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Dissolving the Fermi Paradox (arxiv.org)
50 points by akalin 35 days ago | hide | past | favorite | 71 comments



"When we update this prior in light of the Fermi observation, we find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively). ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable."

Opinions like these (I stop one step short of calling them findings, as this is speculation either way) resonate with me. I'm, too, more convinced by the Rare Earth hypothesis, and I find it quite plausible that we're indeed the sole sentient lifeform in the Universe - at least throughout the time of our existence.

This belief never gained me much popularity though. And this is what I'm fascinated about - how badly a lot of people take to this view. Even seemingly rational individuals seem to have some deeply ingrained, emotional need to defend the belief in ETI.

My personal theory is that this emotional mechanism is actually of religious nature; just in disguise. It's very telling that the most popular narratives involving ETI are usually quasi-religious.

The aliens would typically "teach us how to live in peace" (if we're willing to sit down and listen, of course), or turn away from us in disgust (for our sins), or scold us for our poor moral judgment and deeds; generally trap us in shame. Or they'd be quite diabolical and bring all sorts of plagues upon us, giving us a taste of our own medicine for we're wicked.

But the eschatological component is rarely absent either way.

Even this sceptical paper uses biased language through and through, consistently referring to the belief in the prevalence of ETI as "optimistic", and calling the opposite belief "pessimistic". But why?


It's not religious. If anything the opposite is true. Believing we're the only intelligent life in the universe is an epic violation of the Copernican Principle.

There are so many other explanations for Fermi Silence - from the reality of extremely limited sampling to the creeping suspicion that we're too mediocre and underdeveloped to recognise truly intelligent life - that grand assumptions about our specialness seem more than a little premature.

None of this requires aliens who will teach us anything, one way or the other. It requires aliens who ignore us because we're about as interesting as a termite mound.

And once you've seen a few billion of those, you've more or less seen them all.


"Believing we're the only intelligent life in the universe is an epic violation of the Copernican Principle."

Not necessarily, because the principle collides with observer bias in this case. I don't think it's valid in this context.

"There are so many other explanations for Fermi Silence"

Of course. I'm not concerned about the explanations themselves though - more about the emotional dimension; the attachment to the underlying idea. Lots of people seem to yearn for the ETI to exist at all. They'd be fine with any of the explanations you mentioned to be true, as long as the core concept is protected.

"None of this requires aliens who will teach us anything, one way or the other."

My point is not that they would, or that it's a logical scenario. My point is that humans exhibit a strong cultural need for this type of narrative.

I'm interested in this anthropologically, so to speak. I don't really care about the actual aliens (or the lack thereof).


I find the theological aspects fascinating. If there are alien races, do they get their own Jesuses (Jesii?), or did we get the only Son of God? If there are multiple Jesii, are they considered to be the same person (to make the Trinity) or is the Trinity a little larger than 3? Did all the Jesii occur at the same time? Or at the same developmental point of the alien race (assuming a standard civilisational progression for all species)? Are there sapient, spacefaring aliens who have yet to have their own Jesus, and are therefore still in the "virtuous pagans" category?

I realise this is kinda poking holes in Christian theology (always fun), and there are these kinds of questions for all religions. Can an alien reach Nirvana through meditation? Are there alien Buddhas? Are there Mecca-equivalents on all inhabited planets, or do aliens need to know the direction to our Mecca to pray?

The woo-woo "aliens are gonna come and teach us how to be better humans" is less interesting, I think. The underlying psychological need for some beneficent parental authority figure to come and solve our problems is almost too obvious.


> Jesuses (Jesii?)

Pet peeve, honed by endless discussions on Slashdot in the late 1990s: -ii is not a Latin plural marker. -i is a Latin plural marker which can correspond to a singular -us. Plurals can look like -ii, but only if the singular word ends in -ius. That's simply because you replace -us by -i, and if there was an i before the -us, then there will be an i before the -i. (Example: the gladiator's sword, gladius, becomes gladii. But one of those i-s is part of the stem already.)

