1) the likelihood rate of abiogenesis ({\lambda}A);
2) evolutionary timescales (Tevo); and
3) probability of self-annihilation of complex life (Pann)
To my understanding:
1) Unknown.
2) Unknown outside earth.
3) Unknown.
Given the title and the problems above, I didn't read beyond the introduction as time is limited.
It sounds like an updating of the Drake equation without addressing the fundamental problems with that as an estimation tool rather than a more modest method for informing interesting speculation.
Yeah, statistics isn't really good at extrapolation from a single sample.
I think statistics is entirely bad approach to resolving this problem at least until we have more data.
We need to know more about how planets form (again, we have rather small sample we have studied well), we need to know what exactly is necessary to jumpstart life and how likely it is to happen. Then we have a hard task understanding why exactly intelligent life evolved and whether it is unavoidable or a fluke. And a bunch other questions that statistics is entirely unprepared to answer.
Abiogenesis is known on Earth. Life appeared quite soon after Earth had cooled down enough, within the first couple of 100 million years. Of course, we don't know if it took 1 million or 300 million years. And it might be difficult to find out.
Isn't abiogenesis just a fancy way of saying that somehow life began from organic compounds that were created by inorganic means? To my understanding the somehow part is exactly the reason why we don't have enough information to make any intelligent guess on the probability of it happening elsewhere.
It doesn't matter to the Drake equation except to make it far less pessimistic. Abiogenesis had to happen somewhere for panspermia to occur so if it happened so early in the history of our galaxy to then migrate to our planet, the probability of many such colonizers converging on intelligence goes up drastically. Panspermia might even simplify other parts of the equation, like the probability that we'd coexist in the same time period or in range to detect each other's radio waves.
I would recommend reading the conclusion before dismissing this as "they picked numbers to throw at the Drake equation". The point of this paper is to provide modeling not only of the scalar output of the drake equation (which is... not used at all) but of the possible spatial and temporal distribution of intelligent life in the galaxy. For example, it turns out that even for wildly different choices of the unknowns, the region (and age) of the Milky Way that contains most life (i.e. that SETI should focus on) is the same.
Also, why do you consider "unknown" a problem when they explicitly set out to investigate the influence of these parameters? For example, they explore Pann of 0.0, 0.5 and 0.99 (per Myr). Could you explain what problem you see here?
I would recommend reading the conclusion before dismissing this as "they picked numbers to throw at the Drake equation
That's a misrepresentation of what I said.
I made it clear I had only read as far as I had because the premise of the title was unpromising given the unknowns, and that it sounded like an updating of the Drake equation without its flaws in the calculating of probabilities (as implied by the title) addressed.
Feel free to summarise how it fundamentally differs from Drake in that important regard, with the findings and their usefulness in the context of the unknowns and title which promises an estimate of extraterrestrial intelligence.
Without looking up the Drake Equation, here's a rough estimation of the problem.
Ignoring all extinct species, there's an estimated 8.7 million unique species of plants and animals currently on Earth. So let's do some dumb estimating and say that there's a one in 10 million chance of "intelligent" life evolving on a planet that supports life. (I will not address the controversial issue of whether or not human life is actually intelligent.)
So whatever estimation is used for the number of habitable planets in our galaxy, Only 0.00001% of those planets might have intelligent life. Next, you must factor in how many of the intelligent species develop technology capable of interstellar communication, and when do they do it? Humans have existed for a few million years, but we have only had radio for a hundred years. With the development of technology comes the risk of self annihilation. We humans have had the ability to destroy ourselves for roughly 60 years. How much longer we go is anybody's guess, but given that life on our planet has existed for roughly 3.5 billion years, and the planet will become uninhabitable in another 5 billion (when the sun changes modes), the time window is pretty small. It's likely that life needs some elements that were less available in the early universe, so let's assume that it's only possible on planets of third-generation stars like ours. Also consider the speed-limit of EM propagation (C). There are only 76 stars within 100 light years of us. It's unlikely that intelligent life exists in any of those systems, but if it did, the inhabitants (if they were listening) would just now be able to hear us. Assuming we survive our technological revolution/evolution for another 100 years, we might get a message from a nearby system. Before then, we might receive some communications from systems farther away, but how long does a technological civilization use radio with simple modulation schemes that we would recognize as something other than noise? Maybe in less than a hundred years, we will have gone through radio, optical, and then quantum communications technology. It's likely that other technological civilizations (if they exist) are using communication technology that is incompatible with ours.
I'm not sure if Drake considered all of these things, but it looks pretty bad for us with regard to our ability to confirm the existence of extraterrestrial intelligence any time soon.
> there's an estimated 8.7 million unique species of plants and animals currently on Earth. So [...] there's a one in 10 million chance of "intelligent" life evolving on a planet that supports life
Isn't that the probability that a species is intelligent. The probability that intelligence will eventually evolve on a planet with life is 1.0, from the evidence that we have so far.
Sure, the probability is 1.0 given infinite time. It took 4.5 billion years for us to get here, and we didn't get started until 5 million years ago. That means Earth went through 99.89% of its existence with no intelligent life.
Also, Earth has had numerous extinction events that killed off at least 3/4 of land-based life (and 96% of marine life). We have no way of knowing whether extinction events are more, or less common on other habitable planets, or whether such events might even be necessary for the evolution of intelligent life.
This is a serious misunderstanding of probability. When someone won the lottery in the past he did not have a 100% chance of winning the lottery even though in hind sight he won.
