It’s very possible to reach a wall where zero teraformable planets are within reach of your ships. For large civilizations that’s unlikely to totally block expansion, but it might make the path very convoluted thus increasing total time by a rather extreme factor.

The transport layer is the easy part. Content integrity is a much harder problem.

All of your probes and colony ships have to reproduce the source culture - or some viable subservient spin-off - with 100% accuracy.

This explicitly means 100% reproductive success of all features, especially the politics and economics, with no errors.

For a successful colony, stability and conformity have to be maintained for long periods - centuries at a minimum, perhaps even millions of years.

And of course this assumes the source culture is stable in the first place.

Otherwise you're just seeding the galaxy with potential competitors, and/or setting up some kind of galactic Battle Royale.

I'm bemused by the suggestion the first option is actually possible. The second seems more likely, but might not be considered a success in the sense of creating a stable galaxy-spanning civ capable of common strategic goals.

The only thing that needs to be preserved is the desire to build more colonies. I'll grant even that's a stretch, but demanding 100% cultural fidelity is silly for discussing the Fermi paradox.

Terrorism, as you mention, might be possible (but again remember, no stealth) and claim jumping (where you displace another group that got there roughly when you did). But even in densely packed stellar neighborhoods the average star is surrounded by a moat several light years across. Once the locals are developed enough to mount a serious defense, they're probably immovable.

More generally, the point I'm raising is symbolized in entirety by the Spartan faction's ideology in that narrative environment.

Dropping asteroids on habitable worlds and causing ice ages to clear out the population _might_ still be faster/cheaper than terraforming a semi-hostile world.

Further starship drive capable of reaching a significant fraction of the speed of light make one hell of a weapon. But you still need to deal with space based assets that can dodge your initial bombardment and at a minimum are armed with powerful engines. So sure you can destroy planetary populations etc, but now your still out gunned 1,000:1 locally and pissed off a civilization capable of doing the same thing to you. Net result MAD.

A large technical advantage may make up for this, but that means the winner has better tech is much harder to take over a second time. On top of this the only thing worth shipping between stars is information at the speed of light. Making conquest largely pointless without FTL.

It could be worthwhile to beam energy out to interstellar distances (also at the speed of light). This is probably needed for interstellar travel anyway.

That's hard. I'd say harder than solving the physical problems of interstellar travel. Once a generation has learned to live with the limited resources of a starship, living with the limited resources of a planet is going to be a very attractive option. What's their incentive to colonize more from there?

If more technologically advanced aliens exist then our not sensing them is much more likely because they don't want to be sensed than some other consideration like them stopping to setup on some habitable planet. I'm horrified about war, and I'd hope they would be too, but it may be that aliens come to understand species or ecosystems in a more expansive way and may consider the process of ending war as a necessary one for the maturation of an ecosystem.

Or the great filter is true. We all end up killing ourselves because it's impossible to escape exponential technology growth and mismatched incentive problems, or something else like that.

That is, if we are talking about something comparable to current humans. Immortal super AIs might don't care about idling in the void for a few million years, just for the opportunity to re-sync those gained experiences to their decentralized knowledge a few million years down the line. I really like the single omnipotent AI scenario, since being immortal and not depending on others changes quite drastically what strategies can be successful - it won't be anything like human kings who need to keep their subjects at bay and working for them to support their power and limited life. But we shouldn't restrict our imagination, if we are talking about possibilities and galactic time-spans.

The important part is, as mentioned by GP, the desire to expand, since this is a dominant strategy. In comparison, not every living being on earth has the drive to participate in evolution by e.g. creating offspring. Those usually just drop out of the "game" and likely won't matter in the long term, at worst making it a bit harder for the others initially till their disappearance. What matters are those who have persistent impact... e.g. by colonizing/making offspring.

Further it seems much less likely the populace would be so willing to send aide to Britain during WWI if it weren’t for the cultural similarities. If instead Spain had colonized the US it seems very likely the country would have remained neutral as Spain did.