Neither Jesus nor virus end in -ius, so their plurals can definitely, certainly, 100% never be Jesii and virii. They also happen to be words that end in -us but belong to declensions that don't use -i for the plural at all. (So no Jesi and viri either. "Viri" is a Latin word but means something else.) And on top of that IIRC virus is uncountable in Latin and Jesus is irregular even for the declension it sort of belongs to, and are proper names even countable?

Thank you for coming to my TED talk.


thank you for the informational pedantry :)

So what would the plural of Jesus be?

My name is Marcus, and I whenever I meet another Marcus, I wedge the "Marcii" joke in there somewhere. I would like to be able to refine this. What would two Marcuses (which sounds so wrong) be called?


Wiktionary says "Marci", or "Mārcī" to be pedantic (I'm not sure how strict this is; when I was learning Latin in high school we weren't taught to care much about diacritics on vowels), for Latin: https://en.wiktionary.org/wiki/Marcus#Latin and doesn't give an English plural: https://en.wiktionary.org/wiki/Marcus#English

Note that Marcus is a second-declension (https://en.wiktionary.org/wiki/Appendix:Latin_second_declens...) noun, which is the class where a singular -us turns into plural -i (again, only a single one).

But Jesus is fourth declension (https://en.wiktionary.org/wiki/Appendix:Latin_fourth_declens...), so if it has a plural, then in Latin it's something more like Jesūs (or, again, Jesus without the diacritic; I believe it only marks lengthening of the vowel, no change of the quality of the sound). But https://en.wiktionary.org/wiki/Jesus#Latin says that while it's fourth declension, it's also "highly irregular", and "singular only". It would seem plausible to me that the question never arose in Latin practice, because multiple people called Jesus could always be described as "multiple people called Jesus", and multiple instances of the Jesus would be an unspeakable heresy.

As for English, well. Though I was pedantic above, I should also note that I know that language is what people make it. If the vast majority of English speakers decide that the plural of Jesus is "Jesuseseses", then that's what it is, in English. Even if "just" a certain community decides on a certain usage, then that usage is what the plural is -- at least in that community's variant of English.

Having established that, https://en.wiktionary.org/wiki/Jesus#English lists "Jesuses or Jesi" for the given name and "Jesuses or Jesusses or Jesi or Jesii" for the noun denoting the Christian savior. The variants with i-s hurt my eyes (pun not intended, but I'll take it), and as I explained above, have no roots in Latin (or the Ancient Greek that Latin got it from) but try to look Latin while showing deep misunderstandings of how Latin works, so I would advise against them -- they don't make you look smart or learned. "Marci" seems fine in this regard, but again "Marcii" is not. (Interestingly, a bunch of the Wiktionary quotations for "Jesi" are of the form "Jesuses (Jesi?)", i.e., cases where the author was questioning themselves on this point, which is kind of weak for a dictionary.)

I would say that since -s is the dominant way of forming plurals in English, "Jesuses" and "Marcuses" are the most natural choices, inasmuch as forming plurals of given names can ever sound natural. But I'm not the English police (nor even a native speaker). Only the don't-randomly-double-i-because-you-think-that's-Latin police :-)


Some religions: From the Book of Moses 1:33, a Mormon scripture

> And worlds without number have I created; and I also created them for mine own purpose; and by the Son I created them, which is mine Only Begotten.


Exmormon, they basically believe all other planets are nicer than this shithole....and Jesus had to come here because the Jews were the only ones who'd be evil enough to crucify the son of god for ALL earths that ever will be.


Or the rather more gloomy explanation that there is no economic way of breaking out of most gravity wells & interstellar life is practically impossible. So there are lots of little earth-like civilisations out there, but too rare for us to detect them, and none ever grow large.


https://www.archbalt.org/vatican-sponsored-meeting-discusses...

The laws of physics results in occasional clouds of dust and water (life) that can contemplate their unlikely existence (humans).


