A core idea of this is that there are various filters that separate a new planet from one hosting spacefaring life. There are lot of these filters proposed. One category is the Great Filter. These are where very few lifeforms are expected to pass.
So what we're talking about here is an early filter where a planet forms in a relatively stable and suitable star system and single cellular life forms. Based on our own understanding of biochemistry, that pretty much requires amino acids. Now there might be other forms of life out there but they're all theoretical. We have one which is real (ie ours).
We've had a lot of experimentals that show that amino acids can form in deep space on icy bodies. What we have here is direct evidence from an essentially random asteroid that it has amino acids on it. We can and will speculate as to the origins of these. Did they form on the asteroid? Elsewhere? When?
You can't obviously draw too many conclusions from a single data point but to suggest we got extremely lucky to find the a super rare asteroid with amino acids on it stretches incredulity.
So the conditions that lead to life similar to ours forming being relatively common only gets stronger. This is similar to the number of expoplanets we've found. We've shown that planetary systems are exceedingly common, which was something we could only speculate about a mere 40 years ago.
More planets, more conditions for life forming. This means more species are likely getting filtered further down the chain.
The dinosaurs had 180 million years or so to get it right, and we find no evidence of so much as a simple tool. Were they no smarter that crows? All that time?
And Homo has been around, what, 2 million years? In just 2 million years we've gone from basically zero tech to outer-freakin-space.
Arguably, we've gone from nothing to outer-freakin-space in the last 6000 years, starting around the Bronze Age. That's astoundingly quick given how long life has existed on Earth.
So it seems like as the dice were being thrown around we were just waiting for that magic run of all sixes that enabled us to, in the blink of an eye, become spacefaring.
What was it? (Opposable thumbs? Language? War? Big brains? Etc?) And how likely are these things to happen in a magical combination? It took its sweet time here. Did we get lucky it only took 4 billion years? Or unlucky it took that long at all?
But it never happened to the hapless dinos. Which is too bad, because space dinosaurs would be _awesome_.
[Meme of dinosaurs looking up at the asteroid falling from the sky and one saying, "Oh fuck! The economy!"]
My lacking-evidence and very unverified theory is that it's something like bicameral mind theory. It wasn't until we developed a complex enough brain to have self metacognition that we started to take off as a species.
I would assume our style of intelligence isn't any kind of "goal", it just happened.
We went from the invention of radio in 1895 to a moon landing within 74 years. And 53 years later we have tech that is vastly superior to what we had in 1969.
Consider if you agree with these propositions:
- Consciousness is an emergent property of computation
- Computation is possible in any media
- Computation is more efficient in smaller, less massy media
- We are already beginning to fiddle with our own brains and this will accelerate
- Our bodies in general have huge room for optimization and eventually will be completely unrecognizable or even unnecessary as we currently imagine them
- Progress is exponential as our population grows in education, size and free time
If these are true, what does that mean for our destiny as a species in 100k years? 1M years?
I think we can all agree we will become cyborgs, but I think we still imagine our bodies having the same form factor. But that's the flawed assumption. Really we will shrink down. And what's the limit to how far down we shrink and how efficient and massless our bodies/brains get? How would we even be communicating in 1M years? Through entangled qubits? Vibrations in subspace? Who knows, but it's probably not something 21st century earth would even notice with a radio telescope.
So the answer to the Fermi paradox isn't that intelligent life snuffs itself out after a few million years. That's terribly unimaginative. The answer is that from our perspective intelligent civilizations disappear because they change themselves so radically that they transcend our concept of what to look for.
Well, obviously! Who could imagine any other scenarios?! My mom just called me asking if i could replace her right foot with a hoverboard. I cant wait until I can no longer feel sunshine or grass. Living forever as a process in a virtual machine... my ancestors could have never dreamt of having such fulfillment.
That is quite a leap. I hope it is true but you never know what kind of quantum/other shenanigans sneaky evolution has latched on to to end up with the brains of today.
