6 ms·

The Fermi Paradox and the Aurora Effect: Exo-Civilization Settlement

92 points by pkrein 7y ago

coolspot 7y ago
> Using our steady-state model we constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the Galaxy. Explicitly, our solutions admit situations where our current circumstances are consistent with an otherwise settled, steady-state galaxy.
andrewfelix 7y ago
Interesting premise. Pity I can't read the article.
- deleted 7y ago
  [deleted]
- archi42 7y ago
  Maybe the link was updated? It now points to arxiv, from where you can download the paper (or does arxiv implement some geoblocking?).
  - andrewfelix 7y ago
    yep, was just abstract earlier
xcq1 7y ago
https://arxiv.org/abs/1902.04450 https://arxiv.org/abs/1902.04450
- sytelus 7y ago
  Another relevant paper: https://arxiv.org/abs/1612.03238 https://arxiv.org/abs/1612.03238
solotronics 7y ago
All of these calculations are predicated on us existing in a physical universe and not a simulation (simulverse?) it could be we are the only life in this specific simulated existence, even though the mathematical rules of the place would make it appear there should be others.
- namanyayg 7y ago
  there's so little evidence of it being a simulation just for us. Even if all of this is just a simulation, I'd bet that we're just forgetten children of the simulgods and the true focus is something more obvious. See also Omphalos by Ted Chiang.
- tsimionescu 7y ago
  The assumption is that there is a set of laws of physics which are consistent with our observations, that are the same across space, that do not vary with time, and that all phenomena in the universe are ultimately caused by these laws. Whether these are the laws of nature, the laws of a simulation, or the laws of some Gods playing around, it makes no difference. Unfortunately, without these assumptions it is impossible to have any kind of scientific knowledge - if we can't assume that the sun rising for the last hundred thousand years means it will rise again tomorrow, or if we don't assume that the universe extends in the past as well as the future, there is nothing meaningful to study. Note: the laws of physics I am talking about above could be very different from what we know today - just as QM and Relativity are to Newtonian physics - but that would not change the assumptions I'm talking about.
  - solotronics 7y ago
    Even if my half baked thought experiment was true I agree in that it shouldn't make any difference in our goals or ideals. I was merely positing a possibility for why if statistically our spacetime could be packed with neighbors we haven't noticed anybody. Another reason could be there are visitors they just exist on dimensions perpendicular to the 3d space we perceive, maybe even our concept of spatial dimensions is a oversimplification or a small slice of a full spectrum.
- 7y ago
hoseja 7y ago
I find the assumption that a space-faring civilization would need ideal planets to settle on somewhat questionable.
- XorNot 7y ago
  I mean a lot of this all turns on what happens to us in the next 200 years. Which... That's slightly less time then federated America has existed. Are we at the peak of what people achieve on temperate world's? Maybe technology doesn't meaningfully advance much beyond what we already know - you get a computing boom, Moore's law ends and then a couple decades of discovering no substantial alternatives to the silicon chip.
  - simonh 7y ago
    I've been homing in on this conclusion, or a neighbour of it for a while. Take the periodic table. That's it people, we already know all the stable elements. Nobody's going to discover unobtanium. Aside from some high energy physics and some details of quantum mechanics, we probably know most of the useful practical physic there is. The open frontiers are biology and chemistry, but those are all about combinging things we mostly already know about in new and interesting ways. Eventually we'll figure all of those out as well. Then what? I'm not saying it's impossible we'll discover some amazing, paradigm shaking new physics that will upend everything. Maybe. But we can't bank on it and it's entirely possible no such civilisation shaping new physics exists. If that's the case, then the future will all be about engineering based on parameters we already pretty much know. I often see the Daedalus project held up as 'proof' interstellar travel and even interstellar colonization are possible. That was a designs for a very modest space probe payload, but even so the resources required to build them would pauper our whole civilization. Even if, or when, we master the resources of our whole solar system, those probes would be a significant cost and it seems likely they're way too puny to deliver a robust self-replicating bootstrap infrastructure. There's nothing inevitable or necessary about interstellar colonisation. The universe doesn't owe us Star Trek.
  - goatlover 7y ago
    Why would technological advance be entirely limited by the end of Moore's law? There's still advances to be made in biology, nanotech, materials science, and making full use of the computing we already have. And there are plenty of proposals for future engineering on and off world, if we have the motivation for those projects.
roca 7y ago
They talk about planets and generation ships. Isn't it obvious that a multimillion-year spacefaring civilization would be mostly autonomous machines that have no need for habitable planets and can sleep for aeons? They also talk about civilization lifetime and interstellar resettlement. But interstellar resettlement doesn't make sense to me; simpler for machine civilizations to hedge their bets by putting resettlement sleeper ships in highly eccentric orbits with some desired period. Maybe there are civilization-killing effects that disable those resettlers, but they would apply to interstellar resettlement too.
