Summary: "Because it means life is not incredibly unlikely (after all, it occurred on two planets in our own solar system); ergo what must instead be incredibly unlikely is the ability for life to progress to the point where it can spread across the galaxy (after all, no other life form has contacted us); ergo we are doomed."
You can't summarize that paper. The responses to the various objections are vital; they are part of the central argument, not tangential to it. The positive argument is also much richer than you portray it, and therefore much more convincing.
Save your summaries for techcrunch. They are not for refereed writing on subject X (i.e. 'existential risk') by the foremost authority on subject X. If you're not reading the whole thing (perhaps 2 or 3 times), you may as well not read it.
For one, there is no "ergo, we are doomed" - quite the opposite:
"So this is why I conclude that the silence of the night sky is golden, and why, in the search for extraterrestrial life, no news is good news. It promises a potentially great future for humanity."
He had a good point and took so long to make it so carefully because he knows that if he doesn't, people will make all sorts of dumb comments & objections.
This HN submission actually isn't even all that bad as far as it goes; check the comments on some of Bostrom's submissions to other, more popular, fora and you'll be routinely smacking your forehead.
See in particular the most recent paper from NASA (November 2009):
Life on Mars: New Evidence from Martian Meteorites
"New data on Martian meteorite 84001 as well as new experimental studies show that thermal or shock
decomposition of carbonate, the leading alternative non-biologic explanation for the unusual nanophase
magnetite found in this meteorite, cannot explain the chemistry of the actual martian magnetites. This leaves the biogenic explanation as the only remaining viable hypothesis for the origin of these unique magnetites. Additional data from two other martian meteorites show a suite of biomorphs which are nearly identical between meteorites recovered from two widely different terrestrial environments (Egyptian Nile bottomlands and Antarctic ice sheets). This similarity argues against terrestrial processes as the cause of these biomorphs and supports an origin on Mars for these features."
The problem with saying 'there is no extraterrestrial life because we haven't observed it and it would probably be here by now' is that there is always the first wave of lifeforms who would come to the same conclusion.
You could make a good case that we are part of this first wave:
-The stars created after the big bang would not have had any heavy elements and therefore wouldn't have had the resources to create life.
-These stars lasted ~10Bn years before they started to go nova (which creates the heavy elements for the next generation of stars)
-Based on our experience, it takes ~4bn years for life to evolve in a planetary system.
-Therefore the first lifeforms wouldn't appear until roughly 14bn years after the big bang.
-The universe is currently 14bn years old.
The problem with saying 'there is no extraterrestrial life because we haven't observed it and it would probably be here by now' is that there is always the first wave of lifeforms who would come to the same conclusion.
True, but that a form of reasoning inevitably gives a wrong conclusion under rare circumstances is only a weak argument against it.
-Based on our experience, it takes ~4bn years for life to evolve in a planetary system.
I don't think we have a strong reason to believe that there's something special about that length of time. Not much change happened on Earth for most of that time, suggesting dependence either on stochastic evolution of a few things like photosynthesis (so 4bn probably isn't much more likely than 3bn) or on something like increasing solar output crossing a threshold (it's doubtful such a threshold would be crossed at ≥ 4bn years at every location). That aside, even a few tens of millions of years is plenty of time for life to cover a galaxy.
Wait. So this guy doesn't want us to find life, which would be super cool and advance scientific knowledge significantly... because it might mean that human civilization might not last that long in the timescale of the universe?
I mean, I think we knew that already. The vast majority of species that have lived on Earth have gone extinct, and almost all of the rest have evolved to be completely unrecognizable. It's unlikely we'll be an exception to that rule, and I'm okay with that.
Yeah, but for all he knows they'll have the intelligence of the common house fly. And not only is that incredibly unlikely anyway, it's essentially no different from dying out altogether. And who really cares? None of us will live that long anyway.
Even if we can't intercept their communications, we should be able to see their works. The universe looks far too natural to contain much technologically advanced intelligence.
No, that we may be looking for the wrong things. The ants could search every floor tile on Earth, but they wouldn't find pheromone trail messages from us. The modest scale of SETI is just a secondary point.
