation of the galaxy might be bleak. It looks like it might be really, REALLY
hard for intelligent, space-faring civilisations to arise. So, is it conceivable that, maybe, in fact we're alone in the universe. I mean what are the chances of our moon being just the right size, at just the right distance. A Goldilocks moon around a Goldilocks planet. When you look at our existence in this level of detail, it's incredible that any of us are here at all. And, you can take this idea even further. Instead of their just being a few
checkboxes for life to tick... ...imagine if there were lots more. More hurdles for life to overcome. And just as a thought experiment, imagine if there was a 1 in 1000 chance of overcoming each one of those hurdles. So, if the galaxy contains a trillion planets... ...how many would host a civilisation with a technology similar to our own? First checkbox habitability. The right sort of planet around the right sort of star. A trillion potential planets in the galaxy becomes a billion. Then stability. A climate that stays benign for eons. That billionth becomes a million. Next up, abiogenesis. Life has to start. A million planets in the galaxy becomes just a thousand. Then complex life forms
must arise. That thousand becomes just one. Sophisticated tool use must develop.
That's one planet in a thousand galaxies Then the development of Science and
Mathematics. That's one planet in a million galaxies. to reach the stars
they'll have to be social creatures capable of discussing abstract concepts using complex grammar. That's one planet in a billion galaxies. Oh, and then they have to avoid disaster. And not just self-inflicted, but also from events like meteor strikes too. And now that's just one planet in a trillion galaxies. Just as we currently see in the visible universe. Us. Humans. But if we ever do come into contact with aliens, I don't think we're gonna be seeing any little green ones or any big skinny grey ones either. Or anything called organic at all. Space is so unimaginably huge that traversing in the search of other civilisations... ...would most likely take far longer than any alien's lifetime. So, in the same way that we send probes to the outer reaches of our solar system... ...I think it makes more sense that if we ever encounter aliens, they'll actually take the form of machines. Like cosmic robotic ambassadors. These advanced, self-replicating, artificial
intelligences would probably be nothing like... ...the robots and AI that we know today. Or anything that we can even dream up in science fiction. As Arthur C. Clarke once said... "any sufficiently advanced technology would be indistinguishable from magic". And, once they found us, it might be that these robots don't report back to their creators. There might not be anyone to report back to. They could be the legacy of a failed alien civilisation, and, for whatever reasons... ...that might be the fate of many civilisations in the universe, even our own. One day in the future there may be other barriers that are just too difficult for us to overcome... ... and if that day does arrive, then the robots that we've sent out into the cosmos.. ...maybe the only evidence that we ever existed. So, I don't buy the 'Rare Earth' theory that we're all alone. I think there must be others out there. And, it's actually that thought that kind of troubles me, because it's the point at which fact... ...inevitably brushes with faith. You see, you can do all the fancy maths that you like to estimate how much life is out there in the universe... ...but, until we actually find some, it's kind of just down to, well, believing. And, although I don't agree
with much when it comes to religion... ... the one thing that we do share, is the belief that we're not alone. Get away from me you BITCH! Sorry about that. I just noticed you'd left your door open. Yes David! Yes. Cuppa tea? Yes. Coming right up. Hey! Thanks for watching! It's a big experiment for me this one. It's the first time that I've tried to mix a short film with a science video... ...and I really enjoyed making it and I really
want to make more videos like this... ...so I really hope you guys liked it!? Before I go I want to say some big thank yous. Firstly to my camera operator and director of photography, Phil Beastall... ...who's helped me out on a bunch of videos for this channel. A big thank you to Richard Bertenshaw who was the assistant camera on this film. I've never worked with him before but oh my god, Rich, I'll work with you again. That sounded a bit sexual! Maybe I'll take that bit out!? Big thank you to my friend Joe Simkins and Nicky Burgess and Carrick Smithen-?-?-? Mathason??? Sorry Carrick. I can never remember your
surname. It's kind of double-barrelled and crazy posh. Um, but yeah - thank you so much
guys for helping out on the shoot it was a really long one! And finally, a huge thank you to the Vlogbrothers. Yes, John and Hank green. So, basically, if you didn't know, Vlogbrother put all their money that they get from their advertising... ...they put it all into a pot, and at the end of the year that money gets divided up between... ...educational YouYubers like myself. So, I was really lucky this year to get a little piece of that pot. I can't...I was... I was just blown away, I
can't even talk! Thank you guys, hope you watch this video. Um, I know it's a long one and you guys are so busy so probably not. Ahhhh man. Ok, well that's it. Um I think I've got an eyelash on my face. Hopefully not there for the whole video. Thanks. Bye.