- ymolodtsov 7y ago
  Well, no. That assumption is as good as any.
- joe_the_user 7y ago
  When one is talking aliens, some number of things might seem obvious but the reality is we're dealing from intense ignorance and the things that seem obvious to us probably shouldn't be taken at face value.
tiku 7y ago
Given the scale and vastness of the universe, if there was/is other life we have a good change of finding some remnants of them, most likely spaceships?
- tzfld 7y ago
  Given the vastness of the Universe, I would say there is low chance finding some spaceships wandering out there even if they are present.
  - 14 7y ago
    This is how I feel as well. Some will say it would be so obvious by now we would have seen some sort of indication but then I think of all the planes that crashed without a trace and we have not been able to find even with an idea of where they were flying. The universe is huge. We have no idea how they will try and communicate maybe it's not something as obvious as radio transmission but maybe they have figured out quantum entanglement communication or something beyond our means but super obvious and useful to species who have figured it out. I grew up watching all the Star Trek shows. I have to believe the universe is filled with other civilisations waitin to talk with us.
- Cthulhu_ 7y ago
  Actually I'd argue that the scale / vastness of the universe is the main reason we HAVEN'T seen anything yet. I mean we can barely make out the planets in our own solar system, let alone asteroids - even assuming there's derelict spaceships out there several kilometers across, we can't really tell the difference between them and asteroids. Take Oumuamua, the asteroid (?) that passed through our solar system - even when all of our equipment was trained on it, we still could only make vague guesswork about its nature. But anyway, that already assumes there's tons of spaceships out there, enough to actually show up on our equipment. Even if there's a galaxy-spanning civilization out there, the chances of running into them are low. I mean for a close analog, look at the game Elite: Dangerous, that can give you an appreciation of the scale of the universe - and in that game it's basically cheating because you can jump from one solar system to the next in seconds. And even at those speeds it takes forever to get anywhere.
_Nat_ 7y ago
I thought that we already conclusively ruled out alien life by observing that there aren't huge, galaxy-sized smoke signals, generated from their massive candles to heat their galaxy-sized cottages? I mean, if aliens were out there, then surely they'd have sent us a notarized letter in the mail by now, as would any civilized culture. I bet they use really fancy quill pens, too! ...seriously though, I can't fathom why people are so caught up on the Star-Trek-like predictions where hyper-advanced aliens are still essentially humanoid. It's at least as absurd as [protocells](https://en.wikipedia.org/wiki/Protocell https://en.wikipedia.org/wiki/Protocell) assuming that all advanced life would be essentially protocelluar.
- johnchristopher 7y ago
  > ...seriously though, I can't fathom why people are so caught up on the Star-Trek-like predictions where hyper-advanced aliens are still essentially humanoid. I can't fathom why people fail to realise that being bombarded for decades with pictures of hyper-advanced aliens still essentially humanoid somehow shapes the general public imagination regarding "aliens". /s
- kayaeb 7y ago
  Some people claim to have ruled out type III civilizations [1], which I think is what you're referring to. I thought also that some researchers claimed a star had signals consistent with a type II [2]. [1] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale [2] https://www.space.com/30832-kepler-telescope-alien-megastructure.html https://www.space.com/30832-kepler-telescope-alien-megastruc...
  - dvdkhlng 7y ago
    According to recent news, the alien megastructure proposed in [2] may just be a shredded moon [3]. [3] http://www.astronomy.com/news/2019/09/evaporating-exomoon-could-explain-weird-light-patterns-of-tabbys-star http://www.astronomy.com/news/2019/09/evaporating-exomoon-co...
    - 7y ago
nabla9 7y ago
Fill in time: > unless the effective probe launch time is greater than 270 million years, the galaxy is old enough for every system to have been settled from an initial single civilization Conclusions: > When diffusive stellar motions are accounted for,they contribute to the Galaxy becoming fully settled in a time less than, or at very least comparable to its present age, even for slow or infrequent interstellar probes. >While settlement wave crossing and fill-in times are short, consideration of finite civilization lifetimes in a steady state model allows for conditions in which the settled fraction X is less than 1. Thus the galaxy may be in a steady state in which not every settleable system is currently settled. Conclusion basically says that if there are expanding civilizations in our galaxy, they spread very slowly, have filled the galaxy sparsely or have limited lifetimes. Assuming they are not avoiding contact.
- johnchristopher 7y ago
  What if we are the probe and we haven't figured it out yet ? Or what if we somehow didn't get the memo telling everyone to stay hidden because of danger, because we are late to the party ? What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone ? ^^
  - trumbitta2 7y ago
