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In this universe humans aren't the first civilization to reach space in the local stellar neighborhood (a bubble of ~1000 light years across). In fact for the past several billions of years civilizations were popping in at a rate of roughly once every couple hundred thousand years to a million years or so. Each went to interstellar age, founded several colonies, then fizzled out over a course of several thousand years (since their first spaceflight) or rapidly went extinct for various reasons (Who said "Reapers"?!). There was no communication or influence between those civilizations. So each civilization roamed the stars in search of the various resources it needs. Some went full-on megastructure building, but assume that time is relentless and in absence of people to keep maintenance, most of them eventually got destroyed and fallen into their respective suns by the time humans arrived, and similarly most of the remnants of these civilizations were lost to time, decaying orbits and geological processes as well.

The question is - why instead of stars upon stars of mined-out systems where no easily accessible resources had left over the course of billions of years and millions of civilizations that roamed there, we see that there are still asteroids rich in metals, lots of ice, oils on planets that can have oils, and so on (Including, what's important, completely pristine Solar System among all of that)? I suppose on planets some geological events might eventually renew deposits of ores, but what about outside of the gravity well? Yes, the space is huge and has a tremendous amount of resources in it, but we're talking billions of years and a very large crowd of those who want these resources, and the new star systems aren't popping up all that often. Ancient humans could find large chunks of raw copper ore just laying around on the ground - that's impossible in the modern world, everything useful was scooped out and dispersed long ago.

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  • $\begingroup$ One answer is that we are alone. It might not be fashionable or popular to say so but it is entirely possible. The real answer to the Drake equation at the moment is that we simply don't Know. It's not highly likely or highly unlikely it is indeterminate as we only have one example to work with. $\endgroup$ – Slarty Jan 15 at 12:07
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    $\begingroup$ "Ancient humans could find large chunks of raw copper ore just laying around on the ground - that's impossible in the modern world, everything useful was scooped out and dispersed long ago" is completely different to the title. I think the problem is that you simply don't understand just how large a galaxy is. $\endgroup$ – Ian Kemp Jan 15 at 16:34
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    $\begingroup$ A few starfaring civilizations cropping up per million years only gets you tens of thousands of civilizations over the 13.7B year history of the universe, not millions as mentioned in the question. That's a pretty sparsely populated universe, with a civilization appearing in one of roughly every ten million galaxies, and a 1000LY sphere of influence is only enough to explore a fraction of a percent of even a single galaxy. Your "very large crowd" isn't nearly as big as you think, when compared to the size of the universe. $\endgroup$ – Nuclear Hoagie Jan 15 at 18:09
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    $\begingroup$ @Ian Kemp: Galaxy? How about just a solar system? Or even a planet? The resources that have been used, like the chunks of copper laying around, are just those that nature has concentrated from the upper 1% or less of the planet, and left in easy to get to places. $\endgroup$ – jamesqf Jan 15 at 18:44
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    $\begingroup$ "Ancient humans could find large chunks of raw copper ore just laying around on the ground - that's impossible in the modern world, everything useful was scooped out and dispersed long ago" - if we somehow reverted to the stone age due to a global collapse, there would be plenty of copper around to satisfy the needs of a pre-industrial civilization. The mined out copper is still around, in machinery, piping, etc, and good parts of it would be easy to scavenge. $\endgroup$ – vsz Jan 17 at 14:21

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Few reasons:

  1. Supernovas keep seeding new elements

    • Every few thousand years another supernova goes off, seeding the nearby area with fresh elements.
  2. Alien megastructures collapse into gravity wells.

    • The gravity well pulls in rock and compresses everything into a new molten planet. The materials used to make the megastructure are now ore deposits deep underground.
    • Indeed in your fiction, certain valuable ores are eventually discovered to be not actually form in nature, but were refined by aliens, and then found their way into gravity wells and back into planet formation.
  3. Different races have different priorities.

    • One mans trash is another mans treasure right? Different lifeforms categorise minerals differently. It is entirely plausible that one race moves waste quartz rock to get to the valuable iron, another race moves waste iron to get to the valuable quartz rock.
    • Perhaps the valuable asteroid of rare metals that you're going to mine was nuclear reactor waste a million years ago that was recklessly shot into space and has decayed into another form.
  4. The neighbourhood is constantly shuffled by its orbit around the galactic central point.

