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00:00 Why are you here? Why is anyone here? And why is the universe here to begin with?
00:05 If existential questions are your kind of thing, then this is the video for you.
00:10 Today we're taking an in-depth look at the theories and philosophies seeking to answer
00:14 the greatest and deepest inquiry of all. Because ultimately, it's a dilemma,
00:20 a problem, that affects everyone and everything, across all of time and space.
00:25 This is Unveiled, and today we're answering the extraordinary question;
00:30 What is the meaning of life?
00:32 Do you need the big questions answered? Are you constantly curious? Then why not
00:37 subscribe to Unveiled for more clips like this one? And ring the bell for more thought-provoking content.
00:43 [OPENING MUSIC]
01:08 Sometimes life is beautiful, but sometimes it can seem like a drag. And for all of the
01:13 fantastic moments that they throw our way, our lives are also punctuated by tragic events,
01:18 and guided by the inevitability of suffering, ageing, and our own mortality, too. The problems
01:24 and pains that we all must endure from time to time can often lead us to wonder in our low moments,
01:29 what's the point of it all? But, as it turns out, there are lots of responses to that one crucial inquiry.
01:36 [OPENING MUSIC]
01:46 First up, the ideas of one of the most famous philosophers of all time, Plato. For Plato,
01:52 the ultimate goal of any life worth living is to obtain the highest form of knowledge possible.
01:57 This word "form" is important here. Plato believed in the existence of universal forms,
02:02 which are ideas or concepts in their purest, most abstract state. These forms do not exist in the
02:08 real world, but rather in a kind of spiritual realm. And accessing that realm is to pursue
02:14 the meaning of life. Plato's forms could be anything, from beauty to squareness to blueness
02:19 and so on. A particularly important form, however, is that of goodness. And for Plato, the purpose of
02:25 all of our lives is to try to obtain the highest possible understanding of the good. A different
02:30 philosopher, Antisthenes, took a different approach, though, one which emphasised virtuous
02:35 action as opposed to knowledge. This school is known as cynicism. And to a cynic, the purpose
02:40 of life is to distinguish between wholesome and unwholesome values. Do so, and it's believed that
02:45 one can live a happy life in accordance with nature. To be a cynic, you must reject unvirtuous
02:51 desires such as fame, possessions, power, and wealth… as these things will never bring you
02:56 the peace that true happiness needs. Get rid of fame, possessions, power, and wealth, and you
03:01 free yourself from unhealthy mental baggage in favour of leading a pure life. Serenaicism offers
03:07 a vastly different approach, however. It's a smaller school coming out of Ancient Greece,
03:11 but it advocates most of what cynicism denies. Serenaics believe that the most sensible course
03:16 of action for each individual in their individual life is to constantly seek short-term gratification,
03:22 including things like money, material goods, and physical experiences… even if doing so means
03:27 sacrificing their long-term interests. In stark contradiction to followers of Plato, too,
03:32 Serenaics are sceptical of the value of knowledge. Instead, they exclusively trust in their immediate
03:38 perceptual awareness. Again valuing short-term pleasure over long-term gain, they see the
03:43 meaning of life as being clearest when we trust our innate instincts about what we want, right now.
03:49 They don't delay, they don't second-guess themselves, they just go for it. To flip the debate
03:53 again, the school of Epicureanism takes an often opposite approach, despite also valuing the
03:58 pursuit of pleasure. For its founder Epicurus, the ultimate goal in life is to maximise long-term
04:04 pleasure, and you do that by minimising pain and fear. With most humans wanting to be free from
04:09 pain and fear, this should perhaps be one of the more straightforward worldviews out there. But,
04:14 of course, inconsistencies arise by the fact that different humans find different things
04:18 pleasurable and painful. There doesn't appear to be one right answer here, but Epicurus generally
04:23 believed that the pursuit of mental pleasures is more meaningful than chasing the physical ones,
04:27 because physical is usually short-term gratification, whereas mental can often
04:31 result in long-term wellness. Next, there's Nihilism, a famously pessimistic philosophical
04:37 movement, it would seem, which refuses to believe in any kind of objective meaning to existence.
