The Most Disturbing Solution to Why the Universe Is Silent

[00:00:00]On the 16th of November 1974, in the green mountains of Puerto Rico, a radio dish 1,000 [music] ft wide turned its face toward the stars and for just under 3 minutes, it screamed.

[00:00:14]The Arecibo telescope broadcast the most powerful [music] signal our species had ever deliberately aimed into space.

[00:00:21]A beam so concentrated >> [music] >> that for those few minutes at its own frequency, it briefly outshone the sun.

[00:00:29]The message had been composed by the astronomers Frank Drake and Carl Sagan.

[00:00:34]It was a simple thing. A string of just 1,679 ones and zeros.

[00:00:41]But arranged in the right grid, those bits formed a picture.

[00:00:45]They drew the figure of a human being.

[00:00:47]They drew the double helix of our DNA.

[00:00:50]They drew our solar system with the third planet nudged upward and out of line to show which of those worlds the signal had come from.

[00:00:58]It was a postcard. A greeting.

[00:01:01]A message in a bottle thrown into the cosmic ocean.

[00:01:04]And what it said was this.

[00:01:07]We are here.

[00:01:08]This is what we look like.

[00:01:10]This is where we live.

[00:01:12]It was one of the most hopeful things human beings have ever done.

[00:01:16]It may also have been one of the most dangerous.

[00:01:19]Because there is a question that has haunted scientists for more than half a century.

[00:01:24]And the most disturbing [music] answer anyone has ever offered to it suggests that sending that message was a terrible mistake.

[00:01:31]Not because no one is out there listening, but because someone might be.

[00:01:36]This is the story of why the universe is so silent and of an explanation for that silence so unsettling that some of the people who have thought about it the longest now believe we should stop calling out into the dark.

[00:01:50]It is called the dark forest.

[00:01:53]Let us begin.

[00:01:55]Start with how loud the universe ought to be.

[00:01:58]Our galaxy, the Milky Way, contains somewhere between 100 billion and 400 billion stars.

[00:02:05]Most of them, we now know, have [music] planets. And our galaxy is old, roughly 13 billion years old, which means there has been an almost unimaginable amount of time for life to appear, and to evolve, and to grow clever, and to spread.

[00:02:21]If even a tiny fraction of those billions of stars had given rise to a civilization, >> [music] >> and if even a fraction of those civilizations had lasted, then the galaxy should be crowded. The sky should be alive with signals. We should, by any reasonable accounting, be surrounded by the chatter of a thousand distant voices. [music] We have been listening for that chatter for more than 60 years, since 1960, when the astronomer Frank Drake first pointed a radio telescope at another star and waited. We have swept the sky again and again, scanning millions of stars across a vast range of frequencies, >> [music] >> straining to catch any whisper of an artificial signal.

[00:03:01]And in all that time, across all those years of listening, we have heard exactly one thing.

[00:03:07]Silence.

[00:03:09]Complete, [music] total, unbroken silence.

[00:03:13]The universe that should be full of voices says nothing at all.

[00:03:17]This is the puzzle that the physicist Enrico Fermi famously put into a single question over lunch one day.

[00:03:23]If the universe should be teeming with life, >> [music] >> then where is everybody?

[00:03:28]And over the decades, we have told ourselves a number of comforting answers.

[00:03:33]Perhaps life is far rarer than we think, and we truly are alone.

[00:03:38]Perhaps intelligence almost never arises, or almost never survives its own technology for long.

[00:03:44]Perhaps the distances are simply too great, and everyone is too far away to hear.

[00:03:49]These are the answers we prefer, because each of them lets the universe remain a safe and empty place with nothing in the dark but rock and gas and light.

[00:03:59]Notice what all of those comforting answers have in common.

[00:04:03]Every one [music] of them treats the silence as good news or at least as harmless news.

[00:04:08]If we are alone, then the universe is ours to inherit.

[00:04:12]If everyone is simply too far away, then the quiet means nothing and threatens no one.

[00:04:18]We have grown [music] used to hearing the silence of the sky as a kind of reassurance, a gentle confirmation that there is nothing out there that we need to fear.

