Why Humanity Will Never Leave The Solar System

At a glance

Kurzgesagt has spent a decade making videos in which humanity spreads across the galaxy, and this one takes that future away. The argument is not that interstellar travel is hard engineering. It is that a barrier made of distance, dust and disappointing destinations sits between us and everything else, and that the barrier is built out of fundamental physics rather than out of a missing invention. The video builds the case in three moves, each one a floor we fall through after thinking we had found solid ground.

First, scale. Take the fastest object humans have ever built, the Parker Solar Probe at 635,000 km/h, imagine a crewed ship that fast, and watch the itinerary: Mars in two weeks, Pluto in a year, past Voyager 2 in four, and then the true edge of the solar system, the outer boundary of the Oort cloud, in 2,500 years. Second, speed as its own trap. Grant the optimistic assumption that fusion or antimatter gets a ship to 20% of the speed of light, and space stops being empty: a single iron atom carves a damage track, a grain of dust detonates like a grenade, and a golf ball sized rock arrives with more than double the energy of the Hiroshima bomb. Third, destinations. Even at 20% of light speed, a realistic 40 year one way trip reaches only 8 light years, and our stellar neighborhood, a 25 light year bubble holding 34 stars and 6 brown dwarfs, contains almost nothing worth 40 years in a box.

The conclusion is deliberately uncomfortable and applies to aliens as well as to us. There may be millions of civilizations out there, all of them locked in the same way. The video's last move is to undercut its own certainty with a story: in October 1903 the New York Times published an editorial confidently predicting that powered flight was one to ten million years away, and 69 days later the Wright brothers flew. Kurzgesagt says out loud that they hope this video ages exactly that badly.

The claim, stated flatly

The video opens without warmup. You will never leave the solar system. Nobody alive today will. And maybe no human ever.

Then it widens the claim past our species. This is not a story about human technology being immature, or about political will, or about funding. Kurzgesagt asserts that we are locked in by an invisible barrier, one that is impossible to overcome for carbon based animals like us, and that we are almost certainly not alone in being locked in. There may be millions of alien civilizations in the universe, and none of them may ever venture into deep space in a meaningful way.

The channel is explicit that this contradicts its own back catalogue. They have made countless videos imagining the exploration of the galaxy and beyond as a question of time, sort of mandatory for civilizations at a certain point, something a species does once it is grown up enough. The catch, they say, is that we are pushing up against fundamental physics. Not against engineering difficulty, not against cost, but against the shape of reality.

So the question the video sets itself is precise: what is this barrier, made of dust and nothingness, and why is it so hard to overcome?

Part one: you do not understand how large space is (and neither do they)

The first section title is a confession as much as a claim. Conceptualizing the size of space is impossible for our ape brains, which evolved to understand distances like "right here" and "over the next hill". Space is so absurdly huge that we simply check out and hear "very far". The failure mode Kurzgesagt names is the important one: "very far" and "a million times very far" feel identical inside a human head, and they are not. Every intuition you have about interstellar travel is built on that broken feeling.

The fix they choose is to stop talking about distance and start talking about speed, because speed is the thing that actually converts distance into time, which is the only unit a human life is measured in.

The two speed records that matter

The fastest a human being has ever traveled is 40,000 km/h, achieved by astronauts returning from the Moon in 1969. That is the ceiling for meat. Every human who has ever lived has gone slower than that.

The fastest thing humans have ever built, by a very large margin, is the Parker Solar Probe. Kurzgesagt is careful to describe how it gets its speed, because the mechanism matters: the probe uses what they call a physics cheatcode, hurling itself around the gravity well of Venus, using each pass to accelerate and get closer to the Sun. After seven years of doing this, the probe is shooting through space at 635,000 km/h.

They make that number tangible in two ways, both of which are worth keeping. At 635,000 km/h you could go around the world in 4 minutes. You could cover the distance from Earth to the Moon in 36 minutes. That is not a rounding error above the human record. It is roughly sixteen times faster than any person has ever moved.

So the video builds a fantasy ship: something as fast as the Parker Solar Probe, with a human crew aboard, ready to explore the universe. No new physics required, just an engineering miracle that packages the fastest speed we have already achieved into a crewed vessel.

