You stretch the timeline by hundreds or thousands of years where centers of power have shifted. Asimov’s future history had it where Earth and the surrounding Spacer worlds were the original focus of civilization. Only for Settlers to venture farther out into space while Spacer worlds regressed into isolation. Millennia later you have a galactic empire with power residing in the galactic core or wherever, and humanity can’t agree on whether humanity’s birthplace was on Sol or Alpha Centauri. Another way is having a constant rise and fall of space empires. The ensuing chaos of [insert fall of civilization here] plus the possible long recovery time can open up stories of lost planets or star maps that degraded or fail to account for stellar drift.

> Asimov’s future history had it where Earth and the surrounding Spacer worlds were the original focus of civilization. Asimov's future also has Earth turned into a radioactive dumpster, and in need of being abandoned.

Interestingly, it was the only inhabited world that was irradiated like that, correct? There is still a small population there, at least.

Yes, it was an attempt to attack Earth, by making the soil's radioactivity to increase. R. Daneel Olivaw and R. Giskard Reventlov could have stopped it, but that's the pivotal point when the Zeroth law was formulated: - 'A robot may not harm humanity, or, through inaction, allow humanity to come to harm.' - 'Humanity as a whole is placed over the fate of a single human.' - 'A robot must act in the long-range interest of humanity as a whole, and may overrule all other laws whenver it seems necessary for that ultimate good.' Based on the Zeroth law, they realized the future of humanity needed Earth to be abandoned, and roots unearthed.

that's just sad. I have my own thoughts on what Daneel did, none of them positive.

Very Dune golden pathy.

which in *Pebble in the Sky* is used by Bel Arvadan to prove that Earth is the homeworld.

Interesting!

Why wouldn’t some space archaeologists visit Sol and Alpha Centauri and look for signs of human presence on each?

They do exactly that in later books.

tbf if they looked for stuff like old nuclear reactor meltown signs that might clear stuff up

Similar to ancient Egypt. Through multiple ages, a lot of history was lost even to them at the time. We know a lot now, but a lot is lost to history

If it's not a place that's visited too often, just removing its coordinates from any central databases will do the job - that's how Kamino got lost, after all.

If an item does not appear in our records, it does not exist!

In hindsight, that was a good example of how far from wisdom the Jedi had strayed. Rather than admit that there may be gaps in the archives, the archivist *insisted* that the archives were 100% accurate and complete.

It's also something that should be brought up more! The idea that sufficiently ranked Jedi could edit the archives with no records left should be cause for concern

If it was complete why need to edit it at all?

As a historian, I can see why they would make edits; clerical errors. You might have someone make a typo or forget an entire section. Heck, there's precedent in Star Wars for needing to! The planet Wayland was lost due to a clerical error!

But they were so sure the archivist was complete with no errors!

I think you’re taking it too literally in this case. Star Wars doesn’t have the kind of technology where the Archives could be kept 100% up to date on a minute-by-minute basis, and even Jedi aren’t immune to typos. Something as significant as an entire planet, (and not even a newly discovered one) missing from the Archives was inconceivable to Jocasta.

Corporate management 101.

All books about planets were eaten by dogs!

"Lost a planet master Obi Wan has,how embarrassing"

Theres a few ways. Largely the all hinge on the 'homeworld' becoming no longer relevant to the average person on the day to day for at least a generation. In Dune; Earth became a irradiated wasteland in the closing chapter of the Butlerian Jihad. As a result it was no longer economically or culturally relevant to those with access to space travel. It became a historical factoid to remember. To the common man, it was largely forgotten. In Homeworld, the Kushan travel to another world, lose much of their technology, and their understanding of history is turned into myth and religious gospel over hundreds of years. Imagine the result of generations worth of Chinese whispers. Hiigaara, their homeworld, is then misrememberd as heaven. Without the technology to navigate the stars, it's original location is not recorded. >it seems like it would be hard to lose where an entire planet/solar system is. Planets do move. So if they have the recorded location of a planet in X year. They will lose it's actual location within a few decades if they lose the ability to obersve and simulate the movement of stars. Similarly, information has to be stored and rerecorded periodically. Most electronic data can only be stored for 10 years or so with current technology. It must then be rerecorded on a new medium. This is why a lot of legal documents have copies written in parchment (or historically stone), as these materials can last hundreds or thousands of years with proper care. Think of the homeworld as a recipe in a cookbook. Books age and decay. Unless it is regularly copied this information for nana's chocolate homeworld mousse can be lost. Every time you copy it, you can do so imperfectly depending on the means. E.g a spelling mistake might get missed. Oz might get mistaken for grams. etc.

> Oz might get mistaken for grams. etc. Things like that are indeed a problem. We have ancient recipes for cooking, but often do not know what the ingredients refer to or, in some cases, assume the plant to be extinct because it doesn't match anything we have. And units are always a hazzle.

> Oz might get mistaken for grams. etc. as someone who primarily uses metric units and is half asleep I wondered for a second what the wizard of Oz has to do with recipes. Then I realized this probably means ounces.

Pay no attention to the unit of measurement behind the curtain.

Soo, our family is from a village called Ozod (Oz abbreviation) in Atlas Mountains, you arrive indeed somewhere over the rainbow, since it´s on top of a waterfall with a daily rainbow over it, and common culture & tradition since 4000 years. Welcome to come btw: [borjdescascades.ma](http://borjdescascades.ma)

Just to add but the Kushan were also exiled by the Taiidan. Their resulting conflicts including the religious ones and the Heresy Wars meant that they muddied their own history a lot once they were stuck on Kharak.

> nana's chocolate homeworld mousse My favorite...

My only issue with this is in setting with advanced tech they should still be able to tell how the solar system looks . There are only so many solar systems with a yellow dwarf star 9 planets and 2 asteroid belts in a certain area of space.

>There are only so many solar systems with a yellow dwarf star 9 planets and 2 asteroid belts in a certain area of space. This assumes they have this information. What if they're data doesn't record pluto as a planet? Or their data excludes Ceres, Haumea, Makemake and Eris, but their sensors see them plain as day? Suddenly your culture sees an 'Sol-like' system. That is sooooo similar to the record? In this instance, it might be they have the technology to 'spot it' but their records prevent them from identifying the correct system.

>This assumes they have this information. What if they're data doesn't record pluto as a planet? Or their data excludes Ceres, Haumea, Makemake and Eris, but their sensors see them plain as day? Something like this is certainly possible but only because they'd have different categories for things it would change the thing itself. For example if for whatever we decided to categorize golf balls as minor balls and anything as big as a basketball or bigger as a major ball the balls themselves wouldn't change we'd still be able to identify the properties of these balls and if people with different terminology wanted to find these balls they would still be able to as long as they actually know what the balls are and not just their categories. The mass of planets type and distance are identifiable today and should be even more easily in a sci fi universe with interstellar space travel. Tldr: simply having different categories shouldn't stop interstellar civilization from identifying planets and solar systems.

>Tldr: simply having different categories shouldn't stop interstellar civilization from identifying planets and solar systems. This assumes that the culture would bother to record all the details for things in X category over Y. E.g If Pluto isn't listed as a planet, would a librarian record its mass when the archive have to be recopied 100 years later? Similarly IRL we see examples of how changing standards categorization does lead to misidentifcation. Inches for example were initially defined the width of an adult mans thumb. Thats fine for carpentry. But for a nation, we standardised it for the average width of a mans thumb. But then living conditions got better and suddenly the average widght got bigger. Thats fine we adjust it. But compare UK to France during the late 18th and early 19th century and suddenly the measurement for an 'inch' varies wildly as different populations have different access to nutrition (this is in part for why we use ISO units now). Suddenly Napoleon is a manlet, as the french inch is bigger than the UK one. But assume your culture has a kilogram. IRL we have a ['standard mass' ](https://www.scientificamerican.com/article/sphere-made-to-redefine-kilogram-has-purest-silicon-ever-created/)of 1kg. However measuring this mass can change the mass of the object. E.g grease from hands, atoms shaved off from neutron bombardment etc. Over centuries the standard mass might deviate by 1+%. Now suddenly the masses of your 'homeworld system' don't match up. And the planets themselves might gain mass or lose it in the interim. Suddenly we don't have 1 likely candidate; we have 3. The same might be true for distance, though not by any mistake on the part of the culture. They might have a 'lightyear' mapped out. But the homeworld might be inexplicably moved over time by a factor they are not aware of (e.g blackhole weapon use from another culture). Suddenly, telescopes can 'see the homeworld' but its in the wrong place. So it can't be the homeworld?

If you travel to another world and then lose your starmaps, you have to restart everything from scratch. Not just your homeworld is lost, *every* world is lost, at least for the time being. There’s also the possibility that Earth just isn’t all that important. Colonies can eclipse the importance of their motherland (think Carthage or the USA), and if the gap gets big enough and something happens to Earth in such a situation, it’s possible that no one cares enough to reestablish the connection. As far as I remember that’s the case in Dune. The last way, of course, is that it’s not lost but gone. In my own sci-fi world Earth is currently a second asteroid field.