    > What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone ? Mass Effect Reapers, anyone?
  - dvdkhlng 7y ago
    See also the Zoo Hypothesis [1] :) [1] https://en.wikipedia.org/wiki/Zoo_hypothesis https://en.wikipedia.org/wiki/Zoo_hypothesis
  - nirui 7y ago
    > What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone? Guess that one of the benefits of living in suburbs[1]. 1: https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html Back to the topic. Let's assume there is a space nomad nazi species out there right now, will that species survive long enough to conquer the entire galaxy?
OscarTheGrinch 7y ago
One universal law that these discussions usually fail to consider is opportunity cost. There are a near infinite number of constraints and competing priorities at every stage of civilisional development, and that's why we don't see any Dyson spheres or similar grandiose outputs.
aylmao 7y ago
Here's the thing— we're assuming advanced civilizations want to expand in the first place. Why? Life in OUR planet was shaped by competitive evolution and we have reason to believe life in other planets has been as well— it's how natural selection works after all, and at least in our planet it's proven to be an effective way to go from primordial soup to complex, intelligent life that can out-smart its competition hoard all the resources. But how do we know that this is not a behaviour that civilizations, well, outgrow once they've hoarded all resources? Unbound growth is an effective strategy in a competitive scenario like the evolutive stage of species, in large part because it's also one of simple incentives. When a species becomes dominant though, it is very dumb, because the species will just end up reaching the limit of available resources and burning through them, thus killing themselves, like bacteria in a petri-dish multiplying until all the food has been eaten and they all starve to death. The argument goes, that's when a civilization would expand. Those bacteria would try to find another petri-dish. The species finds more resources so it can keep growing, but, can this incentive of "we have to keep growing" stand the test of time? Simply from a practical standpoint, Alpha Centauri is 104691 times further than Mars. The technological gap between sending a colony to a planet in your system, versus one in another star is gargantuan. First of all let's consider that planets are all ballpark similar in size and resources, therefore value. Is the investment even worth it? Is traveling 104691 times more for the same resources a stronger incentive that simply learning to find equilibrium with the resources easily available in your system? Even if for the sake of argument the civilization decides it is, could they even achieve it before running out their available resources? It'd be a race against the clock. There is reason believe the civilization would be forced to find stability and equilibrium within their existing system before developing the technology to be able to feasibly colonize a neighboring star system for the purpose of extracting resources. And if not to extract resources, why put the effort to continue expanding? Fear? Of what? A nonexistent galactic empire? Pride? If their history is anything similar to ours (which, since we're talking about similar motivations, is perhaps a feasible assumption to make), they would've learned colonizing far and wide does anything but promote a stable, unified, timeless nation. Therefore, my guess is one of two things might happen: 1. They achieve stability because it's the only way to survive, and the motivation to expand to another system dies off. Probe and explore, perhaps. But if in a stable system, there's no incentive to introduce instability once again by adding another habitat. On the contrary, the prospect of instability is incentive to not. 2. They don't achieve stability in their system, and so collapse. In a nutshell, I don't think there's incentive for unbound expansion once stability has been achieved, and I don't think unbound expansion can be achieved before stability. Of course, this is all just my opinion, but it's worth thinking perhaps the entire premise of extrapolating primitive evolutive behaviors to an advanced civilization is out of frame. Consider the future world of Brave New World by Huxley, or even the Time Machine by H. G. Wells. Neither seem to have galactic empires; instead opting for (very distinct) forms of stability (and decay).
doctor_eval 7y ago
I’ve always felt that the reason we haven’t heard from aliens is because they know New Physics and they use it to communicate. Given how much of the universe is made up of dark energy, dark matter and other unknown physics, it seems reasonable that there are significant discoveries to be made which could perhaps be exploited. I mean let’s say we discover a new, non-electromagnetic way to communicate reliably over vast distances using some kind of low power, high bandwidth signalling system. We’d abandon EM in a geological heartbeat. In cosmic terms we would emit a wafer thin EM shell just 150 light-years thick - and then we would fall silent. So basically I just think we don’t know enough physics yet. We are perhaps a few discoveries away from being able to listen in on alien conversations.
- nabla9 7y ago
  If they are using orbital angular momentum (OAM) coding in normal EM radiation we would not discover it yet because we don't listen for it.
  - galangalalgol 7y ago
    Would we hear it even with simple on/off keyed modulation even? The distances are so vast that even a directional link with anything but our nearest neighborhood seems unfeasible. We should have met a von neuman probe though.