A person who has a 1 in a million chance to win the lottery CAN still win the lottery. And if he does win the lottery, his chances of winning was STILL one in a million.
Same with life in the universe. Just because it happened does not make the probability of it happening at all 100%. Far from it.
I was only joking when saying 100%, but it is high. It is like having a bag of 1000 marble and you put your hand in and pull out a green one. You now know that the probability that there are a lot of green marbles in the bag is high.
1/10 million species on Earth being intelligent doesn't really imply that 1/10 million planets with life would have intelligent life. Any planet with life undergoing evolution may also develop millions of species, with "intelligence" being an important trait for some of them. Problem is, that tells us nothing about how many planets could sprout life in the first place.
Even right now on Earth, we have multiple tool-using species spanning mammals, birds, and cephalopods, separated by hundreds of millions of years of evolution. They all seem like good candidates for developing technology at some point over a few million years.
In the billion or so years life has existed on earth, there’s no evidence any species built a nuclear bomb or had large plastic manufacturing or left anything in GEO, all of which we’ve achieved in the last 100 years.
Progressing to that stage this seems unlikely for a planet with life on.
It's not like every species rolls the dice independently to see if it will be an advanced civilization. That the smartest animal to ever live on this planet is alive right now is no less probable than the largest animal to ever live on this planet (the blue whale) is alive right now - both are products of evolutionary processes that took many millions of years and are continuing. In addition to increasing size, there is a trend in the fossil record of improving intelligence for species throughout the animal kingdom since the extinction of the dinosaurs, which themselves had undergone many millions of years of increasing complexity since the previous mass extinction.
As for the sudden nature of humanity's major technological advances, that's just the nature of geometric growth - every advancement makes more advancements easier. The humans that took thousands of years to go from agriculture to writing were biologically no different from and no less capable than those who went from first flight of a plane to first walk on the moon in a single lifetime.
The most recent common ancestor with our primate cousins was about 7M years ago. There have been various hominid species, but I don't think we call them humans. I thought the general rough guess is homo sapiens are on the order of 200K-300K years old.
Another thing that may affect the probability of life in a solar system is the number of planets. More planets seem to make the planetary orbits much more circular and stable, allowing more time for life to occur and develop.
This matters because, as far as we can see, our solar system has more planets than any other system we have been able to observe (so far.)
> as far as we can see, our solar system has more planets than any other system we have been able to observe
I may be out of date, but I thought that was an artefact of our methods and equipment rather than anything else — we can only see big things close to their stars, so if we were looking at our own system we’d miss (I forget, so e.g.) Mars, Uranus and Neptune?
Whenever I contemplate this, I always return to the notion of concurrence. Any sentient alien life we'd hope to encounter alive will need to exist at the same (relative) time that we do. The Earth is 4.5 Billion years old. Man has existed as 'man' for about 5 million years. That's 0.1% of the age of Earth. If alien species evolved in a similar manner, but 0.1% faster or slower, we'd miss them by millions of years.
Proof of aliens need not be actual living specimens.
Left over artifacts from their civilizations are just as exciting a find.
Personally, I feel the thought that we are alone in this universe is a wee bit arrogant.
The universe is so big and existed for so long, we have to assume that sentient life existed in the past, perhaps exists now and will definitely exist in the future.
Hopefully, we find at least artifacts that prove alien life, just because the minds of humans expand a bit more, because imagine how shocking it is to religions around the world if existence of aliens is confirmed.
Universe no, our galaxy, probably. A species that doesn't colonize beyond their homeworld will sooner or later be wiped out by natural phenomena if not their own mistakes. A species that colonizes will fill the galaxy in a few million years unless it just decides to stop.
If anything like us existed in the milky way it's almost certainly dead now. If there's something alive it will be almost incomprehensibly different than us.
> A species that colonizes will fill the galaxy in a few million years unless it just decides to stop.
I think this may be making some weird assumptions about motivation. Let’s say, for the sake of argument, that travel at 5% of the speed of light is practical. Would you be signing up to go colonise a planet around Alpha Centauri? What would be the motivation opportunity such colonisation? Who would pay for it?
If interstellar travel turns out to be permanently slow, difficult, and expensive, then that may cast doubt on the idea that anyone who theoretically can spread out all over the place given a hundred million years actually will.
I suspect solving those problems within a solar system will almost always be easier than traveling to other systems. Then again maybe travel to neighboring systems is easier in a denser neighborhood.
If you have the energy technology to build enough starships to put a dent in your population, you probably don’t have to worry too much about space or water unless you have runaway population growth.
It’s interesting to me that in these conversations, some people think it’s inevitable that intelligent life will want to colonize other systems (or die trying) while others think it’s impractical.
But I think both of these opinions come from human-centric reasoning. A species that could hibernate may be able to control hibernation through technology, so a ten year journey wouldn’t be as complicated for them. Other species on earth simply don’t have the curiosity to explore the way humans do.
Speculation about alien intelligence is interesting to me, but I imagine it’s a lot weirder than we think. Especially around topics adjacent to intelligence, like curiosity, motivation, and cultural values.