    • The neighbourhood isn't static, everything is orbiting the galaxy center, but from the fundamentals of orbital dynamics, those orbits are all different, you're all orbiting the galaxy at different speeds simply because you're all different distances from the centre. The 1000 light years surrounding a star are going to be very different after a few million years.
    • This constantly shuffles resources between neighbourhoods.
  5. Space is really really big, especially if there is no FTL

    • A society with no FTL, that goes extinct a few thousand years after achieving space flight, is not going to mine the entire 1000 light year region. There are 8 million stars in this neighborhood. They're likely to only explore a few hundred or thousand of them in their short life time.
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  • $\begingroup$ Also see @Willk 's answer below: once you advance sufficiently enough you don't need raw materials! Your only raw "material" is energy! Heck, your civilization may even be creating raw materials at a rate higher than the normal stellar nucleosis! $\endgroup$ – stux Jan 18 at 14:19
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"then fizzled out over a course of several thousand years (since their first spaceflight)"

Right there is your answer. You species died out very soon (galactically speaking) after achieving space.

Space is huge
A spacefaring species that only hangs around "for several thousand years", and then fades away, will have visited an infinitestimal slice of their environment, even if we assume they had access to FTL travel.

Remember, these are races that did NOT spread to conquest everything in sight, because such a culture would not just fade away. A rapid expander might fail as a whole, but parts of them on the periphery would just keep on expanding, forever. Like a fungus.

There are mined-out planets and systems, you just haven't located them yet. They are a few hundred, at most, scattered among the 5-10 million stars in your designated distance.

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  • $\begingroup$ This reminds me of the Heechee series by Frederick Pohl. $\endgroup$ – computercarguy Jan 15 at 17:16
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    $\begingroup$ For perspective, the universe as a whole is nearly 100 billion LY across, making the odds of 1000LY-diameter civilizations overlapping basically nil. With only a few starfaring civilizations arising every million years, there will only be a few ten thousand such civilizations over the entire history of the universe. With each civilization occupying such a tiny region of the universe, that's not nearly enough to have any reasonable chance of overlap between any pair of civilizations, much less between one specific civilization and any other.. $\endgroup$ – Nuclear Hoagie Jan 15 at 17:57
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The nature of stars

What are "resources"? There are really three fundamental "resources" that are needed:

  1. Energy. Stars just keep making energy available to anyone who can collect it. Unless some selfish, destructive type with "magic-level" technology "drained" a star of energy (whatever that means), a star will happily keep producing usable energy for the benefit of any life form who arrives at that star today, no matter how many solar cells were used to collect energy fifty thousand or fifty million years ago. Energy is not in short supply if you are in space and reasonably close to a star.

  2. Matter. A technological civilisation needs varying amounts of most of the elements in existence (with the possible exception of some of the short-lived ones). It is convenient to have some of those elements pre-packaged into a useful form by long-duration biological and/or geological processes (ie hydrocarbons such as oil) but by the time a civilisation can manipulate such vast quantities of energy that it can attempt interstellar travel, it can manufacture materials from the raw elements.

The question lists the concern that structures in space will eventually "fall into the sun". This is an understandable misconception, as satellites in low orbit around the Earth eventually "fall" down - meaning that they slow enough to lower their orbit to impact the atmosphere and then it's all over very quickly. This is not the case with the sun - there is no "atmosphere" that extends out a long way. It takes far more delta v to send a spacecraft from Earth orbit to impact the sun than it does to impart escape velocity so it can leave the entire solar system. As noted by NASA here, it takes 55 times more energy to go to the sun than to go to Mars. Structures may end up crashing into other celestial bodies, being captured and ground against other debris in Lagrange points or suffer other fates, but unless there is deliberate expenditure of more energy than is needed to send them to other stars, they will not "fall into the sun". So the vast majority of the raw material in a star system will still be available when the next civilisation arrives.

