I suppose some individual cases might work that way; but it seems to me unlikely to happen often enough to keep your supposed chain going. People tend to think that they’ve learned better over thousands of years, after all; and also to assume that the thought patterns of thousands of years ago were far more similar to their current ones than they actually were, so that even if they think they’re replicating the teaching information they include, they probably wouldn’t be.
Plus which, ten thousand years later they might be either unwilling or unable to send generation ships out at all.
Lifespans of tens of thousands of years might change that – although in that case what’s going out wouldn’t be generation ships, really. I wonder whether such lifespans are possible, and if so whether the individual change accumulated in such a lifespan would result in similar degrees of difference between the individuals in their first centuries and the same ones in their tenth or twentieth centuries as we now have between generations. With the information we have, and are likely to get, I think the best we can do about this is guess. But I also wonder whether our relatively short lifespans might be necessary to produce a technology-using species in the first place – maybe that frequent reset to new people is necessary for innovation to take hold.
We don’t have the same civilization as we had when our species expanded out of Africa, nor are we the same as when European powers expanded into the Americas.
There does not need to be any sort of cohesive civilization in order for individual groups to continue to expand.
Right, sci-fi writers are looking to tell a story, and actual physics takes a back seat to that.
There is no reason that we cannot managed thousands or even millions of “seeds” per solar system.
The very much least likely way for a species to expand is for them to fill up a ship and point it at another star, where it will arrive in hundreds to thousands of years and then everyone will disembark at their destination, blinking in the sunlight.
The way future expansion works is that we colonize an asteroid. Dig down a little bit to be protected from radiation, build a rotating habitat, then start mining materials to expand and to replace lost volatiles. Once the population gets high enough, they branch out, dropping some more colonies on nearby asteroids.
Various pieces of rock of all sizes extend all the way out through the Oort cloud, if you keep expanding just to the next rock over, eventually you notice that you are closer to another star than you are to the Sun.
Some colonies may choose to speed up the process, and pull an Oberth Maneuver around the Sun to get themselves to the next star over in mere thousands of years, rather than the tens or hundreds that just expanding may take.
But we aren’t talking about a “generation ship” with thousands of people somehow crammed onto a ship that has to provide supplies and support and not break down, we are talking about an entire world of millions of people, with an asteroid worth of material to replace things that don’t get recycled, and the ability to build more habitat, as well as repair anything that breaks. They can afford to take their time.
They wouldn’t be looking for a planet to colonize, but more rocks floating in space to expand into.
The speed of expansion may well be way lower than the speed of light, but it would be continuous and constant in all directions. If the fastest we could go is the speed of the Parker Probe, then it would take around 40-50 million years to fill the galaxy. That’s a long time when you are waiting for the bus, but it’s not that long in terms of the age of the galaxy. If dinosaurs had developed space travel, they’d have filled the galaxy by now.
Now, back to the OP. If the universe is infinite, then of course there are other intelligent species out there, if nothing else, if you go far enough, you find an exact copy of us. But in this galaxy or any nearby ones? Probably not.
It would take an unlikely fine tuning of probability to see what we see, and also have other space capable civilizations within the same galaxy. One in a trillion would mean that we are the only one in our galaxy cluster. If it’s a bit higher, we get inundated with aliens before we ever evolved. But anything lower keeps showing us the same thing we see. If it is one in an octillion chance, then we would still see exactly what we see.
Now, I do fear that the argument that the great filter may be in front of us has merit. That any species capable of space travel is also capable of destroying itself on the whims of an individual. It’s pessimistic, but certainly plausible.
But the argument that I give little credence to is the one that says that we will one day decide that we have enough. It’s not just human nature, nor animal nature, but the nature of life itself that it’s never enough. Besides, what is the point of leaving all that stuff out there if no one is going to use it? Every second that goes by, stars burn fuel that could sustain a more efficient civilization for hundreds of trillions of years. If someone actually does care about “environmentalism” on the scale of the galaxy, then they should want to go do something about those burning oil wells.
I really haven’t. And such things are not needed for these discussions.
Who in this thread has invoked FTL as being necessary for interstellar expansion?
A point; though most of the people referring to it seem to expect it to be.
