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00:00Human beings on Earth live about 25,000 light-years away from our galactic center.
00:06Our planet speeds around the Sun at about 66,000 miles per hour.
00:11We have our own unique place in space that seemingly, by some miracle, has allowed life
00:17to thrive.
00:18Except, what if it isn't actually that miraculous at all?
00:23What if really there are many reasons why we should be, even are, surrounded by other
00:29alien life in the cosmos?
00:33Let's get straight to it with reason number one, the commonality of life in the universe.
00:40When looking at instances of life, we of course have only one sample to draw upon, life on
00:45Earth.
00:46And there are plenty of studies and theories, including the Rare Earth Hypothesis, to suggest
00:50that maybe that's all there is.
00:52But equally, and in more recent times, we've seen more and more papers published arguing
00:56that life actually could be all around.
00:59One such paper was published in May 2020 by the Columbia University astronomer David Kipping,
01:05with a key takeaway being that it's potentially nine times more likely that life is common
01:09in the universe than rare.
01:11The study models the likelihood of abiogenesis, of the emergence of life, on other planets
01:16as per what we know to have happened on Earth, and concludes that there's good reason to
01:20believe that it would happen again, on another Earth-like world.
01:24For Kipping and his team, however, the likelihood of intelligent life isn't as high, with
01:28close to a 50-50 chance.
01:31But still, the suggestion is that if there are any alien species out there, then some
01:35of them will have developed into an advanced civilization.
01:38So, what are the chances that they're close by?
01:41Reason number two as to why we could be surrounded is the growing list of potentially Earth-like
01:45exoplanets.
01:47Exoplanets are planets outside of the solar system, and charting them is actually a relatively
01:52new prospect for astronomers, with the first official detection of an exoplanet coming
01:56as late as 1992… but, as of March 2021, there are now more than 4,400 confirmed exoplanets
02:04in the sky.
02:05Meanwhile, the topmost predictions for how many there could be in the Milky Way claim
02:09that there are multiple billions of other worlds in just this galaxy.
02:13Of course, not all of those will be Earth-like… but, according to a June 2020 paper by a team
02:18at the University of British Columbia, we can estimate that one in five sun-like stars
02:23does have an Earth-like planet in its habitable zone… which amounts to around six billion
02:27celestial masses within the Milky Way that are something similar to our pale blue dot.
02:32If we then imagine that, first, life can exist somewhere other than Earth, and again reason
02:37that it's nine times as likely that it's common than not, we could estimate that something
02:42lives on at least 5.4 billion planets that aren't our own.
02:46Then, if the chances of intelligent life really did turn out to be roughly 50-50, we're
02:51talking more than two billion alien civilizations.
02:53What's important to realise, though, is that this is still just one conclusion we
02:58could reach.
02:59It still stands that, actually, we've only recorded less than 5,000 exoplanets in total…
03:05and that only a fraction of those could claim to be in a habitable zone, as we currently
03:09understand it.
03:10It also still stands that we haven't discovered even one alien lifeform so far, intelligent
03:15or not.
03:16But, a growing number of scientists and astronomers do argue that the galaxy really could be birthed,
03:21bursting with life nonetheless… it's just that we need to work out how to access
03:25it.
03:26On to reason number three as to why we're probably surrounded… time.
03:30We know that the Milky Way has been around for around 13.5 billion years, and we also
03:35know that it hasn't always been the exact same cosmic mass as it is today.
03:39It's shifted and developed over time, and indeed, the evolution of our galaxy to this
03:44precise point is one of many key reasons why we can exist right here, right now.
03:49In the search for alien life, we so often speak of habitable zones.
03:53We've already mentioned them in this very video… but we're usually contemplating
03:57them as a physical space, as a band around a star wherein a life-supporting planet could
04:02orbit.
04:03Alongside all of that, though, there are temporal habitable zones… moments in, and periods
04:08of time when conditions align to create the best chances to form life.
04:12And the interesting thing is that, according to one study, the Milky Way's optimum time
04:16for life was long ago, to the tune of 5.5 billion years back in cosmic history.
