One problem with this article, and many others of its ilk, is that they somewhat underestimate the enormous complexity of this thing we call "life". Here's an incomplete list of what the most primitive single-celled lifeform has to do:
-- create some way of sustainably separating "self" from its environment, so that all the components of downstream steps don't diffuse away. The separating material, which could be a cell wall or cell membrane, also has to allow selective exchange of raw materials in and out of the cell, and provide protection against damage to the cell.
-- design and build a chemical template (DNA/RNA in our case) which allows it to reproducibly recreate itself and all its components.
-- design the molecular machinery which builds that chemical template, and which is also responsible for reading and interpreting the template, regulating its use, and providing error correction. Instructions for creating machinery that makes the template are encoded in the template.
-- design the molecular machinery (enzymes and other proteins) that builds molecular machines, using a design language encoded in the chemical template.
-- establish a chemistry program that takes in raw materials from the environment, and converts it to energy, building blocks for the machinery and template, and allows for repair, defense, and other tasks.
-- establish and implement reliable reproductive (data backup) framework, minimally involving the creation of a copy of the chemical template, and often copying and spinning off a second, complete cell.
These are the elements of basic, independent (i.e. non -parasitic) life. As far as we can tell, the core elements (information stored in DNA/RNA encoding proteins as molecular machines) of this life solution emerged fairly early in this planet's 4.5 billion-year existence, and every other organism since then has simply iterated on the same solution -- no other competing solutions exist to our knowledge.
It thus makes sense to account for this complexity when we calculate the odds of finding life in the universe. In my opinion, the Fermi paradox is nonsense.
And on top of this complexity of life, it took like 4 billion years on earth (that's roughly 1/3 of the age of the universe) from RNA/DNA to intelligent life forms that can talk about this on the internet. And during this time, no catastrophic global event has happened to undo all that development. Comparing Earth to other planets in our solar system (we cannot really compare to other systems, obviously), Earth is really lucky that there was no such catastrophic event. So many factors are important for this -- our sun is just the right size (not too harsh UV radiation (bad for molecules to be stable), not too small to make our orbit so small that rotation would stop (blowing away the atmosphere)). Our moon is unusally large for a planet like ours, yet it was vital for stabilising the Earth's axis (stable axis == stable weather) and slow down its rotation. And for the moon to emerge, a very nearly fatal impact from another body of the right mass (Mars sized) needed to happen at the right time (very early). At the right speed and the right angle. The availability of water and oxygen at the right times in Earth history where also quite a big unlikelyhood. And it goes on and on: Earth is unimaginably lucky.
Taken all this together, I doubt that anyone could multiply the probability of life on a planet with the amount of planets in the Milky Way (or the universe) we think would be Earth candidates, and claim to have a sensible number. The later is an unimaginably large number, but the first is an unimaginably small number and also a very unknown number. So: we just don't know how often life happens.
And also, detection is not trivial: it is not that easy to see other planets (they are far away), or alien space probes (they are small, space is large), other radio waves (they are weak), or any other signs of intelligent life.
I mean, it's potentially possible Earth is the only planet with intelligent life (though highly, highly improbable). But the moment we discover any other planet with intelligent life, then we must assume there are an infinite amount (if the universe is infinite).
Of course this brings up more questions about what is intelligence? Is a slime mold intelligent?
> In real-world software design, violations of this rule of thumb are common. For example, the FAT16 file system imposes a limit of 65,536 files to a directory.
If the rules of software design apply to the universe, what is to stop us from assuming that our almighty creators are storing an $intelligent_life_form_count variable in a single byte somewhere and there can only be 255 of us ?
Or there could be a maximum on brain processing power and we're hitting that with our population growth. Possibly affecting intelligent life elsewhere as well.
I agree with your conclusion, but it does not follow from that statement, which is just a made up rule of thumb. I'd rather apply Bayesian statistics. If we found life on one more planet, what were the chances of that assuming those are the only two planets with life? Pretty low I'd say.
Actually, without any additional knowledge I'd assume that some sort of seeding has happened, as that's presumably more likely than live developing independently.
Its highly probable that, if human-scale intelligence/civilization exists on other planets, Von Neumann probes (or some similar, highly detectable signs of activity) would have reached us by now.