    - about_help 7y ago
      Or possibly advanced civilizations had the same realization that many scifi authors have had about such probes. Something goes wrong and they cause widespread destruction. Or they work fine but still end up causing widespread destruction simply by replicating.
      - ncmncm 7y ago
        Once it happens once, it's too late for everybody. Naturally, they evolve, and soon invent interstellar travel. So much for that galaxy. (Cue Fed Saberhagen, *Berserkers".)
mprev 7y ago
The Fermi Paradox always strikes me as hubris. As Douglas Adams wrote, “Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” We've been looking for alien life for, what, 50 years? And we've made various assumptions about what we should be looking for. Oh, and we've been doing so on a very limited budget, with the technology available to us, in a tiny part of the sky .
- goatlover 7y ago
  Yes, but Fermi's Paradox is based on calculating that it would only take an alien civilization a few million years at the most to colonize our galaxy, which has been around for billions of years. Add to that the likelihood that a slightly more advanced civilization than ours would be able to make self-replicating probes. And it only takes one civilization to do it. So where are they? Think about it this way. If human civilization persists and continues to advance, what's stopping us from spreading out to nearby stars within the next thousand years? And that's nothing on the cosmic timescale.
  - throwaway-hn123 7y ago
    Exactly. The problem with most of these responses is that they don't truly understand the Fermi Paradox.
  - pbar 7y ago
    We have to remember the Fermi Paradox is a Fermi estimation and only that
  - neuronic 7y ago
    Uhhh that assumes alien life has the same intent as current us. Intelligent alien life may just as well have explored a lot, figured "meh..." and build a few Dyson spheres to spend the rest of their existence in a perfectly pleasing simulation. People already get sucked up by Warcraft and not even 100 years after computers made their breakthrough we fiddle around with haptic dual-4K VR.
YeGoblynQueenne 7y ago
- Where are my socks? - Did you look in the drawer? - Why, I've searched everywhere! I can't find them! - Well, then - you must have no socks. Your socks never existed.
YeGoblynQueenne 7y ago
>> Unless the individuals in the species driving the settlement have very long lifetimes (> 100 y) it is dicult to see how a galactic scale culture can arise (i.e. commerce etc. Krugman (2010)). Why is a mere "more than 100 years" considered a "very long lifetime"? Is there any reason to assume that the majority of intelligent species, capable of technological civilisation, that may inhabit the galaxy, will not have a lifetime measured in thousands, or even hundreds of thousands of years? The lifetime of the averarge star is a few billion years. We can assume that mos species will not have naturally evolved lifetimes lasting bilions of years, but a) species may evolve lifetimes lasting millions of years, or, b) a technologically advanced species may extend its lifetime indefinitely. A species whose individuals lived for a few hundred thousand years would have plenty of time to visit the Earth by travelling in sub-relativistic speeds, from a significant portion of the galaxy. A species whose individuals lived for a few million years would have plenty of time to visit the Earth and wait for our own civilisation to die out. A species whose individuals lived for billions of years could pay us an intergalactic visit and still have time for tea. Extremey long lifetimes are not impossible and they are not even particularly improbably. Here we are wondering whether there are other technological civilisations among the stars. Why should we assume that they are anything like we are?
- ryandvm 7y ago
  Long _natural_ lifetimes are a fundamentally at odds with evolutionary progress. The lifespan of a species is directly related to how quickly that species can iterate generationally. Fewer generations mean less natural selection, which means a less evolved life form. Also, if the organisms don't die off fast enough, they end up competing with their own offspring for resources. That said, I would imagine that once most life forms get to the point that they are able to extend their lifespans with technology, they probably always do. They just don't evolve anymore...
  - YeGoblynQueenne 7y ago
    >> Long _natural_ lifetimes are a fundamentally at odds with evolutionary progress. I'm not sure I see that. For example, humans live many orders of magnitude longer than bacteria and yet we have both evolved just fine. Anyway, I don't see why a species is pressed to evolve quickly in absolute terms. If all species on a given world evolve lifetimes many orders of magnitude longer than on the Earth, then there's no reason for any particular species to hurry. I think how long or short a species' lifetime is can only be understood in the context of the environment in which it evolves. In any case, we don't know anything about life on other worlds, and my point is that we can't really make such big assumptions based on the single example we're aware of.
julius_set 7y ago
I mean if there are no other intelligent civilizations (yet) in the universe — which seems highly unlikely based on the numbers, then we have an obligation to seed the universe with ourselves and propagate other species through genetic enhancement and grooming. We might be the progenitors of other intelligent species who might look back at us fondly and remember our shepherding. Again highly unlikely, but a good point that we should not kill ourselves beforehand.