[00:04:27]But there is no law of nature that says a quiet universe must be a safe one.

[00:04:32]What if we have been reading the silence exactly [music] backward?

[00:04:35]What if that quiet is not the absence of danger but the precise shape of it?

[00:04:40]What if the most dangerous thing a young and noisy civilization could possibly hear >> [music] >> when it points its instruments at the stars and listens is nothing at all?

[00:04:51]Because there is another answer.

[00:04:53]And this one does not assume the universe is empty.

[00:04:56]It assumes the exact opposite.

[00:04:58]It assumes the universe is full, brimming with life, crowded with civilizations far older and far wiser than our own.

[00:05:07]And it says that the silence we hear is not the silence of an empty room.

[00:05:12]It is the silence of a held breath.

[00:05:15]It is the silence of everyone hiding.

[00:05:18]Imagine the universe not as an empty ocean but as a vast forest at night.

[00:05:23]A dark forest stretching in every direction, far larger than you can see.

[00:05:29]And the forest is not empty. It is full of life.

[00:05:33]Hidden among the trees, moving without a sound, is a multitude of hunters.

[00:05:38]Every civilization that has ever survived in this forest >> [music] >> is one of those hunters, armed, careful, and utterly silent, creeping through the dark.

[00:05:49]Why silent?

[00:05:51]Because every experienced hunter in this forest has learned a single brutal lesson.

[00:05:56]The moment you make a sound, the moment you reveal where you are standing, you draw fire.

[00:06:03]Somewhere out in the blackness, another hunter you cannot see will hear you, will turn toward the noise, >> [music] >> and will eliminate you before you ever know they were there.

[00:06:13]So, the only way to survive in a dark forest is to make no sound, >> [music] >> to show no light, and to treat any other living thing you stumble upon as a threat to be removed.

[00:06:24]The forest is quiet, not because it is dead.

[00:06:27]It is quiet because everything in it that is still alive has learned to keep quiet, or has already been killed for failing to.

[00:06:35]That is the dark forest.

[00:06:38]And if it [music] is true, then the silence of our sky is not loneliness.

[00:06:42]It is camouflage.

[00:06:44]And we, broadcasting our location with a thousand-foot radio dish, are the one creature in the forest that has not yet learned the rule.

[00:06:53]Now, that image of the forest comes from fiction.

[00:06:55]>> [music] >> It was made famous by the Chinese novelist Liu Cixin in a celebrated science fiction novel published in 2008, where the hunter in the dark is used to explain why a universe full of life might choose to stay hidden and lethal.

[00:07:11]It is a story, but the cold logic underneath the story is not just a story, and it is taken seriously by people whose job is to think carefully about these things.

[00:07:22]As early as 1983, >> [music] >> long before that novel was written, the astrophysicist David Brin laid out the same grim possibility in a careful scientific essay on the great silence.

[00:07:33][music] He pointed out that the quiet of the cosmos might not be the quiet of absence at all.

[00:07:39]It It be the quiet of fear. [music] And he noted something chilling.

[00:07:44]It would not take a galaxy full of monsters to produce a silent sky. It might take only one.

[00:07:50]A single hostile civilization or a single fleet of self-replicating machines built to hunt and destroy could be enough to teach every other civilization in the galaxy to stay silent [music] and to keep them that way for billions of years.

[00:08:05]So, this is not merely a novelist's nightmare.

[00:08:08]It is a possibility that sits quietly and uncomfortably [music] within the real science of why we have never heard from anyone.

[00:08:16]And it raises a question that is far harder than it first appears.

[00:08:21]Why would the forest be dark in the first place?

[00:08:24]Why would civilization after civilization across billions of years and countless worlds each independently arrive at the same terrible conclusion that the right thing [music] to do is to hide and to shoot anything that doesn't?

[00:08:38]It is not because aliens would be evil.

[00:08:41]>> [music] >> That is the part most people get wrong.

[00:08:44]It is not about cruelty or malice or some dark impulse buried in the hearts of the stars.

[00:08:50]It is something far colder than that and far harder to escape.

[00:08:55]It is a chain of pure logic, step following step that any civilization anywhere, no matter how kind, no matter how wise no matter how much it longed for friends among the stars would be forced to follow to the same dreadful [music] end.