And they have not. This is an interesting paradox.
Why, though? I hear this argument a lot, but never ever is it backed up by actual facts aside from assumptions (i.e. that technological civilisation build Von Neumann probes in the first place).
So first question: why even Von Neumann probes? What would be the purpose of a self-replicating spacecraft? If it's science, then there's no reason to assume we would even be able to detect it. If it's some kind of colonisation effort, it only requires more assumptions.
The basic assumption that the Fermi "Paradox" (I refuse to see it as a paradox) requires, is that technological civilisations remain unchanged over geologic time spans. That's a bold assumption, judging from our sample size of 1. Another assumption is that such civilisations grow exponentially for a practically unlimited amount of time (yeah, yeah, millions of years isn't exactly "unlimited", but on a human time scale it kind of is).
Given the vast distances in both time and space, it's much more reasonable to acknowledge that technological civilisations are simply too far apart (in both time and space) to make contact in most cases. A thriving local interstellar civilisation on the other side of the Milky Way within the Zone of Avoidance would be virtually undetectable by us, for example.
> that technological civilisations remain unchanged over geologic time spans
Actually I think the opposite assumption, that civilization radically changes over time, is an argument for it. Future humanity is not people on (sublight) space boats touring the stars like Star Trek, its seemingly some kind of unfathomable transcendent intelligence. Maybe its not even recognized as "civilization" by our standards.
And why would such an intelligence not explore its environment? What's the likelihood, if there are many such intelligences, that essentially all of these intelligences choose to remain static, stagnant and stealthy instead of making their presence known within their light horizon?
Well, there are a couple of problems with that. The god-like alien hypothesis is basically useless, as they would have no interest in us and would be undetectable anyway.
The exploring civilisation falls into a similar category: if they are super advanced, they wouldn't be seen unless they want to. So no data point to be had there either. If they're just advanced enough to cross the vastness of interstellar space, they'd take hundreds or thousands of years to get around, so very little chance for them to randomly bump into us at this specific point in time.
"Making your presence known" is also on shaky grounds, since it only takes one. By that I mean it only takes one locust-like civilisation that matches the "Grabby Aliens"-hypothesis to conquer the known universe within just a few billion years. This would imply, that it'd be highly likely that we ourselves would be part of- or descended from this super-civilisation. Again, the facts don't support that.
OTOH, it also only takes one civilisation that wants to prevent such scenario. They don't even have to be around anymore. All it takes is seeding the universe with self-replicating "sentinels" that simply sit dormant around M-, K-, and G-type stars and watch. Once they detect a space-faring civilisation popping up, they'd being their assessment. If the AI suspects a "Grabby-Aliens"-scenario, it's time for Exterminatus or some other, more subtle means of preventing the scenario from materialising.
So subtle in fact, that the affected civilisation might not even be aware of it. In fact, it could happen to us right now and we'd be none the wiser - ever wondered why it haven't made it back to the Moon in over 50 years ;)
The fun part about this hypothesis is that it's just another scenario that we wouldn't be able to detect or rule out: GRBs happen all the time, good thing Earth hasn't been in the way of a nearby one... Or imagine another Carrington Event, only 50x stronger, blasting us back into the stone-age - just another otherwise oddly calm G-type star having a little hiccup; nothing unusual our extra-terrestrial neighbours would think...
Basically the number of scenarios that would match our observations so far while still allowing for a universe teeming with technological civilisations, outnumbers any hypothesis that would truly present a "paradox" IMO. (just an opinion, not a fact, I could be very wrong on this)
There doesn't need to be a why. With the time scales involved one successful Von Neumann probe civilization would quickly (at time scales of the universe) take over everything. That we don’t seem to see that is suggestive-either there’s no one else or there's a very strong, effective galactic or universal ban on VN probes.
This somewhat suggests or relies on humans not being uniquely territorial and resource hungry.
Kind of like the saying that if you see one cockroach you have many, many cockroaches.
Why doesn't there need to be a why? Outside of art (and even there I'm not sure), there's always a reason - especially if we are talking about an advanced civilisation. There's also no reason to believe this hasn't happened:
1) Galaxies far away are also far back in time - they could all be Dyson-sphered by now and we would be able to know for millions or billions years.