It's interesting to see the negative comments about this here because I agree with you. "Consciousness" or even "sentience" is notoriously difficult to define. Even defining what an organism is isn't entirely obvious (eg some might consider a colony of ants or bees as being organism-like). Our views tend to be extremely human-centric because we can relate. I imagine once we actually invent an AGI many will debate if it's truly sentient or conscious for a long, long time afterwards.
> Computation is more efficient in smaller, less massy media
There are physical limits on computation. A smaller package ultimately has a lower limit. That alone will (IMHO) keep a space for very large computational units. At the top end of this is Matrioshka Brains [1].
A digital existence looks highly likely in the black hole era of the universe [2]. This is the era after all the stars have faded out and will be much longer (based on current understanding) than the stellar era, so much so that the 13-14B year lifetime of the universe thus far will be like the blink of an eye.
As for detecting communication, that's too narrow a focus. Whether we're miniscule cyborgs that communicate with qubits or living as virtual beings in a world-sized computer, the ultimate limits of what any such civilization can do is is the amount of energy they can consume. More energy means more is possible.
So even if we end up living as a K2 civilization in a billion orbitals around our Sun or one of the alternatives or build a Matrioshka Brain or simply collect all the power with satellites, all of these will have a similar IR signature that will be extremely detectable.
That was a leap.
I think we will become more like mycelium, or a root system connected in the ground. Still limiting us to terrestrial communication on the planet the network is placed on, but an optional ability to blast messages out if necessary.
I think this is a huge leap, especially when it comes to computation. As far we can tell, the brain is amazingly energy efficient compared to to any electronic chip. It's hard to estimate exactly what kinds of computation our brains are doing so that we could compare in terms of teraflops, but the energy consumption is many times better than any processor that could come close in any reasonable estimation.
Sent from my iPhone
This 12 minute video does a good job of explaining the fairly non intuitive reasoning: https://www.youtube.com/watch?v=l3whaviTqqg
As I understand it (it's not an easy theory to wrap your - or at least my - mind around), the reason we don't see any other civilizations is that we're among the first ones.
This seems very unlikely, but is actually not. Because a successful hi tech civilization would likely be inclined to expand ("be grabby") and fill up the galaxy in ~100 million years, as Fermi pointed out. That would mean all habitable planets would then be taken, and no more civilizations would rise up from primordial goo like ours.
That means - and it's a weird mental leap, but I think it's correct - that almost all civilizations arising "naturally" would have the same experience we have: The universe seems weirdly empty.
I guess it also means that the galaxy is ours for the taking!
"Figby, get those doom-chompers synchronized with the shooting flames!"
"Yes sir!"
"And think of something more profound than 'Be nice to other beings and remember to call your mother(s)' for that final secret. Maybe get someone in the art department to help out."
It's not easy being the Elder Race, but someone has to do it.
You seem to be saying the theory implies we are early when in the first video I got the impression that is statistically implausible.
I guess my main confusion is, if they are grabby, why haven't we been grabbed?
edit: watched the second video further, I think I get it a little better now. We are generally early and/or somehow advanced aliens expand quickly, otherwise we'd see signals because the signals would propagate faster than their expansion, whereas if they expand quickly, they'll invade us before we see signals, and dominate a larger portion of visible universe.
So seeing no one else out there is to be expected.
It's a bit like how it's NOT weird that we happened to evolve on a planet that is so extremely favorable to our form of life.
The second issue is that planets don't really matter other than being essentially "mass repositories". They're a highly inefficient way of creating living area. I'm speaking of course of Dyson Swarms as a highly likely alternative. I saw "highly likely" because it requires no new physics, no new materials beyond what we already have, is orders of magnitude more efficient (in living space per unit mass terms) and is essentially just an engineering problem (obviously a big one).
If you accept that premise then it's even less likely there are other spacefaring civilizations within our light cone because they would stick out like a sore thumb. Certainly a whole galaxy of these would be detectable by us currently from millions of light years away.