[00:09:11]To understand why the universe might be a dark forest we have to follow that chain ourselves, one link at a time.

[00:09:18]And once you see where it leads the silence overhead begins to feel very different.

[00:09:24]We want to believe that a civilization advanced enough to cross the stars would also be advanced enough to be kind.

[00:09:30][music] It is a comforting idea and a deeply human one.

[00:09:35]Surely, we tell ourselves [music] any species that survives long enough to build starships must have outgrown its aggression, must have learned cooperation, must have left war and fear behind it.

[00:09:47]Surely the truly advanced would be wise, and surely the wise would be gentle.

[00:09:53]It is a lovely thought.

[00:09:55]And it is the very first thing the logic of the dark forest takes away from you.

[00:09:59]Because the terrible power of this idea is that it does not depend on aliens being cruel at all.

[00:10:05]It works just as well, and perhaps even better, if every single civilization in the universe is good.

[00:10:12]The argument begins with two simple statements, two foundations so basic that they are difficult to argue against.

[00:10:20]The first is this.

[00:10:21]For any civilization, survival comes first.

[00:10:25]Above every other goal, every dream, every value a civilization might hold, sits the one precondition for all of them, which is the act of continuing to exist.

[00:10:35]This is not greed. [music] It is not even ambition.

[00:10:38]A civilization that is destroyed loses everything it has ever cared about in a single instant.

[00:10:44]Every song it has written, every truth it has discovered, >> [music] >> every life within it.

[00:10:50]So, survival is not merely one priority among many.

[00:10:53]It is the ground that all the other priorities are standing on.

[00:10:57]The second statement is just as plain.

[00:10:59]Civilizations grow.

[00:11:01]Life expands, populations rise, needs increase, and a thriving civilization reaches outward for more room and more resources.

[00:11:11]But the universe, for all its staggering vastness, does not hold an infinite supply of what civilizations need.

[00:11:18]Matter is finite.

[00:11:20]Usable energy is finite.

[00:11:22]The worlds worth having are finite.

[00:11:25]And so, given enough time, expansion eventually meets expansion.

[00:11:30]Growth runs into growth.

[00:11:32]What looks like endless and empty room today becomes across millions of years a quiet competition for a limited pool.

[00:11:40]On their own, those two statements are not so frightening.

[00:11:44]Plenty of things in nature grow and compete without exterminating one another.

[00:11:48]What turns ordinary competition into something far darker is a pair of additional truths.

[00:11:54]Two facts about the particular situation of civilizations separated by the immense gulf of space.

[00:12:00]The first of them is called the chain of suspicion.

[00:12:04]Imagine that two civilizations, each unaware of the other until this moment, suddenly detect one another across the void.

[00:12:11]Call them simply us and them.

[00:12:15]Now ask [music] the single most important question that exists.

[00:12:18]Are they friendly?

[00:12:20]Or are they dangerous?

[00:12:22]And here the trap springs shut.

[00:12:24]We cannot know.

[00:12:26]We can hope and we can guess.

[00:12:28]But we cannot be certain of their intentions because we cannot see inside their minds.

[00:12:34]And we share no history by which to judge them.

[00:12:37]And it runs deeper than that.

[00:12:39]Even if they happen to be perfectly friendly, we cannot know whether they believe that we are friendly.

[00:12:45]And even if they do believe we are friendly, we cannot know whether they trust that we believe they are friendly.

[00:12:51]The uncertainty folds back on itself over and over with no bottom to it.

[00:12:57]On Earth, we have a way out of this particular trap.

[00:13:00]We call it communication.

[00:13:02]Two suspicious nations can talk, can negotiate, [music] can take small risks and slowly build trust over years until the suspicion finally eases.

[00:13:12]But that escape route depends on one thing above all else.

[00:13:16]It depends on conversation back and forth in something close to real time.

[00:13:21]Across the distances between the stars, conversation in real time is impossible.

[00:13:26]If a civilization a light years away sends us a message, our reply will take 100 years to reach them, and their answer to that will take another 100 years to come back to us.