Man, this is exactly why I dislike this paper. Somebody reads abstract and conclusion section, sees those probabilities, and then runs with them, possibly forming an entire world view around that. But there are such massive asterisks that should be attached to these numbers which are completely absent in that kind of presentation.

The ~50% probabilities from the paper are not fundamentally more founded in reality than "Did another planet in our galaxy develop intelligent life yet that attempted to communicate? I don't know, so let's assume 50% either way. Therefore, we are alone with 50% probability." Should that number be 50%? Or 10%? Or 99%? You're choosing some prior there. So does this paper, and the priors chosen gravely affect the result. Of course, the paper has more intricate math and more solid reasons for their priors, but fundamentally it is still just assigning almost arbitrary probability distributions to parameters that we have no grasp on. Specifically (see my other comment), the numbers that they get primarily depend on the choice of prior distribution for the abiogenesis rate, which overshadows all other parameters. It has such massive error bars (>200 orders of magnitude by their own account) that arriving at a concrete probability (in the way that you understood it when reading the paper) is somewhere between misleading and a lie, because it's more or less just a projection of that prior into a single number.

In other words, I'm convinced they could have easily arrived at probabilities like 0.1% or 99.9% by reasonably varying their prior distribution for that parameter alone.


> In other words, I'm convinced they could have easily arrived at probabilities like 0.1% or 99.9% by reasonably varying their prior distribution for that parameter alone.

In other other words, this reading of the paper also confirms the general point it makes: The Drake equation is garbage-in garbage-out. There is no way to determine what numbers to plug into it. So let's just drop the whole unscientific nonsense.


> I'm, too, more convinced by the Rare Earth hypothesis,

I think you are misinterpreting the conclusion of the paper. The conclusion is that there is "a substantial probability that we are alone in our galaxy". This extra probability is because of the extra uncertainty within our estimates of the parameters in the Drake equation. But "substantial probability" is something entirely different than being sure.


Also this from abstract: "we find a substantial ex ante probability of there being no other intelligent life in our observable universe"

The keyword is "observable" universe what about probability of life in unobservable universe. When we discovered microscope and telescope only then you could say that we started "observing" something. Modern science is only 100 years old and we can not even imagine what would be invented and discovered for 50 or 100 years.


C. G. Jung, Collected Works, Vol. 10, Civilization in Transition: Flying Saucers: A Modern Myth of Things Seen in the Skies (pg. 320 of pdf)

http://cista.net/tomes/Carl%20Jung%20Princeton%20imprint/10%...


The streetlight effect, we are searching in our close neighborhood, for signals that we would use in our current kind and stage of civilization, and because we didn't find anything we conclude that in the whole universe there is no life or intelligent life at all.

Maybe SETI search should add several terms to the drake equation to understand odds of hitting gold. Is not enough to be intelligent life, to be found in the way we are searching for it, distance, way of communication, culture, kind and stage of civilization, wish to be found, wish to expand, biology, and probably more are just terms in the equation that lowers the probability for us to find anything. There are too much implicit assumptions about what we are searching for, and maybe there is none that fits that because some basic rule that we don't know yet, as we are not advanced enough (a dark forest is just an example).

Is like assuming that advanced enough cavemen will be communicating across the galaxy with louder drums. And that as we hear no drums in space, there is no life anywhere.


People over-estimate the scope of the Drake Equation.

fc - "the fraction of civilizations that develop a technology that releases detectable signs of their existence into space"

This term for many people, is near 1. They assume that "detectable" means that WE can detect them with our current level of technology, and/or that "releases" means that it would be something familiar like radio or laser beam transmission.

...but the scope of this assumption is based upon a scant hundred years of human history. The rate of technological and AI advancement (on galactic timescales) is so brief, it is imperceptible. ...and recall that if life exists, the average age of such civilizations would be hundreds of millions to billions of years older than ours.

When we look at popular sci-fi media, one thing that is blatantly obvious is our inability to even imagine what our "civilization" will look like beyond a few hundred years - and often those shows are even superficially wrong.