  1. Knowledge. Once a civilisation has energy and matter, it needs knowledge in order to use them constructively. Scientific and engineering knowledge to know "how" to do things, social knowledge to know "when" and "if" to do things. The nice thing about knowledge is that it doesn't get used up if other people have learnt it in the past. Examining the relics of previous civilisations may give the latest starfaring race more knowledge, but they will not be unable to build solar cells because someone knew how to do that before.
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  • $\begingroup$ "The question lists the concern that structures in space will eventually "fall into the sun". This is an understandable misconception" I was thinking more of the likes of Dyson spheres. Those require constant active balancing (even the swarms), without of which they'll quickly tear themselves apart and crash into the sun due to the mass shifts. $\endgroup$ – Darth Biomech Jan 15 at 17:16
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    $\begingroup$ @DarthBiomech Actually a Dyson sphere that falls apart would more likely have the pieces flung off randomly into deep space, which would actually make them less accessible than if they fell into the sun, or other gravity wells within their solar system. $\endgroup$ – aslum Jan 15 at 17:56
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    $\begingroup$ @RossPresser acknowledged, but couldn't think of a succinct way to describe the heliosphere and why it didn't matter. I may incorporate your wording into my answer. $\endgroup$ – KerrAvon2055 Jan 16 at 0:42
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    $\begingroup$ @DarthBiomech any realistic Dyson sphere will be composed of many satellites that orbit the star. If they stop functioning they'll go into different orbits, and maybe collide, and maybe coalesce into a new planet or something, but they absolutely won't fall into the star. $\endgroup$ – Nathaniel Jan 16 at 14:59
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    $\begingroup$ @DarthBiomech A solid shell, sure - but that's a ridiculous idea anyway (and not what Dyson had in mind at all). But for a swarm of satellites, absolutely not. You would need to rob the satellites of humongous amounts of energy to make them "fall" into the star! And unlike low orbit satellites around Earth, which experience significant amounts of drag and eventually do lose enough orbital energy, a satellite in an orbit around the Sun will be pushed away by the radiation and solar wind, and eventually captured by one of the planets in the system. $\endgroup$ – Luaan Jan 18 at 8:24
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Some early estimates according to Drake equation gave that there were probably between 1000 and 100,000,000 planets with civilizations in the Milky Way galaxy.

Astronomers estimate there are about 100 thousand million stars in the Milky Way alone.

Even assuming that the early estimates were too optimistic, we end up with on average more than 1000 planets per civilization, in the Milky Way.

If we extrapolate the same ratio to the other galaxies, and consider that as you state that they went extinct in few thousand years, it's easy to see that they didn't have time to consume all those 1000 planets they had available.

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You could handwave it away and claim that is why asteroid belts are as sparse as they are rather than being as dense as how they appear in Star Wars.

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    $\begingroup$ This could be expanded to explain why our moon is so lacking in minerals, as it's the "garbage dump" of vast mining exploits from millions of years ago. $\endgroup$ – computercarguy Jan 15 at 17:23
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    $\begingroup$ "What? You humans mine ore deposits with less than 1% concentration of useful stuff? You guys are hilarious!" $\endgroup$ – Luaan Jan 18 at 8:31
  • $\begingroup$ I've read that it's economically viable to extract silver from Roman mining waste. It might be waste by ancient Roman standards, but it still contained enough silver and was already conveniently dug up. And maybe the uranium we keep digging up has to be enriched because all the good stuff was used up and we're really digging up depleted uranium waste. $\endgroup$ – MSalters Jan 18 at 11:58
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I agree with the points about space being huge and the number of races small, an additional point could be technological advances in:

  • disintegration of matter, to get huge amounts of energy of whatever is around you, and

  • transmutation and other forms of construction of materials from the scratch (so you can get a bump of, say, iron, into an equivalent mass of carbon and the other way around, and you can use those atoms to efficiently build whatever you want built).

That will mean that those civilizations would not have a need to mine until depletion scarce resources, as suddenly there are no longer scarce resources as you can get anything you want out of whatever you had at hand.

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Space is big

There is a lot of space. It takes certain kinds of growth curves to saturate a galaxy. They might not have time to go everywhere.

Resources are what is rare

There are lots of empty solar systems; a generic empty solar system is thus cheap. Getting to that solar system, and specific solar systems, might have value.

If every human went "poof" today and an animal was uplifted to sentience 10000 to a million years later, there would be more resources up until the modern age for that animal to harvest from the ruins of our civilization. What more, there would be relatively pristine wild lands as well. They might have problems finding easily accessible coal or similar, but for entire phases of technological growth things are going to be easier.

Technology advances faster than growth

At "we are at K-1 scale" civilization, a 2nd solar system is worth a lot. But by the time you have turned a few 100 systems into dyson swarms, you tech up beyond the need to turn systems into dyson swarms.