However, it needs to be at least as much the same civilization so as to a) want to send out generation ships and b) be capable of sending out generation ships and c) not just send them back into the area already covered, either because they’ve forgotten what that is or because they’re not interested in expanding, but in trying to reconnect with the areas which they know were once populated by people they’d expect a good chance of being able to communicate with.
Energy cost, of a “seed” that carries with it enough to accomplish anything?
Where’s your energy coming from, on a cold rock that far from any sun?
There are individuals within our own species, right now, who feel that they have “enough”. There are large numbers of species that grow to a certain size and then stop growing, that live to a certain age and then die. Organisms survive within any ecosystem only to the extent that they don’t overrun that ecosystem and thereby overly reduce the numbers of those they need to live on.
I am highly dubious that it’s “the nature of life itself that it’s never enough.”
It certainly is the nature of our current culture; which is what, IMO, causes a lot of the problems we’re having. And it’s quite possible that we’ll never decide otherwise. I think it’ll kill us if we don’t.
Why does the “point” of everything have to be to be used?
Well, I’ve invoked it as being necessary for any kind of remotely coherent interstellar civilization. Not sure whether that’s what you mean.
I think this is the crux of the debate: you think this is a plainly obvious statement, but I disagree. Even if a species develops space travel, it does not mean that, given enough years, it will fill the galaxy. There are lots of impediments besides time that may make that impossible/impractical.
I don’t know that many have that expectation, it’s just one of many misconceptions that gets tossed out by naysayers that isn’t worth swatting down every time.
It is possible to maintain some level of cohesiveness if that is desired. Earth can constantly communicate broadly to everyone current cultural and technological trends, keeping everyone more or less in the same place.
And, once again, “generation ships” are by far the least likely way that we would expand, compared to all the other ways.
If other solar systems are similar to ours, they would contain millions of asteroids that would work just fine as a seed.
Nuclear power. Probably using the Thorium cycle. Maybe fusion as well, if that seems viable.
Sure, there are individuals who feel that way. But there are individuals who don’t. And the ones who feel as though they have enough and don’t reproduce get replaced by those who want to expand.
They are limited by the resources of the ecosystem. They don’t decide that they have gotten a large enough population and stop, they keep going until they’ve stripped everything bare, and then lots of them die off when they no longer have resources to sustain them.
Your incredulity ignores the fact that life started as some simple chemical process billions of years ago, and now empompasses every single crook and cranny of this planet.
Give me any example of any form of life that self limited itself. Not limited by environment, but by making the choice that it had enough and would now stop expanding.
Even down to bacteria, you can see this ipteus to grow and expand until it reaches its limits. That’s not going to change, so what is going to kill us is fighting over limited resources as we increase our needs and desires. What could save us is expanding our access to the resources that we need to fulfill them.
Not really, as my point was more that those who see galactic expansion as being plausible do not invoke FTL as being necessary to do so. Only those who think that galactic expansion is impossible seem to do so.
What impediment do you see that prevents this? I laid out a future that fills the galaxy with our descendants within 50 million years time. What part of that is impossible/impractical? It doesn’t require FTL, or even relativistic speeds, doesn’t require commitment of more than trivial resources, doesn’t require the effort of more than a comparatively small number of beings, and doesn’t require any sort of extreme longevity of the individuals.
How far can Earth broadcast into space before the signal decays too much? 10 lightyears? 20 lightyears? the issue becomes how do we power those receivers/broadcasters. Broadcasting, especially will require vast amounts of energy. Do we put them near stars or will the star noise interfere?
If interstellar travel is limited to no more than a quarter or so of lightspeed, it’s likely that they wouldn’t bother with planets except as objects of scientific curiosity; they’d have to be adapted to life in space habitats to make trips that would take decades or centuries. Civilizations like that could have visited this solar system many times without leaving any traces we’d notice, picking up anything they might need from stray space rocks and iceballs but not doing much of anything on Earth.
If our needs and desires increase as our access to resources does, it won’t help. We’ll just kill ourselves on a larger scale.
Already our needs and desires are decreasing our ability to access resources. Because of our other needs and desires, we’re highly unlikely ever to fund your asteroid program before we’ve used the resources that we’d have to have accessible here in order to get it started.
We’d have to be adapted to life in space habitats in order for that asteroid program to work, also.
I suspect we’d have to become a different species to pull that off (which isn’t to say that somebody else, somewhere in the universe, hasn’t done so; or even to say that we might not manage it, if we survive long enough. And if we choose to put resources in that direction, and if those who choose to do so aren’t prevented from being able to by other needs.)