2) This also might have happened elsewhere - we have no means of detecting what's going on in nearby galaxy clusters, or even within our own Milky Way really.
3) In this line of thinking, alien civilisations are always a walking oxymoron or paradox themselves: so they are super-advanced, yet have to be detectable, and they think like us but also don't, because they know about the consequences but don't care about them. They also act without reason but at the same time with purpose. And they are superlong lived (or their machines are) yet feel the need to breed at insane levels to settle entire galaxies because of... of the resources they actually don't need if they wouldn't expand like crazy? - but wait, you said there is no reason - ah my head's spinning :)
There is no sign that we will ever send out Von Neumann probes, so why should I believe that any other intelligent civilization will do the same thing.
Or, how do we know they haven’t reached us? Maybe they stayed in the outer solar system. Maybe they came, looked, and left. Maybe they have some sort of cloaking device technology. Maybe they are really small. Maybe they came during the age of dinosaurs and probe is still out there in space, shut down and waiting to be discovered.
> There is no sign that we will ever send out Von Neumann probes
Unless human civlization collapses, why not?
> Or, how do we know they haven’t reached us? Maybe they stayed in the outer solar system. Maybe they came, looked, and left. Maybe they have some sort of cloaking device technology. Maybe they are really small.
Ifthere is even one more civilization sending out probes, that implies there are many within our light horizon sending out probes. I find it implausible that every single one would choose the same strategy of keeping probes stealthy and undetectable.
Note that mankind cannot make Von Neumann probes. We're still having troubles landing serious equipment on the moon (see recent crash), let alone create a probe that would be able to harvest raw materials for making a duplicate probe, refining those to the ingredients needed, converting those to probe building blocks, assemble the new probe, provide it with propellant, program it, and launch it.
So I'm not sure why you'd think that a civilisation comparable to humans would be able to.
Also:
if you can build Von Neumann probes, you can construct a Dyson swarm. You just instruct the probes to create the components of the swarm from the raw materials in your star system. But that would massively boost a civilisation's energy budget. Therefore, it's quite likely that any civilisation capable of building Von Neumann probes will have built a Dyson swarm.
So, secondly, it's about as paradoxical as the lack of detected Dyson swarms.
I mean our sun is 4 billion years old, it took that long for us to show up and even contemplate the possibility of a Von Neumann probe, we may or may not build one someday. How do you build an autonomous system which is rated to last and self-replicate for, say, 250 million years, until you've done a few trial runs which lasted about that long? The universe is only 14 billion years old to begin with and the Milky Way has hundreds of billions of stars to explore... the math is admittedly above my pay grade, but if you assume ultra-advanced technological civilization is rare and interstellar travel is only possible at a small fraction of C, it seems plausible enough to me that simply no one has managed to send Von Neumanns into our neck of the woods yet. The hypothesis handwaves the question of whether such an invention is even possible.
Assuming that they are currently roughly at the same stade of evolution as us, or less, and knowing that Voyager 1, the farthest human made object in space, only crossed the heliopause eleven years ago, it's not highly probable that "something" would have reached us by now.
Of course, it's based on an assumption, but the contrary is too. The thing is we don't know enough to estimate when, where and how life might have appeared elsewhere.
Where is that assumption coming from? Different planets could easily sit a billion years apart in evolution, based on the age of their star. Meanwhile a thousand years is a long time for technology.
To me, this seems to vastly underrate the scale of the universe. Even if our galaxy had significant amounts of life in it, and civilizations were sending out hundreds of Von Neumann probes, it feels improbably as heck that we'd have seen any in this brief modern stage of human development where we could spot such things.
Second, life just seems not easy. Intelligent life doesn't necessarily have conditions to be sending out masses of timeless void travelling probes on and on. Probably a lot of the advanced ones struggle or lurch along as we do trying to subsist off the local ecospheres.
VN probes work more like the lily pad riddle that humans commonly fail to understand.
>In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half of the lake?