Whether they want to or not is irrelevant. I'm only concerned with whether or not they do. My point is that for a civilization to have an unlimited lifespan it either has to exist in multiple star systems or progress beyond the need for a star system at all. A single planet is just too vulnerable. Nuclear war, biological war, grey goo, supervolcano, gamma ray burst, ecological collapse. To exist for billions of years on one planet requires that a species be dynamic enough to create hyper-advanced science but so peaceful it doesn't kill itself with it while being so incredibly culturally stable that doesn't change for eons. I don't buy it. Living on one planet is a death sentence in probably much less than a billion years.
Multiple is not the same as all. Once a civilization colonizes a handful of solar systems, it is essentially impervious to any disaster. Further expansion produces diminishing returns. There is no resource which can justify the cost of interstellar travel, and any civilization capable of making technology on that scale will have to be social enough that a latency of years to centuries in communication with the civilization's core would be a major disincentive. Even if there were a brief exploration phase when everything was new and uncharted, there would be no reason to maintain all those colonies indefinitely. A civilization inhabiting a dozen star systems all within a few lightyears of eachother would not be significantly more detectable than a single planet civilization.
That's a lot of assumptions you're making. For example, some undiscovered resource could be that valuable. Perhaps the species has a slow enough physical metabolism and mental process that interstellar travel times are only mildly inconvenient.
It is easier to synthesize any substance from scratch than it is to transport it between even the nearest star systems. The only way such a resource could exist is if our entire understanding of physics is way off.
Earth gives us a wide range of organisms with different lifespans and metabolic rates. There are not that many species that live longer than us, and extremely few that live significantly longer than us. Even if something lived 100 times longer than us, only a very small portion of the galaxy would be traversible within a lifetime, and there is still no reason to go more than a few lightyears.
i hear this argument constantly, but i've never been able to understand it. you say the universe is big and has existed for a long time, but compared to what? if i say the universe is small and new, how would you counter that? i don't mean to come across as aggressive, but if there's any arrogance on this issue, i'd suspect it lies in thinking we have enough information to come to any meaningful position on the issue.
the most convincing meta-analysis i've seen, which considers the probability distributions implied by the error bars in our current best estimates of the relevant parameters (https://arxiv.org/pdf/1806.02404.pdf), suggests a 39–85% chance we are alone in the observable universe. i'm less impressed by those particular numbers than by the attempt to rigorously quantify our ignorance on the issue, where some component values span fifty orders of magnitude. while the universe may indeed be big, i'm not sure it's broader than the sheer span of our ignorance.
> i hear this argument constantly, but i've never been able to understand it. you say the universe is big and has existed for a long time, but compared to what? if i say the universe is small and new, how would you counter that? i don't mean to come across as aggressive, but if there's any arrogance on this issue, i'd suspect it lies in thinking we have enough information to come to any meaningful position on the issue.
Basically, the universe is so ludicrously huge and so ludicrously old that it is as close to statistically impossible as one can imagine that human beings are the only things ever to evolve in such circumstances as to be sapient.
Note that the paper you have linked uses the term "detectable civilization", which is significant limitation due to our current level of technology, the age of the universe, and the propagation speed of light. It wasn't that long ago that we couldn't even detect extra-solar planets.
There is of course an argument to be made for us being "alone" in the universe in the sense that sapience is rare enough that pretty much all species, including ourselves, will die out before ever meeting another sapience, but the idea that in all the unimaginable vastness of the universe we are the only ones?
Other than arguing that the infiniteness of the universe somehow indubitably lends credence to the emergence of some convergent sentience, could you or anyone point to something a bit more rigorous (such as the paper your parent comment linked to)?
We are aware of the evolution of one sapience in the universe. What argument do you provide that suggests this is such a mind bogglingly unique occurrence that it cannot have happened anywhere else in the universe's volume of over 400,000Gly^3 at any time during its age of 13.8 Gyr?
In other words, the fact that it has happened at least once very strongly suggests it has happened more than once.
I guess I disagree with the basis of the argument that it happened once, it has to have happened another time. I don't think a single instance of very unique set of circumstances is the basis of a pattern.
I don't think the argument is that it "has to have happened another time". The argument is that if it is possible to happen once, it's likely to have happened more than once, the "existence heuristic." It proves only that it might be worth looking, unless perhaps further research indicates that we on earth are not, in fact, intelligent life, and then the likelihood of intelligent life elsewhere in the universe falls off dramatically.
"In other words, the fact that it has happened at least once very strongly suggests it has happened more than once."
No, it doesn't at all.
Maybe just the opposite.
The universe is mind-bogglingly large, but it's also really, really empty, and really, rally sparse. The numbers games starts to dwindle very quickly in terms of all the ingredients necessary.
And the Fermi paradox helps provide crudely indirect evidence.
If there was any validity at all to the 'common life theory' - then it would have started long ago and probably spread everywhere to the point wherein there would probably be ample evidence.
In the 'common life' scenario, it should be rare/impossible to find life that's disconnected from other life scenarios.
Without specific numbers and calculating chance of life like ours to occur I don't see how you can confidently make such claims. It could very well be the case that even for a universe this large, it was a statistical anomaly for it to have life. Maybe out of 1000 similar universes only 1 would happen to have life. How can you tell the odds so confidently?
Maybe even out of 1,000,000,000 of similar universes only 1 would actually happen to have life. It's similar with planets. If you only know of 1 planet within 1B to have life, how can you tell the odds are not low enough to have 1 universe out of 1B to have life?
This could be an awesome example of survivorship bias to assume because there's life here, there must be life elsewhere in the universe too. We only have experience with a planet where there's life, so we are innately biased to think that it might be more frequent occurrence than it really is.