04:43 And claims that all value systems are baseless. Nihilists view other philosophies as just
04:48 desperate attempts to find meaning in what's really an unforgiving and meaningless world.
04:54 With that said, there are some Nihilists with at least a little optimism. Many, for example,
04:58 refuse to let the meaninglessness of everything get them down. And so they develop a more heroic
05:04 mindset that strives to preserve their own happiness, in spite of the lack of meaning.
05:09 Others go one step further, to emphasize the positive side of the lack of meaning itself.
05:13 Namely, that if everything is meaningless, then that takes the sting out of all of the
05:18 apparently negative aspects of life, too, such as fear, humiliation, and guilt. Because if,
05:23 in the end, nothing really matters, then all of those things that we worry about on a daily basis
05:28 don't matter, either. There's also Absurdism, which could be considered a branch of Nihilism,
05:33 put forward by, amongst others, the French writer Albert Camus. The "absurd" part here
05:38 is directly referring to the contradiction between an individual's innate desire to find a meaning
05:44 to life, and the impossibility of doing that in an ultimately meaningless universe. This leads
05:50 to an unavoidable dissatisfaction with pretty much everything. But one solution is again to simply
05:55 accept the absurdity of life, and to live it regardless, without any identifiable reason
06:01 for doing so. But the final philosophy we'll examine today is something of a meeting point
06:06 for many philosophies. Existentialism holds free will as the most important value in life.
06:11 Existentialists, therefore, believe in the uniqueness of all individuals, and generally
06:16 deny that it's even possible to prescribe a one-size-fits-all rulebook or meaning for everyone.
06:22 From cynicism to nihilism, no one idea could ever solve all of life's big questions. Instead,
06:28 for existentialists, it's the individual's responsibility to seek their own meaning.
06:33 And this can be found in a variety of places. The existential dread we sometimes feel is then
06:39 not an indication that life is pointless, but rather a motivation to seek our own truth,
06:44 and to discover for ourselves why we are here. To finish, however, we know that most religions
06:50 offer their own take on the meaning of life, too. And there are some common themes. The major,
06:54 monotheistic religions, for example, preach that a single god created the world, and that it's our
06:59 duty to submit to this god in order to lead a good life. The specifics of what we should and
07:04 shouldn't do often differ from religion to religion, though. In Christianity, for example,
07:09 the purpose of life is to seek salvation through the grace of God… with most denominations implying
07:13 that all people are sinners by nature, but that all can be forgiven for their sins by following
07:18 the Christian teachings. Islam also refers to life as it being a kind of test, although it places
07:23 more emphasis on service to God, with the purpose of life being to know and worship God.
07:28 Generally speaking, Eastern religions differ in a number of ways, with one common theme being
07:34 that the universe, and therefore our existence in Eastern faiths, has a cyclical nature. In Hinduism,
07:40 for example, it's believed that human beings have an immortal soul that's reincarnated after death.
07:45 The purpose of our existence, then, is to gain liberation from the concept of karma,
07:50 which is the idea that all of our actions have future consequences, even if those consequences
07:55 don't occur until a future reincarnation. Worship of gods, moral action, and enjoyment of life are
08:01 worthy pursuits in Hinduism, too, but the meaning of life is more about arriving at a higher level
08:06 of existence, beyond the cycles and structures that bind us. Buddhism also refers to higher
08:12 levels of being, but never really concerns itself with directly answering the question of existence.