[00:13:37]A single exchange, one question and one answer, can swallow centuries whole.

[00:13:43]You cannot build trust at that speed.

[00:13:45]You cannot read an expression or hear a tone of voice or quickly take back a misunderstanding before it festers.

[00:13:52]By the time you have finished even a single sentence of the conversation, entire civilizations may have risen and crumbled to dust.

[00:14:00]The delay imposed by the speed of light does not merely slow the dialogue down.

[00:14:05]It renders the dialogue meaningless.

[00:14:08]And so the chain of suspicion, >> [music] >> which on a single shared planet can be broken through patient talk, out in the vastness of space can never be broken at all.

[00:14:18]It simply hangs there, permanent and unresolvable, stretched between every pair of civilizations in the cosmos.

[00:14:26]And then comes the second truth, >> [music] >> the one that turns a tense standoff into a death sentence.

[00:14:31]It is called [music] the technological explosion.

[00:14:35]Suppose we detect another civilization, and suppose that to our great relief, they appear to be far behind us, >> [music] >> primitive, harmless, centuries away from posing any kind of threat.

[00:14:47]Surely then we can relax. Surely we have nothing at all to fear from a people so far beneath us.

[00:14:52]But we cannot relax, and the reason is buried in our own history.

[00:14:57]Civilizations do not advance at a steady and predictable crawl. They advance in sudden, violent leaps.

[00:15:03]Look at what we ourselves did.

[00:15:05]>> [music] >> In the span of a single century, human beings went from horses and wooden sailing ships to nuclear weapons, to computers, to rockets that climb off the surface of the planet entirely. 100 years.

[00:15:17]And on the time scale of the cosmos, where civilizations may be separated by thousands or even millions of years of development. A single century [music] is less than the blink of an eye.

[00:15:28]So, when we gaze at that distant [music] primitive civilization, we are not even seeing them as they truly are.

[00:15:34]We are seeing light that left them long ago.

[00:15:37]We are looking at a ghost of their past.

[00:15:39]And in the time it would take us to reach them, that harmless little species could undergo its own explosion, leap clean past us, >> [music] >> and become something immeasurably more powerful than we are. While we went on thinking of them as no threat at all.

[00:15:53]You cannot afford to assume that anyone is harmless.

[00:15:56]The weakling you choose to spare today may be the god who annihilates you tomorrow.

[00:16:01]Now, place all of the pieces on the table at once, and look hard at the position you find yourself in.

[00:16:07]You have detected another civilization.

[00:16:10]You cannot know whether they mean you harm.

[00:16:12]You cannot speak with them long enough to find out, because the conversation would take centuries you do not have.

[00:16:18]You cannot assume they will remain weaker than you, because they might explode past you without warning.

[00:16:24]And your own survival, the survival of everyone and everything you have ever loved, depends entirely on getting this single decision right. In a universe where resources are finite, [music] and where expansion, in the end, means conflict.

[00:16:38]So, what exactly do you do?

[00:16:40]You have, when it comes down to it, >> [music] >> only two real options.

[00:16:44]You can reveal yourself and reach out in friendship, and in doing so, gamble your entire existence on the hope that this unknown civilization is kind, that it will stay kind, and that it will not simply take the location you have just handed them, and use it to erase you.

[00:17:00]Or you can stay perfectly hidden, say nothing at all, and quietly remove the threat before it has [music] the chance to grow, before it can find you, before it can tell anyone else that you are here.

[00:17:11]And here is the final turn of the logic, the part that seals the trap completely.

[00:17:17]You know that they are thinking through all of this, too.

[00:17:20]You know that they face the very same impossible choice about you.

[00:17:24]You know that even if they are gentle, even if they would never in their hearts wish you harm, they cannot afford to take the risk of trusting you any more than [music] you can afford to take the risk of trusting them.

[00:17:36]Which means that if you hesitate, if you choose patience and friendship and the benefit of the doubt, they might choose [music] to strike first, driven by the exact same fear that is now pressing on you.

[00:17:48]And so even a wholly peaceful civilization, one that wants nothing more than to live quietly and harm no one, is driven by cold and inescapable logic to the same final conclusion.