92 points by pkrein 7y ago

> Using our steady-state model we constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the Galaxy. Explicitly, our solutions admit situations where our current circumstances are consistent with an otherwise settled, steady-state galaxy.

andrewfelix 7y ago

Interesting premise. Pity I can't read the article.

deleted 7y ago
[deleted]
archi42 7y ago
Maybe the link was updated? It now points to arxiv, from where you can download the paper (or does arxiv implement some geoblocking?).
- andrewfelix 7y ago
  yep, was just abstract earlier

xcq1 7y ago

https://arxiv.org/abs/1902.04450 https://arxiv.org/abs/1902.04450

sytelus 7y ago
Another relevant paper: https://arxiv.org/abs/1612.03238 https://arxiv.org/abs/1612.03238

solotronics 7y ago

All of these calculations are predicated on us existing in a physical universe and not a simulation (simulverse?) it could be we are the only life in this specific simulated existence, even though the mathematical rules of the place would make it appear there should be others.

namanyayg 7y ago
there's so little evidence of it being a simulation just for us. Even if all of this is just a simulation, I'd bet that we're just forgetten children of the simulgods and the true focus is something more obvious. See also Omphalos by Ted Chiang.
tsimionescu 7y ago
The assumption is that there is a set of laws of physics which are consistent with our observations, that are the same across space, that do not vary with time, and that all phenomena in the universe are ultimately caused by these laws. Whether these are the laws of nature, the laws of a simulation, or the laws of some Gods playing around, it makes no difference. Unfortunately, without these assumptions it is impossible to have any kind of scientific knowledge - if we can't assume that the sun rising for the last hundred thousand years means it will rise again tomorrow, or if we don't assume that the universe extends in the past as well as the future, there is nothing meaningful to study. Note: the laws of physics I am talking about above could be very different from what we know today - just as QM and Relativity are to Newtonian physics - but that would not change the assumptions I'm talking about.
- solotronics 7y ago
  Even if my half baked thought experiment was true I agree in that it shouldn't make any difference in our goals or ideals. I was merely positing a possibility for why if statistically our spacetime could be packed with neighbors we haven't noticed anybody. Another reason could be there are visitors they just exist on dimensions perpendicular to the 3d space we perceive, maybe even our concept of spatial dimensions is a oversimplification or a small slice of a full spectrum.
7y ago

hoseja 7y ago

I find the assumption that a space-faring civilization would need ideal planets to settle on somewhat questionable.

XorNot 7y ago
I mean a lot of this all turns on what happens to us in the next 200 years. Which... That's slightly less time then federated America has existed. Are we at the peak of what people achieve on temperate world's? Maybe technology doesn't meaningfully advance much beyond what we already know - you get a computing boom, Moore's law ends and then a couple decades of discovering no substantial alternatives to the silicon chip.
- simonh 7y ago
  I've been homing in on this conclusion, or a neighbour of it for a while. Take the periodic table. That's it people, we already know all the stable elements. Nobody's going to discover unobtanium. Aside from some high energy physics and some details of quantum mechanics, we probably know most of the useful practical physic there is. The open frontiers are biology and chemistry, but those are all about combinging things we mostly already know about in new and interesting ways. Eventually we'll figure all of those out as well. Then what? I'm not saying it's impossible we'll discover some amazing, paradigm shaking new physics that will upend everything. Maybe. But we can't bank on it and it's entirely possible no such civilisation shaping new physics exists. If that's the case, then the future will all be about engineering based on parameters we already pretty much know. I often see the Daedalus project held up as 'proof' interstellar travel and even interstellar colonization are possible. That was a designs for a very modest space probe payload, but even so the resources required to build them would pauper our whole civilization. Even if, or when, we master the resources of our whole solar system, those probes would be a significant cost and it seems likely they're way too puny to deliver a robust self-replicating bootstrap infrastructure. There's nothing inevitable or necessary about interstellar colonisation. The universe doesn't owe us Star Trek.
- goatlover 7y ago
  Why would technological advance be entirely limited by the end of Moore's law? There's still advances to be made in biology, nanotech, materials science, and making full use of the computing we already have. And there are plenty of proposals for future engineering on and off world, if we have the motivation for those projects.

roca 7y ago

They talk about planets and generation ships. Isn't it obvious that a multimillion-year spacefaring civilization would be mostly autonomous machines that have no need for habitable planets and can sleep for aeons? They also talk about civilization lifetime and interstellar resettlement. But interstellar resettlement doesn't make sense to me; simpler for machine civilizations to hedge their bets by putting resettlement sleeper ships in highly eccentric orbits with some desired period. Maybe there are civilization-killing effects that disable those resettlers, but they would apply to interstellar resettlement too.