If AI surpasses us (or integrates us, or exterminates us), our technological existence to "release detectable signals" will be a relative flash in the pan. Remember that AIs aren't limited by our meat lifespans. To them, taking 100 million years to populate the entire galaxy, is a reasonable amount of time. To them, WE may not be the life they are looking for - the emergence of an AI might be of some significance (or perhaps even not), and we are just the slime on the surface of the rock. ...the precursor to what THEY consider THEIR abiogenesis.

...and if AIs encountering one another in space are constructive rather than combative, then the rate of abiogenesis may not be all that relevant. It might simply be like adding another drop of water to an already full glass.


The paper basically says that the Drake equation is just a guess, and if we’re going to guess, we might as well do so using probabilistic models. Their model puts the Great Filter behind us.

This makes intuitive sense too — an early Great Filter simply has to stop life from occurring, while a late Great Filter has to deal with the complexity of preventing life from doing what it does best (surviving and spreading in a “Life finds a way” style). Concretely, an early Great Filter has fewer variables it must affect than a late Great Filter. Like the paper says, we are probably alone, but there’s little reason to be alarmed about it.

And if you happen to believe that AGI and a Singularity are the inevitable outcome of intelligent life, the case is even stronger that we are the first, last, and only. However powerful the Great Filter might be, it’s unlikely that a super-intelligence would succumb to it.


I'm fairly confident the great filter is ahead of us. It won't be long (20-50yrs) until any hacker minded 14yr old can create a virulent virus in their bedroom and release it to the world when their girlfriend/boyfriend dumps them or just for the lulz.

And that's just one of the many ways coming where any average person can decide to ruin the world. It's already possible today for a single rich person, if they wanted to, to destroy the world. I don't remember exactly how. Something like buy 1k airplanes and have them seed the atmosphere IIRC. Those kind o things get cheaper and cheaper until their in reach of your average joe


You paint a compelling picture here. But if we extend this picture to a galactic timescale and space, then even a minuscule chance of surviving distributed technology would mean a galaxy full of intelligent life. So if we can imagine even a small chance of humanity surviving itself, then we’re no longer dealing with a Great Filter, but a Small (and in the aggregate, Ineffective) Filter.

We don’t really have to imagine ourselves, since enough science fiction novels have already been written where humanity nearly extinguishes itself (sometimes multiple times) but then finally gets its act together. There would have to be something more fundamental than technological power being too cheap and widespread for a late Great Filter to get to 100% effectiveness. The only thing I can think of is that every super-intelligence checks out of our universe for some reason — that the ultimate end of technology is always effectively (if not literally) suicide. But this goes against the very nature of technology — to reshape existence to fuel the battle against entropy. Perhaps every Singularity sees that this battle can’t be won, and decides to call it quits? Maybe. But it seems more likely it would fight until heat-death itself.

In fact, there’s a great short story about that too.

If there’s hope in our imagination, I think it’s likely there’s hope in our reality too.


Or maybe the singularity realizes there's more to existence than indefinite propagation.


To address your scenario concretely, though, technology advances generally – not just giving the power to destroy, but also giving the power to protect and restore. Covid and mRNA vaccines are a good example – globalization surely contributed to the pandemic, but the creation of the vaccine is also a product of globalization. If a single 14-year-old can create a virus, then thousands of 20-to-70-year-olds can create a vaccine even faster.

I might be wrong about this, but I think intelligence and benevolence are more strongly correlated than intelligence and malevolence, and that as the world becomes more educated, it is also becoming more intelligent and more benevolent. An evil-genius is a trope because it is an anomaly. For every evil-genius there are thousands if not millions of good-geniuses. Evil tends to look like Hitler and Stalin, not Einstein and Turing.

It won't be a 14-year-old that brings the world to its knees. It will be old men (and women, I suppose) spewing hate and lies from their Oval Offices.


The Sum Of All Fears was partly about this. In that case it was atomic weapons being in reach of wealthy individuals, but the same principle applies. The barrier to entry is just getting lower every year.