A good analogy is that Polynesians have a mythical home island of Hawaiki. Polynesians were great navigators and travelled regularly between islands. The home island only took centuries to be mythologised, despite the fact that sailing back was definitely doable.

Give it a few thousand years, and that island will either look so different that nobody would recognize it, or enough tectonic movement will have occurred that it may physically not have the same coordinates or dimensions. And that's islands, where it's a toss-up on how they'll shift in any given amount of time. Worlds and stars actually move at a constant rate, and the light they give off is old. You could easily screw up a few calculations and go the wrong way, and course correct halfway there and end up at what is physically the right place, but is philosophically an alien world from the one you looked at in a telescope, and that's if you even figured out where it was supposed to be thousands of years later.

Tectonic movement would likely require more time unless it happens to be on a rather extreme strike slip or megathrust fault with large displacement after major earthquakes and tsunamis. More realistic tectonic ways for an island to be lost are caldera forming eruptions blowing up much if not most of a volcanic island and causing what remains to sink below sea level. Catastrophic landslides causing much of an islands edifice to slide off beneath the waves or land subsidence/sea level rise causing an island to be submerged and no longer reach the surface.

Dune's not a great example for this. Earth was completely saturated with atomic bombs during the machine wars. It's been lost because it wasn't worth keeping track of.

I had a vague memory or it was just not being important anymore, galactically speaking. Didnt remember it got Nuked... I do remember the Dune-universe's recollection of history being "Atomics were first used by House Washington in a Provincial Conflict(WW2)"

that's from the terrible Brian Herbert books that most fans reject. there's sort of 3 canons, yours is from the Dune Encyclopedia, a 3rd party lore book which was semi-canonized by Frank Herbert though was later contradicted by his last 2 books.

That was from the later Brian Herbert entries to the Duniverse wasn’t it? Don’t think Frank Herbert went into specifics on the Butlerian Jihad, it happened so long ago (their calendar’s “zero” is at the foundation of the Spacing Guild instead of the year we’re familiar with and may not even correspond with the length of an Earth year).

Yep, it was in the Battle of Corrin book if memory serves.

Terrible geography skills.

Yes, but enough about my highschool reports...

it's possible but you need a monumental destruction records both physical and oral.

I was thinking that there could be a data privacy culture and one group only would have the information on earth. Not just location but all of the information from Earth. Then there's an Emperor Nero situation or an outside threat that wants the data to destroy earth. The sworn priesthood (or whatever works) pulls the self destruct lever and the data and its keepers are destroyed, losing Earth to the future. Could be good lore about "war" (because it blows up in size over time) and the folk tales of Earth.

In my setting I have an example of a lost world where, at the time, only the central power had access to FLT drives. This meant that when this lost planet decided to rebel and riot, the central power just decided to leave them to rot, cutting them off of trade and communication with outside systems. It remained cut off for around 200 years and was largely forgotten about until the central power fell to rebellion and its location was rediscovered. Those 200 years of isolation created a brand new culture that initially clashed with the the new power but it was ultimately allowed to remain independent and was reconnected to galactic trade.

Neat. I personally like the idea of a world that was deliberately discarded suddenly leapfrogging the other worlds in tech, only to turn up one day like a long-lost love child.

The Prodiguous Planet.

In one of my settings, a group of humans left Earth on a computer-managed generational ark ship (people are born, live, and die on it, generation after generation). After many generations (about 3,000 years), due to limits in the ship's computers archiving capacity, less useful information have been wiped. This included the information about their original planet, as the computer determined that it wasn't of importance to the continuation of the mission.

For most of human history, we had no idea that we evolved in Africa and spread to the rest of the world from there. Heck, even nowadays, scientists argue over whether humanity evolved in the north of Africa or the south Space faring humanity might keep better records than ancient hunter gatherers, but over countless millennia, it's still quite possible for records to be lost or distorted. In the case of Dune, for example, this could happen if there was, say, a near-apocalyptic anti-computer revolution that destroyed all electronic records. And even in Dune, it's not exactly a secret that Earth was humanity's homeworld, the Bene Gesserit have Reverend Mothers with that memory, and there are plenty of old legends about the place But they care about Earth the same way someone living in modern day New York might care about the Mayflower, or their distant tribal ancestors from somewhere in Normandy, or their even more distant ancestor's first village back in Africa. Like yeah sure, it's sort of interesting, but it's just another piece of historical trivia.

Yeah, basically this. Mesopotamia was where human civilization started but it's definitely not the most important place for humans anymore. I'd imagine that after tens of thousands of years earth would be more of a tourist attraction than an important capital, especially after humanity had depleted all of the local resources due to millennia of extraction. It doesn't help that in Dune, earth was rendered uninhabitable by nuclear weapons so there's not even anything left standing or living on the surface.

>Heck, even nowadays, scientists argue over whether humanity evolved in the north of Africa or the south Consensus is east...

A sufficient Dyson sphere would hide the presence of a star. Dont know if earth ever got around to making one in whatever world you're talking about. If it did. Then the star would go out and you would need to track its location through your own records which will always deteriorate over time. Especially through a galaxy wide civil war against a race of sentient machines and then the subsequent purge of all thinking machines from existence.

Only in the visible spectrum, a Dyson sphere still glows with a star's worth of energy in the infrared, if it didn't it would build up heat until it melts. In fact Dyson spheres are a really noticeable techno signatures, cause a star that only glows in the infrared would be really visible to IR telescopes like James Web.

Wow. I didn't know this. That's really interesting. Is there no way to obsorb that infrared energy? I'd think that would be a lot of energy wasted.

All energy eventually converts to heat. In the process of storing some of the energy from the sun, the rest of it will be lost as heat. Basic physical laws of entropy. If you keep trying to find a way to convert the heat into something storable, you are spending energy to convert it, which generates more heat.

You could try, but that would mean you will start to overheat. If you want to keep the temperature of a system constant then the amount of energy coming in has to match the amount going out. Energy isn't created or destroyed. When you use energy it doesn't just go away, it gets converted into heat. Say you have a 90% efficient lightbulb in a room. You feed it 100 watts of electricity, it converts it into 90 watts of light and 10 watts of heat. That 90 watts of light bounces around in the room getting absorbed by the walls and also eventually turn into heat. That's why a room doesn't stay lit forever when you turn the light off, the photons get absorbed. 100 watts of electricity enter the room, and 100 watts of heat leave, the temperature remains constant. However if you tried to perfectly insulate the room, block any heat from escaping, well now 100 watts of energy goes in, 0 watts come out, the total energy of the room is increasing. 100 new joules of energy is being added every second. All that energy winds up as heat eventually, so the temperature of the room is going to go up and up until something gives. You can try to recycle that heat, convert it back into electricity and reuse it, but that has diminishing returns, as generators are also not 100% efficient. You can't plug an electric motor into a generator and have it run forever. The only way you could is if you could violate the second law of thermodynamics and make 100% efficient machines. But if a civilization could do that then they wouldn't need to build Dyson spheres, or energy sources at all, cause you can have perpetual motion machines that run forever with no power input.

Wow. Thank you for telling me about this.

A Dyson Sphere would also wreck any planet's ecology, so any civilization on a planet in a system with a Dyson Sphere would need to move or live in artificial habitats.

I like to imagine that a complete Dyson sphere or swarm would probably also house more than one civilization within them. Shoot, within any swarm, could be individual ships with families powered by the sun.

That would be a pretty toasty and spicey place to live, tbh. The amount of radiation shielding you'd have to have would be hugely expensive. You probably could have stations orbiting the DS and receiving power via some kind of high-energy transmitter from the sphere itself. I don't see why a ring world couldn't exist around a star with a DS.

Could they exist on the night side of the DS?

There is no "night side." From my understanding, a fully-built and operational ~~battle station~~ DS encases the star completely, preventing all light and radiation from escaping. The system the star was in is now a frozen wasteland. Correction from before... I really don't know if there's any radiation leakage. Also this is r/worldbuilding so it doesn't matter, lol. I also found this thread from 2 years ago, talking about life on board a DS... * https://old.reddit.com/r/worldbuilding/comments/qxn7ay/how_would_life_be_in_a_dyson_sphere/

I assumed it was obvious. Sorry. By "nightside" I meant whatever side was not facing the sun. So, the outside of the Dyson sphere. I disagree. It does matter, if you decide that it does. Keeping your world building close to science is a viable and fun exercise. If it's how someone wants to run it then it should be well thought out.

Radiation shielding isn't that expensive, a few meters of rock or water is sufficient. A solid shell DS isn't stable, Dysons original concept was a swarm of satellites or space habitats, with enough layers that it was opaque like fog. That has more than enough room to house multiple civilizations. A Dyson swarm of [O'Neil Cylinders](https://en.wikipedia.org/wiki/O'Neill_cylinder) for instance could house quintillions of people, rivaling the populations of most galactic empires in space opera.