The visible universe is so large it is effectively infinite. And that’s just the visible universe. With 125 billion known galaxies with a 100 billion stars in each it definitely feels arrogant to imagine that we are literally the only sentient beings.
It might still be that there is probably barely 1 advanced life form per galaxy. We know that organic molecules and related evolution requires air, water, temperature and stability that Earth like planets can afford. Unfortunately, to be Earth like planet, you don’t just need right distance from the star but abundance of water, minerals and so on. You must maintain magnetosphere otherwise water will be gone. You must have right moon otherwise axis will wobble with eradicate seasons. Even there life had been almost wiped out many times. There are half dozen human like species which were extinct and never panned out. All these goes on to show that even with 100B stars, you just need handful of probability to chope it down to one or so instances.
The non-existence proof of ETI also means laws of physics are cruel and cannot be violated. There is almost 100% chance that advanced life forms exist in other galaxies, may be even billion year old. But no one has figured out how to travel faster than light.
> i hear this argument constantly, but i've never been able to understand it. you say the universe is big and has existed for a long time, but compared to what?
I think compared to how long it took for somewhat intelligent life to evolve on Earth, from the point of first life. Assuming* a comparable evolutionary cadence, the question then becomes - how often does life begin?
*This I assume because the cadence of living things on Earth is at the very least tied to the day/night cycles, winter/summer seasons, and lunar tides, none of which are especially unique.
There is an argument that one instance of life evolving does imply there should be much more. I personally don't believe this though, though it is a valid argument. There is a counter argument too.
The common argument in favor of more life is that the probability of life evolving is some very small number, such that there must be a very large number of opportunities for life to evolve in order for life to actually evolve. At the same time, there are a large number of opportunites given the size of the universe. Given that there is presumably no relation between the "small" probability for life to evolve and the "large" number of opportunities in the universe, we don't expect these two numbers to conspire to be near the same size, which is what would have to happen for just one life to evolve. Rather, we expect there should be lots of life that evolved in different places or that the probability that any life evolved at all is extremely (vanishingly) small. So if this argument is correct and we know of one life form, we should expect many more in the universe. (Not to imply we would necessarily be able to find them.)
There is one potential problem with this argument. It assumes there is just one universe. If there are many universes then it is possible that life did not evolve in almost all of them. In universes where life did evolve, odds are it happened just once. And of course, that life (us, for example) would see that univese and the life that evolved there, however improbably that would be.
I read a saying "You know an argument is wrong if it invokes quantum mechanics." But I'll do it anyway. Some educated people believe quantum mechanics works this way - the univese effectively branches into parts that are essentially distinct (referred to as different universes too). It is not as outlandish as it may seem. The whole reason quantum computers are supposed to be powerful is that different things happen in parallel.
You don't have to buy the quantum mechanics part. If there are multiple universe for whatever reason then the probability argument above is not valid.
I do want to add one thing. The number of "opportunities" for life in our universe grows linearly with each dimension in the universe. (Lets just say to the fourth power of the size of the universe.) On the other hand, the size of probability grows/shrinks exponentially. So it is not hard to imagine between the two of these numbers, the exponential one wins.
Our Universe may support life for at least a trillion years. If so, our existence a mere 14 billion years after its creation is so improbable that we may well be the first
Your comment is burried below dozens more optimistic views that life "should" exist and evolve intelligence, but I like your take. We are so wildly improbable that most of us can't even fathom it. That our minds exist at all is so impossibly unlikely that by all accounts we should not exist.
For most I think that we are hear seems to indicate some inevitably but I like that we are an anomaly, we shouldn't exist, the we die.
I do think this idea answers the Fermi paradox. We are here early in the universe’s life. Especially considering it was mostly just hydrogen and helium for the first few billion years.
I don’t know how shocking to religions it would be. Surely it would be to some. But if I remember correctly the Catholic Church had some positive statement about alien life. And I know of another christian sect for whom it is a tenant that the universe is full of planets that have been populated by God. Then of course you have scientiology that has some... interesting takes on this issue. And, I don’t think religions like Buddhism would look askance at alien life.
Religions are usually quite adaptable, otherwise they don't survive very long. For example Christianity was originally a doomsday religion that expected the second coming any generation, but it eventually outgrew that too.
Even still, artifacts don't last forever. The vast majority of the things our civilization has built would be destroyed or rendered unrecognizable within a few centuries of being abandoned. Even things specifically designed to stand the test of time are unlikely to last more than a few orders of magnitude longer than the civilization that produced them.
Steel structures actually are much shorter lived. Without active maintenance, odds are neither tower would last a century. Generally the more advanced a technology is, the more fragile it is, and the more reliant on other advanced technology to maintain it. If you want something that lasts a long time, you're best bet is to stick to something simple like solid granite, though even if your artifact remains mostly intact, it's useless if it gets buried under sediment or weathered to the point that it's unrecognizable as an artificial construct.
Personally, I feel the thought that we are alone in this universe is a wee bit arrogant
An insult repeated to the point of cliche in this context which I suspect isn't normally personally meant, but nevertheless seems to deny the counter-arguer the abilities of imagination and wonder, and also presumes ("arrogantly"?) they haven't considered the known numbers first before coming to their conclusion that either there is little hope of communication or we don't know enough to decide.