08:17 Nor does it especially claim to understand how the world was created. Buddhism, instead,
08:22 emphasizes the impermanence of all aspects of our lives, and suggests that all human suffering
08:27 comes from our tendency to cling to things that can't last. While there's no explicit meaning or
08:32 purpose to life here, Buddhists do still follow a path - the path to enlightenment, or nirvana,
08:38 a state of being in which suffering has been eliminated. Meanwhile, Daoists also seek a
08:43 similar inner peace by trying to follow the Tao, or the Way, which is the perceived natural order
08:49 of the universe. You follow the Tao by trusting your intuitive knowledge about how to proceed
08:54 through life toward wisdom. We've briefly covered a wide range of philosophies and ideas today,
09:00 and we can already see how links can be made across almost all of them. Life is certainly
09:04 complicated, then, and people have always and will always see through different lenses.
09:09 Whether or not there's truly any meaning to existence may not be a question we can ever
09:14 definitely answer… but which of these modes of thought most resonates with you?
09:19 Do you ever contemplate the universe and feel totally overwhelmed? Do you ever wonder what
09:24 difference you can make in something so unimaginably vast? Well, hold tight, because
09:28 according to one idea, it could be that actually, no one is more important than you are right now.
09:35 The Egg Theory was born via a short story written in 2009 by the US novelist Andy Weir.
09:42 Weir is also known for The Martian, which was in 2015 adapted into a Hollywood movie starring Matt
09:47 Damon. But perhaps the Egg is what will truly enshrine him in the annals of theoretical science
09:52 and the science of the universe. The story is about a man who is trying to solve a mystery
09:57 that is so complex that it's almost impossible to solve. The egg is a simple,
10:02 but powerful tool that can be used to solve a complex problem. Weir himself has expressed
10:08 some surprise at the enthusiasm shown for his egg idea, which he says took him less than an
10:12 hour to jot down before posting to an online forum. But really, in a modern world where a
10:18 meaning for life perhaps feels more and more difficult to understand, maybe it's not so
10:23 surprising that the egg should catch on. So, what actually happens in the story?
10:27 Weir's main character is known simply as "You". And quickly, you meet God, who's referred to as
10:33 "Me". What follows is essentially a conversation between you and God, then, through which the true
10:39 nature of reality is revealed. At the beginning, the bad news is that you've just died in a car
10:45 crash. God explains this to you, but also explains that you'll soon be reincarnated as somebody
10:50 different - as a young Chinese girl, alive almost 1,500 years ago. God further reveals that this
10:57 isn't your first reincarnation, either. Far from it. You've actually been brought back countless
11:02 times before, into countless different bodies, living in all earthly locations, at all times,
11:08 in the past, present, and future. You then muse over the fact that this means you were once the
11:14 likes of Abraham Lincoln, Adolf Hitler, and even Jesus Christ. While God reminds you that you've
11:20 also been everyone else, too - including Lincoln's assassin, Hitler's victims, and Jesus' followers.
11:27 God continues, explaining further that, in fact, the universe was made "for you" - as a kind of
11:33 structure through which you could live every human life possible. The realisation is that now,
11:39 and actually always, you are, or have been, so much more than just the person who died in the
11:44 car crash at the apparent beginning. Rather, you are everyone. Everyone that's been, and everyone
11:50 that will be. Essentially, the universe is for you. Finally, God explains what the thinking
11:56 behind all of this is. The idea is that through being everyone, you would learn that everything
12:02 you do, you do to yourself. Every time you hurt someone, you hurt yourself. Every time you help
12:08 someone, you help yourself. Every time you've been kind or mean, happy or sad, selfish or selfless,
12:15 you're actually being all of those things, as everyone. Every human experience that ever was,
12:21 or will be, is your experience. And, when you've lived every human life possible, today and in
12:27 history and in the future, then, so the story says, you will become a god just like the one
12:34 you're currently talking to. Only then will you have infinite wisdom of what it really means to
12:39 live. And so, the story ends. For the reader, there's perhaps a clear moral message here.