The answer of course is the answer 47 to the riddle. With VN probes the answer would be "who the hell knows" at this point. Maybe interstellar space is a whole lot more dangerous than we expect and sending out countless self replicating probes isn't possible. Maybe the intelligent aliens out there are a whole lot smarter than us, and the idea of sending out probes that you effectively lose control of is recognized as a bad idea. Or, maybe there is no one else is out there. Hard to figure out with a sample size of one.
One strategy for estimating bugs is to intentionally seed your code with bugs and then see how many of them the QA team find. ie, if the QA team identifies 5/10 intentional bugs and 20/?? true bugs you can estimate there are 40 true bugs (20 still unidentified).
Likewise, we just need to seed other star systems with intelligent life and see how many our astronomers can find.
I think this could be a maybe a way to assess the efficiency of the QA team, but I am skeptic of using it as a metric about estimating the number of bugs. This is because QA is there to help with reducing the probability that an important bug will happen to a real user. But the total number of bugs a system have is a sum of bugs found by developers + bugs found by QA + bugs found by average users + bugs found by power users + bugs found at scale/big numbers.
The more we move to the right of this sum the hard is to replicate conditions to find bugs and so we move from finding to probabilities and risk management.
For the moment, astronomers found 0 life forms out the 42 we seeded. Unfortunately, 0/42 is equal to 0/n where n ∈ ℕ, so we don't gained much knowledge on the matter so far.
Conversely it’s impossible to prove there is life beyond earth.
PROOF is a high standard.
All our existing evidence seems to point to the fact that we are indeed alone in the universe.
I would in fact postulate that sufficient intelligent life would have moved beyond 3d/physical and would have exist in higher dimensions/virtually but hidden from sight. The way humans is trending certainly is going towards virtual/ augmented reality, virtual reality. In even 1000 years I can imagine direct brain implants for some reality augmentation. Also in 1000 years what other physics will we discover and able to manipulate? Certainly if we discover ways to manipulate actual reality, we will.
With that said, this could explain why we will not detect life because we only had the technology to detect what we call life, and this window could be only 1000-2000 years before we moved beyond physical reality. So the chance that a similar intelligent life with similar tech era out of billions of years makes it almost nil. Both windows has to match.
It is probable that Mars had life even before Earth. It had water oceans for hundreds of millions of years, which is approximately how long it took life to emerge on Earth. Venus potentially had life as well, in addition to some of the moons. Let's be conservative and say that 2 of the n bodies in the solar system had life and one had so-called intelligent life emerge. It seems pretty damn likely given the sheer numbers of the Universe that intelligent life also emerged elsewhere. We currently can barely detect exoplanets. It isn't a surprise that we haven't detected intelligent life. How can you find something you can't see?
From what we know, life is effectively guaranteed to emerge on a planet with a rocky core and water in the habitable zone. Are there planets like this? Yes, lots, probably.
We can't know that life is guaranteed unless we find another example of life arising independently.
We don't know how many random chemical reactions are required for life to be likely. We probably agree that a small puddle isn't likely to spontaneously generate life within a century. We like to think that one planet for a billion years is about the right size. But it could be that it takes a whole universe of planets before it's likely to happen once.
If that were the case, then the universe would look exactly like it does now, with us living on the planet where it happened and no life discovered elsewhere so far.
> We can't know that life is guaranteed unless we find another example of life arising independently.
Of course not. But that's why we discuss probabilities.
We also can't discuss definitively about things that we have no reasonable ways to detect. So claims about there's no life because we would have seen them is completely worthless given that we have very, very few, if any, ways to detect such life.
Assuming it existed, are we even able to detect a planet like Earth with similar animal and human activity in any other solar system, even in the Milky Way? I am personally not aware of such general capability.
Yes, but we have no idea what the probabilities are. We have no basis for saying "it is probable that Mars had life."
If we found native life on Europa or something, that would change things completely. Independent life arising at least twice in the same solar system would make it clear that life is common. But a sample size of one, with the anthropic principle, leaves us no clue. Life might be common, or we might be unique.
Your post goes off the rails on the third word ("probable"). That's not probable, without a whole lot of assumptions, even assuming that Mars did in fact have water for hundreds of millions of years.
You're assuming something. Maybe something like "a world with water has high probability of life emerging". That is a massive assumption.