Author and professor Timothy Ferris explained this well in the PBS documentary Life Beyond Earth with a Christmas tree light analogy. Ultimately it comes down to how long other civilizations last for and are willing to communicate. If a civilization either kills itself off or turns inward (cyberspace life, no radio outward communication) then the chances of concurrence decrease significantly.
This would be true if we were the first or near first advanced species. But we cannot be because there far many more older stars and planets. If you believe that advanced life forms will revolve in 3B yrs given hospitable planet then there had probably been many many such opportunities before Earth in Milky Way. At this point then we should expect to hear other civilizations screaming all over.
Indeed, within those 5 million years, we've produced coherent electromagnetic signals for just a bit over 100 years, and will probably go dark again before another 100 years elapse. Already, most of our electromagnetic information bandwidth is confined to fiber optic cables. Like a primitive Dyson sphere. Our remaining free space communications are increasingly designed to be virtually indistinguishable from noise.
Perhaps the evolving spectroscopic signature of our atmosphere will provide a durable signpost. The earth terraformed itself well before intelligent beings ever evolved, and maybe an astute and patient observer might have been able to guess that we were on our way towards intelligent life at some point.
Backtrapolating the rate of increase of complexity of life over time suggests "intelligent life has just begun appearing in our universe". https://arxiv.org/abs/1304.3381
For me the timeframe for life doesn't sound that relaxed.
Getting to complex cells took 2 billion years. And getting to where we are now another 2 billion years.
All that time conditions were fairly stable.
Given that life might need some elements created in supernova explosions mixed into other solar systems, and that we had just 13 billion years since the beginning, when you add some randomness, schedule starts to look tight for me.
We might be one of the first civilisations in our neighborhood.
I'm not saying that I believe that's the case but that's entirely possible.
Read the conclusion, imho, this is very interesting:
“ We also concluded that at the current time of the study, most intelligent life in the Galaxy is younger than 0.5 Gyr, with values of probability parameter for self-annihilation between 0 - 0.01; with a relatively higher value of the annihilation parameter (≥ 0.1), most intelligent life is younger than 0.01 Gyr.”
If other intelligent life is very young (just like us) could there be more room for understanding if we ever communicate?
I think what most people mean by intelligent alien civilization is basically illustrated by Star Trek, and I suspect in the entire perceivable universe we will never find anything remotely like that. Even the aliens in Arrival, as well done as they are, are magic humans in disguise
I suspect we will barely recognize even alien sentience, since it will literally be alien to our understanding
that depends on how fast intelligence evolves. If most intelligences are still young (claim in this paper) then we are more likely to understand them. If we ever encounter something which had a billion years head start, then yeah, no way we would comprehend anything
Yeah... this is why I suspect we may see signs of alien life, but just not know what we're looking at. You're not alone in thinking of intelligence as some kind of scalar quantity from bacteria to super beings, and if only we could find creatures in our range, we'll be able to communicate
Embedded in our conception of intelligence is us. We measure intelligence by what we think is important. But creative approaches to fitness in radically different environments will be multidimensional and multivalent, extremely difficult to judge by our own standards
I speculate that if we were to find aliens, we could never communicate beyond basic Skinnerian reward and punishment schema, if that, never mind prime numbers and such, no matter how sophisticated they are. We wouldn't even really be certain if we were witnessing intelligent behavior or autonomic processes, and neither could they. We can't even understand whales or dolphins, and those would be vastly easier to understand than anything without DNA, emergent from a completely different planet
How could we possibly communicate with a civilization that communicates in the time scale of oaktrees, or are sessile, or communicate using flashes of microwaves in patterns we have no hope of even discerning?
The earth is a life bearing planet with only 1 technological advanced life form. I would think this has a large impact on the possibility of detecting alien life (its rare for life bearing planets, rarer to evolve sentient, even rarer to create a civilization)
It's actually quite possible that earth has had one or more technologically advanced, for certain definitions of the term, lifeforms in its 4 billion year history but these have all been wiped out in one way or another before being able to leave any significant trace in the geological record. The best evidence against this is the lack of evidence of plastics and isotopes indicative of atomic energy use.
Nice, I've seen large Egyptian exhibits at the Louvre and the King Tut traveling exhibit in San Fransisco. Very impressive indeed.
The same day I saw the King Tut exhibit I also saw an exhibit from feudal Japan. The workmanship of the Japanese items was absolutely stunning, much more impressive than the King Tut items as one would expect from a period many centuries later. All of these examples were still done by hand. It's hard to imagine a person in the modern era devoting a lifetime to make only a handful of swords.
What makes these items interesting is that they were made without modern tools or technology. Today our manufacturing technology could replicate these achievements easily. Even common items like grave tombstones can be produced in short order with highly polished stone and precise engraving. See [1].
the easiest way to find possible life on a planet isn't technology but gas composition of the atmosphere, in particular 'biosignature' gases like ammonia, nitrous oxide, and oxygen among a few others.
Is being sentient or having a civilization actually required though?
Given the wide variety of environments where life can reproduce, shouldn't even non-sentient life eventually escape into space? This removes many of the 'great filter' arguments. This would be more likely on a planet with a shallower gravity well than earth.
Life, even bacterial-level life tends to spread out exponentially as resources allow, which should make it easier to detect.