The itinerary that starts great and ends in the Roman Republic

The tour begins well. Current rockets need seven to ten months to reach Mars. The new ship covers the distance in two weeks. That is a genuine transformation of the inner solar system, the difference between an expedition and a commute.

Next stop, Pluto, reached after about a year. Longer than you hoped, but still inside the span of a normal human deployment. Two more years gets you past the heliopause, the boundary where the Sun's outward wind of charged particles finally loses its argument with interstellar space. One more year after that and you pass Voyager 2, a probe that traveled for over 50 years to get that far. Four years of flight to overtake half a century of coasting. Great.

Then the real edge of the solar system: the outer boundary of the Oort cloud, the diffuse shell of icy bodies that marks where the Sun's gravitational grip finally gives out and open space begins.

We reach it in 2,500 years.

The video lets the number sit there. Oh. Oh no. And then it delivers the comparison that makes 2,500 years mean something: that is the amount of time it took to get from the founding of the Roman Republic to the present day. Every empire, every language, every book, the entire recorded arc of Western civilization, spent aboard one ship. And when you arrive, there is nothing out there.

The zoom out problem

Kurzgesagt names the psychological trap directly, and it is the single most portable idea in the video. Space tends to work like this: there is a place that is very far away, but with human ingenuity and billions of dollars we can get there. Then you zoom out one more time and all hope leaves your body.

And the punchline is that we have barely started zooming out. The Oort cloud is not a distant landmark. It is the front door.

Part two: why not just go faster?

The obvious objection gets an immediate, honest answer. We do not know of a non magic way to travel faster than light, to teleport, or to freeze people. No warp drive, not for now, not on any timeline anyone can point to.

But the video refuses to argue against a strawman. Instead of stopping at "we cannot go faster", it grants the optimist the best case that physics actually permits. Propulsion systems that use nuclear fusion or antimatter, powerful enough to reach a substantial fraction of the speed of light, are in the realm of the physically possible. Ignoring the technical details and the various problems those energy sources have, Kurzgesagt makes what they call a reasonable and very optimistic assumption: a spaceship flying at around 20% the speed of light.

That number deserves to be felt rather than read. 20% of light speed is 60,000 kilometers per second. It is 216 million kilometers per hour. It is roughly 340 times faster than the Parker Solar Probe, which itself is sixteen times faster than any human has ever moved.

And it works. The itinerary transforms completely:

• The edge of the solar system (the heliopause) in 3.5 days.
• The outer edge of the Oort cloud in eight years, down from 2,500.
• Alpha Centauri, the closest star system to our own, in 20 years.

Twenty years is a long time but it is not a civilizational project. It is one career, one shift, one crew that leaves young and arrives middle aged. Kurzgesagt's own verdict on this ship is two words: we can work with that.

A word about the sponsor break

The video's transition into its ad read is one of its better jokes and it is part of the structure, so it belongs in the rebuild. Having just declared the 20% light speed ship workable, the narrator says there is only one small problem: we do not have internet. Wait, what? Just kidding. The sponsor is Saily, the eSIM app from the makers of NordVPN, offering data plans across more than 200 destinations, plus an app based phone number for calls and SMS that stays the same wherever you go, with the code "kurzgesagt" for 15% off a first data package. The narrator signs off from the ad by promising to go back to solving the trickier travel problems, and does.

Part three: space hates you, and the barrier is made of dust

Here is the first thing that only becomes a problem once you are moving. Space is very empty, but it is not actually empty. There are energetic particles, gas, dust, and things bigger than dust.

The video states the underlying principle in the plainest possible terms: as a lot of unhappy people experience every day, if you are going really fast and smash into something, you have a huge problem. What changes at relativistic speed is what counts as "something".

The ladder of things that will kill you

An individual iron atom. At 20% of light speed, a single iron atom striking the hull carries enough energy to carve a damage track tenths of a millimeter deep. One atom. Over the course of a voyage the hull would be riddled with microscopic bullet holes, which, as the narrator understates it, is not great.

The engineers anticipated this, of course. The ship gets a shield: a sort of protective sail out in front that absorbs, or at least slows down, most of the molecules it smashes into. This makes the journey much safer. It does not make it safe, because there are things floating around out there that are larger than atoms.

A grain of dust. Running into a single grain of dust at 20% the speed of light is like running into a grenade. The dust explosively evaporates on contact, a tiny detonation, and each one grinds away a piece of the protective shield. The shield is consumable. Every hour of flight spends some of it.