I’m imagining a manned mission that takes 10,000 years to get to another star, only to discover that their studies were incorrect and the habitable planet wasn’t actually a place they could live.
Such a mission is possibly challenged by the sorts of things already being mentioned in this thread - societies would greatly change over that time; a mutiny is possible, and even a cohesive society may drift from its original mission.
There’s additional challenges related to maintaining a sustainable environment in space - you can’t pack for such a trip; are you bringing a farm?
You might also consider recent studies showing the impact of long term space travel on the body - it might be impossible for an earth bound species to replicate successfully in space.
What about disease? In a cloistered environment, the risk of some mutated virus killing everybody is something to consider.
I’m sure there are other challenges to millennia-long efforts to colonize space that I haven’t thought about.
Depends on how much power we want to devote to it, and how large of receivers that want to use to pick it up. The Sun puts out a whole lot of power that can be used to this effort. We could choose to make it broad beam, or directed at specific solar systems. The signal could be picked up and relayed along the way.
But most importantly, none of this is necessary. A cohesive civilization is not necessary to expand into the galaxy, any more than a cohesive civilization was necessary to populate the Earth.
If they happened to come across a habitable world, I could see people choosing to put roots down there. But I think the chances of there being habitable words is pretty small, and terraforming probably wouldn’t be worth it.
If they visited, why didn’t they stay? Why do none of the rocks left show any signs of having anything built upon them?
Probably, but we are looking at the heat death of the universe eventually as well. What do you mean by “we” here, anyway. The whole point is that there would not longer be a cohesive “we”, but trillions of communities spread across the galaxy.
Once again, who is “we”? If Elon Musk chooses to do so, is that still “we”? Are you unilaterally declaring the asteroids off limits? I suppose you don’t think that we will ever have any sort of off world mining and manufacturing, and that’s valid, it’s quite possible that we kill ourselves off first. But having offworld mining and manufacturing reduces our needs to exploit the resources here on Earth, and is fairly inevitable assuming we don’t kill ourselves off first. Once again, a true environmentalist would want us to start moving these disruptive and polluting industries off of the planet.
Why? If you have a rotating station that provides about a gravity, air of a similar pressure and mixture than here on Earth, what changes do we need to make to adapt to it?
That’s not saying that we won’t. I suspect that it won’t take long before our descendents are barely recognizable as humans in many ways, but it wouldn’t be necessary specifically for the purpose of traveling in a space habitat.
I mean, that’s pretty much the problem. You are imagining something that is unlike what we are saying would be the likely future. You are making up a scenario in your own mind, and criticizing it rather than engaging in the discussion that we are actually having.
All of your objections apply only to your imagined scenario, and not to the one that I laid out.
Let’s assume a narrow beam directed at a specific solar system. How far then?
I agree that it may not be not necessary for expansion for the same reason you mention.
However, I am reminded that error correction mechanisms exist both in the computer/telecom world and the natural world. Think of the other potential value of said signal:
Our cousins could get a bunch of free scientific knowledge that vastly exceeds their abilities to produce.
The same can be said for recreational and educational videos.
Such a signal would be incredibly precious. Especially until the new civilization gets big enough to produce enough of their own science/arts/etc.
One possibility is travelling to and starting a civilization in another star system is so difficult that civilizations only do it when their own world is facing some form of existential threat. Their star is going nova, or whatever.
I put out the linear expansion thing as just one possibility. We can’t rule it out, because we don’t know anything about other civilizations, how they might behave, how difficult the trip might be, how high the success rates are, etc.
And what does it look like if, when a civilization does establish a colony in another star system it takes 100,000 years to build up a population and resource base capable of doing it again to another system? And what if 99% of those colonies die off before they ever reach that stage? Shepherding a new colony from a small size to a planet spanning civilization may be extraordinarily difficult.
What does the math look like if every attempt to seed a new star system fails 99% of the time?
What if spacefaring civilizations with the ability to go to new star systems therefore have the ability to terraform all the worlds in their own system first? Because the ability to send significant resources to other star systems at a significant fraction of the speed of light might imply the ability to do all kinds of things that might make the need to colonize other stars irrelevant or rare?