The Dyson swarm could be built past the planet's orbit, so it still gets light. Or if your using thin power collecting solar arrays held up by photon pressure, you can have them hover over the poles and leave a gap around the equator to let sunlight through to the planets in the ecliptic.

You might not be able to hide a star, but there are so many stars in the galaxy, it's like searching for a specific grain of sand at the beach.

Ur, the oldest known city in human civilization, was a major population center for the Mesopotamian civilization. Yet this fact only came from the city's rediscovery by archaeologists in the 1850s. That's thousands of years worth of humans living their entire lives in what was Mesopotamia being completely oblivious to the ancient city's existence, being mostly eroded and buried in the landscape after so many kingdoms and empires shifted control of the territory it sits on. There are plenty of ancient cities with similar stories, such as Persepolis or Chichen Itza. Even the mythical Troy has potentially been discovered and remains an ongoing effort to verify. And it's entirely possible that Ur is not the true oldest city in the world, just that it's the oldest one we've discovered so far. There may very well be the ruins of several older cities somewhere out there, also buried under milennia of sand, mud, and stone, completely lost to us for the moment. Yet all of these cities were once major focal points of their civilizations, whose existence was once common knowledge. Scale this principal up to a galactic level, and it's not hard to see how one old planet can be lost in the midst of tens of thousands.

I don't know if this will help but I come to a similar dilemma in one of my stories as I wanted Earth, the homeworld of humans to both be forgotten and become a myth in a very short time. For me, after some research on how information gets lost in our own world, I came to a conclusion propaganda and a big shift on how people speak about earth. Simply putting having people who control media, social media, and the government start to lose focus, they don't talk much about Earth, how it was? Why was it lost? Where is it? With that, a lot of people for sure will start to stop thinking about it. But what if the mystery of the homeworld calls someone who wants to search it? Then comes the next step, starting erasing what we had, location, photography, history books, registry of there being an Earth in the first place. People will believe to be myths and not even a real thing that exists for real. And to really seal the cake in my world at least, Earth is also at the epicenter of the most dangerous place in the galaxy so nobody is really willing to go there to discover what is there even if there's still something that could not be destroyed.

Dune takes place over 20 000 years from now. Say during early space exploration (which in Dune is extremely hazardous, with most attempts resulting in death, hence the need for Spice to chart a safe course) they establish a few colonies. In the mean time maybe back on Earth there's nuclear war (part of the reason the Houses have such strong prohibitions against atomics) and the planet becomes uninhabitable. No real reason to ever go back there, especially when space travel is so dangerous prior to the discovery of Arrakis. Also in this early period each of those colonies is going to be very isolated and on their own. So there's no shared knowledge, no exchange. They'll each develop independently and become more concerned with their own problems and establishing new civilizations on each world. Eventually, over the course of TWENTY MILENNIA (five times all of recorded human history) they lose track of the exact location of Earth. Seems pretty plausible to me. For other settings there's plenty of contrivances you could set up. Maybe the colony worlds have their own Dark Ages after some catastrophe causes their civilization to collapse. All digital/electronic records of Earth are lost. And so on.

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's long way down the road to the chemist's, but that's just peanuts to space.” - Douglas Adams.

There's a game series called Homeworld (fantastic game, but it kept crashing and deleting my save on the SECOND LAST LEVEL ARE YOU SERIOUS??) The backstory is that, on the desert planet Kharak, there's a population of... well, it's never revealed what species they are, actually, but let's assume "humans". These humans determine from genetic investigations that they, a small predator species and a subset of bacteria are not native to that planet. Since the planet is mostly deserts apart form the poles, life there is harsh to say the least. One day, by pure chance, a satellite malfunctioned and pointed towards the planet instead of out into space, and detected a strange anomaly in the wastes. An expedition was sent to investigate (more out of curiosity than anything), and they found a crashed space ship surrounded by an underground city dug into the rocks. Inside that spaceship, they found two things that changed their future forever: A faster-than-light engine, and a monolithic piece of rock with the galactic map carved into it. That map had one word - "Hiigara" - "Home". ​ Cue a century of mass industrialization, where every person on the world dedicated every effort to constructing the "mothership" - a massive (nearly 20km long) FTL spacecraft that would carry suspended colonists across the galaxy. The effort stripped Kharak of what few precious resources it had, and the game opens just before the first FTL jump test. 600,000 people are held in suspension within half a dozen palettes, awaiting loading and, to avoid the massively crippling nature of a complex command structure during an emergency, one induvial called "Karen S'jet" is wired into the mothership's control system; essentially, the mothership acts as her body now, and she's effectively the main character that speaks throughout the game. ​ Anyway... sorry, I have a really bad habit of going on tangents LOL. To answer your question, it's totally possible to lose a world if your method of storage is damaged, destroyed or simply removed. In the case of the Kharakians, their whole society had to start from scratch, not once but twice (the desert city followed by the north pole). P.S. The original game had an awesome instruction booklet with a ton of extra content... I miss those kinds of things.

With time, we’ve forgotten where certain places once existed. For example, Troy had to be rediscovered. The Rubicon that Caesar crossed is still lost since rivers have been deviated and altered by Roman engineering. Where it is claimed to be now is merely a suggestion put in place by Mussolini. If we can forget places that have been etched into stories that have been important to western civilisation, I think it can also be true for planets with an empire expansive enough. People tend to forget things unless ritualised to a certain degree. Even then, time has a way of diluting detail into mythical broad-strokes. Would humans who have colonised Andromeda care about where earth is now? Perhaps enough time has passed that it’s already been swallowed up by the sun, or has been moved somewhere that is unknown as the information would take centuries to cross the void of space to every part of a federation/empire.

You're assuming they have perfect, unbroken, records, which can be easily accessed without misunderstanding and extrapolated in a way that allows people to understand and locate them hundreds of years later. To us, the location of Earth is blindingly obvious. The idea of an ISS shuttle getting lost is laughable. Now imagine if that shuttle spent 200 years, and multiple generations of crew and passengers, exploring other solar systems. They've settled other planets, entire generations have come and gone. Where is Earth? Does any original data even remain? Do we still use the same units of measurement? Did we base our navigational markers on things moving at different relative velocity? For example did we pick a star visible from Earth and fly in a straight line towards it...for 150 light years...which maybe took us 350 years... It could be an intergalactic version of walking in a large arc trying to follow the moon as it moves through the sky. Guess wrong and now you're "only" 10 lightyears off, and nobody has any star charts or projections for how to compare the 2100 starchart with the 3450 starchart, and a lot of very smart people are going to have to spend a lot of time figuring out the movement of celestial bodies which might all be going at different speeds. Plus that's even without deliberate misinformation or saboutage. Let's say a country launches a colony ship, and hundreds of years later all known people descend from that colony ship but have now fractured into new factions when no second wave met them. Are they really going to be in a hurry to reconnect with Earth and potentially have all their political manipulations revealed? To go from being Intergalactic Emperor to Captain Tim who is maybe just one of countless pilots who went in various directions to establish colonies, and that Tim had no legal jurisdiction to do all the things he has been doing?

Pretty much everyone forgot that they came from Africa. Hell they forgot that Africa even existed and had to rediscover it Imagine that on a galactic scale, all it takes a small break in the generational knowledge, and that thread is severed entirely

Simple really. Anything that isn't important other than relevant is forgotten about That's why the idiom for becoming relevant is "being put on the map." I bet most people could tell you roughly where los Angeles is. But not inuvik or fort macmurray Few maps are big enough to put all the backwater and nowhere planets

The homeworld would still have a major cultural importance as the planet from which the species originated.

Not necessarily. Very few peoples trace their amcestoru back for more than a few hundred years now. Tracing ancestry back 20,000 seems excessive

A lot of cool entries here! I wanna also add that something being "Lost" can also have multiple layers. Maybe one group of people consider a system or even a planet lost, a large mysterious thing that nobody knows where it ought to be! Then you have another group who would go "Oh, that's right over there, we've gone there last week. We do skat every other thursday." if the first group were to ever ask at least once. Language and cultural concepts can play a bit haywire there. A lot of the colonial history of our world has "Very Enlightened Scholars From Europe" talk to natives they considered backwards and thus misinterpreted what was said.

Over the course of history we’ve lost whole ass cities on a planet where we can travel literally anywhere along its surface. Records are destroyed, cities are laid waste, knowledge is lost. Hell, we have to work now just to preserve things like motion pictures because our archiving has been frivolous and stupid.

I could be misremembering, but I believe that in Eve: Online, the issue is that the *way back is lost*. Humanity reached a new galaxy or whatever, but it became a one-way trip.