ymolodtsov 7y ago
Well, no. That assumption is as good as any.
joe_the_user 7y ago
When one is talking aliens, some number of things might seem obvious but the reality is we're dealing from intense ignorance and the things that seem obvious to us probably shouldn't be taken at face value.

tiku 7y ago

Given the scale and vastness of the universe, if there was/is other life we have a good change of finding some remnants of them, most likely spaceships?

tzfld 7y ago
Given the vastness of the Universe, I would say there is low chance finding some spaceships wandering out there even if they are present.
- 14 7y ago
  This is how I feel as well. Some will say it would be so obvious by now we would have seen some sort of indication but then I think of all the planes that crashed without a trace and we have not been able to find even with an idea of where they were flying. The universe is huge. We have no idea how they will try and communicate maybe it's not something as obvious as radio transmission but maybe they have figured out quantum entanglement communication or something beyond our means but super obvious and useful to species who have figured it out. I grew up watching all the Star Trek shows. I have to believe the universe is filled with other civilisations waitin to talk with us.
Cthulhu_ 7y ago
Actually I'd argue that the scale / vastness of the universe is the main reason we HAVEN'T seen anything yet. I mean we can barely make out the planets in our own solar system, let alone asteroids - even assuming there's derelict spaceships out there several kilometers across, we can't really tell the difference between them and asteroids. Take Oumuamua, the asteroid (?) that passed through our solar system - even when all of our equipment was trained on it, we still could only make vague guesswork about its nature. But anyway, that already assumes there's tons of spaceships out there, enough to actually show up on our equipment. Even if there's a galaxy-spanning civilization out there, the chances of running into them are low. I mean for a close analog, look at the game Elite: Dangerous, that can give you an appreciation of the scale of the universe - and in that game it's basically cheating because you can jump from one solar system to the next in seconds. And even at those speeds it takes forever to get anywhere.

_Nat_ 7y ago

I thought that we already conclusively ruled out alien life by observing that there aren't huge, galaxy-sized smoke signals, generated from their massive candles to heat their galaxy-sized cottages? I mean, if aliens were out there, then surely they'd have sent us a notarized letter in the mail by now, as would any civilized culture. I bet they use really fancy quill pens, too! ...seriously though, I can't fathom why people are so caught up on the Star-Trek-like predictions where hyper-advanced aliens are still essentially humanoid. It's at least as absurd as [protocells](https://en.wikipedia.org/wiki/Protocell https://en.wikipedia.org/wiki/Protocell) assuming that all advanced life would be essentially protocelluar.

johnchristopher 7y ago
> ...seriously though, I can't fathom why people are so caught up on the Star-Trek-like predictions where hyper-advanced aliens are still essentially humanoid. I can't fathom why people fail to realise that being bombarded for decades with pictures of hyper-advanced aliens still essentially humanoid somehow shapes the general public imagination regarding "aliens". /s
kayaeb 7y ago
Some people claim to have ruled out type III civilizations [1], which I think is what you're referring to. I thought also that some researchers claimed a star had signals consistent with a type II [2]. [1] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale [2] https://www.space.com/30832-kepler-telescope-alien-megastructure.html https://www.space.com/30832-kepler-telescope-alien-megastruc...
- dvdkhlng 7y ago
  According to recent news, the alien megastructure proposed in [2] may just be a shredded moon [3]. [3] http://www.astronomy.com/news/2019/09/evaporating-exomoon-could-explain-weird-light-patterns-of-tabbys-star http://www.astronomy.com/news/2019/09/evaporating-exomoon-co...
  - 7y ago

nabla9 7y ago

Fill in time: > unless the effective probe launch time is greater than 270 million years, the galaxy is old enough for every system to have been settled from an initial single civilization Conclusions: > When diffusive stellar motions are accounted for,they contribute to the Galaxy becoming fully settled in a time less than, or at very least comparable to its present age, even for slow or infrequent interstellar probes. >While settlement wave crossing and fill-in times are short, consideration of finite civilization lifetimes in a steady state model allows for conditions in which the settled fraction X is less than 1. Thus the galaxy may be in a steady state in which not every settleable system is currently settled. Conclusion basically says that if there are expanding civilizations in our galaxy, they spread very slowly, have filled the galaxy sparsely or have limited lifetimes. Assuming they are not avoiding contact.

johnchristopher 7y ago
What if we are the probe and we haven't figured it out yet ? Or what if we somehow didn't get the memo telling everyone to stay hidden because of danger, because we are late to the party ? What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone ? ^^
- trumbitta2 7y ago
  > What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone ? Mass Effect Reapers, anyone?
- dvdkhlng 7y ago
  See also the Zoo Hypothesis [1] :) [1] https://en.wikipedia.org/wiki/Zoo_hypothesis https://en.wikipedia.org/wiki/Zoo_hypothesis
- nirui 7y ago
  > What if there's a natural/alien occurring culling of some kind and we somehow slipped through and now we are alone? Guess that one of the benefits of living in suburbs[1]. 1: https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html Back to the topic. Let's assume there is a space nomad nazi species out there right now, will that species survive long enough to conquer the entire galaxy?