A rock the size of a golf ball. Hitting that at 20% the speed of light releases more than double the energy of the nuclear bomb dropped over Hiroshima. The video declines to discuss anything larger, which is the correct editorial decision, because there is nothing left to say. Atoms, dust and pebbles are dangerous enough.

Why this is a speed limit and not an engineering task

This is the part of the argument that is easy to miss. Kurzgesagt is not saying that relativistic dust impacts are a hard problem to be solved with better materials. They are saying we might have reached our natural speed limit right here, and the reason is the shape of the curve rather than the height of any one obstacle.

Two things stack. First, we do not have a good idea how we could possibly fly any faster than 20% of light speed in the first place. Second, and worse, all the damaging effects of hitting things floating around in the void get much worse fast as speed rises. The kinetic energy of an impact scales with the square of velocity in the everyday regime and climbs faster still as you approach light speed, so every increment of speed you buy costs you disproportionately more shielding. The faster you go, the more expensive the next increment of speed becomes, and the expense is not linear. That is what a natural limit looks like from the inside.

Having said all that, the video is fair. It concludes this section by granting that with enough shielding, our ship should probably be able to survive traveling at roughly 20% the speed of light long enough to reach at least nearby stars in a reasonable amount of time. The dust does not stop us. It caps us. And then comes the third problem, which is the one that actually breaks the dream.

Part four: almost everything in space that is close is super lame

The first proper target outside the solar system is the Alpha Centauri system. Roughly 10,000 years away with the original, slow, more realistic Parker speed ship. Only 20 years with the fast fictional one.

So the video does it. It crams a few unlucky humans into a tiny box for 20 years, sends them on their way, and assumes they somehow make it without murdering each other.

Four years after their arrival, the message reaches Earth. People around the globe gather together and hold their breath. And what they get is one of the funniest and bleakest things Kurzgesagt has written:

"We arrived! Alpha Centauri and its planets are very pretty up close! Unfortunately they are all super deadly and uninhabitable. But we are doing extremely cool astrophysics and are learning a LOT, which is pretty exciting! We are getting kind of tired of freeze dried food and desperately need new shows to watch though. Not sure what we were thinking coming here…"

That is the whole third argument compressed into a postcard. The mission succeeded. The science is real. Nobody would do it again.

The scientific case versus the human case

Kurzgesagt is careful here, and the carefulness matters because it is what keeps the video from being cynical. Close destinations being lame is not a scientific judgment. From a scientific perspective it would be an absolute dream to have the privilege to set foot on foreign planets and marvel at the wonders of our universe. The problem is not that there is nothing to learn. The problem is the ratio between what you learn and what you spend.

And what you spend is specific: dozens of years in a tiny box, traveling through one of the deadliest environments imaginable, one way. The video's framing is that none of the targets remotely within range, within a human lifetime, may be worth that.

The 8 light year bubble

Then comes the arithmetic that defines the reachable universe. If 20% of the speed of light is our speed limit, and we give humans a realistic travel time of, say, 40 years, then we can reach things up to 8 light years away. That is the sphere. That is what a human being can physically get to, granting every optimistic assumption the video has already made.

Kurzgesagt adds one geographic note that is easy to skip and worth keeping: our solar system is a bit unlucky in that regard, because we sit in a relatively empty pocket of the galaxy. This is not a permanent condition. It might change in a few million years as we move through the galaxy, and there might be small, localized star spanning civilizations in denser regions, a possibility they say they discussed in another video. But it is our condition now, and "wait a few million years for the neighborhood to improve" is not a plan.

What is actually in the neighborhood

The video then generously widens the circle past what humans can reach, to the entire stellar neighborhood: a sphere about 25 light years in diameter. That is 0.02% of the Milky Way.

Inside that bubble:

• 34 stars and 6 brown dwarfs.
• Only three stars similar to the Sun. One of those three is the Sun. Another is Alpha Centauri A. So the neighborhood contains exactly one other Sun like star that is not already accounted for.
• The rest are mostly red dwarfs, with planets that the video ranks on a scale from deadly to super deadly.

The habitable zone is not a promise

There are a few planets in the habitable zones of their stars, the orbital band where water can be liquid. Kurzgesagt punctures that phrase immediately with the most effective possible counterexample: Mars is also in the habitable zone of the Sun, and it is really bad.