What if it turns out that ‘habitable’ worlds are rare, and the average civilization is hundreds or thousands of light years away from the nearest habitable solar system? Now their 10,000 year trip might be 500,000 years, and totally infeasible. Maybe only a lucky few civilizations are close enough to other habitable worlds to make traveling to them reasonable, and once they colonized those they were done.
We can’t even conceive of a ‘generation ship’ that could sustain a colony inside it for thousands of years, let alone have the energy and mass on board to accelerate it to a reasonable fraction of the speed of light and decelerate it at the other end.
For all we know, the math could look like this:
Number of technological civilizations in the galaxy; 1 million.
Number that reach the level where they could and do send a colony to another star system: 10,000
Number that actually reach another star system and form a colony that survives long enough to be able to build a ‘generation ship’ and do it again: 100
So now you have 100 civilizations that managed to replicate themselves on another star system and build another generation ship. Of those, only one might be successful at doing it again, and the odds are that that’s the last time it happens.
Of course you can create scenarios where civilizations that can do this should be common, and once they get to that point they can spit out a generations ship per year. And maybe their tech is so good that they make it a high percentage of the time.
But we don’t know. Simplistic exponential equations are pretty useless when dealing with complex phenomena. There could be a thousand factors that go into interstellar travel that we have not yet discovered. It could be that the places in theh galaxy that have the most civilizations also have a lot of interstellar debris that makes high speed travel impossible.
Maybe long before you get to the ability to send serious mass between stars you develpp incredibly powerful telescopes, and they reveal that for most civilizations there is nothing interesting close enough to travel to. Or maybe civilizations that could travel between stars are so good at manipulating mass that they just don’t need to do it unless their star is failing.
Or maybe there is just so much we have yet to understand that we are not even asking the right questions and the aliens would laugh at our childish assumptions.
Depends on how much power is put into it, and how big a receiver is built.
As a very general estimation, from any distance you can see the Sun, you’d be able to detect a signal, if both parties cared enough.
Right, and if Earth has a desire to maintain some level of homogenous culture across the galaxy as it spreads, then they will make the effort. If they don’t care, then they won’t.
And at that point, it may be worth sending signals back to Earth, to show what has been found.
Which will happen eventually, one way or another. Maybe another threat is that we are running out of resources for our growing population.
Well, you are asserting that you know about other civilizations with this. The most likely way that anything grows is radially and exponentially, why would a space faring civilization do otherwise?
It would be like saying that this field could never be filled with grass, if every year, only one new grass seed is grown.
I don’t know what the fixation is with planets. Why do you even think that they would care about planets? They come into a solar system in their asteroid colony, and as they approach, hundreds of small colonies split off to start growing on new asteroids. Some may fail, but what makes you think that most will?
Give me a reason why that’s a reasonable predictor.
Can they create matter and energy out of nothing? If so, then sure, they don’t have to go anywhere. If not, then they’d have to go somewhere else.
What is with the fixation with habitable worlds? They are not needed for expansion.
I present to you, Spaceship Earth.
And for all you know, those numbers could have nothing to do with reality. They certainly are not based on anything.
Lotta maybes there. Nothing with any substance at all.
Indeed, a habitable world may also be a life-bearing world, and I would be much happier if the colonisation process kept well away from any life-bearing worlds. Any world that can develop life by itself should be left alone to develop in its own fashion, without interference from the descendants of humanity.
This is one reason I’m not too keen on the term ‘colonisation’. It mixed up in peoples minds with ‘colonialism’, which has been the cause of endless abuse and suffering on our own world; if a space-faring civilisation wants to establish colonies in other systems in the galaxy and beyond, they should avoid any adverse interactions with the indigenous lifeforms, and avoid ‘colonialism’ at all costs.
That would still be exponential growth (or decay), though–assuming the probability of an existential threat is somewhat constant for any given colony.
Then the civilization will die off (exponentially) unless the successful ones can send out 101 ships.
The reason why exponential growth is a universal is that it is the only possible function when the conditions are constant over time. It’s the same reason why radioactive decay is exponential.
My point is far more general than specific questions about how the replication takes place, their motivations, etc. The only assumption is that whatever these details are, they are (in a probabilistic sense) the same for each new system. Since the galaxy has (statistically) similar conditions all over, and the timeframes we’re talking about aren’t long enough for significant cosmological evolution to happen, one would expect that to be the case.