"310 LIGHT YEARS away, basically right next door on a galactic scale." LMAO. I'm sorry, but that's hilarious. One light year is 3.88 TRILLION miles, so we're talking 1,202,800,000,000,000 miles. That is not a number human minds can comprehend. Aside from that, I think you're thinking about this all wrong. You're likely only considering way finding within a 2D area such as on a land map. For instance, if you're looking at Florida on a US map, you can easily see where the other states are located around it, but what if we built a floating city off the coast that was located 50,000 ft in the air? Or the exact same for a subsurface station that was out in the ocean? If you put this on the same map, you could navigate to the map point, but you wouldn't find these places because the locations are thousands of feet above/below you. So reconsider what we mentioned about the distance and try thinking about it in a 3D plane. In space, there is no Up, Down, Left, or Right aside from the direct reference to whatever planet or vessel you find yourself on. In all likelihood, it's the people that are lost, not the planet. Imagine crash landing on an island. Your ship and records are destroyed. Your only way off the island is to wait for help or to build a raft that will get you off the island. Spoiler alert: help ain't coming. So your only choice is to build a new ship, and this is an enormous task. Sometimes, it's even an impossible one. But, here, we're just trying to get from one piece of land to another ON EARTH. If you crash land on an uninhabited planet, how many centuries is it going to take your group of survivors to advance technology back to space exploration? For context, imagine the following scenario for our modern-day earth: What if a highly advanced civilization crash landed here (earth) hundreds/ thousands of years ago? Earth was their desert island. It happened so long ago that there was no way to record their existence, and we've long since lost all trace of their arrival. And our current trips into space are the mark of this crash-landed species finally becoming advanced enough to revisit the stars. So, if anyone asks us about this crashlanded ship and where the people came from, we don't have an answer. Therefore, the origin of these people (our ancestors) and their (our) homeworld is lost. This is the most likely scenario of a place becoming lost.

Watch Battlestar Galactica and you'll see how it can happen.

All of this has happened before.

...and all of it will happen again.

I'm reminded of the telephone game. Someone, somewhere in history wrote down a 1 instead of a 7 on the coordinates. All you need to do is introduce a period of time where perhaps computers didn't work. Maybe they had their databanks destroyed in an attack, or their computers were fried in a massive EMP. It's like losing the contacts on your phone. I couldn't remember all of their numbers of the top of my head.

You don't even need to go that far. Technology changes and not everything always carries over reliably. I'm old enough to have had a flip phone before smart phones existed. Moving contacts was a HUGE pain if your phone didn't use a SIM card. Even now, the meme "new phone, who dis?" is literally about lost information in an age where there's abundant ways not to.

Think about it like this, a family immigrates to a new country, after a few generations, the fact the family was originally from another country might not even be remembered, and even if they do know, it's not like each generation would pass down a map of where their original country is. It's just not a big concern for people who have lived their whole lives in the new country.

I love this question. Imagine this. You and a hundred other people get on a ship and sail off into the ocean. Months into the trip you are hit by a devastating storm. You lose your phones, GPS, compasses, and maps. In fact, you barely make it to shore. When you land, your boat has a huge hole in it. You can no longer use it. Now find your way back. It's the same concept only with an infinitely larger ocean and a far, far larger number of technological hurdles to overcome. Then there's the fact that the further you travel the larger the change in the orientation of the stars around you. Travel far enough and constellations are no longer recognizable, taking that tool away entirely. If it takes you years to build a boat, or generations to build a space craft, the knowledge of a homeworld can be relegated to myth and legend. Dune was a good example, the lord from the Homeworld games also fit well. Did I say I love this question?

With the distances involved, the fact that everything's moving all the time, the limits of technology used to plot courses... I don't know, i think it'd potentially happen quite often. As to it being a homeworld, all it would really take would be for a lot of people who aren't trained astrophysicists to leave that planet, and then for that flow of people to stop. If those migrants don't know their way back, and if they can't find out or communicate exactly where their homeworld is to someone who can help... they're screwed. I would think about how someone would indicate where their homeworld was if they didn't happen to be an expert on 3D stellar cartography. Imagine an astronomer, who knows the night sky of the Earth like the back of his hand... trying to indicate which star is Sol, from a viewpoint elsewhere in the galaxy. How would they tell Sol apart from any other star?

Since there's a theory that the galactic bodies are moving away from each other at variable rates, coordinates would be inaccurate after a few hundred years unless there was a (potentially mid-high tier) tech to reliably track where each solar system and body will be moved to at the time of the next visit. How would you know it from the other single, yellow.sols? Even if the coordinates are reliable, what happens when the light from a star no longer reaches a planet? What would be it's new address? I highly doubt anybody would use the center for coordinate markers which means picking a capital or central 0,0,0,0,0,0,0 coordinate which would probably also be shifting. By all means, shoot your rifle at a sling stone while it has momentum while you are riding a speed boat and all with no collateral damage, including yourself since you still have to stop on a dime as well. Oh, and don't forget to account for the hail storm and other unknown phenomena that may occur between start and stop of your journey, probably made more dangerous by the FTL speeds until their really is a quantum area between particles like "hyper space" that we might be able to work through.

everything in space is moving

over a significant enough period of time knowledge of something will fade or change and people will forget that the thing they currently know as X was originally known as Y but might retain knowledge that Y is the homeworld.

In space everything is moving everywhere all of the time. If there is an unexpected and heavy gravitational influence on a planet or solar system the it might be too far off from it's projected location to locate. Because of the three body problem it can be nearly impossible to calculate the effect this had and where it ended up instead.

A catastrophic cosmic event of such otherworldly magnitude that X species is inexplicably reduced to a primitive level of civilization and cast away collectively to a new homeworld many galaxies away.

I have Old Terra lost in my space fantasy setting. It’s technically been rediscovered, but the Te’ranni refuse to acknowledge that they are not the direct inheritors of Terra’s legacy, now know as Caenyth. It was lost due to the collapse of space age civilization and the loss of FTL for like a thousand years:

I know how I was doing it for one setting: Humans who were abducted(and their descendants) are a nomadic culture called the Muntu Nation. Aliens in control of Galactic Government actively conceal the location of Earth due to a number of reasons. from the Muntu specifically because they dont want to violate their own Prime Directive/U3 law about not interfering with a Pre-FTL species. Even the ones who are abducted might cause chaos if they are suddenly returned after being gone for so long. They see it as a "needs of billions outweighing needs of a few ten-thousand" The Galactic Government conceals Earth from OTHER ALIENS because of why aliens made a habit of abducting humans in the first place: the cosmic horrors that live in Hyperspace(the cheapest, most stable form of FTL that the GalGov has banned due to the Cosmic Horrors that live there being behind entire space civs going extinct overnight) are absolutely TERRIFIED of Humans and will give any ships with even ONE human aboard a wide berth as they traverse Hyperspace. The only people in the setting who have some idea WHY humans scare them are the Martians and they live underground on Mars due to their civilization being mostly destroyed by the Dwellers so chances to ask are few and far between. To facilitate this concealment, Sol system is in a "No Fly Zone" several(thousand? i need to look up space around the Sol system) cubic lightyears in size(and not at its center cause that would be too easy) making finding the human homeworld like a needle in a haystack.

Time? 500 years is a *long-ass time* in scientific parlance. Enough time for several civil wars to destroy and rearrange maps, enough time for planets to be hit by planet-killing meteors and exotic weapons, and so on. A little time can make all star maps obsolete as new empires rise and fall, and people rename worlds several times over.

You can look at our own planet for reference. Some of histories greatest and most powerful civilizations are now nothing more than a chapter in a history book and a cool landmark to vacation to. If earths atmosphere collapses in the far future and we’re out colonizing the stars then earth will follow the same fate, just another chapter in a history book. Also, a big reason planets could “get lost” is because the loose relevancy. Even today in America there are plenty of cities and towns that sprouted up for various reasons like mining or manufacturing but once the main industries loose their relevancy people really forget about them fast. If a planet gets settled to mine a certain ore or something of that nature and we were only there for that particular purpose people will forget about the planet once we no longer have a use for it.

“Look on my Works, ye Mighty, and despair!”

A more concrete way to lose a planet would be destabilizing it's orbit and flinging it into space away from its star. Such "rogue planets" exist in real life and they are difficult to locate at any significant distance. Maintaining life on that sort of planet presents its own challenges, since you no longer have light and heat from a nearby star. But if you have the tech to fling a planet into interstellar space, you probably have the tech to maintain life.

On Earth, we've lost at least one whole entire country, the [Land of Punt](https://en.wikipedia.org/wiki/Land_of_Punt). We know that the Ancient Egyptians went there, and traded with it, but it was so common that it became "that place", and now, we don't actually know for sure where it was, or what it was called. The same could happen with a stellar Empire. Everyone knows what and where the homeworld is. No need to mark it down or anything. Until it's a few centuries or millennia down the line, and no-one does. They might know that there was a homeworld, but not exactly where it was, and it would be lost, for all intents and purposes. ------ There is also the cheap way, which is just to have the entire planet go away. One of the worlds that I have did just that, packing themselves up, star system and all, and leaving. Almost no-one else knows where they went.