Even the planets we currently think look most like Earth come with no guarantees. The video names GJ 1061 d specifically, one of the more promising temperate worlds around a nearby red dwarf, and then delivers the line that carries the emotional weight of the entire section: imagine traveling your entire life and then arriving at a Mars. What a brutal letdown that would be.

This is the real trap, and it is not physical. You cannot know before you go. The instrument that would tell you whether a world is worth a lifetime is not obviously easier to build than the ship.

The good targets are behind an even worse wall

The video does not claim the universe is uniformly disappointing. There are a few stars that would be genuinely interesting targets and may have actual habitable planets: worlds with oceans and breathable atmospheres, which would probably mean they carry some form of microbial life, if not more. Kurzgesagt is unambiguous that it would be extremely interesting and definitely worth it to check those out.

But they could be dozens, if not thousands, of light years away. Which means journeys of hundreds or thousands of years even at a large fraction of the speed of light. The good destinations exist. They just sit on the far side of the same wall, and the wall does not care that the prize behind it got better.

The escape hatches, taken seriously

To its credit the video spends its last analytical minute steelmanning the optimistic case rather than dismissing it. It grants that a future humanity, technologically far more advanced than us and very motivated, could conceivably find solutions:

• Solve biological aging. If people do not die on schedule, a travel time of a few hundred years may stop seeming unreasonable. The trip does not get shorter, the traveler gets longer.
• Send AI spaceships carrying embryos, or some version of that. Take the humans out of the box and the box gets much easier to build, because most of what makes a crewed starship hard is the crew.
• Build far better telescopes. This one is the quiet key. With good enough instruments you would never again send a 40 year mission to a system that turns out to be deadly and empty. You would know before you launched. It converts the gamble into a choice.

And then the honest limit on all three: it is still hard to imagine, without real science fiction technology, how such a humanity could build and sustain a connected civilization. You might scatter. You might even scatter successfully. But light speed still governs every conversation, so the pieces would not be able to stay one thing. Spreading is not the same as expanding.

Conclusion: the greatest challenge humanity will ever face

Kurzgesagt closes with a summary that reads like a verdict. The longer you think about deep space, the less it makes sense. The distances are too vast. There is a deadly speed limit. And even if we could solve those two, almost all the destinations remotely reachable may not be worth the trip.

Their framing of what that means is generous rather than defeatist: space is the greatest challenge humanity will ever face. Right now we are just not equipped or able to solve it. And the inventory of what is not enough is deliberately brutal. Rockets, computers, and even nuclear fusion reactors are hopelessly underpowered. Fusion, the thing we have been chasing for seventy years as the answer to everything, appears here in the list of things that do not clear the bar.

What would clear it is something they describe rather than name: technology that is overwhelmingly transformative. Something as wild to us as flying to the Moon would have been to a hunter gatherer. Note the structure of that analogy carefully. The hunter gatherer is not missing a component. They are missing metallurgy, chemistry, calculus, thermodynamics, electronics and the concept of an institution that outlives a person. The gap Kurzgesagt is pointing at is that kind of gap, not a better engine.

Will we ever get there? Their answer is two words long and it is the honest one: we genuinely do not know.

The New York Times, 1903

Then the video does something most doom arguments never do. It hands you the weapon to use against it.

There are few things, the narrator says, that make you look dumber than predicting the future of technology. In 1903 the New York Times published an editorial titled "Flying Machines Which Do Not Fly", confidently predicting that it would take humans one to ten million years to achieve powered flight.

69 days later, the first successful flight happened. 66 years after that, humans landed on the Moon.

Kurzgesagt's closing wish is explicit: they really hope this video will seem as dumb as that article in a hundred years.

The other option: maybe the direction is wrong

The final beat is a teaser, and it is more interesting than a teaser needs to be. There is another option entirely: maybe our thinking about all of this is just completely wrong. Maybe the future is not out there, but deep down.

They do not elaborate, promising to explore it in another video. But the shape of the suggestion is clear enough. If the barrier is real and physical, then a civilization's growth curve cannot keep pointing outward, and the alternative direction is inward: into simulation, into computation, into the very small, into whatever a species does when the sky turns out to be a ceiling. It reframes the entire video from a tragedy into a redirection, and it is the reason the ending does not feel like a funeral.