My personal hunch is the filter is around multicellular life. We'll find lots of planets with single-celled goop. Many fewer with animals.
The unions that created photosynthesis and mitochondria look to have happened only once (successfully) in Earth's history [1], and sound more like voodoo than science the more one thinks about it. (Cell ate another cell then changed its mind and adopted it for 1.45 billion years.)
[1] https://www.nature.com/scitable/topicpage/the-origin-of-mito...
If photosynthesis only evolved once, another explanation is that it only needed to once because it was so wildly successful.
Multicellular is interesting. That obviously took much longer but once it did? Holy crap did things take off. I kinda wish I could have a time machine just to visit the Cambrian Explosion era.
[1]: https://en.wikipedia.org/wiki/Evolution_of_photosynthesis
The most obvious, but least talked about filter is time.
Let’s assume there is a civilization just like us on the other end of the Milky Way galaxy, it’s not like we can just “look out” and observe them. Assuming they blasted out radio signals, those radio signals would have to have been sent 100,000 years ago for us to detect them today. Alternatively for that same civilization to detect our earliest radio signals it take another 999,900 years.
If this technologically advanced civilization was in the closest galaxy instead of the opposite end of the Milky Way, then our ability to detect one another’s signals traveling at the speed of light would be separated by over 2.5M years.
For good reason: there's been a lot of it so far. Even at slower than light speeds, it would be possible for a sufficiently advanced civilization to send probes to ever star in the galaxy (or even colonize it) in just a few million years. So why don't we see any evidence of any prior civilization having done that? It would only take one.
Whatever the variance is we've had ~3x that for other civilizations to arise in our galaxy alone.
Yes we could be "first" (within our cone of spacetime). First of 3? That's possible. First of 1000? Way less likely. There's some BAyesian reasoning about probability spaces you can do here. The very fact that we can't seem to detect anyone else in our galaxy changes the probabilities making it much more likely (but not impossible of course) that we're effectively alone.
Also the odds that another civilization evolves over 4B years and reaches spacefaring technology within 100,000 years of us is, statistically speaking, incredibly unlikely. It's way more likely they'll be way ahead of us or way behind us.
I think the "billions of years" part is key.
Humanity might die in the next centuries, or at least stop progressing technologically due to our lack of sustainable planning. If a human like life existed 100m years ago in a nearby planet we wouldn't now even if we sent basic probes, you'd need to dig just like we need to dig to find dino bones.
Modern civilisation are maybe 5000-7000 years old, that's not even a blip in the universe history. The universe could develop millions of technologically advanced civilisations on different planets with no time overlap
I also feel like lots of people are too much into sci fi, nothing guarantees technological progress can go much further than what we have and allow for large scale space exploration. We might not see signs of technological life because the most advanced thing they came up with are a few probes and some radio signals sent from so far away that you statistically will not find even if you look for them.
The universe physical and time scale raise the fermi paradox, but the same physical and time scale give you an answer as to why we might not be able detect life
Perhaps even the most basic property of life, the self-preserving tendency of a self-preserving structure once it randomly emerges, can lead with mathematical precision to its own destruction a few billion years later, regardless of the specifics and despite the profoundly complex mechanisms evolved in-between.
Perhaps long-lived advanced civilizations are not possible at all, and can be seen as a weird transient natural phenomenon; starting with hydrothermal vents and ending with billions of odd etched silicon fossils.
"Possible CETIs Within Our Galaxy and Communication Probability Among CETIs ": https://news.ycombinator.com/item?id=31449404"
"...human beings need to survive 50 (+250 -49) Myr to receive one signal from other CETIs. Our results may quantitatively explain why we have not detected any alien signals so far. The uncertainty of the results has been discussed in detail and would be alleviated with the further improvement of our astronomical observation ability in the future..."