[00:18:00]The safest move, the only move that reliably keeps you alive, is to remain utterly silent and to destroy anything that reveals itself at once, >> [music] >> before it can do the very same thing to you.

[00:18:13]This is the equilibrium that the universe settles into.

[00:18:17]Every civilization that thinks the problem all the way through arrives at the same answer independently on world after world after world across billions of years.

[00:18:28]The ones who arrive at it survive.

[00:18:30]The ones who do not, the trusting ones, the open-hearted ones, the ones who called out into the dark in friendship, are found and they are silenced.

[00:18:41]Over enough time, the galaxy is [music] swept clean of the naive. And what remains is a population of cautious survivors who all obey the same two iron laws.

[00:18:51]Never reveal your position and destroy any position you happen to detect.

[00:18:56]The forest goes dark and it stays dark, not because it is [music] empty and not because the things moving within it are monsters, but because silence and the [music] first strike are the only two strategies that live long enough to matter.

[00:19:12]Sit for a moment with the worst part of it.

[00:19:15]Because this is what makes the dark forest so much more disturbing than any simple tale of evil invaders.

[00:19:20]None of it requires a single villain.

[00:19:23]There is no malice anywhere in the chain.

[00:19:25]Every civilization caught in it could be filled with beings who love their children, who make music, who dream of peace, and gaze up at the stars in exactly the same wonder we feel.

[00:19:36]It changes nothing.

[00:19:37]The logic does not run on cruelty.

[00:19:40]It runs on fear, and on uncertainty, and on the cold arithmetic of survival.

[00:19:45]And those things live inside any mind that wants to keep on existing.

[00:19:50]Kindness cannot save you from it.

[00:19:52]Wisdom cannot save you from it.

[00:19:54]A universe filled from end to end with good and gentle civilizations, handed these same rules, would still curdle into a place of hidden hunters and held [music] breath, and sudden death in the dark.

[00:20:06]That is the true horror of the idea.

[00:20:09]Not that the universe might be full of demons, but that the universe could be full of people remarkably like us, and turn out to be exactly as deadly.

[00:20:18]Now, I have to be honest with you, because honesty matters more here than fear.

[00:20:22]We do not know that any of this is true.

[00:20:25]We do not know that the universe is a dark forest.

[00:20:28]We do not know that these two axioms truly hold, or that every civilization would reason its way to the trigger, or that there is anyone out there reasoning at all.

[00:20:38]The silence overhead may yet turn out to be the simple silence of an empty cosmos.

[00:20:43]And there are serious, sober reasons to doubt the dark forest, which we will come to.

[00:20:48]But suppose, just for a moment, that the logic is sound.

[00:20:52]Suppose the forest really is filled with silent hunters who fire at any sound.

[00:20:57]If that is the universe we happen to live in, then there is one thing, above all other things, that a young and fragile civilization must never, ever do.

[00:21:06]It must never stand in the darkness and shout.

[00:21:10]It must never announce to whoever or whatever might be out there listening the exact place where it lives.

[00:21:16]And that, of course, is precisely what we have already done.

[00:21:20]Not once, but again and again, on purpose, using the most powerful transmitters we knew how to build.

[00:21:27]For 50 years and more, we have been standing up in the dark forest and calling out at the top of our lungs.

[00:21:33]The only questions left are whether anything has heard us yet and whether it is already far too late to quietly sit back down.

[00:21:42]We are the newborn species in the dark forest.

[00:21:45]As a technological civilization, we are barely a century old, a single heartbeat in the long life of the galaxy.

[00:21:51]>> [music] >> We do not know the rules.

[00:21:54]We do not even know for certain that there is a game being played at all.

[00:21:58]And for the last 50 years, using the most powerful transmitters we knew how to build, we have been doing the one thing the logic of the dark forest says a young civilization must never do.

[00:22:08]We have been announcing ourselves loudly, deliberately, and with a map.

[00:22:13]Think back to that hopeful signal from Arecibo, the postcard we sent in 1974.

[00:22:19]It did not only say, "We are here."

[00:22:21]Drawn into those 1,679 bits was a diagram of our solar system with our own planet lifted out of line to mark it.