The video signs off with the shop pitch that funds it: the limited edition Vanishing Stars pin, part of the Cosmic Time Collection, an animated lenticular pin showing the stars dying one by one until everything is swallowed by darkness, in an edition of 10,000 individually numbered pieces. The framing they attach to it is on theme rather than incidental: wear it as a reminder that you exist right now, in a brief and extraordinary moment in cosmic time when the universe is still filled with stars and light and there is so much left to discover. They also point at the Cosmic Milestones poster collection covering the first Moon landing, the Mars rover Curiosity, and Wilson Observatory, described as things humanity has already achieved while still confined to a tiny corner of the cosmos.

Where it stands: checking the numbers

The video is a scripted argument built on real figures, so it is worth doing the arithmetic yourself. It holds up better than most videos of this shape, and where it rounds, it rounds in a defensible direction.

• 40,000 km/h human speed record. Real, and the record belongs to Apollo 10 in May 1969, which hit about 39,900 km/h on reentry. The video says "returning from the Moon in 1969", which is exactly right and slightly more precise than most people assume.
• 635,000 km/h for the Parker Solar Probe. A genuine published figure from its perihelion passes. Worth noting that the probe has since gone faster still on later close approaches, widely reported at roughly 690,000 km/h, so the number is conservative rather than inflated.
• 3.5 days to the edge of the solar system at 20% c. Work it out: 3.5 days at 59,958 km/s is about 1.81 x 10^10 km, which is roughly 121 astronomical units. That is almost exactly where Voyager 1 crossed the heliopause. The number is not a vibe, it is the real boundary.
• 2,500 years to the Oort cloud's outer edge at 635,000 km/h. That implies an outer edge around 1.5 light years out, which sits at the far end of the standard estimate range (roughly 0.5 to 1.5 light years, or up to about 100,000 astronomical units). The video takes the generous outer boundary, which makes the number a ceiling rather than a typical case.
• A golf ball sized rock at 20% c. Take a golf ball sized rock at ordinary rock density, roughly 120 grams, and the relativistic kinetic energy comes out near 2.3 x 10^14 joules, or about 54 kilotons. Hiroshima was about 15 kilotons. So "more than double" is not hyperbole, it is an understatement by roughly a factor of two.
• "0.02% of the Milky Way." This one reads as a comparison of widths rather than volumes: a 25 light year bubble against a galaxy roughly 100,000 light years across is 0.025% by diameter. By volume the fraction is unimaginably smaller, which only strengthens the point being made.

The place where reasonable people disagree with the video is not the physics but the framing of "worth it". Kurzgesagt evaluates destinations against a single human life spent in a box, which is the correct frame for the question they asked. Change the frame to generation ships, to a species that has solved aging, or to uncrewed probes with no return requirement, and the arithmetic reads differently even though not one physical number changes. The video knows this: that is what the escape hatches section is for, and it is why the last minute is spent handing you a 1903 newspaper.