This ignores a lot of nuance. There are a large number of species which have independently evolved significant intelligence, many of whom have been observed to use tools at a level comparable to our geologically recent ancestors. We currently occupy the "use tools to dominate the world" niche - any other species that adapts to use more advanced tools will come into direct competition with us. Regardless of how easy or hard it is to get into this niche, it's unlikely that more than one species will occupy it at any given time. However if we were to suddenly disappear, there are many candidates that could potentially get to our level within a few million years. There is no reason to believe life bearing planets are rare (all evidence points to earth-like planets being common), no reason to believe the evolution of sentience is rare (depending on your definition of sentience, it happened more than once here), and no reason to believe it's rare for sentient life to produce civilization (for humans, civilization has emerged independently many times).
Time's too big. There's no reason to assume that the lifetime of technological civilization is more than a few hundred years. By then they will have destroyed their own habitat and - despite some half-hearted (or even serious) attempts on colonizing different planets/planetoids - will have come to an inglorious end.
Let's be generous and say that the lifetime of a technological civilization is a thousand years. That's the time that it can both send and receive signals from another technological civilization.
The chance that one technological civilization is able to receive the signals of another is so vanishingly small as to be zero for all practical purposes.
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[ 3.0 ms ] story [ 151 ms ] threadWe examine three major parameters:
1) the likelihood rate of abiogenesis ({\lambda}A);
2) evolutionary timescales (Tevo); and
3) probability of self-annihilation of complex life (Pann)
To my understanding:
1) Unknown.
2) Unknown outside earth.
3) Unknown.
Given the title and the problems above, I didn't read beyond the introduction as time is limited.
It sounds like an updating of the Drake equation without addressing the fundamental problems with that as an estimation tool rather than a more modest method for informing interesting speculation.
I think statistics is entirely bad approach to resolving this problem at least until we have more data.
We need to know more about how planets form (again, we have rather small sample we have studied well), we need to know what exactly is necessary to jumpstart life and how likely it is to happen. Then we have a hard task understanding why exactly intelligent life evolved and whether it is unavoidable or a fluke. And a bunch other questions that statistics is entirely unprepared to answer.
> 1) Unknown.
Abiogenesis is known on Earth. Life appeared quite soon after Earth had cooled down enough, within the first couple of 100 million years. Of course, we don't know if it took 1 million or 300 million years. And it might be difficult to find out.
https://en.wikipedia.org/wiki/Earliest_known_life_forms
Also, why do you consider "unknown" a problem when they explicitly set out to investigate the influence of these parameters? For example, they explore Pann of 0.0, 0.5 and 0.99 (per Myr). Could you explain what problem you see here?
That's a misrepresentation of what I said.
I made it clear I had only read as far as I had because the premise of the title was unpromising given the unknowns, and that it sounded like an updating of the Drake equation without its flaws in the calculating of probabilities (as implied by the title) addressed.
Feel free to summarise how it fundamentally differs from Drake in that important regard, with the findings and their usefulness in the context of the unknowns and title which promises an estimate of extraterrestrial intelligence.
Ignoring all extinct species, there's an estimated 8.7 million unique species of plants and animals currently on Earth. So let's do some dumb estimating and say that there's a one in 10 million chance of "intelligent" life evolving on a planet that supports life. (I will not address the controversial issue of whether or not human life is actually intelligent.)
So whatever estimation is used for the number of habitable planets in our galaxy, Only 0.00001% of those planets might have intelligent life. Next, you must factor in how many of the intelligent species develop technology capable of interstellar communication, and when do they do it? Humans have existed for a few million years, but we have only had radio for a hundred years. With the development of technology comes the risk of self annihilation. We humans have had the ability to destroy ourselves for roughly 60 years. How much longer we go is anybody's guess, but given that life on our planet has existed for roughly 3.5 billion years, and the planet will become uninhabitable in another 5 billion (when the sun changes modes), the time window is pretty small. It's likely that life needs some elements that were less available in the early universe, so let's assume that it's only possible on planets of third-generation stars like ours. Also consider the speed-limit of EM propagation (C). There are only 76 stars within 100 light years of us. It's unlikely that intelligent life exists in any of those systems, but if it did, the inhabitants (if they were listening) would just now be able to hear us. Assuming we survive our technological revolution/evolution for another 100 years, we might get a message from a nearby system. Before then, we might receive some communications from systems farther away, but how long does a technological civilization use radio with simple modulation schemes that we would recognize as something other than noise? Maybe in less than a hundred years, we will have gone through radio, optical, and then quantum communications technology. It's likely that other technological civilizations (if they exist) are using communication technology that is incompatible with ours.
Isn't that the probability that a species is intelligent. The probability that intelligence will eventually evolve on a planet with life is 1.0, from the evidence that we have so far.
Also, Earth has had numerous extinction events that killed off at least 3/4 of land-based life (and 96% of marine life). We have no way of knowing whether extinction events are more, or less common on other habitable planets, or whether such events might even be necessary for the evolution of intelligent life.
A person who has a 1 in a million chance to win the lottery CAN still win the lottery. And if he does win the lottery, his chances of winning was STILL one in a million.
Same with life in the universe. Just because it happened does not make the probability of it happening at all 100%. Far from it.
Even right now on Earth, we have multiple tool-using species spanning mammals, birds, and cephalopods, separated by hundreds of millions of years of evolution. They all seem like good candidates for developing technology at some point over a few million years.
Progressing to that stage this seems unlikely for a planet with life on.
As for the sudden nature of humanity's major technological advances, that's just the nature of geometric growth - every advancement makes more advancements easier. The humans that took thousands of years to go from agriculture to writing were biologically no different from and no less capable than those who went from first flight of a plane to first walk on the moon in a single lifetime.