A civilization where 99.9% of colonies failed but the successful ones sent out 2000 ships would grow quite rapidly. One where 90% of the colonies managed to send out a single ship but never sent a second would ultimately collapse. This is exponential growth and decay.
The only way to achieve constant (or linear) growth is for that exponent to be exactly 1.0. The probability of that being true accidentally is negligible. The only way it could happen at all is if the civilization was in constant communication with itself and had a feedback mechanism to limit growth. But even that is unstable; any breakaway colony that decided to not follow the rules would then be subject to exponential growth again.
It’s NOT a ‘reasonable predictor’. It’s simply part of a potential solution space to refute the idea that the Fermi Paradox is some sort of logical argument against the existence of other civilizations in our galaxy. I could come up with many more if I spent the time.
The point isn’t to predict anything, it’s to come up with feasible solutions that could answer the Fermi paradox with something other than, “We are the only civilization in our galaxy.”
Yes, I’m very familiar with exponential growth and decay. I think you are missing my point as well. What I have been trying to refute is the idea behind the Fermi Paradox’s “Where are they?” question. Especially the simple notion that if there are other civilizations, some of them would be much older than us and therefore should have already expanded through the galaxy. Therefore, since we have no evidence of them, the conclusion is that we’re alone.
All I’m trying to say is that you can concoct all sorts of solution spaces that allow for lots and lots of civilizations in our galaxy without us ever encountering them or noticing their existence. One of them is that self-replicating probes face some limit we don’t understand. Another is that it turns out to be so incredibly hard to move large masses between star systems that it never leads to any kind of sustained exponential growth.
The Earth is full of creatures that undergo rapid expnential expansion from time to time. But there’s always some limiting factor that prevents the Earth from becoming, say, a giant massive ant colony or the oceans being overrun by squid or algae or anything else and dying off. In complex systems, you can have all sorts of nonlinear responses and exponential growth, but when you put them all together the big picture can be completely stable and still diverse.
We have no idea what kinds of forces exist in the ‘galactic ecosystem’ that might prevent species from colonizing the entire galaxy. We’re babes in the woods and shouldn’t presume we understand any of it enough to make hard predictions.
Sure; I was only arguing against the “linear growth” supposition in your example. I posit that it would be nearly impossible to achieve. Exponential growth or decay, but nothing in between. Assumptions of “knife edge” fine-tuning are not plausible.
After a while, yes, the growth peters out due to competition. But we’re talking more about coverage here than absolute numbers. A civilization that only colonized 1 in a million systems could still be said to have expanded across the galaxy if the coverage was uniform. And since the conditions are uniform (i.e., the planets on this side of the galaxy are basically the same as those on that side), the only thing that would plausibly stop it would be another civilization.
The ‘great filter’ hypothesis also bugs me. There is no evidence for any kind of great filter, nor is there a need for one to explain why we don’t see other civilizations.
There *could be a great filter. There could be several of them. Or, perhaps there’s just zillions of threats that take out civilizations, and we’re the lucky ones who dodged them so far.
The World Series of Poker starts with thousands of players, and ends with one. And there is no great filter that wipes the others out. Just lots and lots of hands, with a non-zero risk of being wiped out on each one. Play long enough, and you can eliminate everyone without there ever being one giant risk that everyone has to face.
The Earth has been hit by many big objects that came close to wiping out the planet. We spent a billion years or so in stasis because the oceans filled with hydrogen sulfide and inhibited anything but bacteria. We have a sun that has proven to be remarkably stable. In billions of years we never had a star come close enough to disrupt the orbits of planets. We never got hit with a gamma-ray burst, or had a supernova go off close enough to sterilize us. Humans came within a whisker of dying off early in their existence.
Maybe the ‘filtering’ is that the march of billions of years to a technological civilization is the equivalent of flipping a coin a hundred times and needing it to come up heads every time or you die. Again, we have no idea. But I don’t see that the assumption of a ‘great filter’ is any more warranted than the assumption that we just dodged a thousand bullets and are the lucky ones that made it to the other side.
Thus the implicafion that there is a looming ‘great filter’ ahead of us is just pure evidence-free speculation with no reason to believe it’s likelier than that we’ll just continue on doing what we’ve been doing and one day some threat will get us - but not necesarily the same one that got anyone else.