12:45 As it's implied that you should always try to think, act and be your best side. Not just because
12:50 it's in your best interest, but because it simply is you. Everything is you. So, would you rather
12:56 everything was good or bad? However perversely, the story also relies on the realisation that
13:02 all bad people are essentially your responsibility, too. This is a wide-open thought experiment,
13:08 then, with endless conclusions that could be reached. Meanwhile, the entire thing doubles up
13:13 as a journey toward your ultimate enlightenment, and your ascension to god status. This is how
13:19 Weir pitches the universe as an "egg", because it's where you grow and develop until you reach
13:25 that stage. There are some schools of philosophical and scientific thought that this story could fall
13:30 into… or at least that it blurs boundaries with. Eternalism is a philosophy of time wherein the
13:36 flow of time doesn't really exist. Instead of the universe, your life and everything else moving
13:41 through time, with the past behind it, the present always here, and the future to come.
13:45 Eternalism says that all of those states of time are real, together. Time is more a box to open up
13:51 and look into, rather than a one-way road down which to travel. In Weir's story, this is one of
13:56 the first major revelations for you, the main character. When you reincarnate in China 1,500
14:01 years ago, it's not exactly as if you'll have "travelled back in time". It's more like you'll
14:06 have opened the Book of Time at a different page. Next, there's the theory of open individualism,
14:12 another key concept in "the egg". Broadly, this is the idea that you are everyone, or that
14:17 everyone is you. There have been many variations to it coined over recent decades, but again,
14:23 it usually relies on the dismantling of the flow or passage of time. Time, as it's commonly
14:28 understood, doesn't really exist for the "open individual". Or how else could it be that you
14:33 could be anyone else at all? Instead, and by some understanding of it, it might be said that you,
14:39 yourself, exists like a sheen over the world, applying itself to all. Or that every apparent
14:46 individual person is, in fact, linked, simply by their shared experience of being here. It might
14:52 feel as though all of us are different, but actually, we're not, at all. At the most fundamental
14:56 layer. We're the same. Literally, the same. Theories of open individualism don't usually lead
15:03 to the final point of We're's story, however, when it's explained to you by God that once you've
15:07 lived as everyone, you too will become a god. Here, the egg takes a more theological turn,
15:13 with similar concepts appearing across most major religions, but especially in Hinduism.
15:18 While most religions have some form of "God the Creator", an all-seeing, all-powerful entity,
15:23 in Hinduism there's the Brahman. This is a kind of topmost, metaphysical layer that rests over
15:29 everything else. Including Brahma, Vishnu, and Shiva, the trinity of supreme Hindu gods.
15:35 The Brahman is unsurpassable. It's the ultimate truth of all things. It never changes, can never
15:41 be changed, and represents the ultimate reality in Hindu thought. One reading of We're's story
15:47 could perhaps cast the God figure within it as something close to the Brahman. Although the
15:52 implication is that even it exists somewhere else. So, We're doesn't quite tie up reality
15:58 in exactly the same way. But what's your verdict? Do you subscribe to the egg theory? Would you like
16:03 to, but can't quite bring yourself to accept it? Of course, it's not as though this is something
16:08 that could ever provide proof of itself. It's an idea, proposed by We're. And a blending of
16:13 various other approaches to life, as well. Similarly, there are perhaps some signs of us
16:18 building in some aspects of the egg with regard to our future lives, as we currently appreciate
16:23 them. The hive mind, for example, is an often-cited advanced technology that human society
16:29 could be moving towards. A unifying something that enables us all to think, understand, and
16:34 perhaps even feel the same things. Usually, it's pitched as though it's a path towards ultimate
16:39 efficiency. But could it also lead to a greater wisdom, and effectively fast-track us - you,
16:45 me - toward the egg's end point? Toward living every human life possible? Or, would a hive mind
16:51 actually take us further away from that total truth? When it comes to future technology like
16:57 that, it's easy to steer ourselves into an early dystopia. But really, and while interpretations
17:02 obviously differ, that's probably not the main takeaway from the egg theory. Instead, it's an
17:08 idea more about the boundless possibilities for life. And it's a re-pitching of the universe,
17:13 with you at the heart of it. But not you, you. Not exactly. Because if the egg rings true,
17:19 then you are me, and I am them, and they are us. You, me, he, she, and they are growing as one.