That experiment/art project with E. Coli on a penicillin gradient a few years back was terrifying.


Any links or more identifying info?

Sounds interesting to me too.


Given the project that Fermi is most associated with in the public mind, I am a little surprised that he found his paradox puzzling.


It seems fairly obvious to me that the vast majority of civilisations will wire head themselves and disappear into virtual worlds of their own making. It takes a very rare soul to forsake eternal bliss and an eternal world of your own creation.

Most civilisations will have just enough of a life support to keep the machines running. They might be spurred into action each time a sun burns out, but other than that why bother with the outside world?


I really like this idea, especially since it plays well with Simulation arguments. But unless there is some kind of inception-like time distortion occurring in a Simulations-all-the-way down scenario, then disappearing into virtual worlds is not eternal. Eventually every star will burn out.

I think that at least some people (and when you're dealing with galactic timescales and spaces, this means a lot of people) would stay in reality to figure out how to get around entropy and heat-death.

So even though we might very well be in a simulation of VR-checked-out civilizations (or even if we aren't), I would expect to see some people in our simulation/reality fighting against the parameters of the simulation/reality that puts a time-limit on existence.


You only need a single Elon Musk and a bit of tech infra slightly better than ours for a civilization to Von Neumann its local galaxy (and possibly its affectable universe).


In what way is a von Neumann machine not alive? Wouldn’t this just change the chemistry?


Exactly, I think life is probably a von Neumann probe. What is the easiest way to spread yourself through the galaxy? Throw bacteria and parcels of your genetics out into the void. Easy and low cost. What about radiation you say? I'm sure there are ways to engineer a survival rate > 0.

It also follows: If it is possible that one civilisation spreads itself in this manner, it is likely that we are decedents of that civilisation. Simply because there will be many more copies of the original civilisation with a penchant for spraying their seed around than other kinds of civilisation.


Bacterial life as we know it here on earth is too low fidelity for an honest-to-$deity, affectable-universe-spanning civ (just look at the temporal distance between a possible paspermia event in these terms in our solar system and replicating into the next couple of star systems).

An _actual_ replicating Von Neumann probe, that we can imagine working within the laws of physics today (even if we don't yet have the engineering capacity to build) can actually clone not just a couple of DNA strands, but can bootstrap an entire new sapient civilization, including technological progress, likely all the way down to the civ's culture.


> This makes intuitive sense too — an early Great Filter simply has to stop life from occurring,

I'm not so sure why this supposed to make intuitive sense. Life is a gradient, so any metabolic process that happens on a energy gradient can be considered 'alife'. I really don't see how an early Great Filter would work - are you going to stop energy gradients from happening? I've read -- will try to dig up the source -- that -- at least simple life -- is pretty much a given since -- even though it creates pockets of lower entropy -- allows for the most paths to thermodynamic equilibrium.

In my opinion a late filter makes more sense. That is; any species that evolves in the confinements of competition for resources and natural selection is -- due to the requirements that competition for resources creates -- necessarily unable to properly transition to a steady-state mode with no competition for resources and no (or limited) natural selection.

The reason for that is that the transition phase from competition for resources to the steady-state phase is simply too short. I'm convinced that this is what we are currently seeing with Humanity on a global scale; even though there's no need for competition for resources, we're still biologically and socially 'programmed' to compete with each other for resources, mates and habitats.

(Biologically, all humans are more closely related to each other than -- for example -- any two chimpanzee tribes. We are not very diverse, genetically.)

That inability to quickly change a species 'modus operandi' to a steady-state model together with the immense power multiplication of technology and cooperation that make it possible for civilization to literally dominate their ecosphere, I don't see how any species is ever going to survive that threshold.

The result of that inability to switch to a steady-state model and the powers achieved - tools and cooperation are the ultimate exploits! -- is simply extinction by habitat destruction.

I think that the current observations quite neatly match this.


The Drake Equation’s always been an exercise in multiplying a bunch of wild-ass guesses together and ignoring the error bars. At least this article pushes it out to ignoring the error bars on the error bars.