Given that I find that assumption implausible, I consider the rest of the post to be built on a flawed foundation.
> You're assuming something. Maybe something like "a world with water has high probability of life emerging". That is a massive assumption.
With what else I added: a rocky planet with water, an active molten metal core, and in the habitable zone. It is indeed my understanding that life on such a planet is quite probable. Life is described as "not hard" given such conditions. And Mars was such a planet.
It is also my understanding that Mars absolutely had large bodies of water. Basins, waterfalls, etc. have been discovered that could have only been formed via large, flowing bodies of water. And this would have been during a time where Mars' core was still active and the Sun was hotter, making Mars warmer than it is now.
> It is indeed my understanding that life on such a planet is quite probable. Life is described as "not hard" given such conditions.
Yeah, see, that's an assumption. And "not hard" is very far from a universally-accepted evaluation of the odds for that situation.
So, when someone like me comes along who doesn't buy the assumption, can you provide a foundation for it that is stronger than "yes, I assume it" or "everyone knows"?
One thing I like to bring to these debates is the idea that people, in general, are really bad at understanding probabilities at the scale that is required here.
And I'm not talking about probabilities that deal with how large the universe is. We know that it is unfathomably huge, with countless galaxies, stars, and planets.
But in "Fermi's Pair o' Decks" there is an illustration of just how few things need to align "just so" to make it almost certain that we are the only life in the universe: https://shaungallagher.pressbin.com/blog/aliens.html
In fact, all you need are two decks of playing cards to understand how combinatorics can very quickly overwhelm our intuitions.
I used to read articles like this and nod my head about the plausibility, perhaps inevitability of life in the universe, then I read this paper and it completely changed my view.
"the results indicate that the probability we are alone (<1) in the galaxy is significant, while the maximum number of contemporary civilizations might be as few as a thousand"
We have a sample size of one but my take on life from that sample is:
Life pops up really fast. Going from Prokaryotic to eukaryotic takes a really - almost weirdly - long time. Presumably going from eukaryotic to something we can easily recognize as intelligent takes an even longer, which again is weird, amount of time.
From that I'd expect life to be common and intelligent life that's reachable to us - that is on a time frame / distance that is reachable for humanity as a species - to be either non-existent or rare as hens teeth. It may be common in terms of the universe though just not knowable.
It will definitely a "no" when we find clear evidence of intelligent life elsewhere, but we should know for sure when we inspect every other place in the universe, in all history of it, and that is billions of light years spanning billions of years to say "yes". And we can't even rule that out even in our closest star system, at just 4 light years from here, yet. Everything is too far away from our view to rule out that is not in some place that we didn't see yet, because practically everything fits in that definition.
The Fermi paradox covers this
quite interestingly:
“The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence.”
Life as we know it seems to depend on have a large Moon, a planetary makeup infused with heavy metals, a distance from our star and rotation that makes most of the planet a temperature good for our kind of life, a star that's safely boring, and LOTS of water.
But with 10 to the 24th stars, even one in a billion odds are no deterrent.
But we also don't know how life started. There's a big gap between the simple organic molecules that pop up everywhere, and metabolizing reproducing life, and we have no idea how many improbable events had to occur to bridge that gap. For all we know, it takes a whole universe rolling those dice before it's likely to happen even once.
Every other planet should have independent probability as earth to have life, so that’s trillions op on trillions. Plus the way we evolved may not be the template on how other intelligent life will evolve. We make the mistake of thinking it can only work the way we’ve seen it done and exclude any other possibilities.
The universe does not appear to be random, instead it appears to be based on a pattern. For every other level of detail we've been able to view with advances in technology the pattern seems to hold. It would be a leap of logic in the wrong direction to assume life isn't part of that pattern simply because we can't yet observe it.
Not only that, but Earth is probably the only planet that has life of any kind.
There is simply no explanation for the existence of life at all.
Nobody has the faintest idea how life came into existence, and the question of the origin of life is, frankly, the only interesting question because it is a prerequisite for the existence of any other question.