[00:22:29]>> [music] >> The message was, in part, a set of directions, a map to our home.

[00:22:35]As it happens, that particular signal was aimed at a cluster of stars 25,000 light-years away, so far that it will not arrive for 25,000 years, >> [music] >> by which time the cluster would have drifted, and the message will sail on into empty space.

[00:22:50]As a warning to the forest, Arecibo was mostly a symbol, a gesture more for ourselves than for anyone out there.

[00:22:57]But we did not stop at symbols.

[00:22:59]In 1972 and 1973, we launched [music] the two Pioneer spacecraft and bolted to each one a small golden plaque.

[00:23:08]A few years later, the two Voyager probes set out carrying something similar, a golden record.

[00:23:14]And engraved on these was something far more precise than a friendly drawing.

[00:23:18]It was a map made of pulsars, a diagram that uses the steady rhythms of 14 of these spinning stellar beacons to mark with genuine accuracy the exact position of our sun within the galaxy.

[00:23:31]We did not just wave hello.

[00:23:33]We etched our home address into metal and we threw it out into the dark, where all four of those spacecraft are still carrying it >> [music] >> silently right now.

[00:23:43]And then, in the years that followed, we went further still.

[00:23:47]We began aiming deliberate powerful radio messages, not [music] at distant clusters tens of thousands of light-years away, but at specific nearby stars.

[00:23:56]Stars close enough that a message will actually arrive and soon.

[00:24:01]Through the late 1990s and the 2000s, a Russian scientist named Alexander Zaitsev used a powerful radar dish to beam carefully composed messages towards sun-like stars only dozens of light-years away.

[00:24:14]In 2008, a message was transmitted toward a planetary system about 20 light-years from here.

[00:24:21]And in 2017, a group called METI International sent a designed message toward Luyten's Star, a red dwarf [music] just over 12 light-years away.

[00:24:31]That message is already most of the way there.

[00:24:33]It will arrive around the year 2030.

[00:24:36]If anything at all is listening at Luyten's Star, it will know that we exist and roughly where [music] we are within just a few short years.

[00:24:45]All of this sits on top of the steady [music] accidental noise we have been leaking into space for a century, the faint spreading glow of our radio, our television, our radar, washing outward in a bubble of human signals more than a hundred light years across.

[00:25:00]By the strict rule of the dark forest, we have not whispered.

[00:25:04]We have stood up in the silent forest, >> [music] >> lit a torch over our heads, and called out our name and our address again and again and again.

[00:25:13]It is worth pausing on what a reply from the forest might actually look like if the dark forest is real and the wrong thing hears us.

[00:25:21]It would not be an invasion fleet arriving with fanfare giving us years to prepare and a chance to fight.

[00:25:27]The most efficient way to silence a noisy world is far simpler and far colder.

[00:25:32]You take an ordinary lump of matter >> [music] >> and you accelerate it to a large fraction of the speed of light and you aim it.

[00:25:39]A projectile moving that fast carries an almost unimaginable amount of energy enough to crack a planet's crust or boil away its oceans.

[00:25:48]And because it travels so close to the speed of its own light, it arrives at very nearly the same instant as the first glimpse of it.

[00:25:55]There would be no streak across the sky, no warning, no chance to launch a defense or send a final message.

[00:26:02]The light announcing our death and the thing that delivered it would reach us together.

[00:26:07]A civilization that has revealed itself in a universe that punishes such things would simply be here one moment and gone the next, never knowing what had found it.

[00:26:19]Not everyone thought this was wise.

[00:26:21]In fact, some of the most respected minds in science have looked at what we are doing and grown deeply alarmed.

[00:26:28]Chief among them was Stephen Hawking.

[00:26:31]In 2010, Hawking warned in plain and chilling language that broadcasting our existence could be a grave mistake.

[00:26:39]He pointed to our own history to explain why.

[00:26:42]When a more advanced civilization on Earth has met a less advanced one, he observed, the encounter has almost never gone well for the weaker side.

[00:26:51]The arrival of Columbus in the Americas was not good news for the people who already lived there.