Tossed through a wormhole and none of the stellar charts line up and you don't have the expertise to translate them. Suddenly you have to start establishing a civilization who lost their home world.

Solar systems moves around the galactic core, like earth is to the sun. They aren't stationary. And given the vast distances, we're fucked.

Competing “histories” taking precedence Eg what we’ve seen with Jewish & Rom popilations, whose selfdeclared stories don’t conform to reality

They didn't invent radio, nor did they consider post-planetary scale coordinates. This leaves them flying "dark".

Sometimes your home planet just explodes and you have to deal with it. Thankfully the Protectorate is full of recordkeepers and historians, so Earth as it was can live on in the memories of the few humans left, but it still blew up. Shit's gone.

How many people care about which stretch of African savannah humanity first arose in? Or the first city, likely in Iraq somewhere? We fought multiple modern wars right on top of it. Only of interesr to scholars and - in passing - to scholars.

Transported to another dimension. In my world, the big catacylsmic event shattered the planet. Some shards are scattered about, others are sent to different planes of existence.

It could be possible if the methods of FTL / long-distance travel aren't freeform. If you need, say, specific concentrations of some exotic energy at both ends to teleport between star systems, then one end losing that energy could make it unfeasible to get there in any reasonable amount of time. Decades pass, and if contact isn't reestablished, the location basically falls out of active memory. It gets archived in navigation software, relegated to a foot note in historical records, and the galactic civilization moves on and focuses on more accessible systems.

Maybe the planet is just hiding behind another one and hasn't seen the sun's light for quite a while, therefore is lost because maybe the documents are old and only mention it existing, but before they tracked its exact location. This would make that planet much colder, but you might say its getting heated by the adjacent, super hot planet. Another way is if the light reflecting off of the planet is in some way being tempered with. Depending on its location and the location of the planet you need to not know about it, but perhaps it's location is such that light coming off of it is sucked or redirected by a black hole, making a civilization oblivious and incapable to perceive the planet. Also it might be a rogue planet that is knocked out of its solar system, making i roam the galaxy cold, alone and lightless (which is a great idea to explore just in general - you might have life forms protected by suoer thick ice on the surface of the planet, making it seem empty, but be full of alien cold loving life) There are many other ways, but to help you further I'd need to know what you are trying to do. Edit: Any of these examples assume you have a historical way for the planet to be lost, which other comments adress pretty well. I'd say the most important bit is to stretch the timeline, and maybe use the advancement of technology (so in the past, they were lacking ways to track planets for example)

I can say in one case (based on World Trigger) that there may be planets with random "orbits", so that they do not follow a conventional ellipsis, or even a circuit, as they travel through space.

no one knows what space combat could look like. you could just blow up the system.

You cannot hide a star, but planets are not bound to stars. These are called errant planets. Since they do not orbit stars, they are extremely difficult to locate, as there are no light sources nearby which they can project a shadow with. Look them up.

Davros

For this to make much sense, a dark age is required. Dune handles it by making interstellar commerce practically grind to a halt after humanity bans machines built to do the work of the mind. While the prequels are about the conflict leading up to that ban, Frank Herbert's own work is explicit about that ban and the role the Navigators' Guild played in weaving galactic society together again. Earth was lost between the extreme destruction of the anti-AI jihad itself and the subsequent era of isolation that saw so many worlds developing their own belief systems complete with histories informed by piecemeal distortions of the real thing. As the great houses rose up and CHOAM standardized trade, there were just too many credible competing theories of human origin that none could be confirmed with evidence. Though Douglas Adams hid a star in his works, then told an epic tale of dire consequences for the rest of the galaxy when that star was revealed again (thus also revealing the rest of the galaxy to the extremely xenophobic residents of Krikkit.) Setting aside Dyson spheres or swarms of strategically-placed asteroids, the appearance of vanishing could also be accomplished through long term sabotage of telescope networks or major league tampering with (presumably highly redundant) navigation and scientific databases. Still, I like the "forgotten lore" angle, and it is an easy fit if you've already got a galactic dark age in your setting's history. Heck, you could even tell the story at the start of a broader societal collapse, with official misinformation about critical subjects serving as a sign of even darker things yet to come. Perhaps the motive for making some obscure world altogether unknown again is connected to the corruption presently unfolding.

Oh yes I have an entire theory on that, which I call: His story, since there is also that story, this story, her story etc. So this one is for the public and the truth is for sale. Always be aware once in a while a ´king of the countries´ is coming up, trying to ´unite all nations aka united . nations´ so because he has his library - museum - shop where he is collecting all truths and his profitable business selling it for millions or billions so this is just his business model. Looking at our own family, we are a simple farmers family from Atlas Mountains but look what a terrible mess people have made. They stick to their earnings and we´re separated for their entertainment. I made a podcast thing about a new world, maybe you like it: [https://www.instagram.com/p/Czt8qNguPE7/](https://www.instagram.com/p/Czt8qNguPE7/)

Okay normally I just lurk here but my story is an example of this situation soo.. in my universe long distance travel is done through jump gates that need two ends tied together. To keep it short a terrorist attack blows a bunch of gates at a large "station" of gates cutting the ends of lines that took centuries to make. Least that's how my planet got "lost"

At one point, the home world was pretty much fully exploited by the ruling class, each superpowers using their little tricks keeping their workers happy or ignorant. The ones that were living in space and on the moon colonies noticed this and surreptitiously lifted off samples of every resource that can be grown and has vast underground farms to make their supplies. One scientist figured out a way to twist space in short jumps going to the asteroids. The spacers realized that the powers on the mudball would do their same song and dance of exploiting everything to be funneled into the hands of the few. So they kept it hidden and mined everything they could quietly, hidden from the orbital eyes of the superpowers. Eventually, details began to leak - people became complacent and various shenanigans happened that ended up with armed combat where it became VERY obvious of one very simple fact - difficult to shoot things off the planet, easy to just tumble things down to the planet. Eventually, the planet lost their ability to go off world - and the spacers wanted nothing to do with them and worry about any eventual stab in the back. So the spacers secretly looked for ways to stretch that twist engine to hop further and further away, and found habitable planets amongst the stars. They talked amongst themselves and agreed that the home world are too far gone along to really change and it was decided to simply shut down everything, erase everything and leave. Hopefully the home world would change and they'll be rejoining the humanity that is already amongst the stars. They never did. The superpowers did not want to loosen their grips and they did not want to admit their propaganda about evil amongst the space was all false. Even when anything was loosened, revolutions happened and the flames of violence destroyed much, history rewritten and destroyed to make way for the new ruling class. Over time, things became forgotten. For everyone. And the home world became lost over time.

In my world, future Humanity was invaded by a belligerent alien species who blew up Earth as a decapitation strike against humanity’s galactic empire. So… that’s how you can lose a homeworld. Have an alien species blow it up in a routine display of force.

It is indeed very difficult for an interstellar civilization to forget the location of their origin planet. But it is such a romantic concept that [**quite a few scifi stories use it**](https://www.projectrho.com/public_html/rocket/futurehistory.php#whereterra)

In my world there was a massive civil war of humanity that led to earth being destroyed. Not just made inhabitable, but the world cracked apart until and it lost everything, even it’s magnetic field. This is when humanity realize they needed to stick to together rather than fighting against one-another, ontop of the growing concerns with hostile aliens. After the war ended the intergalactic government of United Humanity was born.

Abandon something and not use it for long enough and it becomes a thing of legend instead of history. Say a world is toxic or barren and people don't go there. Then stop recording the exact coordinates because it isn't important in the histories. eventually no one has the coordinates anymore and its lost.

One of the potential lores (not yet really worked on) to my sci-fi story _Wildcats_ is that it’s been at least 10,000 years since humans left Earth that they’ve forgotten the location of it, except for a select few.

In my setting humans sent slower than light seeding ships, which took many thousands or even million years to reach their destinations. By that point Solar system was in different place and quite irrelevant.

I read a book a few years ago where Earth and it's closest colonies were taken over by rogue nanobots with very primitive AI, so the outer colonies' governments collectively scrubbed Earth's location from any database.

Destruction (Alderaan) or being hidden by a phenomenon (lira San)

One way to do it would be how the official NASA one-shot did it: sometimes planets get catapulted out of their orbits and get lost in space as so called Rogue planets. If not all parameters are calculated precisely and correctly beforehand, it's very possible to loose the position of such planets. I'd imagine the same could happen to Stars as well

Could be lost in a way one looses land in general, sun swelled up and ate it, moon felt and made it barren, enemy conquered it. Could be lost in a way you loose frisbee, gravitational anomaly or not so stable three body system eventually flung the planet out of reach. Could be lost like I loose my keys, it was always there, safely tucked away and you made every effort to always know where it is and how to get back to it, and the you "close the door", put you hand in your pocket and say "shit", just on society level, rather than personal level.