On the other hand, how exactly do you find things without looking for them - wait to get stepped on? :)
Perhaps I was too terse. The point of the xkcd strip is that the ants conducted a very shallow test (looking for life that was most similar to theirs) and then gave up. The post I responded to made a similar comment generalizing about the nature of "the Universe", which is indicative of the same fallacy.
Which is the point of the xkcd strip (the alt-text makes it even more clear). It isn't about ants, ants don't read xkcd. The point is that despite all of what we've done we have barely scratched the surface of knowing or understanding the universe. We are as ignorant of the nature of intelligent life in the universe, even whether it exists outside of Earth or not, as the depicted ants are of human civilization. Far more so, in fact.
This is an interesting article, well worth posting.
However, to all those saying it needs a "tl;dr": I agree with you. In fact, academic writing has included this concept for decades; it's called an abstract. And this article could use one.
Well, the consideration fails unless the possibility of a common origin is excluded. Just because we find life nearby doesn't mean that the great filter is not already in our past. On Mars specifically, it would be near enough to allow for the possibility that life has somehow migrated from Earth to Mars, or vice versa, or to both from some other source. Finding life far enough away that intelligently developed spaceflight would be the only way for it to migrate would indeed be a depressing thought, but the possibility of migration must be ruled out first if we find life nearby.
It could be something more mundane. The signs we're looking for are stuff like radio signals, which we'll probably be using for how long? 500 years out of the Sun's 10 billion lifespan. That's a pretty big filter already.
Plus, if light speed is really impossible to overcome, then distant stars get less interesting as a civilization progresses. 100 years didn't mean so much for a given population 5000 years ago (not for its individuals, of course), but already are about 3 paradigm shifts these days.
If we evolve into some sort of 'post-human' form, maybe the assertion that we 'have to' colonize everywhere breaks down. I think it's a stretch to assume that every potential life form eventually wants to colonize space. If we as humans or post-humans figure out how to balance our need for resources (by not having to mine space) I think that could change things dramatically.
However I didn't go to Oxford/MIT so I really don't know jack.
Even if we do develop a sustainable human civilization on this planet using Earth's resources wisely ... the most compelling reason to colonize space is still the inherent precariousness of relying on a single locus. There are any number of ways that humans, even peaceful humans, on this planet may be wiped out by natural causes. Our species cannot be truly "safe" until it ventures out into space. It's the eggs in one basket problem.
The problem with this line of argumentation, and a number of other lines of similar argumentation, is that you've explained why a given entity might not want to colonize space. What you haven't explained is why every entity ever in existence anywhere will not want to colonize space. It's not enough to hypothesize the existence of a single future "space hippy" who just wants to live in harmony with nature, man, you have to explain why every post-human(-equivalent) from every species in all the observable universe (or at least all our galactic history) has not chosen to colonize space.
All our current technology says that all future civilizations may have radically greater resources than us, but still finite. Finite resources means there will still be some sort of internal competition. Competition implies that one solution to the local competition is to pack up and head for the next star system to exploit. This logic then applies again from that system once it has been tapped out. It borders on the inconceivable that it is physically possible to colonize the stars, that intelligent life is common, and it is easy to get to "post-human-equivalent", but absolutely nobody has ever chosen to colonize the galaxy. One of those axioms is wrong (including, potentially, the finiteness of future civilization's resources).
This argument is mentioned in the paper, I'm just re-drawing your attention to it. It's a big one that is very important when talking or arguing about this; the answer must not cover 10% or even 99.9% of the cases because if intelligent life is that easy the galaxy still ends up colonized long before humans are sentient. It must cover 100% of the cases across an unknowably wide variety of intelligent life forms in an unknowably wide variety of initial conditions.
It's a tall order and most, if not all, of the self-loathing answers like "intelligent life like humans just suck so hard that they all die" really don't hold up under scrutiny very well; all life forms pollute themselves to death? Any problem we can see, some other life form somewhere will have solved. All life forms develop weapons technology and war themselves to death? Even hyperintelligent bees who early in their human-class civilization's history figured out how to share one mind such that war is impossible? All life forms ever decide to just stay home because they learn to live in harmony? Even on Earth you can see that while some humans may make that choice, other humans quite rationally never will.