Key takeaways

• The barrier is not a technology gap in the usual sense. It is distance, a hard speed limit imposed by relativistic collisions, and a shortage of destinations worth reaching. All three would have to fall.
• Distance is not the biggest number, the zoom out is. Reaching Pluto in a year and reaching the Oort cloud in 2,500 years are the same trip separated by one change of scale, and that is the pattern space follows every time.
• The fastest thing humanity has ever built, the Parker Solar Probe at 635,000 km/h, is not slow. It is 16 times faster than any human has traveled, and it is still roughly 2,500 years from the edge of the solar system.
• Optimism about propulsion does not solve the problem, it just relocates it. Grant 20% of light speed, a genuinely optimistic fusion or antimatter assumption, and the Oort cloud drops from 2,500 years to eight, and Alpha Centauri to twenty. Then two new problems appear.
• At 20% of light speed empty space becomes ammunition. A single iron atom carves a damage track tenths of a millimeter deep, a dust grain hits like a grenade and eats your shield, and a golf ball sized rock delivers more than double the Hiroshima yield. Shielding is a consumable, not a solution.
• The impact problem is a speed limit rather than an obstacle, because the damage escalates faster than the speed does. Every increment of speed costs disproportionately more protection.
• A realistic 40 year one way trip at 20% of light speed reaches 8 light years. That sphere is the entire physically accessible universe for a human being under the video's assumptions.
• The 25 light year stellar neighborhood holds 34 stars and 6 brown dwarfs, only three of them Sun like, and one of those three is our own Sun while another is Alpha Centauri A. The rest are mostly red dwarfs with planets ranked deadly to super deadly.
• Being in the habitable zone means almost nothing. Mars is in the Sun's habitable zone. The best nearby candidates, GJ 1061 d among them, carry no guarantees, and you cannot know before you spend a lifetime finding out.
• The genuinely interesting worlds, ones with oceans and breathable air and probably microbial life, may be dozens to thousands of light years away, which puts them behind the same wall regardless of how good the prize is.
• Even the escape hatches (solved aging, AI ships carrying embryos, vastly better telescopes) leave the hardest problem untouched: light speed makes a connected interstellar civilization almost impossible to sustain.
• Rockets, computers and even nuclear fusion reactors are, in the video's words, hopelessly underpowered. What is needed is something as wild to us as a Moon landing would be to a hunter gatherer.
• The video ends by arguing against itself. The New York Times predicted powered flight was one to ten million years away, and was wrong 69 days later. Kurzgesagt says it hopes to be that wrong.
• The teased alternative reframes everything: maybe the future is not out there but deep down.

Chapters

• 0:00 The claim: you will never leave the solar system, and neither will any alien
• 0:47 You do not understand how large space is (we do not either)
• 1:05 Speed records: 40,000 km/h for humans, 635,000 km/h for the Parker Solar Probe
• 1:50 The itinerary: Mars in two weeks, Pluto in a year, the Oort cloud in 2,500
• 2:50 The zoom out problem, and the fact that we have barely started
• 3:10 Why not just go faster? Fusion, antimatter, and 20% of the speed of light
• 3:45 What 20% of light speed buys: 3.5 days, eight years, twenty years
• 4:06 Sponsor break: Saily eSIM
• 5:22 Space hates you: the barrier of dust
• 5:50 One iron atom, one grain of dust, one golf ball sized rock
• 6:50 Why this is a natural speed limit rather than an engineering task
• 7:28 Almost everything in space that is close is super lame
• 8:20 The postcard from Alpha Centauri
• 8:50 The 8 light year bubble: what a 40 year trip can actually reach
• 9:17 The stellar neighborhood: 25 light years, 34 stars, 6 brown dwarfs
• 10:00 Habitable zone is not a promise: Mars, GJ 1061 d, and arriving at a letdown
• 10:20 The good targets are dozens to thousands of light years away
• 10:40 The escape hatches: solved aging, embryo ships, better telescopes
• 11:20 Conclusion: the greatest challenge humanity will ever face
• 11:50 Rockets, computers and fusion are hopelessly underpowered
• 12:12 The 1903 New York Times editorial, wrong 69 days later
• 12:34 Maybe the future is not out there but deep down
• 12:43 The Vanishing Stars pin and the Cosmic Milestones posters

Notable quotes

"You will never leave the solar system. Nobody alive today will. And maybe no human ever." — Kurzgesagt, 0:02

"There may be millions of alien civilizations in the universe, none of them ever able to venture into deep space in a meaningful way." — Kurzgesagt, 0:12

"Conceptualizing the size of space is impossible for our ape brains that evolved to understand distances like 'right here' and 'over the next hill'." — Kurzgesagt, 0:50

"'Very far' and 'a million times very far' feels the same but it is not." — Kurzgesagt, 1:00

"The next stop is the end of the Oort cloud, the true edge of the solar system where open space begins! We reach it in… 2,500 years. Oh. Oh no." — Kurzgesagt, 2:28

"Not only did we travel for the amount of time it took to get from the founding of the Roman Republic to the present day, there is NOTHING out here." — Kurzgesagt, 2:40

"There is a place that is very far away but with human ingenuity and billions of dollars we can get there! Then you zoom out one more time and all hope leaves your body." — Kurzgesagt, 2:55

"Well we don't know of a non-magic way to travel faster than light, teleport or freeze people. So no warp drive for now." — Kurzgesagt, 3:12

"As a lot of unhappy people experience every day, if you are going really fast and smash into something, you have a huge problem." — Kurzgesagt, 5:35