It's not just the US either. India was a profitable colony at the time but might turn out to be a major detriment to Britain overall, both as a source of cheap skilled labor and as a powerful nation of their own. Who knows what would have happened without the British. A lot of the borders in the Middle East are drawn by Britain as part of their WWI mandates/colonies, and the problems from how those borders were drawn spill over into Britain (yes, it's not the only problem in the Middle East by a long shot, but it's one of them).

I still think overall Britain came out ahead (just look at Hong Kong for what cultural influence can do), but it's not hard to imagine how colonization might be seen as a net negative if a few times things turned out even slightly worse.

https://commons.m.wikimedia.org/wiki/File:Imperios_Español_y...

It could have gone another way, there’s a reason we’re talking about Britain instead of England and Scotland, but I would say it has worked out brilliantly.

Also, a neighbor idea of the scientific progression in thousand years from now on doesn’t account for an artificial biology progression, like the same humans in 1k years would do unimaginable things. Would they be still individual humans? Personally I don’t think it is more than juvenile civilization’s tunnel vision illusions.

The number one attribute that needs to be preserved is the disinclination to blow each other to smithereens. I suspect self-destruction (to a level where technological progress is setback millenia) is a common enough occurrence that would occur well-before FTL becomes a possibility.

I also suspect (despite decades of reading SF and my own wishes to the contrary), that the kinds of attributes that encourage exploration, expansion and risk-taking, are also somehow linked to aggression and violence - "might makes right".

Any empire/political system/civilization needs some means of holding it together. Traditionally this is done through armies. As our transport technology has gotten better, our ability to move armies around the world has increased and with it the ability to control large economic systems without them breaking apart. Nowadays we have a globe-spanning economy. However, time scales of interstellar travel are so big that cultural change is much faster than the method to build a colony. By the time that nuclear bomb ship has arrived at the other planet, we might have changed our mind threefold.

In fact, already if you send a generational spaceship to a star 100 ly away to reach its destination in a thousand years, by the time you receive message from their arrival, both their as our language will have evolved by 1100 years. So yeah you are right, cultural decay (or rather "change") is a big problem.

Currently our governments are run by humans with all the human failings. Instability, corruption, etc are components of the governments due to our human nature. You are right that it would be hard for human run governments to colonize the galaxy as due to the light speed limit, we can't achieve transport scales needed for a human-run civilization.

However, we won't need humans to run the governments. In the future we'll be able to engineer and build extremely intelligent AI systems with multiple layers of error checking to withstand decay for trillions of years. You think that sounds undoable? Check how many cells humans are made out of and how well they work together for decades.

The unsolvable political problem will just be turned into a solvable engineering problem.

Those AI systems would run key parts of the governments and economies themselves (entirely without needing human help) and enforce a set of basic rules like preventing nuclear weapons, bioweapons, torture, etc alongside ensuring they are the most powerful factor in those places, i.e. are able to fend off any kind of attack. Otherwise they won't interfere with human matters and let humans govern themselves with the human imperfections.

Basically, they'd provide the "galactic federation layer" and ensure peace through their programming. Some factors of their programming could be changed by the human population, but others, like preventing nuclear weapons, couldn't. So even if the humans wanted, they wouldn't be able to wage catastrophic war with the neighbour planet, or at least specific types of war (allowing trade war but not allowing nuclear war). Even if the risk for interplanetary war is just 0.1% per year, over millennia that's a large number and interplanetary war can have major consequences.

To the present reader, those AI systems probably seem weird and dystopic, but I think we are already evolving towards them. Already, many parts of the governments and economies of various countries are being automated. One day in the future the automation will have minimized human involvement enough so that you can think about von Neumann probes.

The first people to develop AI ran governments will probably be the dictatorships who want absolute control and micromanagement (single-operator government). But in general, the systems are more efficient than chaotic systems, and with increasing perfection of the technology, once a system is a dictatorship, it probably won't change back to a non-dictatorship without outside interference. It's important to eventually remove human control from them as otherwise over the millions of years, eventually someone will figure out how to flip the switch and create dictatorships. So it's kinda important to get the "right" set of rules into these computers.

Already building these computers is a huge project that would take a long time to get it right. But it's an easier task for humans to do than running an intergalactic civilization.