17:28 And there's literally all of time - in the past, present, and future - in which to do so.
17:34 The universe seems like a vast and empty place, with billions of distant stars but currently
17:43 no substantial signs of intelligent life beyond our own. But maybe there are much
17:48 deeper and more insidious reasons than we even realise for our apparent cosmic loneliness.
17:53 First off, what are the chances of alien life existing in the first place?
18:06 The Fermi Paradox, proposed by the 20th century physicist Enrico Fermi,
18:11 summarises the problem. It argues that, given the billions of stars not just in the Milky Way but
18:16 across all the universe, and the millions of Earth-like or potentially Earth-like planets
18:21 out there (many of which are much older than our own), it stands to reason that at least
18:25 some of those celestial bodies should have developed intelligent life, and even interstellar
18:29 travel. In fact, the Milky Way should have really been colonised already, a long time ago.
18:35 Clearly, though, as far as we're aware, no advanced alien race has yet to conquer the entire galaxy,
18:41 unless they're so advanced that they remain completely undetectable to all of our technologies.
18:45 According to the paradox, this either means there are no aliens at all,
18:49 or that the aliens are purposefully avoiding or hiding from us.
18:53 As such, the idea that our lives could simply be an experiment carried out by an alien race is a
18:58 solid answer to the Fermi Paradox problem. Because, if true, the alien experimenters wouldn't want to
19:03 intervene by alerting us to their existence as it would ruin the integrity of their study.
19:08 Which takes us neatly to the Zoo Hypothesis, another idea on why we seem to be alone in the
19:13 universe. The Zoo Hypothesis suggests that there are many alien civilizations out there much more
19:19 advanced than us, but that the reason they haven't declared themselves to us is that they're waiting
19:23 for us to pass a certain point in our own evolution - be that technologically, ethically or
19:28 philosophically. Only then will they make first contact so that humankind can finally integrate
19:33 into an interstellar community that we're currently unaware of. Until then, we're like caged animals
19:39 in a zoo, with our alien onlookers preferring not to cross-contaminate between their lives and ours.
19:44 While this type of well-meaning observation could very easily fit the definition of an experiment,
19:49 it's not necessarily the active and nefarious brand of alien experimentation we might expect.
19:55 The pseudoscientific Ancient Astronauts Theory claims to offer some kind of reason for what the
20:00 alien's end goal is. The theory, which by contrast isn't widely supported in academic circles,
20:06 focuses on ancient megastructures, which it says are the product of extraterrestrial intelligence.
20:11 The Pyramids of Giza, the Easter Island Statues, the Nazca Lines and Stonehenge,
20:16 all have been linked to supposed ancient astronauts at some stage. According to advocates,
20:21 these buildings and monuments are callbacks to when aliens were setting up their experiment
20:25 millennia ago; they were left here to see how we, the puny humans, would react to them.
20:31 Some versions of the theory even suggest that if we can one day solve the mysteries of places
20:35 like Stonehenge, only then will we be deemed worthy of the attention of our alien overlords.
20:41 Given that archaeologists and historians have more feasible explanations for most,
20:45 if not all, of these structures, though, it's not an idea that has ever especially taken hold.
20:51 So, failing the ancient astronaut proposal, there's the theory of panspermia, which argues
20:55 that human life on Earth is actually extraterrestrial in origin. This could mean that
21:00 we just happened to grow from far-flung materials that by sheer coincidence crashed down onto our
21:05 planet, or that aliens from the distant past purposefully sent us to Earth, once again to
21:10 begin their experiment. Otherwise known as "directed panspermia", the theory has had some
21:15 high-profile supporters, including Francis Crick and Carl Sagan. And, some recent discoveries have
21:21 continued to stoke the debate, including in 2015 when UK scientists found a microscopic,
21:27 metallic, unknown particle during an otherwise routine collection of space debris.