The most recent common ancestor with our primate cousins was about 7M years ago. There have been various hominid species, but I don't think we call them humans. I thought the general rough guess is homo sapiens are on the order of 200K-300K years old.
This matters because, as far as we can see, our solar system has more planets than any other system we have been able to observe (so far.)
See https://www.sciencenewsdigital.org/sciencenews/december_19__..., article #9 (subscription required.)
I may be out of date, but I thought that was an artefact of our methods and equipment rather than anything else — we can only see big things close to their stars, so if we were looking at our own system we’d miss (I forget, so e.g.) Mars, Uranus and Neptune?
Left over artifacts from their civilizations are just as exciting a find.
Personally, I feel the thought that we are alone in this universe is a wee bit arrogant.
The universe is so big and existed for so long, we have to assume that sentient life existed in the past, perhaps exists now and will definitely exist in the future.
Hopefully, we find at least artifacts that prove alien life, just because the minds of humans expand a bit more, because imagine how shocking it is to religions around the world if existence of aliens is confirmed.
If anything like us existed in the milky way it's almost certainly dead now. If there's something alive it will be almost incomprehensibly different than us.
I think this may be making some weird assumptions about motivation. Let’s say, for the sake of argument, that travel at 5% of the speed of light is practical. Would you be signing up to go colonise a planet around Alpha Centauri? What would be the motivation opportunity such colonisation? Who would pay for it?
If interstellar travel turns out to be permanently slow, difficult, and expensive, then that may cast doubt on the idea that anyone who theoretically can spread out all over the place given a hundred million years actually will.
But I think both of these opinions come from human-centric reasoning. A species that could hibernate may be able to control hibernation through technology, so a ten year journey wouldn’t be as complicated for them. Other species on earth simply don’t have the curiosity to explore the way humans do.
Speculation about alien intelligence is interesting to me, but I imagine it’s a lot weirder than we think. Especially around topics adjacent to intelligence, like curiosity, motivation, and cultural values.
Earth gives us a wide range of organisms with different lifespans and metabolic rates. There are not that many species that live longer than us, and extremely few that live significantly longer than us. Even if something lived 100 times longer than us, only a very small portion of the galaxy would be traversible within a lifetime, and there is still no reason to go more than a few lightyears.
the most convincing meta-analysis i've seen, which considers the probability distributions implied by the error bars in our current best estimates of the relevant parameters (https://arxiv.org/pdf/1806.02404.pdf), suggests a 39–85% chance we are alone in the observable universe. i'm less impressed by those particular numbers than by the attempt to rigorously quantify our ignorance on the issue, where some component values span fifty orders of magnitude. while the universe may indeed be big, i'm not sure it's broader than the sheer span of our ignorance.
Basically, the universe is so ludicrously huge and so ludicrously old that it is as close to statistically impossible as one can imagine that human beings are the only things ever to evolve in such circumstances as to be sapient.
Note that the paper you have linked uses the term "detectable civilization", which is significant limitation due to our current level of technology, the age of the universe, and the propagation speed of light. It wasn't that long ago that we couldn't even detect extra-solar planets.
There is of course an argument to be made for us being "alone" in the universe in the sense that sapience is rare enough that pretty much all species, including ourselves, will die out before ever meeting another sapience, but the idea that in all the unimaginable vastness of the universe we are the only ones?
In other words, the fact that it has happened at least once very strongly suggests it has happened more than once.
No, it doesn't at all.
Maybe just the opposite.
The universe is mind-bogglingly large, but it's also really, really empty, and really, rally sparse. The numbers games starts to dwindle very quickly in terms of all the ingredients necessary.
And the Fermi paradox helps provide crudely indirect evidence.
If there was any validity at all to the 'common life theory' - then it would have started long ago and probably spread everywhere to the point wherein there would probably be ample evidence.
In the 'common life' scenario, it should be rare/impossible to find life that's disconnected from other life scenarios.
There's a decent chance we are alone.
Maybe even out of 1,000,000,000 of similar universes only 1 would actually happen to have life. It's similar with planets. If you only know of 1 planet within 1B to have life, how can you tell the odds are not low enough to have 1 universe out of 1B to have life?
This could be an awesome example of survivorship bias to assume because there's life here, there must be life elsewhere in the universe too. We only have experience with a planet where there's life, so we are innately biased to think that it might be more frequent occurrence than it really is.
The non-existence proof of ETI also means laws of physics are cruel and cannot be violated. There is almost 100% chance that advanced life forms exist in other galaxies, may be even billion year old. But no one has figured out how to travel faster than light.
If anything I'd hazard our ignorance is more on the side of things we don't know we haven't observed than things we observed incorrectly.
I think compared to how long it took for somewhat intelligent life to evolve on Earth, from the point of first life. Assuming* a comparable evolutionary cadence, the question then becomes - how often does life begin?
*This I assume because the cadence of living things on Earth is at the very least tied to the day/night cycles, winter/summer seasons, and lunar tides, none of which are especially unique.