Also note that those systems don't have to necessarily deal with humans in their current form. They could also deal with human simulations uploaded to the cloud and the systems would just provide the resources to run that cloud. The "real world" might become utterly uninteresting to humans.

It is not necessarily true that more time is spent aboard a ship than light would spend taking the same path, as measured by an external observer.

If you had a ship capable of accelerating at 1g indefinitely, then as measured by the crew, they could cross the galaxy in only 24 years.

https://en.wikipedia.org/wiki/Space_travel_using_constant_ac...

I like everything else you wrote.

This is why when you're calculating the actual value of time dilation, it considers what fraction of speed of light you're traveling. Because if you were the traveler, time dilates and length contracts EXACTLY enough to make light appear to travel at 1c (regardless of your own speed).

Time dilation is only 1/2 the story. The other half is distance measurements get distorted.

People in the spaceship see the same maximum velocity of objects they pass aka c. However, if a huge measuring tape with say light year tick marks passing them they are going to measure it’s speed at say .99 c and the time between tick marks is X. Alternatively, at .999c they would get a new time period Y. However the difference between X and Y is not simply .999/.99 but rather a more complex relativistic adjustment.

However, this is only important for people on the spaceship. For people staying home the it takes 3.5x the energy to hit .999c vs .99c yet it’s only shaving 1% off the observed travel time. Which is unlikely to be considered worth it by just about any civilization baring significant changes to the laws of physics.

Particle physics get matter to 99.9999% of c which causes crazy time dilation to the particles and nothing to the scientists. Further, constant 1g acceleration of a starship to high fractions of c is basically science fiction. Not even matter anti matter reactions can keep up those energy demands for very long.

https://us.macmillan.com/series/theeschatonsequence/

Why would we stop at a hundred of colonies? A couple of observations:

- in rich countries, the trend is that the birth rate is declining, the population gets "older". There seems to be a link between wealth and birth rate. Even if space conquest gives us a lot of resources, if that trend persists, the lack of people will be the limiting factor.

- there are only really two reasons to go out: curiosity and making sure that a stellar-scale catastrophic event doesn't wipe out our civilization. A bunch of colonies "far enough" from Sol achieves this. And probably after visiting a dozen of systems, the next one will look like one of the previously visited.

You could argue that exploration, migrations, colonization are but the emergent/complex behaviors described by more fundamental principles in psychology, sociology, biology. Conway's game of life, in a way. History being a mere factual, chronological account — a log.

You are thereby operating at a high-level, manipulating complex umbrella objects like "great migrations", "local population pressure", each of whose words (composite concepts) map to lower-level datapoints — e.g. like some eternal tension (psy., soc., hist., bio...) between a desire to look inwards (for security? familiarity? survival, support?) and a drive to seek outwards (for growth? curiosity? lack, want, need?)

We would not observe anything different unless one of them actually flew to our solar system and tried to contact us. That's how bad we are at detecting distant life.

So, some alien unmanned probe the likes of Voyager in large orbit around the Sun? Yeah, no chance in hell we'd detect that by random chance, we'd have to seriously upgrade our space infrastructure to even pretend 'monitoring' our close vicinity, let alone post-Jovian space. And we have virtually no knowledge of about half the distance between interstellar medium and the Sun, that's how limited we are to even modeling the closest star systems.

Edit: apparently double-post with aruggirello; I agree with him.

Oh, and that thing is mostly between the orbits of Mars and earth - much smaller search space than "the entire solar system"

[1] https://www.whereisroadster.com/

Now, exchange that for a black-ish ship a few hundred meters sized, quietly coming from Vega to visit say, Saturn. Nobody would probably notice it coming and going, despite Saturn being one of the most popular targets of the entire sky.

Perhaps you mean in a solar orbit near the Earth?

And while intelligent life may exist on a planet for millions of years, their window of actually emitting something into the void in a manner we can detect with our tech today [0] will probably be a lot shorter than that.

This gives us a relatively tiny and limited visibility window into the history of life out there. Unless we manage to sync our window perfectly with theirs we'll never know they existed.