21:32 According to the theory, that particle was actually a seed sent to Earth to spread biological
21:37 material, and seeds like these could have been showing up for millions of years to essentially
21:41 create humanity. As for where these aliens could've come from, regardless of whether they are,
21:47 in fact, us or they aren't, a couple of relatively close possibilities have been tabled in the past.
21:53 First, there's Mars. In one of the simpler theories around, humankind is but the remnants
21:58 of an ancient Martian race that fled its home when the Red Planet became impossible to live on
22:02 billions of years ago. Elsewhere, we have the very hypothetical Planet 5, an apparently now
22:08 non-existent world which believers say was once a part of our solar system, before it disappeared
22:13 around four billion years ago amidst the late heavy bombardment. In either case, humanity are
22:18 the leftovers of an alien race that we no longer know about because it no longer exists. In this
22:23 way, our lives essentially are a long-winded alien experiment in that we're actually the
22:27 descendants of ancient creatures that hopped off of their original planet rather than perishing
22:32 with it. But those theories still bill us as the almost accidental after-effects of some sort of
22:37 ancient alien behaviour. The more disturbing interpretation of the Zoo Hypothesis has us
22:42 as the specifically chosen guinea pigs or lab rats in an ongoing study conducted by higher beings.
22:48 And, if that's the case, we have to wonder what the aliens' true intentions are.
22:52 Are they really just leaving us alone to develop at our own pace, or are they exerting some sort
22:57 of control like a real-life simulation game? Are they manipulating our world from behind the scenes,
23:02 perhaps to discover new truths about their own existences? And, if they knowingly started the
23:07 experiment, couldn't they willingly end it, too? Perhaps they'll one day decide that it isn't
23:12 going as they had hoped, or that they've collected all of the data that they need.
23:16 What would happen to us, then? Naturally, we'd never actually find out any of this,
23:21 at least not without breaking the bonds of the experiment itself… but, if our lives really
23:25 did turn out to be an alien trial, that trial would never pass even the most lenient ethics
23:30 board in our own world. With no consent agreement or any indication that we're even being studied,
23:35 no right to withdraw from an experiment we don't even know is happening, and no idea about what
23:40 will happen at the end of it because we didn't even realise it had started, we'd be in a
23:44 completely helpless situation. The best we could really hope for is that the all-powerful aliens
23:49 would at least grant us a global Q&A to bring us up to speed with our own insignificance,
23:54 once the experiment concludes. Of course, they could also just plain eliminate us and switch
23:59 focus to another planet, galaxy or universe instead. If we really are just the product
24:04 of extraterrestrial intervention, being watched, controlled and studied from the present day all
24:09 the way back to when we first crawled out of the sea, then the whole of human history could, well,
24:13 feel quite meaningless. But, if these particular theories ever proved even half-true, it'd
24:18 completely change everything we thought we knew. Perhaps the most exciting and fascinating mystery
24:27 in the universe is whether or not we're alone. For many ancient civilizations, it was believed
24:32 that Earth was at the centre of everything. Now, of course, we know that it's not, and that our
24:37 planet is but a tiny speck in the cosmos. So, we have to ask; why don't we see signs of other life
24:43 out there?