Star Trek may have made us think that Class M planets are abundant, but the probability of detecting intelligent life on any given habitable planet is remote. There may be many Class M planets within our detection range, but the trick is to find one that has an intelligent civilization at precisely this moment in time minus the time it takes for radio signals to reach Earth.
Let’s say that Earth is about 4.5 billion years old and that intelligent life has been externally detectable for about 120 years since radio was invented around 1900. And it’s by no means certain that just because a civilization on a given Class M planet achieves radio signal generation that it will soon achieve warp drive technology and build a fleet of starships. That civilization could simply watch episodes of the Golden Bachelor while consuming all of its available resources and then fade away. Or just blow each other up.
I’m not saying that intelligent life outside of Earth does not or has never existed. We can only detect a small part of the known universe. And we can only detect what’s going on roughly right now because there isn’t a WayBack Machine for interstellar radio signals.
All this requires the combination of several low probability events:
* A planet must be within detectable range of Earth.
* A civilization must have developed.
* The civilization needs to survive for a meaningful period of time. One century is not meaningful.
* The civilization must be visible essentially right now.
The combination of those events yields a very low probability.
I’m not saying that the search for intelligent life on other planets isn’t interesting or worthwhile, but I do think that Elon Musk should stop wasting his time on space travel and start spending it on global warming. That will give us the best chance of extending our run as an intelligent civilization.
I doubt it. In fact, due to human activity, Earth may be the only planet that can't support intelligent life in a sustainable way. Even if we were to discover intelligent life on earth, it might not survive long in our current internet-meme-dominated ecosystem.
Given the ever growing discoveries and complexity of single cell life, it is evermore unlikely that life randomly “sprung” into being.
The primordial soup argument is akin to lightening striking a wheat field and spontaneously producing a birthday cake complete with icing, candles, and balloons.
To go from nothing to that level of complexity in one stroke seems impossible. But nobody thinks that single celled organisms sprang into existence like that.
Most theories postulate simpler replicating chemical reactions, maybe around hydrothermal vents or pools, possibly forming in mineral structures and cavities. Later on membranes may have formed, and so on. Many steps, not one.
I would disagree that a series of simpler steps is just as unlikely as life emerging fully formed.
It is of course speculation as we just don't know. But if you agree that life occured naturally without supernatural intervention (or aliens, but that just pushes the speculation to how the aliens occurred), then there must be such a set of steps.
Everyone has a theory just like everyone has an opinion. Some people think Trump won the 2020 election. Other people think life came from crystals. Whatever, man. No one has a clue how life emerged.
Yet, if the primordial soup is indeed what happened, it created a birthday cake complete with icing, candles and balloons, through the creation of humans.
The primordial doesn't speculate that life appeared from one day to another, it speculates a long and slow process, just as the refinery of wheat into flour then a pastry (along with other ingredients) is a long and slow process (faster than the creation of life, but still).
-- create some way of sustainably separating "self" from its environment, so that all the components of downstream steps don't diffuse away. The separating material, which could be a cell wall or cell membrane, also has to allow selective exchange of raw materials in and out of the cell, and provide protection against damage to the cell.
-- design and build a chemical template (DNA/RNA in our case) which allows it to reproducibly recreate itself and all its components.
-- design the molecular machinery which builds that chemical template, and which is also responsible for reading and interpreting the template, regulating its use, and providing error correction. Instructions for creating machinery that makes the template are encoded in the template.
-- design the molecular machinery (enzymes and other proteins) that builds molecular machines, using a design language encoded in the chemical template.
-- establish a chemistry program that takes in raw materials from the environment, and converts it to energy, building blocks for the machinery and template, and allows for repair, defense, and other tasks.
-- establish and implement reliable reproductive (data backup) framework, minimally involving the creation of a copy of the chemical template, and often copying and spinning off a second, complete cell.
These are the elements of basic, independent (i.e. non -parasitic) life. As far as we can tell, the core elements (information stored in DNA/RNA encoding proteins as molecular machines) of this life solution emerged fairly early in this planet's 4.5 billion-year existence, and every other organism since then has simply iterated on the same solution -- no other competing solutions exist to our knowledge.
It thus makes sense to account for this complexity when we calculate the odds of finding life in the universe. In my opinion, the Fermi paradox is nonsense.