[00:26:56]An advanced alien civilization, Hawking suggested, might look upon us in much the same way, as something to be pushed aside or exploited or stripped of resources.

[00:27:07]It would be far wiser, he argued, to listen quietly than to shout.

[00:27:11]He was not alone.

[00:27:13]The astrophysicist David Brin has spent years arguing that deliberately advertising our presence is reckless, a gamble with the survival of the entire species.

[00:27:22]And Brin raises a question that is, in its own way, even more unsettling than the aliens.

[00:27:28]Who, he asks, speaks for Earth?

[00:27:31]Who granted a small handful of scientists with access to a radio dish the right to announce the existence and the location of all of humanity?

[00:27:39]To broadcast on behalf of every person now alive and every person who will ever be born, without asking a single one of them?

[00:27:47]The choice to reveal our world to the cosmos may be the most consequential decision our species has ever made.

[00:27:54]And it has been made quietly, a few times over, by a few individuals, with no vote, no global debate, and no possible way to take it back.

[00:28:04]There is, of course, another side to this, and it is a serious one.

[00:28:09]Many scientists believe the fear is overblown, and they make a genuinely powerful argument.

[00:28:14]It is, they say, already far too late to hide.

[00:28:18]We have been leaking radio signals for a hundred years.

[00:28:22]Our atmosphere has carried the chemical fingerprint of life for billions of years, and the fingerprint of industry for the last two centuries.

[00:28:29]Any civilization advanced enough to cross the stars and threaten us would be more than capable of spotting a living, polluted, electrically lit world like ours from a great distance, entirely without our help.

[00:28:42]If there are hunters out there with the power to find us, then they can already find us, and our silence would protect us not at all.

[00:28:50]So, why, these scientists ask, cower in the dark?

[00:28:54]Why not try instead to join the conversation?

[00:28:58]One of the leading voices for this view, the researcher Douglas Vakoch, did more than argue the point in the abstract.

[00:29:05]His organization is the very one that sent the message to Luyten star.

[00:29:09]When the question is, who speaks for Earth?

[00:29:12]The uncomfortable answer, for the moment, is simply whoever decides to switch on the transmitter.

[00:29:18]And here I have to be as honest with you as I possibly can, because the most disturbing ideas are precisely the ones we should examine most carefully, rather than simply fear.

[00:29:28]The dark forest is a hypothesis.

[00:29:31]It is a chilling, internally consistent, and genuinely unsettling hypothesis, but it is not a proven fact about the universe, and there are good reasons to doubt it.

[00:29:42]The first reason is the simplest one.

[00:29:44]As David Brin himself pointed out decades ago, the entire grim picture can be undone by a single exception.

[00:29:52]It would take only one civilization, anywhere in cosmic history, that refused to play by the rule, that chose openness, broadcast freely, and survived, to prove that silence was never truly mandatory.

[00:30:06]The dark forest requires that every civilization, >> [music] >> without a single failure, across billions of years and countless worlds, arrive at the very same dark conclusion.

[00:30:17]One counterexample is enough to break it.

[00:30:20]The second reason cuts deeper, and it strikes at the foundation of the whole idea.

[00:30:25]The dark forest only works if the forest is genuinely dark.

[00:30:29]If civilizations really can hide from one another simply by staying quiet, but the universe may not be dark at all.

[00:30:37]Space, for all its blackness to our eyes, is remarkably transparent.

[00:30:42]A sufficiently advanced civilization would not need to wait for a radio message from us in order to find us.

[00:30:49]They could read the oxygen in our atmosphere, a signature that life has been painting across our world for billions of years.

[00:30:56]They could see the lights of our cities, the waste heat of our machines, >> [music] >> the strange industrial chemicals now drifting in our air.

[00:31:04]And if a civilization can be found simply by being alive on a planet, then hiding becomes impossible.

[00:31:10]And the cold logic of the preemptive strike begins to lose its grip. Because there was never any real safety in silence to begin with.

[00:31:18]You cannot hide in a forest that casts no shadows.

[00:31:23]There is a third crack in the logic as well.

[00:31:25]The whole argument assumes that civilizations must expand endlessly and hungrily until they are forced into conflict over a shrinking pool of resources.