And the whole "harmony with nature" thing isn't even a very rational idea if you get down to it, it is a very human form of romanticism that I seriously doubt will be a universal among the stars. Not destroying that which you need to live is rational, but posthuman technology generally implies that you no longer need your original natural environment to survive; I seriously doubt that all civilizations and individuals will fetishize their ecosystems the way some humans do, an ecosystem now distinctly more primitive and choatic than their own technology.
(One reason why it matters if a species has infinite resources is that it may mean that it is possible for a species to create it's own universe and migrate there, which would make sense for a lot of reasons, especially if they can guarantee that no other species can ever find it and muck with it. Be it a real universe or an advanced simulation, doesn't matter. "All civilizations, before advancing to the point they can colonize the stars, discover a method of creating a new sub-universe or performing infinite computation in finite time, and instead colonize that new infinite realm since it is so much safer" is an appealing answer since it solves the Fermi paradox in a way that implies a happy future possibility for humanity, but we're running out of physics that might contain such a possibility. It gets to the point where even if we figure out how to trick a string into performing infinite computation it wouldn't matter anyhow since there may be no way to manipulate a string anyhow, for example. This also falls afoul of my own argument above... every member of the species must choose this, no member should have doubts about it and decide to just safely colonize space anyhow and perhaps choose that answer in the indefinite future.)
If we as humans or post-humans figure out how to balance our need for resources (by not having to mine space) I think that could change things dramatically.
Post-humans would need resources too, even if it's just 1 kcal/year to run themselves in simulation. That could add up quickly if even just one of them decided to forkbomb itself.
He doesn't address the possibility that the start of life is "the great filter", but after that point, microbes were shared between planets in our solar system via metoerites, impacts, etc.
In which case it wouldn't matter what we found on Mars.
Right. But that is a big assumption of his position. If there is life on Mars and it is DNA or RNA based I would say the independence assumption is less certain. Then the author can go on happily assuming that the "filter" is probably behind us. Not sure why that is such a big thing though.
Maybe I'm missing something, but finding live on Mars would just be a single data point. It would in no way provide a meaningful forecast to our own fate.
It would be a second data point. If we the Earth was our only data point, we couldn't say whether life was a common trend or an anomaly. But if Mars had life, then we would at least have proof of the former.
There's an alternative explaination in
`Burning the Cosmic Commons: Evolutionary Strategies for Interstellar Colonization` (http://hanson.gmu.edu/filluniv.pdf):
"Attempts to model interstellar colonization may seem hopelessly compromised by uncertainties regarding the technologies and preferences of advanced civilizations. If light speed limits travel speeds, however, then a selection effect may eventually determine frontier behavior. Making weak assumptions about colonization technology, we use this selection effect to predict colonists' behavior, including which oases they colonize, how long they stay there, how many seeds they then launch, how fast and far those seeds fly, and how behavior changes with increasing congestion. This colonization model explains several astrophysical puzzles, predicting lone oases like ours, amid large quiet regions with vast unused resources."
The point of the submitted article seems to be already mentioned in:
"Humanity seems to have a bright future, i.e., a non-trivial chance of expanding to fill the universe with lasting life. But the fact that space near us seems dead now tells us that any given piece of dead matter faces an astronomically low chance of begating such a future. There thus exists a great filter between death and expanding lasting life, and humanity faces the ominous question: how far along this filter are we?
Combining standard stories of biologists, astronomers, physicists, and social scientists would lead us to expect a much smaller filter than we observe. Thus one of these stories must be wrong. To find out who is wrong, and to inform our choices, we should study and reconsider all these areas. In particular we should seek evidence of extraterrestrials, such as via radio signals, Mars fossils, or dark matter astronomy. But contrary to common expectations, evidence of extraterrestrials is likely bad (though valuable) news. The easier it was for life to evolve to our stage, the bleaker our future chances probably are."
Here is one possible (plausible) answer to Fermi, I think:
Some various assumptions:
Space travel is limited by the speed of light and the faster you are going, the more energy it takes to go a little bit faster. Relatively is more or less correct and absolute that way. No Star Trek "hyperdrive" is possible.