Maybe you are extracting energy from the dark energy expansion of the universe, and building solar panels is no longer a big boost. Maybe you have wormholes and pocket universes that let you stuff an unbounded amount of territory within a single asteroid.

Topology

If the ability to travel isn't based on "as the photon flies" distance, then the shape -- topology -- of how travel works could open up places between the eras of civilizations.

This could be hyperspace lanes, primordial wormholes, whatever.

Suppose 1 in a thousand astronomical bodies have one end of a primordial wormhole in them, and those wormholes can be expanded to provide a portal to the other end. Now the graph of travel is based on what wormholes you find, and the other end could be in another galaxy; finding another civilizations wormhole network connects you, but most of the places you connect to are in dark space, and most of the rest are to pristine solar systems.

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  • $\begingroup$ Probably just a typo, but please change "astrological" to "astronomical," unless you really do mean things like a crab, lion, sea-goat, lady of justice, fish, bull, and so on. :-) $\endgroup$ – chris Jan 15 at 23:10
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    $\begingroup$ @s-k- I ain't lion, I'm bullish on the typo theory $\endgroup$ – Yakk Jan 15 at 23:30
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It's all a difference of scale.

Imagine that on modern Earth humans created a giant strip mine for coal or ore. Or maybe humans have cut down all the trees in the forest, leaving a barren dirt field. Then the humans went on to exploit a different natural resource.

Then after some period of time ants colonized the immediate area of the strip mine or the barren dirt field, creating elaborate ant mounds of their civilization. These ants would be eating the leftovers of the human civilization.

According to humans, there are no resources left. But according to the ants the former strip mine or lumber yard contains much more resources than in the surrounding areas. For example where there was a logging activity, although humans took all the trees and maybe even the branches, they left a lot of wood chips, bark pieces, and leaves lying around. For ants it is a real treasure because they have readily available wood chips for eating, that they would have had to painstakingly extract from real trees via a long and difficult process. Now there are wood chips and leaves lying all over the place, and the ant colony expands very quickly. Maybe the ants have now also learned how to utilize coal. Usually the coal would be deep under ground, beyond the capabilities of the ants to reach it, but in the strip mine the humans have done the heavy work to get the coal to the surface. According to the perspective of humans, there is no more coal in the strip any more after centuries of mining, so they abandoned it. But according to the perspective of ants, there is a lot of coal dust and small pieces of coals (giant boulders for the ants) all over the place. Now it becomes a very profitable coal mine for ants. Maybe even the ants do not know how to burn the coal, but they can perhaps eat the coal, using it for their own, but different purpose.

Another example is a garbage dump. The humans put lots of waste together in one place. When the ants find this location, it would be a heaven for them. There is a lot of food, plastic, metal, and other components lying in one place. So the ants will be very happy because the humans have collected a lot of useful resources all in one place, just for them!


Now back to your question, the human space civilization are the ants, and the alien space civilization are the humans in this analogy.

The human space civilization will come across "empty" mines, according to the aliens perspective "without resources". But from the humans perspective there will be a lot of resources. They will find the whole solar system, with a lot of asteroids made of different pure metals orbiting the star. Including rare Earth metals. These are the "wood chips", left over from the aliens mines. According to the humans this is the largest collection of easily extractable metals that they have ever found in their entire history.

What happens if humans space civilization discovers a planet which had been used in the past as a garbage dump by the aliens? There would be mountains made of scrap metals, lakes made of oils.

So the humans space civilization will live off the waste generated by the aliens space civilization.

ants

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  • $\begingroup$ Ants usually don't eat wood, that's termites. (They might use the wood for nest building, though.) $\endgroup$ – Paŭlo Ebermann Jan 18 at 1:05
  • $\begingroup$ Yeah, waste is not a final state of stuff - it's just an intermediate to something useful later on. There's a few exceptions, of course. But I would also expect an advanced civilization to be better at exploiting resource deposits; if we can exploit copper ores with less than 3% concentration profitably, I'd expect a more advanced civilization to do the same with 1%, or 0.1% "deposits", rather than stopping at 15% - unless space travel becomes even cheaper than that, which requires some form of magic like cheap FTL. And anyway, their ruins will become new deposits :) $\endgroup$ – Luaan Jan 18 at 8:29
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Substitution:

Shipping resources across stellar (and even mere interplanetary) distances is uneconomic, so vast space-mining simply won't occur.

