00:00If alien life exists, then it's a good bet that some of it, even most of it, will be considerably more advanced than us.
00:08It's also highly likely that some of it, even most of it, won't be friendly.
00:13To make it in the universe, many believe that any species would need to be ruthless and cunning.
00:19That intelligence alone won't be enough.
00:22The dark forest theory offers one route to survival.
00:26But is it the right route to take?
00:31In fiction, and often in real life, forests are seen as mysterious places.
00:37As shadowy and intimidating worlds, full of beauty but also fear and doubt.
00:42And sometimes monsters.
00:44There's the mystical Old Forest in The Lord of the Rings, the aptly named Forbidden Forest in the Harry Potter books,
00:49and there are countless examples used in horror movies.
00:52Such as in The Blair Witch Project, which is mostly set in the woods.
00:56It's so often a case, then, of trees, trees everywhere, but still no place to hide.
01:01The dark forest theory takes this idea and applies it to the universe as a whole.
01:06We're not still talking trees here.
01:08But we are still thinking about vast, unknowable and potentially dangerous landscapes,
01:12this time stretching from star to star and planet to planet.
01:16The theory first appeared under its current guise in the 2008 novel, The Dark Forest,
01:20by the award-winning sci-fi writer Liu Shixin.
01:23And it offers one solution to that most depressing of scientific predicaments, the Fermi Paradox.
01:28The Fermi Paradox was first posed by the physicist Enrico Fermi in the 1950s.
01:33It highlights the contradiction between the number of alien civilizations we expect there to be in the universe
01:38and the number we've actually found evidence of.
01:40Based on various estimates, we expect there to be thousands of alien species.
01:45But, based on various studies, we've found none of them.
01:48Zero.
01:49Not a single otherworldly being anywhere.
01:51So, what gives?
01:52Well, according to the dark forest theory, fear gives.
01:55And caution is the key.
01:57And whenever any advanced enough civilization moves through space, it does so slowly,
02:02and it's ready to defend itself at a moment's notice.
02:05Imagine, again, that you find yourself travelling through an unknown stretch of woodland.
02:09Imagine, if you like, that you're a hobbit walking past trees that legend says might be enchanted.
02:14You might feel exposed?
02:16Or apprehensive?
02:17Or ready to turn back around and head in the opposite direction?
02:20The dark forest theory suggests that this is similar to how intelligent enough extraterrestrials feel, too.
02:26And that's why we've never heard or seen anything from them.
02:29Because they simply don't want to make themselves known.
02:32They tread super-carefully through space,
02:34shuffling through the leaves and branches of the cosmos, hoping never to attract the attention of anything else.
02:39In many ways, it goes against most stereotypical science fiction.
02:43The Hollywood storylines usually involve aliens that aren't exactly shy to reveal themselves.
02:48They come, they see, they capture and destroy everything in their path.
02:52But isn't all guns blazing mothership really the best way to go about conquering galaxies?
02:56Wouldn't the lights and sounds and signatures of something like that actually render you a sitting duck to anybody else looking in?
03:02The dark forest theory says that any alien civilization seriously hoping to survive doesn't want to be quite so loud.
03:09But that doesn't mean that the dark forest is safe.
03:12It certainly isn't.
03:13Mostly because of that other key aspect to it.
03:16Survival.
03:17Survival at all costs.
03:19To exist in this universe, any alien civilization has to be prepared and able to swiftly eliminate any other civilization that they encounter.
03:27It's kill or be killed in this particular version of the cosmos.
03:30So, while a dark forest civilization tries its best to avoid detection, first of all, it's also ruthless.
03:36And it presumably carries instant, existence-ending superweapons, too.
03:40Which, when you think about it, is a pretty frightening prospect.
03:43It means that any alien civilization that's clever enough to succeed in the dark forest, A, is invisible, and B, could kill us all at any time.
03:51Any time like now.
03:53Or now.
03:54Or now.
03:55Hopefully we're all at least still here for the next part of this video, though.
03:59Because what does this all mean for humans and life on Earth?
04:02And should we more seriously consider the dark forest theory as we move forward with space travel?
04:07For some, we really should.
04:09In the twenty-first century, Earth is a noisier planet than ever before.
04:12For any alien species that's passing through the Milky Way, this green and blue marble, this world that's three worlds away from the sun and in the habitable zone,
04:21is emitting various signals to let everyone know that we're here.
04:24That we exist.
04:25So, why not drop by to visit sometime, and annihilate us all while you're at it?
04:29Sure, that's a somewhat irrational and inflated conclusion to reach, but it is true that we are making ourselves more and more noticeable.
04:36First off, to some degree, there's the oxygen.
04:39Earth's oxygen levels are high, and continually refilled by all the plant life that covers our planet.