Nope, you can't extract energy from a quantum vaccuum or any other such tricks.
Nope, you can't actually scoop up all that much fuel in inter-stellar space. Most viable solar systems don't have all that much practically accessible fuel for inter-stellar voyages. Transmutation of matter into arbitrary elements is possible, but not practical at scale.
You can't, therefore, have (material) trade routes between any but perhaps the closest stars. Even then, the total mass of material you are trading in a unit of time is doomed to be disappointingly low - there is hardly any point to bothering.
With assumptions along those lines, "colonization" per se would not exactly be possible -- if by "colonization" we mean building any kind of empire.
At the very best, a species could accomplish a kind of "panspermia" -- sending out "seeds" to whatever stars are in reach, but once a seed is launched, its subsequent evolution is pretty much on its own. In a few cases, if one lucky civilization is close by a second, resource-rich solar system, maybe you get get a little bit of mining going. But such opportunities would be cosmologically rare and even more rarely economically viable.
Worse, sending out seeds to a near-ish solar system and letting them do what they will would be dangerous to the life back in the solar system of origin. Right now, it doesn't appear that their is a hostile, alien intelligence anywhere in the galactic neighborhood. If we did a good job of launching "seeds", we'd increase the odds considerably.
In short, there will never be a point at which it makes any kind of economic or existential sense for us to begin a colonization project - and the situation doesn't look like it would be all that different for other imaginable forms of life.
So why not signal? Well, we already do a bit. Perhaps in a few years we'll have found some not too far off (but far enough!) solar systems that look like they might host life -- and we'll point some lasers at them and start sending "pings" to see if anyone is home. If other solar systems are already doing that, it would be very hard to detect from here on Earth.
In other words, one answer to Fermi, but not quite the "Great Filter" that Bostrom posits, is simply that galactic colonization is a practical impossibility and, to the extent there is intelligent signaling that spans solar systems, it's a lot more directional and harder to detect than anything you could easily find with a few radio telescopes.
That seems unlikely to me. There's easily enough energy and matter around in our solar system to make a journey to another, and as far as we know, there's plenty of energy and matter in other solar systems also.
So a sufficiently advanced civilization could construct a self-replicating probe that heads to each solar system, replicates and recharges itself, then heads on to the next stars until the whole galaxy is populated.
From the perspective of the civilization sending the probes, this is relatively cheap; just the price of the materials necessary to build a single ship capable of carrying itself outside the solar system, even if it takes hundreds of years to get anywhere.
A "self-replicating probe" is either so weak in capability that it would hardly amount to colonization, or so strong in capability that it would amount to a rival life form. What functionality would you build into such a probe and by what means would you prevent a "boomerang" effect wherein it comes back and causes problems in the home system?
Additionally, if all you are talking about building is a device that would, encountering our solar system, take up residence in orbit, take pictures, and report "back" - how do you know there aren't already several of them present? It would be rather hard to tell!
Colonization on Earth always had economic incentive. Populations migrated for economic opportunities, even if the selection of who did and did not migrate was heavily political. Colonization, as opposed to mere migration, was pretty much always, more or less by definition, for resource extraction. The colonized pay taxes and/or their raw materials and unique finished goods are exported back to the empire, and/or their local economy is converted to the coin of the empire's realm and taxes are extracted. It doesn't seem like any such program of empire building could work at inter-stellar scales unless there is some surprising physics that we've yet to discover that allows super-luminal communication and transport.
Fermi is "wrong" if intelligent, space-faring life only "works out" given the rules of physics at roughly the scale of our higher organisms and if, for organisms at that scale, colonization is not a viable option. There's no need for any "Great[er] Wall" than that.
> A "self-replicating probe" is either so weak in capability that it would hardly amount to colonization, or so strong in capability that it would amount to a rival life form.
Why do you assume that? There are plenty of self-replicating machines on earth that have been extremely successful at colonizing their environment, but we would not typically view them as "rival life forms".
> What functionality would you build into such a probe and by what means would you prevent a "boomerang" effect wherein it comes back and causes problems in the home system?