The common argument in favor of more life is that the probability of life evolving is some very small number, such that there must be a very large number of opportunities for life to evolve in order for life to actually evolve. At the same time, there are a large number of opportunites given the size of the universe. Given that there is presumably no relation between the "small" probability for life to evolve and the "large" number of opportunities in the universe, we don't expect these two numbers to conspire to be near the same size, which is what would have to happen for just one life to evolve. Rather, we expect there should be lots of life that evolved in different places or that the probability that any life evolved at all is extremely (vanishingly) small. So if this argument is correct and we know of one life form, we should expect many more in the universe. (Not to imply we would necessarily be able to find them.)
There is one potential problem with this argument. It assumes there is just one universe. If there are many universes then it is possible that life did not evolve in almost all of them. In universes where life did evolve, odds are it happened just once. And of course, that life (us, for example) would see that univese and the life that evolved there, however improbably that would be.
I read a saying "You know an argument is wrong if it invokes quantum mechanics." But I'll do it anyway. Some educated people believe quantum mechanics works this way - the univese effectively branches into parts that are essentially distinct (referred to as different universes too). It is not as outlandish as it may seem. The whole reason quantum computers are supposed to be powerful is that different things happen in parallel.
You don't have to buy the quantum mechanics part. If there are multiple universe for whatever reason then the probability argument above is not valid.
I do want to add one thing. The number of "opportunities" for life in our universe grows linearly with each dimension in the universe. (Lets just say to the fourth power of the size of the universe.) On the other hand, the size of probability grows/shrinks exponentially. So it is not hard to imagine between the two of these numbers, the exponential one wins.
For most I think that we are hear seems to indicate some inevitably but I like that we are an anomaly, we shouldn't exist, the we die.
An insult repeated to the point of cliche in this context which I suspect isn't normally personally meant, but nevertheless seems to deny the counter-arguer the abilities of imagination and wonder, and also presumes ("arrogantly"?) they haven't considered the known numbers first before coming to their conclusion that either there is little hope of communication or we don't know enough to decide.
https://youtu.be/Y_4roppaq7s?t=1h37m45s
Perhaps the evolving spectroscopic signature of our atmosphere will provide a durable signpost. The earth terraformed itself well before intelligent beings ever evolved, and maybe an astute and patient observer might have been able to guess that we were on our way towards intelligent life at some point.
Getting to complex cells took 2 billion years. And getting to where we are now another 2 billion years.
All that time conditions were fairly stable.
Given that life might need some elements created in supernova explosions mixed into other solar systems, and that we had just 13 billion years since the beginning, when you add some randomness, schedule starts to look tight for me.
We might be one of the first civilisations in our neighborhood.
I'm not saying that I believe that's the case but that's entirely possible.
“ We also concluded that at the current time of the study, most intelligent life in the Galaxy is younger than 0.5 Gyr, with values of probability parameter for self-annihilation between 0 - 0.01; with a relatively higher value of the annihilation parameter (≥ 0.1), most intelligent life is younger than 0.01 Gyr.”
If other intelligent life is very young (just like us) could there be more room for understanding if we ever communicate?
I suspect we will barely recognize even alien sentience, since it will literally be alien to our understanding
Would you mind expanding on that? Why would intelligences being young mean we are more likely to understand them?
Yeah... this is why I suspect we may see signs of alien life, but just not know what we're looking at. You're not alone in thinking of intelligence as some kind of scalar quantity from bacteria to super beings, and if only we could find creatures in our range, we'll be able to communicate
Embedded in our conception of intelligence is us. We measure intelligence by what we think is important. But creative approaches to fitness in radically different environments will be multidimensional and multivalent, extremely difficult to judge by our own standards
I speculate that if we were to find aliens, we could never communicate beyond basic Skinnerian reward and punishment schema, if that, never mind prime numbers and such, no matter how sophisticated they are. We wouldn't even really be certain if we were witnessing intelligent behavior or autonomic processes, and neither could they. We can't even understand whales or dolphins, and those would be vastly easier to understand than anything without DNA, emergent from a completely different planet
How could we possibly communicate with a civilization that communicates in the time scale of oaktrees, or are sessile, or communicate using flashes of microwaves in patterns we have no hope of even discerning?
The same day I saw the King Tut exhibit I also saw an exhibit from feudal Japan. The workmanship of the Japanese items was absolutely stunning, much more impressive than the King Tut items as one would expect from a period many centuries later. All of these examples were still done by hand. It's hard to imagine a person in the modern era devoting a lifetime to make only a handful of swords.
What makes these items interesting is that they were made without modern tools or technology. Today our manufacturing technology could replicate these achievements easily. Even common items like grave tombstones can be produced in short order with highly polished stone and precise engraving. See [1].
[1] https://legacyheadstones.com/gallery/photo-gallery.html
Given the wide variety of environments where life can reproduce, shouldn't even non-sentient life eventually escape into space? This removes many of the 'great filter' arguments. This would be more likely on a planet with a shallower gravity well than earth.
Life, even bacterial-level life tends to spread out exponentially as resources allow, which should make it easier to detect.
Correlation, if any, does not imply causation, and the causality principle has nothing to do with statistics.
Observations (counting), however many, will never reveal causality, because they are orthogonal.
Time's too big. There's no reason to assume that the lifetime of technological civilization is more than a few hundred years. By then they will have destroyed their own habitat and - despite some half-hearted (or even serious) attempts on colonizing different planets/planetoids - will have come to an inglorious end.
Let's be generous and say that the lifetime of a technological civilization is a thousand years. That's the time that it can both send and receive signals from another technological civilization.
The chance that one technological civilization is able to receive the signals of another is so vanishingly small as to be zero for all practical purposes.