24:54 There are an extraordinary number of planets in the universe. According to most estimates,
24:59 planets should be more abundant in space than stars… which is saying something seeing as
25:04 it's thought that there are upwards of a septillion stars in just the observable universe,
25:08 just the parts we can see. As we stand, then, we haven't yet managed to study even close to one
25:14 percent of all the planets theorised to exist, simply because we're too far away from most of
25:19 them. But we have extensively studied those in our own solar system and some more beyond,
25:24 and although some planets might have possibly harboured life at some other time in their past,
25:28 we can't say for certain that any do now. Many scientists do, of course, suspect that there is
25:34 life on other planets - and probably on one or more of the two to ten billion Earth-like worlds
25:39 calculated to exist in our galaxy alone. But others argue that the circumstances which led
25:44 to life on Earth are so spectacularly unlikely that it really could be unique. Whatever your
25:49 view on it, Earth is the only planet we know of that supports life. But why exactly is that?
25:55 The oldest fossils we've found date back to around 3.5 billion years ago. We don't have a definitive
26:01 answer as to how life originally came to be here, but we do have a few theories. One idea, known as
26:06 panspermia, suggests that life didn't actually start on Earth at all but arrived here on an
26:11 asteroid from another planet. That could be the case, but the panspermia theory still doesn't
26:16 answer how life in general began. One of the most popular theories on that is the idea of a
26:21 primordial soup, or that life formed in a specific, circumstantial solution of materials which
26:27 eventually became rich in organic compounds. Life came about because these building-block
26:31 compounds just so happened to form at the right place, at the right time. It was originally said
26:36 that these ultra-early chemical reactions were energised by UV rays from the sun. Then, in the
26:42 1950s, studies including the Miller-Urey experiment moved scientific thought more toward the idea that
26:47 the soup would have had to have experienced an early universe version of something like a
26:51 lightning strike - that it was in some way electrified. More recently, in the late twentieth
26:56 and early twenty-first centuries, some have called for the traditional soup theory to be discarded
27:01 altogether, arguing instead that life most likely started deep in the sea, near hydrothermal vents;
27:06 that it was the vents which provided the energy it needed to form. Most models now have it that
27:11 life did emerge out of the oceans and onto land, but there is still debate over how it occurred in
27:16 our waters in the first place. What we do have a firmer grasp on is how the conditions on Earth
27:21 sustain life as we know it. It isn't just one feature of Earth that makes it the only planet
27:26 with life. There are dozens of small but vital aspects which come together to create the habitable
27:31 world we know. Among these are Earth's magnetic field, its atmosphere, the water cycle, and its
27:37 size. Even the conditions outside of Earth itself seem to aid our existence. Jupiter, for example,
27:43 acts as something like a bodyguard to Earth. It's positioned at just the right location in the solar
27:48 system so that its massive gravitational pull attracts most of the wayward asteroids that
27:52 might have otherwise struck our planet. Our own moon, too, is a key player in our planet's
27:57 habitability, with its gravity helping to stabilize Earth's rotation, which helps to keep the climate
28:02 steady and the conditions reliable. But there are some aspects of Earth that are so important that
28:07 scientists specifically look for evidence of them when investigating life on other planets.
28:12 Water is considered the most vital ingredient for life, and it's almost always the first thing we
28:17 search for when considering other worlds. Today, Mars has water ice, it's thought it could have
28:22 liquid water below the surface, and it's likely that the red planet had lots of water in the past.
28:27 But the only other objects in the solar system we can say with any confidence have water
28:32 are various moons, like Jupiter's Europa and Saturn's Enceladus. For this reason,
28:37 these moons are among the top contenders for harbouring alien life. So, why is water so
28:42 essential? Well, it's important for a few reasons. Water basically acts as a lubricant to facilitate
28:48 all the complex molecular chemistry that occurs on Earth. It's also considered a universal solvent,
28:53 and crucially, liquid water can transport nutrients from one place to another as well
28:58 as acting as a cleaning fluid. It's key to enabling most essential processes to happen,
29:03 so it makes quite a lot of sense that the human body should be sixty percent water.
29:07 In humans specifically, water regulates body temperature, facilitates digestion, protects
29:12 the brain and spinal cord, helps to distribute oxygen, and the list goes on. Because of its
29:17 versatility and uniqueness, it's no wonder that NASA has the strategy to "follow the water" when
29:23 searching for life. It's why determining a given planet's climate is also so crucial, to see whether
29:28 that planet experiences the right range of temperatures for liquid water to exist.