  • It's okay for a few grams of unobtanium shipped from Tau Ceti to cost as much as the GDP of France. But it's not okay for a household vacuum to cost a year's salary merely because the facing was mined in the oort cloud. The vacuum manufacturer will find substitute material to eliminate the cost of all that unnecessary shipping.

Resource demand waxes and wanes over time.

  • Early starships and habitats might be built out of metal, but then supplanted a few generations later by shiny newer spun-carbon hulls, themselves supplanted later by grown bio-hulls.
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  • $\begingroup$ "Shipping resources across stellar distances is uneconomic..." Actually, that's exactly why it will happen, but only when you are setting up colonies. The "home planet" won't want to spend money and resources shipping resources that can be found locally, so they will instead have space mining abilities sent with the colony. But the OP states that the civilizations died, which is unlikely to happen when colonies exist, so there's a contradiction there, too. $\endgroup$ – computercarguy Jan 15 at 17:20
  • $\begingroup$ @computercarguy edited to address your comment. $\endgroup$ – user535733 Jan 15 at 17:54
  • $\begingroup$ Actually, no, that doesn't address my comment. I can see vast space mining happen around the home planet to supply the minerals/etc required to make lots of colony ships that are sent out to other stars, which having their own mining capabilities included, start mining around the new planets, and the trend continuing with eventually the colonies sending out colonies of their own after a few hundred years. This would lead to vast interstellar space mining. It just wouldn't all end up at the point of origin of the species. $\endgroup$ – computercarguy Jan 15 at 18:01
  • $\begingroup$ @computercarguy that seems to rather miss the point of this answer, which is substitution. Distance cost is only one possible reason among many for substitution. $\endgroup$ – user535733 Jan 15 at 18:04
  • $\begingroup$ So where are you getting all the carbon and other minerals from? You still need sources for that. Even "bio-hulls" need minerals. The human body has 11 essential elements and another dozen or more for a healthy existence. en.wikipedia.org/wiki/Composition_of_the_human_body Substitution only means you are simply shifting your reliance onto fewer minerals, which will make them more scarce, not more abundant. $\endgroup$ – computercarguy Jan 15 at 18:12
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Mass to energy to mass conversion.

Raw copper from the ground is nice to make wires out of. But if you can make copper out of whatever you have handy, you can leave the raw copper in the ground. Fusion power turns mass to energy, and a lot of it. Reverse fusion would be turning the energy back into mass.

Once this tech is mastered, one could turn any element into any other element, with appropriate sacrifices to the god of Entropy along the way. The planet of origin might be depleted in raw materials by the early civilization but after this tech is mastered, the civilization can make gold out of silicon or iron out of hydrogen. This will satisfy the need for raw materials useful as pure elements and obviate the need to retrieve elements from wherever chance has placed them in the universe.

Other raw materials become unnecessary. If you have mastered fusion you do not need fission fuels or petrochemicals for energy. I do not need to strip mine my new planet looking for coal if I can warm my hot tub with fusion power.

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  • $\begingroup$ This is exactly what Star Trek's replicators do! :D $\endgroup$ – stux Jan 18 at 14:15
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At 200,000-1,000,000 year intervals between civilisations you're looking at 3,000-15,000 groups over 3 billion years, they're exploiting an area that contains as many as 3 million star systems (that's the standing estimate for star systems within 500ly of Sol, 600,000 Solar Masses of stars all up) for an extremely short, geologically speaking, amount of time. 15,000 civilisations spreading across 100 star systems each wouldn't get everywhere if they didn't overlap at all so a good number of star systems must be left totally untouched. The proposed civisations simply don't have the range or endurance to do much against that scale of available material. There may be some areas that have produced more civilisations, their neighbourhood will be relatively heavily depleted in raw materials but enriched in the processed, but decayed, materials left behind by other civilisations, some of those materials will be more useful than raw ores while others will be less reusable or more dangerous.

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That is exactly what you would expect.

When you're extracting resources, you go for the ones that are easiest to extract first. "Easiest" is a bit of gloss here - it's some complex combination of cost-effectiveness, taboos, energy-efficiency, proximity, current demand for that resource, etc. Complex or simple though, mining sites and resource extraction methods are driven by the situation when they are being extracted.