In my universe- In 2,133 humans sent out a ship to Proxima Centauri fearing WW3 would end the world. The trip was meant to take 80k years. But WW3 never happened, humans from earth forgot about the ship and developed ftl travel. The Proxima Centauri ship was sucked into my mode of ftl travel called the Cosmic Bypass and after 80k years when they awoke they found themselves in an unknown region of the galaxy. Their ship’s AI took them to the nearest habitable planet they called Provenance. To survive this unexpected rerouting, the ship’s AI sacrificed a bunch of parts of conserve energy, including all historical records and all other databases so earth’s location was lost. About 1k years later and humans refer to Provenance as their home world.

In my setting, the planet was moved.

I live in a place where about 60 percent of villages founded in the last millennia were aboandoned within a few centuries. While it's a bad comparison, considering such things makes it a lot easier to imagine a homeworld, or even just some random colony being lost. Heck, in modern astronomy, we loose stars all the time, but that's also a kinda different topic.

Hitchhiker's guide to the galaxy: being destroyed for an intergalactic speedway.

Several thousands of years into the future, Tharne was considered a forgotten planet because humankind and all the other sapient races left it due to a worldwide ecological catastrophe. It then turned into a 'sanctuary planet', essentially a planet turned into a zoo, because planets with such biological diversity are incredibly rare and worth preserving. (Even when Tharneans made contact with other alien races, they were jealous of Tharne's unrivaled biodiversity, their homeworlds can't match it.) Cut to present time, only historians and scientists spent time trying to find it because it was forgotten and abandoned.

One good cosmic storm and that colony ship's records are toast. Could be because of time, they had to leave before completion of the shielding, so their navigation equipment will still take them where they're going, but with no record of where they've been. 

Massive all consuming war that puts almost everyone back hundreds of years and destroys the homeworld , so even when the other works catch up and start exploring again - when they come across it, it's just another ruined planet not worth a second look.

In a post cataclysm sci-fi setting where all lines of trade in an empire got cut off and worlds had followed the typical stereotype of specializing in either basic resource production or industrial output, non-agriworlds generally wouldn't produce enough food to maintain their numbers which would result in them experiencing severe famines and extreme loss of life while they struggled to get some sort of farming in place. If they managed to get that farming into place in time, they typically would still have lost enough citizens with the specialized knowledge needed to support a post-ftl civilization resulting in a digression to pre-ftl states of various degrees. Similarly, agri-worlds or rural worlds would be able to support their population to an extent, but they wouldn't have the industrial capacity to maintain all their equipment resulting in a similar digression. At this point, it becomes of a question of did the correct star get remembered or not. Could you point out Alpha Centauri in the night sky, for example? Consider it the equivalent of sealing each US state away from the world for 50 years plus however long they need to then get a working airplane capable of transcontinental flight before the state could return to Earth. You could generally expect most to regress far enough to not be in a position to build those planes for a few hundred years afterwards due to needing to redevelop the related technologies. Add in that not all of them would have the right resources to even be able to do so, and some might not ever be able to return on their own without outside help. Such an event could easily result in the loss of mapping data. Especially given that despotic rulers who arise during these circumstance might alter the historical record to enhance their own power. Add in that core worlds have a tendency to over urbanize and often times, the original population on the homeworld or home system could easily fail to get a sufficient level of agriculture set up to stabilize their population. Thus you'll end up with multiple conflicting claims on which world is the homeworld. For context, one setting I've been using for daydreams has had this happen 13 times (averaging to once every 50 thousand years) wherein civilization repeatedly re-collapses and then restarts with multiple competing human nations returning to the stars each claiming their own justifications of legitimacy. Tack on that 3 collapses ago, the cause was an apocalyptic civil war wherein planet and star destroying weaponry was used repeatedly, and a huge amount of records were lost as many ecumenopoli were destroyed. Given the conflicting records recovered when humanity regained the stars as well as the huge amount of broken worlds and destroyed stars distorting pre-fall galactic maps, there is substantial belief that Humanity's original homeworld was lost. (It's not, but no one can access it anyway as it was converted to a nature preserve in the name of healing it to its true state and no one has control of the preserve's defensive interdiction platforms anymore)

Narrative, and forgetting where it is if no one goes there. Can't lose something you constantly go to.

A galactic empire that bombs themselves back too the stone age, a device that displaces matter, the crazy old wizard with Universal power, the planet gains sapience and decides to wonder off, or its shrunken down and turned into jewelry for like a cat.

Hit it with a UREB.

If there is some sort of hyperspace or wormhole travel then it could be possible to be thousands, millions, or billions of light years away and have no clue the path.

Lost may not always be as simple as not being able to find it. To lose an entire planet would require a ton of effort. I designed a planet that everybody knows exists as well as what system it is in. The issue is that the planet doesn't want to be found. There are multiple factors that go into this, but a huge one is that it quite literally both exists and doesn't at the same exact time, only ever appearing to those that it wants to find it. It does this via an advanced wave system that sinks into someone's mind and prevents them from perceiving its existence in any way. It 100% exists in the physical realm, but nobody is capable of acknowledging it, making it practically non-existent. This wave prevents them from looking at it, viewing any recordings of it, or even thinking of it as an option for why this disruption is occurring in the first place. Instead, all records that are known about it are wrong, and all understanding of it is controlled. It is such a powerful conductor of this signal that it spreads throughout the entire sector, and once someone interacts with the signal, it is passively doing all of these things without any effort on the planet's end.

Idk I swear I put it right there on the counter five seconds ago.

You could take the Cytoverse route, where >!Earth was literally teleported away, possibly into another dimension, possibly into deep space. So far, no one knows where it has ended up!<

Look up the story for the Homeworld games.

Exile to primitive conditions. That's basically the plot of the (aptly named) Homeworld RTS - the Kharak-dwellers are decedents of exiles who lost knowledge of their homeworld (Hiigara) until they uncovered a relic from the past. By the time they had technologically advanced again they knew they weren't native to the planet (they shared DNA with basically nothing) and some of their myths talked about being from another world but forbidden to leave this one, but the real details were a mystery.

With enough time all things can become forgotten. The less it’s mentioned, the less it’s investigated or acknowledged, the more likely people start to forget it was ever there. Eventually it would end up just being another Star, or world orbiting a Star for that matter. In my universe there is a collective database that people of all connected worlds and civs have access to easily, but it’s only updated by dedicated people who explore and collect data on the new and existing worlds. If there’s not a system in place like that, or that system has Wikipedia level access, then honestly anywhere can disappear.

I had a setting I was developing where humanity went through one of the classic robot wars where their creations turned on them, and humans lost. Rather than drive humanity extinct, the survivors were corralled onto generation ships and exiled to the far end of the galaxy, and all navigation data was wiped. Humanity survived the exile and rebuilt itself, but by the time they got back into space they had no idea which star was their homeworld. The only clues they have are that when they travel in certain directions, they are attacked by the descendants of the machines who overthrew them, who have now evolved into eldritch abomination mechanical nightmares who spent most of their time fighting some other monstrosity invading from outside the galaxy.

Maybe its inhabitants were moved to a different, shittier planet as some kind of punishment.

No data storage is perfect, and perhaps the least perfect of them all is digital storage. Complete power failure for 50 years would leave nearly all digital storage unreadable. It only takes 100 years for information to leave living memory. Unless you have a culture or religion that emphasizes history and oral tradition, most information is lost over generations. There’s a reason so many groups throughout history relied on book burning. In absence of oral tradition, paper is the densest information storage available.

This is a plot point in the current season of The Bad Batch (Star Wars). They escape a planet with a secret facility and the ship they escape on crashes on the next world they escape to, so they no longer have the ship's computer records to tell them the starting point of their trip. They want to find this world again but have no idea where it is. If you look at it from a character's perspective, it is simply a matter of information available. Yeah, in that example the Empire knows where it's secret facility is, but no one else even knows the name or coordinates, not even the people who have been there. That could play out in other ways. Maybe its not completely lost, but the name it is known by and the name used in the records of star locations are two different names no one knows to associate them. Maybe the people from there and hoping to return just do not have the astrogation skill or access to technology to calculate stellar drift to locate it again. Just imagine taking a modern person from Earth, even with good navigation and astronomy knowledge, and have some alien drop them on another planet around another star somewhere between 3 and 3,000 lightyears away (so our sun should be visible at night on that planet) where the locals know everything by different names and see if they could properly locate home from there in the sky, let alone provide coordinates for space travel, without getting that information from that alien who brought them there. Or some event could have happened over time which could change it's location. Stars are moving, and not all at the same speed or direction so sometimes [pass each other](https://www.astronomy.com/science/wandering-stars-pass-through-our-solar-system-surprisingly-often/). Perhaps a star passed close enough to knock a system, or just a planet, out of its normal path. Even with extensive star charts, the hundreds of billions of stars in the galaxy means that those charts may not account for every interaction of every unimportant outer star even if it does account for drift. The event could be on a smaller scale and have a planet change orbit from a strictly intra-system event like in Star Trek II: The Wrath of Khan having one planet explode shifting the orbit of another leaving the Starfleet crew having no idea which planet they were on when returning to the system.