I have a personal theory about the great filter:

The great filter is evolution converging to a local maxima and not evolving creatures capable of higher intelligence.

We're scared about the mass extinctions on Planet Earth while at the same time they were the ones that cleared the field for different animals to evolve. Case in point, the Dinosaurs going bust paved the way for small mammals (then large mammals, etc)

"But couldn't we have intelligent dinosaurs" maybe not? (Because of a bunch of stuff that only came later like animal packs, family life, etc - though it might be argued that some dinosaurs had that)

Then we have the fact that mammals are born much more frail than other species and needs "a family" to take care of them for a while (and human's big heads made that "while" into "a lot of time")

But without that you don't get societies organizing. And the bigger the society the more you can do with it.


The only problem I see here is that if intelligence has a large evolutionary advantage over non-intelligence (or lesser intelligence), then intelligence should always emerge given a large enough population over a large enough time-scale.

Given the galaxy, and given billions of years, the Great Filters that seem most likely are the ones that occur on the edges of the timeline: before multi-cellular life begins, or after a hyper-dominant intelligent species arises.

Having said that, I think you’re absolutely right about mammals and societies. If the Great Filter does occur in between life and intelligence, it seems like it would happen where the first signs of intelligence begin. And for earth, that means mammals and the arms race of mind-modeling that their social lives initiated. No other type of animal on earth has parental-care so fully built into its biology: milk glands and placentas force mammals to be social from the start.

A great book that doesn’t deal with intelligence and mammals directly, but provides a key connection, is “Consciousness and the Social Brain.” The book makes a strong argument that consciousness sprung from evolutionary pressures that were essentially social — that being able to model (and predict) the mind of another is essential for communication and cooperation. But one can only model the mind of another if you first model your own mind, and thus, consciousness (which I would argue is just another name for general intelligence).


The Fermi Paradox always seemed like an incredibly simple-minded idea to me. So much so, that I don't quite understand how someone as intelligent as Fermi could seriously put it forward.

The idea that life in the universe will be comprised of humanoid-esque beings that have the same perception of time as us, or the ability to communicate in a "language", is just a human-centric idea. It's us, projecting our own worldview (which has developed through millions of years of evolution) on to the infinite universe. This is the fundamental problem with positivism; using your current limited sensory knowledge to construct a complete world-picture.

Even life itself is not a neutral word; it mostly just means "carbon-based entities like those on Earth." Perhaps the reason the universe seems so empty is because we only have the ability to see things like ourselves?


> beings that have the same perception of time as us, or the ability to communicate in a "language", is just a human-centric idea

Well, we do see this behaviour in other animals, and not just humans, or mammals even.

I realise that's not broadening the net much - we share a common ancestor with everything that could be considered "living" on this planet, so ultimately it's all "human-centric" to an extent.

But if there are forms of life that are wildly different, to the point we can't communicate with them or even understand that they're "alive" in any meaningful sense, then that's kinda out of scope ;) The definition of "alien intelligence" only includes things that we would be able to recognise as an alien intelligence. Otherwise we're just talking to the trees, and they're dull conversationalists.


I find the Fermi paradox quite shallow too, but for different reasons. Even if a twin sister civilization of humankind existed somewhere on a different planet revolving around a different star, how would we detect it? Space is huge, and hoping to detect some signs of intelligence close to a distant star is like trying to photograph a firefly that flies around a lighthouse, from miles away in the sea, only about 1 trillion times more challenging.

You just need to see what faint a signal we receive form the Voyagers, which are deliberately pointing their antennas at us and are thousands of times closer to us than any star to appreciate how improbable it would be for us to ever detect extraterrestrial communication.


> The Fermi Paradox always seemed like an incredibly simple-minded idea to me

I agree, but for different reasons. My favourite way to dissolve the Fermi Paradox is to simple state that the main assumption, i.e. "the lack of evidence of extraterrestrial civilizations", is just wrong :)


> we find a substantial {\em ex ante} probability of there being no other intelligent life in our observable universe

This is very sobering to read if true. It’s all on us. Life is even more precious than we thought and every human life extinguished even more of a loss to the universe. If we could only band together and see this.