OscarTheGrinch 7y ago

One universal law that these discussions usually fail to consider is opportunity cost. There are a near infinite number of constraints and competing priorities at every stage of civilisional development, and that's why we don't see any Dyson spheres or similar grandiose outputs.

aylmao 7y ago

Here's the thing— we're assuming advanced civilizations want to expand in the first place. Why? Life in OUR planet was shaped by competitive evolution and we have reason to believe life in other planets has been as well— it's how natural selection works after all, and at least in our planet it's proven to be an effective way to go from primordial soup to complex, intelligent life that can out-smart its competition hoard all the resources. But how do we know that this is not a behaviour that civilizations, well, outgrow once they've hoarded all resources? Unbound growth is an effective strategy in a competitive scenario like the evolutive stage of species, in large part because it's also one of simple incentives. When a species becomes dominant though, it is very dumb, because the species will just end up reaching the limit of available resources and burning through them, thus killing themselves, like bacteria in a petri-dish multiplying until all the food has been eaten and they all starve to death. The argument goes, that's when a civilization would expand. Those bacteria would try to find another petri-dish. The species finds more resources so it can keep growing, but, can this incentive of "we have to keep growing" stand the test of time? Simply from a practical standpoint, Alpha Centauri is 104691 times further than Mars. The technological gap between sending a colony to a planet in your system, versus one in another star is gargantuan. First of all let's consider that planets are all ballpark similar in size and resources, therefore value. Is the investment even worth it? Is traveling 104691 times more for the same resources a stronger incentive that simply learning to find equilibrium with the resources easily available in your system? Even if for the sake of argument the civilization decides it is, could they even achieve it before running out their available resources? It'd be a race against the clock. There is reason believe the civilization would be forced to find stability and equilibrium within their existing system before developing the technology to be able to feasibly colonize a neighboring star system for the purpose of extracting resources. And if not to extract resources, why put the effort to continue expanding? Fear? Of what? A nonexistent galactic empire? Pride? If their history is anything similar to ours (which, since we're talking about similar motivations, is perhaps a feasible assumption to make), they would've learned colonizing far and wide does anything but promote a stable, unified, timeless nation. Therefore, my guess is one of two things might happen: 1. They achieve stability because it's the only way to survive, and the motivation to expand to another system dies off. Probe and explore, perhaps. But if in a stable system, there's no incentive to introduce instability once again by adding another habitat. On the contrary, the prospect of instability is incentive to not. 2. They don't achieve stability in their system, and so collapse. In a nutshell, I don't think there's incentive for unbound expansion once stability has been achieved, and I don't think unbound expansion can be achieved before stability. Of course, this is all just my opinion, but it's worth thinking perhaps the entire premise of extrapolating primitive evolutive behaviors to an advanced civilization is out of frame. Consider the future world of Brave New World by Huxley, or even the Time Machine by H. G. Wells. Neither seem to have galactic empires; instead opting for (very distinct) forms of stability (and decay).

doctor_eval 7y ago

I’ve always felt that the reason we haven’t heard from aliens is because they know New Physics and they use it to communicate. Given how much of the universe is made up of dark energy, dark matter and other unknown physics, it seems reasonable that there are significant discoveries to be made which could perhaps be exploited. I mean let’s say we discover a new, non-electromagnetic way to communicate reliably over vast distances using some kind of low power, high bandwidth signalling system. We’d abandon EM in a geological heartbeat. In cosmic terms we would emit a wafer thin EM shell just 150 light-years thick - and then we would fall silent. So basically I just think we don’t know enough physics yet. We are perhaps a few discoveries away from being able to listen in on alien conversations.