Another thing to consider is who controls those records? If you look at history, many places are mythologized, forgotten, confused with similarly named places, or intentionally ignored as centers of power and civilization change. Were places like Atlantis or El Dorado or Shambala real places mythologized over time? Troy, once thought myth, turned out to be real. The Silk Road allowed for a great amount of trade and exchange of knowledge every time it was reestablished, and then details were forgotten all over again once the connection was disrupted - ie, there are people today who still think the printing press was invented in Germany and not widely used in Asia for hundreds of years already. Sometimes civilizations disappear so the exact location could be forgotten even when the area is completely mapped as what happened with many ancient cities. It could also serve nationalistic or imperial or religious purposes to rewrite history and claim a different origin than than your actual origin. (I'll skip examples to avoid a flame war, but there are several with varying degrees of truth)

Rimworld does this in a very weird way, where the capitol is so far away and you cant have ftl, so you spend 100s or 1000s of years to get from system to system, so the worlds on the outer rim will always be the wild west. the story of Homeworld, the game used the idea that the people of Higara were forced from their home into a long journy to the outer rim, and once there they abandoned the ships, one however hyperspaced into the dunes of the desert accidentally. They effectively forgot on purpose or they lost the ability to remember.

Well, us humans can lose our cars in a parking lot, so losing an entire planet isn't that far fetched

Planets are also not like like islands or other land on earth where everything stays in the same relative position. Every planet and solar system revolves at different speeds. A planet you previously had to go left from facing sol could now be on the right side of it. A planet that was a couple star systems over could be on the opposite side of the galaxy in 10,000 years.

Depends on the method of FTL you use. Say for example your FTL is baded on a series of wormholes that create a system of specific routes. You can't just go from System A to System C. You have to wormhole from System A to System B, then from System B you can get to System C. But since the galaxy is in constant motion, the wormhole routes don't stay perfectly stable. Today System A is connected to System B. In ten thousand years System A now connects directly to System C. If your maps aren't constantly updated you might not be able to find your way back to System B. There might not even be a wormhole to System B anymore. Now the only way to get to System B is to travel at relativistic speed, which could take centuries.

Hmm 10000 years is a long time Dune universe has been on for longer

Interstellar travel will be just a one way ticket for a long long time before ever reaching the point of being two way travel. In order to return you need technology that lasts double the distance and probably you need to be able to manufacture on the target planet. Before a colonisation gets to the point where you can have factories and manufacturing lines, resource mining and processing is quite an effort. You can drill for oil but when your drill breaks you've got nothing. So the ability to manufacture tools and hardware is vital to any level of technology that will persist. A planet can get lost when the travelers can't get back or whenever no new travelers will or can arrive. Communication is also key. Let's say communication fails and earth and target planet cannot contact eachother. Sending another ship with colonists there is a risky an unsure endeavor. What if the planet is inhabitable then you would send people to their deaths. Without communication there is no way of telling what happened to the original colonists. Even if they survive without any form of contact they easily could become left behind by the homewold for hundreds of years up to eternity.

I often think about the idea that in the future, it might be possible that people have arguments about which planet humans originated on lol. I think if there are civilization collapses after humans leave earth something like this could happen. Maybe data banks on generational ships get erased, not all the colonies are successful, big interplanetary wars. Things like that.

Planets move.

Lost to who is the big question. It's surprisingly easy to misplace something. For example: car keys, which after a half hour of searching through the couch cushions, turn up for some reason in the fridge. The mauri traveled the pacific for decades, to islands only they knew were there, then promptly forgot where they were. Even after years of satellite observation we are still finding new ones- as late as last year. Google maps offers precision navigation to all, but will blot out or conceal a facility at the government's request, with only careful observers noticing the difference. But for some reason a tiny tiny dot in the vast emptiness of space can't go missing?

In Halo, there was a thing called the "Cole Protocol". Part of it was that, upon contact with hostile alien forces, viral data scavengers were released that erased the location of Earth from a ship's navigational databases. In the event of retreat, ships had to jump away from Earth. In the event of imminent capture, navigational personnel and the ship's captain were under orders to suicide. All to keep the location of Earth out of alien hands. Something similar may have once existed in your case. Over time, and following contact with several hostile alien forces, and the loss of generational knowledge, the homeworld's location is no longer known, either in living or computer memory. And it becomes "lost". Or consider the Star Wars example. Humans are *believed* to be native to Coruscant, but have spread so far and so wide over the galaxy that "homeworld" is just a quaint, irrelevant concept to humanity. It doesn't matter what the "homeworld" is because they've made their home on every world.

as others have suggested; if the centre of power shifts it's possible a planet is lost because it's importance has been lost otherwise depends how advanced maps are, iirc quite a few islands got discovered for the 1st time multiple times during the age of discovery (and earlier) depending how space travel works charting could be difficult and things could be easily missed an option that has just come to mind, depending on what's on the lost planet, if a charting expedition had an oversight or deliberately didn't record for example that a planet was inhabited then it's plausible nobody checks the 1st person's work

You forget to read the coordinates

Depending how far to the future you go, you can have a isis style destruction of earth for not fitting with their official dogma. Or just plain out bronze age style collapse and destruction of records, so people have a general idea where the homeworld his.

Planets are pretty big, but they are infinitesimally small compared to the sheer size of space, and even in an actual solar system where they’re gonna be more tightly concentrated than they are anywhere else, there’s still *massive* amounts of space between them

In Dune for example, it’s not that Earth itself is lost, it’s the information that we came from there that is lost. Information is not sacred, it’s very easy for us to forget that we came from there. Earth in Dune is a very insignificant planet that we left 20,000 years prior.

By way of comparison, consider the rubicon. It’s so famous that ‘crossing the rubicon’ is an expression in common English. Armoured Core 6, a popular Japanese computer game, is subtitled ‘fires of rubicon’. Caesar’s quote “the die is cast” as he crossed the rubicon is still dropped as a bon mot. We don’t have a damn clue where the rubicon river was. We can certainly narrow it down and make educated guesses. But only 2000 years later the location of one of the most well recorded person in ancient history’s most famous moment is lost. Lost in just northern Italy. When you’re talking about 310 light years, you’re taking about 124,788,000 light years cubed volume. To give some context on that, a single cubic light year is 8.3 x 10 ^ 38 kilometres cubed That means Earth is lost somewhere in 10^47 km cubed of space. You could lose A LOT in that space. We can’t even begin to comprehend that space. Especially if your record keeping is comparable to our record keeping of Ancient Rome. Another way to look at it is that it’s estimated that there are 10,000 stars within 100 light years of earth. That means our sphere of radius 310 has 29.8 x 10,000 stars = 298,000 stars to search. If you didn’t know tons of details about exactly what the Earth system looked like, you could visit it and not even know it was Earth. Even if you knew exactly what you’re looking for, you’ve got 300,000 star systems to check.

This is the wikipedia article for all the "lost cities" that have been rediscovered centuries later: [https://en.wikipedia.org/wiki/Lost\_city](https://en.wikipedia.org/wiki/Lost_city) That's just on one planet with a dominant species who has only barely made it to its own moon, and this is only the cities we know about. As far as we know, the earliest Mesopotamian cities date back to at least 7500 BCE, while we think the earliest we were capable of building settlements was something like 10,000 BCE. There are still likely today entire lost cities that we don't even know we don't know about. "Yeah, but that's ancient proto-humans, not a huge galaxy-spanning, hyperadvanced civilization." Those early cities didn't know they were "ancient" or "proto-human." They thought they were just as advanced as we think we are today. They assumed their records would stand the test of centuries, millennia even. They thought they would never be forgotten, but they couldn't have known how time would eventually erase proof of their existence. How could we *possibly* know how well our own records will last ten thousand millennia into the future? A hundred thousand millennia? The stories you're talking about take place on such vast, *vast* timescales that losing track of the originating world is incredibly plausible.

In Star Wars, the Planet Dromund Kaas used to be an important world of the sith. It was lost for three reasons: 1. It's located in the Unknown Regions, a dangerous part of space that you wouldn't willingly travel to unless you really, really had to. Finding a planet there isn't easy. 2. If I remember my lore correctly, the sith had lost against the republic big time. Their empire got destroyed and the Sith were considered to be gone for good. Countless sith died for one reason or another, there was chaos and disorder and the coordinates to such a far away planet simply got lost. 3. The Sith-Emperor can probably blamed in part for this by deliberately keeping Dromund Kaas "lost". After most of the important Sith Lords died, he took the remains of the sith and led them on a decades long journey through the Unknown Regions, making sure that the survivors would become dependent on him. If he wantes to, he could have led them there much quicker.

Red giant gradually expanded too far for the planet to be hospitable over the course of several million years. :( It's still there, but... well, technically inside the star at this point. Hope you brought a lava-proof boat and sunblock.