The simplest method would be to have them accept any order signed by a standard public key. I'm not sure why people tend to assume that a self-replicating machine cannot be controlled. There are plenty of self-replicating programs that are controlled very effectively.
> Additionally, if all you are talking about building is a device that would, encountering our solar system, take up residence in orbit, take pictures, and report "back" - how do you know there aren't already several of them present?
Because if have been many intelligent species in our galaxy over the past billion years, it seems unlikely that all would be careful to remain undetected. Certainly our species has little interest in hiding its activities.
> Colonization, as opposed to mere migration, was pretty much always, more or less by definition, for resource extraction.
Plenty of species on Earth colonize new environments without bothering to send resources back to their origins. And there have been plenty of human colonizations not linked to a controlling empire, especially when we were just hunter-gathers.
1. The current rate of technological advancement is so steep as to make even 100 years hence, a nanosecond in the grand scheme, absolutely unknowable.
2. Sufficiently advanced technologies would be indistinguishable, intentionally, a la Star Trek's noncontact per Federation agreement.
3. In terms of the author's "Great Filter" idea, maybe some fraction of the supernovas observed by astronomers are really interstellar industrial accidents.
> 2. Sufficiently advanced technologies would be indistinguishable, intentionally, a la Star Trek's noncontact per Federation agreement.
would be? Why on earth would they inevitably - every single one of them - develop such a civilization? We most certainly haven't; we'll set aside a few areas as parks, but even those are heavily contaminated by our civilization.
Why wouldn't they make Dyson spheres around all their stars - spheres which ought to have shown up on our infrared surveys - and use that energy? Think of all the computations and matter they'd be wasting by just letting the star blaze away. A few parks, sure, but an entire universe of them?
That point sounds like wishful thinking. 'They'll be, like, cosmic hippies man - they won't want to go around harshing Mother Nature's groove.'
> 3. In terms of the author's "Great Filter" idea, maybe some fraction of the supernovas observed by astronomers are really interstellar industrial accidents.
Then why aren't the astronomers & astrophysicists in a tizzy about how all these supernovas simply don't mesh with the well-thought-out models? Supernovas are the outcomes of processes which take millions upon millions (or billions) of years to finish. I doubt their models of include a random fudge factor to explain away alien Homers.
2. "...cosmic hippies man -" We are not hippies (there are some) but we have to struggle to get permission to remove a beaver dam even if it is flooding our home, and we are far from ADVANCED! The reasons for noncontact may be as beyond our comprehension as a sump pump is to a beaver.
3. Don't get too attached to current favorite theories-Dark Matter-Dark Energy-etc(massive fudge factor) because they are always subject to reinterpretation when new data is uncovered. "Difficult to see, Always in motion the future is."
Said beaver dam is filtering a river bearing thousands of chemicals and substances foreign to it before man; is constructed of trees which flourish in the area because of man - where it isn't using outright man-made ingredients like plastics; and supports a pond with alien invaders or just smaller species (because of the excess heat caused by the lack of forest). And this isn't even trying very hard for examples of how even 'natural' features are unnatural and modified for our convenience. Radionuclides are a signature of man's presence that will never go away.
> 3. Don't get too attached to current favorite theories-Dark Matter-Dark Energy-etc(massive fudge factor) because they are always subject to reinterpretation when new data is uncovered.
And what does dark energy and other fudge factors relating to the overall structure of the universe have to do with narrow models of stellar evolution and the inevitable supernovae of any stars over the Chandrasekhar limit? Either admit it's baseless speculation (and not even bad humor), or provide an example of a star blowing when our equations say it shouldn't.
Which "we" are you referring to? Your idealized American conservationist, Canadians, Mexicans, Brazilians? Tibetans? Chinese? North Koreans? Australians? Indians? Nigerians?
There are many human cultures on our planet which haven't created bureaucracy preventing them from taking advantage of natural resources, and some of them are as technologically advanced as any other culture on our planet.
I'm sorry you missed the point. I think I offended your sensibilities, but I was referring to all mankind and how we do care about other forms of life and propose that more advanced civilizations would even more so.