[0] https://www.xkcd.com/638/

[1] Particularly if your operation is covert, discrete, observational, non-disruptive: you'd want to avoid signaling your presence in all directions, while wasting 99.99% of that energy away from your intended receiver. It's just military efficiency, a photon-VPN so to speak, that you'd need to "physically MitM" to hack.

https://en.m.wikipedia.org/wiki/Planet_Nine

https://www.sciencemag.org/news/2019/09/planet-nine-may-actu...

...because organisms (and presumably cultures) without that characteristic wouldn't be as numerous as otherwise identical organisms which do have that drive, in a given environment.

How is that supposed to work?

Just look at what we have achieved in Earth vs. what we have achieved on the moon, or anyone's plans for a Mars colony. Mankind may set for on Mars eventually, but i don't think we'll ever do something like set off fireworks there.

Any colony that moves past the immediate survival stage is a success. That does not mean they have millions of years of fossil fuel stored to start further exploration.

Your scenario requires a uniformity of outcome across all the parts of that civilization, spread across multiple stars, and spread across all future time. They all have to go down and stay down.

So, if a stable multistellar society is not building colony ships, it's not because it can't, but because it has chosen not to. How does that uniformity of choice get enforced across time and space?

What you have are individual civilizations which may or may not, as you mention, decide to invest the time and resources into interstellar travel. But that investment isn't guaranteed. We've had the technology to send out interstellar probes for decades, yet we haven't committed to sending them out by the hundreds or thousands. We could have colonized Mars or the Moon by now, built Orion starships, but we haven't. Technology doesn't govern the advance of space travel, politics does.

>How does that uniformity of choice get enforced across time and space?

I think it's just a matter of probability. I don't believe technological development, much less to the degree of having a space program, are an inevitable result of intelligence or the presence of civilization. It's easier not to have a space program. It's easier, if you have a space program, to only explore your own solar system. Any number of issues, such as not being near enough to a colonizable star, not having sufficient energy or resources, natural disaster, giant ants, robot uprising, superflu, etc. could keep a civilization from starting, much less maintaining, a project of the necessary magnitude for the necessary amount of time.

And then you have to survive the trip, and actually succeed at colonizing another planet.

I think it's entirely within the bounds of reason for every civilization which has attempted interstellar travel to have failed up to this point.

They'd more or less evolve completely independently and it's conceivable that having these limitations will mean they never reach the same potential as the original humans did on Earth.

Usually the comparison with colonists of the past pops up. But they had the distinct advantage of being perfectly adapted to the planet and many civilizations still perished. Seeding another planet with humans raises a lot the bar for successfully developing a thriving civilization capable of reaching the levels required to further spawn successful colonies.

And a philosophical thought: would they even still be humans after (tens of) millennia away from the home of humanity, in vastly different conditions from the ones that evolved us? Would they be "our" thousands of colonies?

However, the economic cost of making an interstellar colonisation ship is so vast, that from where we are it seems reasonable to assume that anyone who does it has fully automated manufacturing and resource gathering – or, to put it another way, they are post-scarcity. If you’re post-scarcity, then you’re no longer fragile, because you can have a complete backup of everything you need, including the skills needed to rebuild.

Of course, there’s lots of ways for things to go wrong, and if I were to imagine badly written control software that means the fully automated manufacturing kills everyone, I’d be accused of being too derivative rather than implausible…

Also, we were able to land men on the moon 50 years ago, and now that knowledge is basically gone, and the tapes lost, and people are starting to believe the Earth is flat and that the moon landing never even happened.

Meanwhile, we can still read tax records from ancient Sumeria because they were carved into clay.

Complex systems are always more fragile than simple ones. It seems to me like we've been standing on a house of cards for the last century.

I assume that it will require population control, because we will not be able to find enough habitable planets to keep up with the growth we have today. Basically a choice of "immortality" or procreation. This will also set a limit to how many colonies that are practical to create.

Also some may not accept the risks of travelling to other solar systems. Why risk dying "young" when you can expect to live for thousands of years?

If all these long living people dont have to much new children (and might not be able to ? eq. if fully digitized or with body fully replaced with mechanical parts), it might be even easier.

We'd see more red than we do - more heat and less light. Civilization produces heat. Advanced civilizations would presumably convert starlight to energy and produce waste heat.

Or planetary surfaces.