29:32 The easiest way to do this is to see if the planet you're studying is in the habitable zone
29:37 around its host star. Earth happens to be positioned inside this range of distances
29:41 out from our sun, which allows it to sustain water. If our sun were a different type of star,
29:46 however, that range would change and Earth would be a totally different, most likely totally
29:50 inhospitable place. Just being in the habitable zone isn't enough, though. By some accounts,
29:56 both Venus and Mars are in the confines of the habitable zone at certain points in their orbits,
30:01 but only one planet out of three actually has life. We also have to take into consideration
30:06 a planet's immediate atmosphere, to see what types of gases it's made out of. Venus, for example,
30:11 is just on the inner edge of the habitable zone and has some of the right conditions to maintain
30:15 liquid water on its surface, but not all. Not by a long shot. And that's because the Venusian
30:21 atmosphere is mainly carbon dioxide, meaning that, thanks to the greenhouse effect, the average
30:26 temperature skyrockets to about 462 degrees Celsius, at which point water can only exist as a
30:32 gas. By comparison, Earth happens to be the right distance from the sun, and it has a favourable
30:37 atmospheric composition to sustain liquid water. It's capable of hosting life, while Venus…
30:43 really isn't. There's one final thing, though, that most other planets don't do (or don't do as
30:48 well as Earth does) - recycle. Earth is able to recycle and reuse its resources naturally,
30:54 and in various ways. The water cycle allows water to be naturally cleansed, and the carbon cycle
30:59 allows carbon, life's primary building block, to be scattered around the surface. The acceleration
31:04 of the greenhouse effect caused by man-made pollution is one thing, but Earth's own carbon
31:08 churning processes are integral to how it works. Much of what makes Earth tick rests on tectonic
31:14 plates. The movement of whole sections of the Earth's crust helps to shift and release stored
31:18 carbon dioxide back into the atmosphere, but it also moves, redistributes and facilitates other
31:23 chemical processes all over the planet. At the highest level, it creates and destroys land;
31:28 it ensures that our planet's surface is always under development. Nothing on Earth is left to
31:33 stagnate, and everything is part of one giant, moving machine. Scientists think, then, that
31:38 tectonic plates are the major reason why Earth boasts such a vibrant and diverse terrain, from
31:43 barren deserts to vast oceans to dense jungles. And, therefore, plate tectonics could be the reason
31:49 that life has been able to survive for as long as it has - long enough for intelligent life to form.
31:54 There's strength and resilience in the variety of life, and that variety has come about because
31:59 Earth itself is constantly changing. The challenging part about drawing conclusions from
32:03 Earth is that, in the grand scheme of space, life on our planet is just one piece of data.
32:08 And it's the only piece of positive data we have so far. By studying the diversity of life as we
32:14 know it, we can better gauge its possibilities and constraints, but only from our perspective
32:18 on Earth. Perhaps life elsewhere constitutes something that's actually incomprehensible to us
32:23 in our form. It could be rare, it could be abundant… we could be right on the cusp of
32:28 discovering it, we might never discover it. It could still truly just not exist at all.
32:33 So, what's your verdict? Taking into account the various philosophical approaches,
32:39 the many religious doctrines, the growing scientific understanding, and the far-out
32:44 alternate theories including the potential guiding hand of an alien presence… why are we here? What's
32:51 the reason for all of this stuff? This universe, this world, and this life? Clearly, in searching
32:58 for the answer, there's a lot to think about.
33:01 [MUSIC]
33:25 The mystery continues. Some of the unknowns remain. But, ultimately, that's the meaning of life.
33:33 What do you think? Is there anything we missed? Let us know in the comments,
33:37 check out these other clips from Unveiled,
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