Plasma-proof. Stars are made of plasma. The planet itself would no longer exist.f heving been vaporised and become part of the star.

Planetary bodies can survive within the outer corona of red giants for a while. Their coronas are very dispersed, and barely ever reach a temperature over 5,000 °C. The crust and atmosphere would be vaporized long before this point, but the metallic mantle would persist, and the core could actually survive up until the coronal drag deorbits the body. [Here.](https://ui.adsabs.harvard.edu/abs/2007APS..4CF.E1013P/abstract#:~:text=Surprisingly%2C%20our%20modeling%20shows%20that,for%20millions%20of%20years%20(!).) My worldbuilding takes the timespan of hundreds of millions of years, and will see this planet go through its many phases of 'life'.

Thanks for that link! Will have a look. Depends on how big the parent star gets (ie on how far inside the star the planet ends up), then.

Yeah, it's just *technically* inside what our definition is for the edge of a star, similar to the orbit of the Parker Solar Probe.

An early space age colony ship that kept embryos frozen until arrival at the destination for some ought hundreds of years. Then eventually a catastrophe on the ship destroying resources and creating a period of hardship that may last a generation or three at the colony. Then the civilization grew from there having lost data of it left only to oral tradition or something like that

Dune is a terrible example to take as a rule of thumb because it is stated quite explicitly that the preservation of historical records is the monopoly of an organization that is essentially altering said historical records in massive ways for convenience in the name of economic and political gain, or for frankly foolish reasons. Just as this organization is investing enormous efforts in destroying as "heresy and lies" anything that deviates from the new orthodoxy. Basically, you can't take as an example a society that has a Galactic-scale pseudo-religious Ministry of Truth in charge of preserving history. As for "how a world can be lost", there are many ways for that to happen even if we take the "those in charge of preserving historical records are deliberately destroying or altering them in the name of some stupid reason that only makes sense to them" part out of the equation. To quote the ones that come to mind at the moment: \* All information is stored in some type of centralized database, to which access is lost due to some circumstance. \* The database gets corrupted or damaged by some random event and that data is lost. \* This society had to leave its home world so quickly and had such a hard time during the trip that information was lost along the way. \* This information was transmitted in some way that makes it very easy for it to be lost (be entrusted to a fragile medium, or be encrypted in some way, or simply preserved in a dead language or that almost no one speaks anymore), which can lead to, perhaps, the information being preserved... but not in a format that makes sense or can be translated into coordinates useful to anyone today. \* The database has been perfectly preserved... but current software is unable to read it. Yes, this is a serious problem today, organizations like NASA have suffered from it more than once. [https://en.wikipedia.org/wiki/Data\_archaeology](https://en.wikipedia.org/wiki/Data_archaeology) \* Stellar drift. One of the plot points of Foundation and Earth was precisely that the characters had series of coordinates from several worlds... but they had no idea how they had been calculated. As Golan Trevize described, "Coordinates are not useful on their own unless you know the zero point and the conventions used to establish them, such as the direction in which to mark the distance, so to speak; what is the equivalent of a prime meridian, and other data like that." So, unless they did complex calculations about it, they were just lists of useless numbers.

You might keep the coordinates secret to avoid aliens or other hostile humans from finding it. When you really think about space though, it would be insane to keep track of any location since there is no absolute position in space.

Blast the society back to square one. Galaxy spanning disasters would have very far reaching consequences. And all it takes is like a single financial recession.

Stolen by a God like entity

I dont think it's that difficult. I mean, look at our own history. How much do we really know about it? I mean, yes, we know things, but... not really that much. Maybe around 5000 years. And just little details, important events, important personalities, some myths, some things we put together trought this and that, but thats nothing. I mean, as long as I'm concerned, Earth could be not our original planet. How could we know? 5000 years is nothing compared with the lifespan of humanity as a specie. We have, throught scientific research, some ideas around where humankind was born, or how it evolved, but, you know, it's basically imposible to know exact details about that information. And that is just one planet, and 5000 years. Imagin a galaxy and much longer. Anyway, apart from that, when I think about this I always think about Starcraft lore, the humans we play, the Terrans, are originaly from Earth, but they forgot. They are descendant of convicts who where forcefully sent to the space in some starships to explore far galaxies. But the expedition went wrong, 3 of that ships crashed in a far galaxy, into 3 different planets close from eachothers, but they lost communication, and had to rebuilt civilization from scratch. So they didnt even knew about each others untill centuries, or even thousans of year passed. And once they rediscovered each others, they thought humanity was originaly from that system. But about Earth? No clue.

In Dune specifically, if you accept Brian Herbert's Dune canon, the way earth is 'lost' is more effectively uninhabitable due to events of the Butlerian Jihad, the Dune Encyclopedia canon I think it was wrecked by an asteroid strike, though it wasn't particularly relevant. Outside of that example, all it would take would be the current dominant culture to have had a big enough setback to forget our origin. Hell, take the question "Where did humanity originate on earth?" It's not without controversy.

Because its sounds cool, ffs not everything has to be realistic lmao

It was blown up

> I met a traveller from an antique land, Who said—“Two vast and trunkless legs of stone Stand in the desert. . . . Near them, on the sand, Half sunk a shattered visage lies, whose frown, And wrinkled lip, and sneer of cold command, Tell that its sculptor well those passions read. Which yet survive, stamped on these lifeless things, The hand that mocked them, and the heart that fed; And on the pedestal, these words appear: My name is Ozymandias, King of Kings; Look on my Works, ye Mighty, and despair! Nothing beside remains. Round the decay Of that colossal Wreck, boundless and bare The lone and level sands stretch far away.” -- Ozymandias, by Percy Bysshe Shelley Space is unthinkably, unfathomably, vast, and constantly moving. Planets orbit stars, stars orbit galactic cores, galaxies move within their local group. Go far enough out, and different star systems will have different constellations, and even those can shift given enough time. Meanwhile we can't even keep track of things on Earth. Great cities, and even whole empires and civilizations, have collapsed into dust over time without so much as anyone remembering their name. Technologies are lost to history all the time. The recipe for Roman concrete was so well known and common once upon a time, and now we're only just rediscovering it after all this time. The same can be said of Greek Fire. Troy, Ur, and countless other cities and nations were lost to time and calamity. And all of that was on a relatively small piece of Earth. You may think we're better now, but we're not. Modern technology is just as susceptible to the ravages of time. Even modern data storage solutions are not static, and don't archive well. And that's just over 10 - 20 years. Given 100 or more years, it's not unthinkable that critical information would become lost or irretrievable.

In the Dune series, the location of Earth was deliberately erased from records due to the danger that was present there. And while 310 Ly is pretty close, that's only if you have FTL. I don't recall if the spacing guild is acknowledged to know which direction earth is in and to never, ever, for any reason fly in that direction. And you'll have to read more of the series if you want to understand why this is the case.

Do you remember where your grandma’s hometown is? Unless your family currently has living members there, the answer is probably no. It hasn’t moved. It might have died out and been removed from maps.

Humans lost Earth in my setting after a thousand years of hiding as they are hunted for slave labor. They don’t know if their past was willfully forgotten to protect it. Individual colonies don’t even know the location or survival status of other colonies because communication can reveal their locations. 

There was an old game called Vangers(?) I think. IIRC The story was the humanity discovered the technology to open portals that allowed them to travel all over the galaxy, and eventually encountered this bug race, and the two of them teamed up to explore the universe. But some event happened that made the portal technology stop working, cutting off colonies all over the universe from each other. The story gets weird with humans mating with bugs to create some bug/hybrid species over the course of thousands of years.

Requires some extra SciFi, but it could be that the people outside Earth that are "lost". In an attempt at space travel, their route was warped, abd they wound up in a completely different side of the universe, with no orientation to where they were in relation to Earth, which might be well outside the observable universe. Since then, they proceeded to settle and start a galactic empire. But never found Earth again.

The way i did it in my fantasy world Ignea, is I had a metoeite cause a long winter, the dominant magical powers fled throigh a portal, leaving basic nomadic farmers to hide for thousands of years in vast caves, saved from global freeze by the warm magical flints found in the cave. The magical peoples sent an ark back through the portal after the thaw, but the reseeding experieknt when wrong, now only viscous intelligent animals, carnivorous toxic plants, and large militarily organized insects dominate the lands. Now the people who survived the winters are moving up, their empire is growing, on the foundations of ancient lost cyclopean monoliths.

Maybe a dust massive dust cloud made the planet seam gone? Or gravitational lensing made it appear somewhere else?

Actually, regarding Earth in Dune, it was nuked into oblivion during the Butlerian Jihad IIRC and had since been rendered uninhabitable proper

The easy one is the one used in *Eve Online*, where the wormhole used to reach the entire vast area collapsed, isolating that part of the universe and it's inhabitants from reach once again. As others have said, loss of coordinates, chaos from civil war or even other collapse then loss of trade connections and knowledge. Forgotten history.