nabla9 7y ago
If they are using orbital angular momentum (OAM) coding in normal EM radiation we would not discover it yet because we don't listen for it.
- galangalalgol 7y ago
  Would we hear it even with simple on/off keyed modulation even? The distances are so vast that even a directional link with anything but our nearest neighborhood seems unfeasible. We should have met a von neuman probe though.
  - about_help 7y ago
    Or possibly advanced civilizations had the same realization that many scifi authors have had about such probes. Something goes wrong and they cause widespread destruction. Or they work fine but still end up causing widespread destruction simply by replicating.
    - ncmncm 7y ago
      Once it happens once, it's too late for everybody. Naturally, they evolve, and soon invent interstellar travel. So much for that galaxy. (Cue Fed Saberhagen, *Berserkers".)

mprev 7y ago

The Fermi Paradox always strikes me as hubris. As Douglas Adams wrote, “Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” We've been looking for alien life for, what, 50 years? And we've made various assumptions about what we should be looking for. Oh, and we've been doing so on a very limited budget, with the technology available to us, in a tiny part of the sky .

goatlover 7y ago
Yes, but Fermi's Paradox is based on calculating that it would only take an alien civilization a few million years at the most to colonize our galaxy, which has been around for billions of years. Add to that the likelihood that a slightly more advanced civilization than ours would be able to make self-replicating probes. And it only takes one civilization to do it. So where are they? Think about it this way. If human civilization persists and continues to advance, what's stopping us from spreading out to nearby stars within the next thousand years? And that's nothing on the cosmic timescale.
- throwaway-hn123 7y ago
  Exactly. The problem with most of these responses is that they don't truly understand the Fermi Paradox.
- pbar 7y ago
  We have to remember the Fermi Paradox is a Fermi estimation and only that
- neuronic 7y ago
  Uhhh that assumes alien life has the same intent as current us. Intelligent alien life may just as well have explored a lot, figured "meh..." and build a few Dyson spheres to spend the rest of their existence in a perfectly pleasing simulation. People already get sucked up by Warcraft and not even 100 years after computers made their breakthrough we fiddle around with haptic dual-4K VR.

YeGoblynQueenne 7y ago

- Where are my socks? - Did you look in the drawer? - Why, I've searched everywhere! I can't find them! - Well, then - you must have no socks. Your socks never existed.

YeGoblynQueenne 7y ago

>> Unless the individuals in the species driving the settlement have very long lifetimes (> 100 y) it is dicult to see how a galactic scale culture can arise (i.e. commerce etc. Krugman (2010)). Why is a mere "more than 100 years" considered a "very long lifetime"? Is there any reason to assume that the majority of intelligent species, capable of technological civilisation, that may inhabit the galaxy, will not have a lifetime measured in thousands, or even hundreds of thousands of years? The lifetime of the averarge star is a few billion years. We can assume that mos species will not have naturally evolved lifetimes lasting bilions of years, but a) species may evolve lifetimes lasting millions of years, or, b) a technologically advanced species may extend its lifetime indefinitely. A species whose individuals lived for a few hundred thousand years would have plenty of time to visit the Earth by travelling in sub-relativistic speeds, from a significant portion of the galaxy. A species whose individuals lived for a few million years would have plenty of time to visit the Earth and wait for our own civilisation to die out. A species whose individuals lived for billions of years could pay us an intergalactic visit and still have time for tea. Extremey long lifetimes are not impossible and they are not even particularly improbably. Here we are wondering whether there are other technological civilisations among the stars. Why should we assume that they are anything like we are?

ryandvm 7y ago
Long _natural_ lifetimes are a fundamentally at odds with evolutionary progress. The lifespan of a species is directly related to how quickly that species can iterate generationally. Fewer generations mean less natural selection, which means a less evolved life form. Also, if the organisms don't die off fast enough, they end up competing with their own offspring for resources. That said, I would imagine that once most life forms get to the point that they are able to extend their lifespans with technology, they probably always do. They just don't evolve anymore...
- YeGoblynQueenne 7y ago
  >> Long _natural_ lifetimes are a fundamentally at odds with evolutionary progress. I'm not sure I see that. For example, humans live many orders of magnitude longer than bacteria and yet we have both evolved just fine. Anyway, I don't see why a species is pressed to evolve quickly in absolute terms. If all species on a given world evolve lifetimes many orders of magnitude longer than on the Earth, then there's no reason for any particular species to hurry. I think how long or short a species' lifetime is can only be understood in the context of the environment in which it evolves. In any case, we don't know anything about life on other worlds, and my point is that we can't really make such big assumptions based on the single example we're aware of.

julius_set 7y ago

I mean if there are no other intelligent civilizations (yet) in the universe — which seems highly unlikely based on the numbers, then we have an obligation to seed the universe with ourselves and propagate other species through genetic enhancement and grooming. We might be the progenitors of other intelligent species who might look back at us fondly and remember our shepherding. Again highly unlikely, but a good point that we should not kill ourselves beforehand.