“A telescope about 51,075 ft (15,568 m) in diameter would be required to resolve the Upper stage from Earth. A smaller one could see him as an unresolved dot, about 98.2 ft (29.9 m) in diameter, in ideal conditions”

So I recon that reinforces the hypothesis.

To image something like the roadster on a Planet orbiting Vega (~26 LY away, furthest star anyone on Earth could visit and then return from in a lifetime) you're looking at lenses greater than the orbit of Pluto, ish.

Optics/Physics is a bitch here. To really see/prove there are aliens running about, they have to screaming at the top of their lungs for a very very long time, hoping against hope that anyone will hear. It's just really really hard to build equipment that can passively listen for accidental broadcasts and spy on alien cars. At least under our current understanding of physics.

[0] http://hosting.astro.cornell.edu/academics/courses/astro201/...

It is not necessarily true that more time is spent aboard a ship than light would spend taking the same path, as measured by an external observer.

If you had a ship capable of accelerating at 1g indefinitely, then as measured by the crew, they could cross the galaxy in only 24 years.

https://en.wikipedia.org/wiki/Space_travel_using_constant_ac...

To an observer who is self-propelled (and has enough energy), the speed of light (as seen by others) is no limit. It's not like you can fire your thrusters and NOT gain momentum and speed; or that, as you accelerate, the stars start passing by at the speed of light, and suddenly your ship jerks, ceasing to accelerate, because you hit an invisible velocity brick wall.

https://en.wikipedia.org/wiki/Deimos_(moon)

https://en.wikipedia.org/wiki/Apparent_magnitude

Edit: corrected

Why send the robot or alien at all if you can instead send the design/machine to make the alien. Perhaps they need send nothing more than RNA/DNA on an incoming space rock....

A much larger range of the parameter-space could produce either thousands+ of technological species (which we have pretty good evidence is not the case) or less than one on average pretty galaxy.

So we have the options:

Lots of species (contradicted by the evidence)

A handful of species (inherently unlikely)

Very few species (current best bet)

We do not know how to detect life outside of our solar system. The only way our measurements would change is if one of them literally landed on top of us.

And if there are all these technological species, we would expect some of them to be much more advanced than we are. Why haven't some of them noticed us?

You can come up with possible answers to these questions, it's just that those answers look less likely than, "those species aren't actually out there."

You can't see a laser transmission off-axis if there aren't any stray photons reaching your detector - that's just physics.

You can't detect a radio signal below the noise floor without some a priori knowledge about the statistics of the signal.

These aren't justifications, these are simply facts about the current limits of our ability to detect far-away signals. These limits suggest that millions of far-away worlds could be extremely chatty between themselves, but unless they decided to point a transmitter at us, we would be none the wiser.

You shouldn't use a measurement that looks identical for case A and case B to decide which one is more likely.

Imagine if we had thousands of microsats in orbit around the various planets that we could triangulate data amongst? We need to be more aware of our solar system before we can even make reasoned arguments about life within it alone.

That's an excellent point, for all we know we have intelligent, non-spacefaring life right in our solar system. It's unlikely, but there's still plenty of oceans, gas giant atmospheres and lava tubes that we haven't looked at yet.

So, question: how strong does an undirected, random signal need to be to be reasonably detected at 10 light years away?

We already know neutrinos can travel through most mass, so modulating those would let you transmit through the Earth and Sun with lower latency and without a repeater constellation routing around the object.

Whatever aliens might be using to transmit information is likely more advanced than we're able to detect.

But a simpler explanation that has many more paths to being true is "there's nothing out there."

To be clear, I don't think the evidence suggests near-certainty here. I wouldn't say that there's a 99% chance that we're alone in the galaxy. But it's also not a wide open field. There is some evidence, and so far that evidence suggests that we're likely alone.

Alien life forms wouldn't need to use technology to make themselves harder to detect. It's extremely difficult by default.

They would need to use technology to deliberately spread a message in a way that is at all likely to be detectable, and even then would still have to get quite lucky.

Maybe they have?

We don't "contact" every pack of deer that we notice.

It is not that humans are technologically primitive (which we are), it might be we are too intellectually/capacity primitive to be seen as "contact" worthy.