Except that human life is causing many other species to be extinguished here on Earth so perhaps it would be better for the universe if humans would go extinct, in a gradual and humane way: see vhemt.org.


vhemt.org = The Voluntary Human Extinction Movement

I imagine that people attracted to this movement to either stay true to the "voluntary" aspect and pay with genetic demise for their mental susceptibility, or realize that their movement will be never manage to voluntarily attract the number of people necessary for movement's "success" and at some point look for more effective ways of achieving the said human extinction. Anyway, this is next level kind of awkward stuff.


It would also mean humans are the only species that has potential to spread life throughout the stars. I agree with JohnJamesRambo that we should see how precious human lives are.


No specie on this planet can go extinct voluntarily that's not how Biology works. Life on Earth is exactly opposite meaning survival, reproduction and evolution as core rules.


I would argue that a species going extinct is neither good nor bad, so neither better nor worse. This applies to the human species, as well as others.


TL;DR: "We don't know how often abiogenesis happens, and our uncertainty for its rate is extremely large. The error bars extend so far into 'effectively zero' that we could or could not be alone, it's a toss-up". Seriously, this paper hinges entirely on the prior distribution for the abiogenesis rate.

Longer comment:

The paper considers each parameter of the Drake as a probability distribution over some range. Notably, they assume that f_l in the Drake equation (the fraction of habitable planets that actually develop life) may vary over (at least) 200 orders of magnitude. Yes, you read that correctly.

Naturally, they thereby get a long tail of "planets essentially never develop life, even despite there being so many of them".

My main critique (as someone with no further credentials) is that the prior probability distributions they assume for the parameter distributions are more or less meaningless. Their results say "if we assume that the log of f_i (life-bearing planets that develop intelligent life) is uniformly distributed between log(0.001) and log(1), similar for other parameters, then the probability of being alone in the milky way is > 50%".

Specifically, by far the largest impact here is from assuming some distribution for f_l that covers 10x as many orders of magnitude (!) as the remaining parameters together. I'm very certain (but haven't done the math) that slightly tweaking the sigma they assume for the corresponding log-normal distribution (that sigma is 50 orders of magnitude) would drastically impact the results. They do a lot of dancing around that fact (discussing how little impact the priors of other parameters, or even the center of the log-normal distribution for f_l have), but fundamentally the result boils down to:

"We're extremely unsure how often abiogenesis happens, and this parameter dominates everything else." Followed by some math that (oversimplified) boils down to "if we set the rate of abiogenesis to effectively zero half the time, then half the time we are alone in the universe."

PS: Title should probably have (2018).


Basically, they've replaced ass-pulling the factors in the Drake equation with ass-pulling probability distributions for those factors.


The other thing I believe they are missing is that they are treating the Earth as a single data point for ambiogenesis.

The entire Earth's history is hundreds of millions of data points.

Each year that a habitable Earth existed prior to life evolving can be seen as a data point. ... and with life emerging very very near its habitability transition, this reduces the drake error bars considerably.

The real limitation of the Drake equation is the duration at which life sends out radio signals - which given technological advancement and AI is probably only a couple hundred years.



> We're extremely unsure how often abiogenesis happens

Lacking any credentials on the subject whatsoever, and based on what (little) I know about abiogenesis, intuition tells me it happens with a probability of 1, if (and here's the key) the conditions are right, and given enough time. (A fun corollary of this is that intelligent life also happens with a probability of 1, under proper conditions [1]).

So, we just need to find how many planets have had the right conditions for a long enough period of time.

[1] p(abiogenesis)=1 + "evolution is a universal law" => p(intelligent_life)=1


The claim that we are alone in the observable universe seems incredibly arrogant. We don't have enough data for such an extraordinary claim.