[00:31:34]But that may simply not be true.

[00:31:37]A civilization advanced enough to cross between the stars might also be advanced enough to master its own growth, >> [music] >> to live comfortably within its means, to discover that it already has everything it needs without having to seize anyone else's.

[00:31:50]>> [music] >> Even here on Earth, empires have often reached a certain size and then stopped, content to hold what they had for centuries rather than conquering without end.

[00:31:59]>> [music] >> If expansion is a choice rather than an iron law of nature, then the very engine that drives the dark forest toward slaughter >> [music] >> may never start at all.

[00:32:08]So the genuinely honest truth is that we do not know.

[00:32:12]We do not know whether the universe is a dark forest, or an empty room, or a quiet neighborhood of cautious but curious neighbors.

[00:32:19]We do not know whether our shouting has doomed us >> [music] >> or meant nothing at all, or might one distant day be answered by a friend.

[00:32:27]But here is what we do know, >> [music] >> and it is enough to sit within the quiet.

[00:32:31]Whatever the universe turns out to be, we have already made our choice.

[00:32:35]And we made it before we understood the game we might be playing.

[00:32:38]The signals are gone.

[00:32:40]They are traveling outward at this very moment at the speed of [music] light in every direction. And there is no power on Earth or anywhere else that can ever call them back.

[00:32:50]The pulsar maps are leaving the solar system.

[00:32:52]The message to Luyten star is nearly at [music] its destination.

[00:32:56]The radio glow of a hundred years of human noise is already breaking over thousands of nearby stars.

[00:33:03]None of it can be undone.

[00:33:05]A single young civilization barely a century into its technological life not yet sure whether the dark holds friends or hunters or no one at all >> [music] >> has spoken on behalf of everyone who will ever live.

[00:33:18]And the words cannot be unsaid.

[00:33:20]Consider for a moment the position we are truly in.

[00:33:24]We are young [music] and we are loud and we are utterly inexperienced.

[00:33:28]A species that learned how to send signals between the stars >> [music] >> less than a single human lifetime ago.

[00:33:34]And we are doing it inside a universe that is old almost beyond comprehension.

[00:33:39]One that has had more than 13 billion years in which to [music] fill with civilizations far older, far quieter, and far wiser than we are.

[00:33:47]If any of them are out there, >> [music] >> they have known the rules of this place for longer than our planet has even existed.

[00:33:53]We are the only ones still learning them.

[00:33:56]We are like a child who has wandered into a vast dark room [music] full of strangers and hearing nothing at all has decided that the safest [music] thing to do is to call out and ask loudly whether anyone is there.

[00:34:09]Perhaps the room is empty.

[00:34:10]Or perhaps it is [music] full and everyone inside it has long since gone silent and is now turning slowly toward the sound of our small voice.

[00:34:19]>> [music] >> The strangest part of all is why we did it.

[00:34:23]We did not call out into the dark because we were foolish or careless.

[00:34:27]Though perhaps we were a little of both.

[00:34:30]We called out because we could not bear the silence.

[00:34:32]Because the loneliest thought a conscious species can hold is the thought that it might be utterly alone.

[00:34:38]And we would almost rather risk the hunters than believe that the entire vast universe holds no one but us.

[00:34:45]So we reached out.

[00:34:47]We drew a map to our small blue world.

[00:34:49]And we sent it into the night. Hoping against all caution that somewhere out there something gentle would hear it and answer.

[00:34:57]As you hear this, those first words of ours are still traveling.

[00:35:02]They are out past the nearest stars now.

[00:35:04]Moving quietly through the dark forest toward worlds that may be empty or may be listening.

[00:35:10]Or may be holding their breath.

[00:35:12]We cannot take them back.

[00:35:14]So we do the only thing that is left to us.

[00:35:17]We sit on our small, bright, exposed planet >> [music] >> and we listen.

[00:35:21]And we wait to learn which kind of universe we were born into.

[00:35:25]The forest for now is silent. [music] And we still cannot say whether that silence means that we are safe and alone. Or whether it means that something [music] somewhere out in the trees has finally heard us. And is already turning to look.