"An individual iron atom that hits your spaceship at this speed has enough energy to carve a damage track tenths of a millimeter deep." — Kurzgesagt, 5:52

"Running into a single grain of dust at 20% the speed of light is like running into a grenade." — Kurzgesagt, 6:15

"Hitting that at 20% the speed of light releases more than double the energy of the nuclear bomb that was dropped over Hiroshima. We'll not even talk about anything larger." — Kurzgesagt, 6:30

"So let's cram a few unlucky humans into a tiny box for 20 years and send them on their way and assume they somehow make it without murdering each other!" — Kurzgesagt, 7:45

"We arrived! Alpha Centauri and its planets are very pretty up close! Unfortunately they are all super deadly and uninhabitable. But we are doing extremely cool astrophysics and are learning a LOT, which is pretty exciting! We are getting kind of tired of freeze dried food and desperately need new shows to watch though. Not sure what we were thinking coming here…" — the crew's message home, 8:20

"But, Mars is also in the habitable zone of the Sun and it is really bad." — Kurzgesagt, 10:02

"Imagine traveling your entire life and then arriving at a Mars. What a brutal letdown that would be." — Kurzgesagt, 10:14

"The longer you think about deep space, the less it makes sense." — Kurzgesagt, 11:22

"Rockets, computers and even nuclear fusion reactors are hopelessly underpowered. We need technology that is overwhelmingly transformative. Something as wild to us as flying to the moon would have been to a hunter gatherer." — Kurzgesagt, 11:52

"There are few things that make you look dumber than predicting the future of technology." — Kurzgesagt, 12:08

"So we really hope this video will seem as dumb as this article in a hundred years." — Kurzgesagt, 12:28

"Maybe the future is not out there, but deep down." — Kurzgesagt, 12:36

Resources mentioned

The video's own sources

• Sources and further reading for this video (kurzgesagt publishes a full citation document for every video, and this is the one for "The Barrier")
• Kurzgesagt, In a Nutshell on YouTube (the channel, including the other video referenced for small, localized star spanning civilizations, which is not named on screen)

Spacecraft and missions cited

• Parker Solar Probe, NASA, the fastest object humans have built, using Venus gravity assists to reach 635,000 km/h
• Voyager 2, NASA, the probe that took over 50 years to reach the distance our fictional ship covers in four
• Apollo 10, NASA, the 1969 lunar return that set the 40,000 km/h human speed record
• Apollo 11 Moon landing, the milestone 66 years after the 1903 editorial
• Curiosity, the Mars rover, featured in the Cosmic Milestones poster collection
• Mount Wilson Observatory, the third subject in the poster collection

Places in space

• The Oort cloud, NASA, the shell of icy bodies marking the true edge of the solar system
• The heliosphere and heliopause, NASA, the boundary reached in 3.5 days at 20% of light speed
• Alpha Centauri, NASA, the closest star system and the video's first target
• GJ 1061 d, one of the most Earth like nearby candidates, and the video's example of a world that comes with no guarantees
• The circumstellar habitable zone, the orbital band where liquid water is possible, and which Mars is also in
• List of nearest stars, the census behind the 34 stars and 6 brown dwarfs figure
• Red dwarf stars, what most of the neighborhood is made of
• Brown dwarfs, the six objects that are not quite stars

Physics and propulsion

• Nuclear fusion propulsion, one of the two propulsion routes the video grants as physically possible
• Antimatter propulsion, the other
• Interstellar medium, the gas, dust and energetic particles that make space not actually empty
• Interstellar dust, the grains that hit like grenades at relativistic speed
• Atomic bombing of Hiroshima, the roughly 15 kiloton yield used as the energy benchmark

The 1903 prediction

• "Flying Machines Which Do Not Fly", The New York Times, 9 October 1903, the editorial predicting powered flight was one to ten million years away
• The Wright brothers' first flight, 17 December 1903, 69 days later

Sponsor and shop

• Saily, the eSIM service from the makers of NordVPN, sponsor of this video, code "kurzgesagt" for 15% off a first data package
• The Vanishing Stars limited edition pin, the animated lenticular pin in the Cosmic Time Collection, 10,000 individually numbered
• The kurzgesagt shop, including the Cosmic Milestones poster collection
• Kurzgesagt on Patreon, the Bird Army that funds the channel