Time and time again we have discovered that we are less special than we thought. Life appeared quickly after Earth was formed. I'm convinced the universe is teeming with life.


Being convinced that the universe is teeming with life is one thing. Intelligent life is quite another.


Seems to be breakthrough work. I never went really far into the Fermi paradox and was scared a "great filter" was in front of us. This article seems to imply it is behind us. That makes the need to have a backup planet and expand into the universe even more vital to keep the tiny flame of life and consciousness alive. Why shouldn't we put more ressources into it ? My reference source about it is https://waitbutwhy.com/2014/05/fermi-paradox.html


If we just stop for a moment and think how little we can “receive” from our surrounding (100 hundred light year max?) and how vast the universe, even our galaxy is and how incredible long the time span between the birth of the first stars and the birth of our petite civilization then we will realize we still can deduce nothing about the existence or non-existence of other civilizations.


What do you mean? Why can't we receive signals from more than "100 hundred light year" away?


Well, signals sent from Earth (radio, TV, etc...) are indistinguishable from noise at about that distance.


Because of the very large amounts of energy to transmit information in all directions from such a large distance. Also because it's such a stupid waste of energy. Why send radio waves out in all directions in order to communicate with a neighbor? Use a light beam instead.

So the lack of huge radio transmitters that we can detect really just means aliens aren't investing huge amounts of money into letting us know they exist. Why would they? Especially if they already know of other civilisations.


I mean, we definitely can. We see stars that are thousands of lightyears away! However, maybe OP means "receive" as "response to a message we sent". This is indeed something we are able to do since ~100 years, so our communication bubble is currently ~100 lightyears.


This is only for omnidirectional radio signals. Directional beams can go arbitrarily further.


What kind of “directional” signal you can think of sending from a planet millions years ago that can hit earth exactly in the moment a SETI antenna directed at it and ready to receive? And how much energy should this civilization keep pumping in the signal to increase the probability that someone can receive them? And why it should make any sense to waste energy like this when the probability that you can receive a confirmation is equal zero even when other civilizations are out there?

About the required power and signal degradation over distance, see this: https://www.quora.com/How-far-do-radio-signals-travel-into-s...


We were all taught that humans are not special and the earth is common. Well, it looks like everybody was wrong. We are unique after all.


(2018)


When government literally admits that we have daily sightings of UAPs they cannot explain - i do not understand why we still also say there is no evidence of alien life?

https://www.reddit.com/r/UFOs/comments/nf7h0x/wow/


several of the unexplained videos are debunked. The pilots testimony does not match what their equipment is saying in the videos. The media is grossly negligent when covering these topics. The recent UFO tringle is following FAA rules and regulations with lighting its been discovered its tringle due to the lensing. UFO does not mean alien it means unidentified.


I do not understand why we would only be seeing UFOs at convenient airplane altitudes inside our atmosphere, but not detect them while they approach Earth, despite the fact that space is constantly being scanned for all kinds of stuff. I also don't understand why the daily UFOs would choose to just confuse us by flying around in a sorta-hidden but also sorta-not-hidden way. Why don't they interact with us if they go to the trouble of visiting?

Everything about UFOs is so implausible that the alternative explanation of "we don't know what we saw, but almost certainly not a UFO" seems to be much better.


A UFO literally means "we don't know what we saw" however the parent used UAP which gives the meaning of alien to something unknown.

This contextualises the issue and brings up the questions you mention. Without this imposed meaning the questions go away.

People like giving meaning to the unknown.


Doesn’t UAP just mean unidentifiable aerial phenomena? That doesn’t say alien to me.


> A UFO literally means "we don't know what we saw"

In common parlance UFO also means "spacecraft of extraterrestrial origin", and I very obviously used it in that sense.


Why would UFOs be "evidence of alien life"? They would have to be identified in some sense, otherwise they are just as much evidence of fairies or saints as they are evidence of aliens.


When someone says we have daily sightings of UAPs they cannot explain you have to remind yourself that one possibility is that they're simply lying.




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