Currently in the real world, for a few examples: one of the places we mine resources is from the tailings of earlier, less efficient mines. Hydraulic fracturing is driven by manipulation of well depreciation rates. West Virginia is full of beautiful rolling rills that were constructed to make it look nice after strip-mining it for coal (and also still has a bunch of coal).

Additionally, we concentrate a lot of resources in ways that will turn them into rich mines for future generations, once a few millennia have gone by (junkyards and dumps).

So, just following the patterns we see already on Earth: you don't have a good view of how many resources were floating around 1 billion years ago; nothing suggests that the "abundance" you see now is anything more than mine tailings. The local area might also be way out on a spiral arm of the galaxy, which is inconveniently far from the civilization, so not worth exploiting yet. There may be some taboo about mining most places near us, (just like you would not expect to see Yellowstone strip-mined or clear-cut). Planets are least likely to be mined out, because the additional expense to extract resources from the bottom of a gravity well will make mining planets inefficient.

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The universe is very young

After the big bang, there was a lot of hydrogen, helium and a smattering of lithium laying around, but virtually nothing else. It has taken time for the elements needed to support life of any kind, to be produced by stars. The supposition that there have been millions, or even thousands of space fairing species in our galaxy is nonsense.

As the percentage of metals (elements heavier than helium) accumulates due to novae, the probability of life forming increases. The scarcity of available metals in the early universe is the reason there are few if any interstellar capable species at this time. There will likely be more interstellar capable species in the future.

The rate of supernovae was higher in the past, and will continue to decline gradually over time, as free hydrogen gas supplies dwindle. The rate of supernovae correlates with the rate of species extinction. So over time, the odds that a space fairing species will survive long enough to scatter beyond the reach of a single supernovae will increase. The odds of survival were very low in the past, and some have argued, continue to be too low for any species to spread far enough to survive a single supernova.

It will likely be hundreds of billions of years before the galaxy is safe enough for any species to use up all the available metals in even a single star system, much less an entire stellar neighborhood.

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When people think of interstellar civilizations, they usually have an exponential growth model in mind, as that is what we know historically. But fact is, our growth is slowing and already negative in some regions, correlating strongly with the standard of living.

Your past civilizations died out after a few thousand years, that means they weren't aggressively expanding, but instead focussing on a high standard of living. By the same mechanism we can observe in our world, their expansion slowed to a stop, eventually regressed.

So, you have not only an explanation for their disappearance, you can also see that they won't have spread across all that many systems, and won't have used up that many ressources.

Your newcomers will find ruins etc., but also plenty of freah, unspoiled systems.

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Slowing down to collect resources takes a lot of time. A space-explorer civilization would travel close to c all the time.

1000 light years is a long distance, and cubed it is a even huger volume. If you want to explore any significant portion of it, you want to be travel fast.

Thanks to relativistic time dilation, once you get close to speed of light, distance starts to matter less and less as time goes slower for the traveler. But unless you have very powerful motors, slowing down to mine anything will take years.

As such, a true space explorer civilization would make a few colonies in the most interesting places, but other than that they'd be zooming around without ever slowing down enough to collect any resources in solid form. If the whole civilization travels at standardized speed, you can have inter-ship communication and meetings as if the galaxy was a lot smaller. But if you settle down on a planet, your 100 year lifespan will be just a few weeks for the rest of the population.

They might have developed technology that is able to collect interstellar dust and gas clouds without the high speed difference destroying the ship. Maybe a huge magnetic field could accelerate the particles to match the ship speed before capture? This could be a plot point, detecting some lines of lower density inside a gas cloud.

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  • $\begingroup$ Don't forget time dilation only affects the progression of time inside the spaceship. For the "empire" as a whole, distance is very important indeed - even if you're travelling so close to the speed of light that a difference of 1000 ly is just a couple of days for the crew, it still means that it will take ~2000 years for a roundtrip from the perspective of the people left on the planets. The fuel and supply cost will be much the same, sure, but that's not all there is to it :) $\endgroup$ – Luaan Jan 18 at 8:36
  • $\begingroup$ @Luaan That's why the whole civilization would travel, and no-one would want to be stuck on a planet. But yeah, they should of course travel in a similar direction on parallel paths, instead of going in opposite directions. $\endgroup$ – jpa Jan 18 at 16:30
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Resources are expensive/impractical to move

You'd practically need to convert the resources into starships to move them; it may be much more practical to just pack up, take a small group of starships and move elsewhere, using the resources in the new system, especially if fuel is limited.

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