04:22A December 2020 paper by Caltech calculated that the probability of life in the Milky
04:27Way peaked around 8 billion years after it formed, and around 13,000 light-years from
04:32the galactic centre.
04:33Earth and the solar system are now almost double that, at around 25,000 light-years
04:38away from the heart of the Milky Way, and 5.5 billion years further down the timeline.
04:43We took a closer look at this study in another recent video on our channel, so check that
04:47out after this.
04:49But say there was a population boom at an earlier stage in our galaxy… then couldn't
04:53we now expect there to be various ancient civilizations dotted around us?
04:58And if they've potentially been evolving for billions of years longer than life on
05:01Earth has, then could they potentially be far, far more advanced than we are?
05:06Again, there's no way to know for sure until we encounter one… but the thought begins
05:10to make the whole of human history feel really quite small, alongside the potential for everything
05:15else.
05:16But, even though there has seemingly been time enough, there are potentially planets
05:20enough, and studies show that the likelihood is that alien life does exist somewhere…
05:25the disappointing reality remains that we still haven't discovered anything.
05:29A growing number of scientists believe that there must be extraterrestrial intelligence
05:33in the universe… and probably in our galaxy… but nobody has found it.
05:38So, reason number four why we're probably surrounded is because we're not yet advanced
05:42enough to know what's really going on.
05:45Across the many ecosystems of Earth, humans reign supreme.
05:48We've built towns and cities across most of the world map, and we've travelled to
05:52almost all Earthly locations… and yet, our successes outside of Earth's atmosphere
05:57are limited.
05:58There's no doubt that our space travel achievements thus far should be celebrated, but they still
06:03only amount to a small number of far slower-than-lightspeed machines.
06:07Only two of which, the Voyagers, have ever broken out into interstellar space.
06:12And a handful of human travellers making it onto the next closest thing to us, the moon.
06:17Our impact on the wider universe is, then, at this stage, very small.
06:21The Great Filter is an often-debated concept whenever talk of advanced civilizations comes
06:26up.
06:27It proposes that there's something, at some stage of civilization development, that puts
06:31a halt to it all.
06:32There's some kind of biological or technological hurdle that very few civilizations can pass.
06:38And that's why space appears to us to be so… silent.
06:41The next question is, has humankind already passed the Great Filter, or are we yet to
06:46encounter it?
06:47If that second scenario is true, then it could be that we're just not at the required level
06:51to engage with alien civilizations yet… and we might never be.
06:55Meanwhile, those select few alien groups who have passed the filter have steadily grown
07:00and grown all around us, despite us being naturally oblivious to them.
07:05Finally, filter or no filter, it could simply be that we haven't allowed ourselves enough
07:09of an opportunity yet, to encounter and understand any potential alien groups.
07:14In a joint-authored 2016 paper by Cornell University students Evan Salamonides and Yerban
07:19Terzian, it's argued that we could be waiting 1,500 years before any real progress is made
07:25toward first contact with aliens.
07:27The study, entitled A Probabilistic Analysis of the Fermi Paradox, reminds us that we've
07:32only truly been searching in earnest for aliens for about a century, and also predicts
07:37that less than 1% of the Milky Way has been reached in any way, by anything… which offers
07:42one explanation as to why we so far haven't crossed paths with aliens, but also opens
07:47up the possibility that there could be plenty of them out there.
07:50It's just so unlikely at this stage that we'll have clocked them, or they'll have
07:54clocked us.
07:55So, there we have it.
07:57It can be argued that it's statistically likely that aliens abound.
08:00It's becoming clearer and clearer that there are enough exoplanets in the Milky Way to
08:04host them all.
08:05According to one recent study, there's been comfortably enough time for them to have emerged
08:09in this galaxy… and the final explanation as to why we've not spotted them yet is
08:14because we're not advanced or clever enough ourselves.
08:17Or we're just too impatient.
08:19And those are four reasons why we're probably surrounded by alien civilizations.
08:24What do you think?
08:25Is there anything we missed?
08:26Let us know in the comments, check out these other clips from Unveiled, and make sure you
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