The universe is a big, big place and civilizations come and go. We would need to be around for 50 million years, to have a good chance to catch a window that would match another civilization. We are barely around as a species for 2 million years and civilization is maybe 10,000 years old...
The biochemistry of life is likely to be common, the conditions for complex or even intelligent tool using life are likely to be rare.
To have an earth, you need to have a moon comparable in mass to the planet to avoid atmospheric stripping. A temperature regime stable enough to support long term life development between 0 and 100 C. A star that doesn't blasttge planet in radiation every few thousand years. Along with a reasonable balance of materials, and a stellar neighborhood which wont swing the balance too badly every few million years.
Lastly, although untested, To have tool use, you likely need a planet with gravity thats strong enough for the atmosphere to be stable, but weak enough for organic molecules to hold together complex life and enable the construction of material objects. A super earth covered in algae is interesting, but may not be capable of traditional human intelligence.
I mean, would we be able to detect our own civilization from a few lightyears out? Apparently, unless you're pointing a radio telescope right at something, you woudn't be able to pick up human civilization levels of radio from more than a lightyear out. Say there's one smart tool-using civilization per 5000 lightyear volume, then they're unlikely to meet.
Could you elaborate on this? I'm aware that magnetospheres protect atmospheres from solar wind stripping (e.g., https://science.nasa.gov/science-news/news-articles/earths-m...), but have never heard of the role of moons, and can't find anything via Google right now.
Get any of it wrong and life either won't develop, or will wreck its own biosphere in an unrecoverable way very early on and get wiped out (if there was ever life on Mars, that's my bet for why traces of it are elusive—it wasn't around very long, wasn't very complex, and it was a very long time ago).
Silicon life could definitely be a thing.. However silicon bonds are a lot lower energy than carbon bonds are, for most substances. (I would argue that oxygen would be toxic to silicon based beings, due to Si-O.). So, I'd theorize that silicon based living beings would have to be in an atmosphere of, say, methane. And the phasegraph of methane ( https://www.engineeringtoolbox.com/methane-d_1420.html ) would seem to show that -175c and around there would be ideal temps for silicon life.
However, if we're exclusively only looking for carbon/oxygen/water based lifeforms, then I think the 0-100c is a reasonable assumption.
There are at least 100B stars in our galaxy. Over the last 20+ years we've gained a lot data on exoplanets. Exoplanetary systems seem to be really common. So stability, the right elements, etc no doubt all play a role but we may be talking over WWhata trillion planetary bodies (including large moons).
What's more, our understanding of where live can evolve, survive and thrive has greatly expanded in recent decades and now includes volcanic vents on the ocean floor, for example.
So yes a lot of things have to go right but we're rolling an awful lot of dice.
We don't know what conditions life 'needs' since we only have a sample size of 1. We can speculate, but nothing yet is a known fact.
It's not perfect, but it goes over a lot of possible explanations (75 different explanations!) for the Fermi Paradox. It covers pretty much every theory I've seen when people discuss the topic, aside from a government cover-up haha.
Simulations, aliens hiding on Earth, von Neumann probes, signals that we don't understand, distances being insurmountable, self-destructiveness, inescapable planets, singularities, it's got it all! A lot of the explanations ultimately can't get over the "OK, but surely there are at least a few exceptions" problem, but it's very fun to think about nonetheless. A really engrossing read if you like thinking about this stuff!
https://www.goodreads.com/en/book/show/180506.If_the_Univers...
As far as I understand, exoplanet discovery and study is still incredibly rudimentary.
So what could we observe instead? The answer is Dyson Swarms. These aren't rigid spheres as some seem to think (the original term was "Dyson Sphere" but is largely abandoned because of the confusion). It's merely a collection of orbitals to consume all the energy a star produces. Many (myself included) think this is the inevitable direction of our species.
The only way to get rid of heat in space is to radiate it away. The frequency of the light emitted depends entirely on the temperature of the radiating object. This means a full Dyson Swarm would have a huge infrared signature. That sort of thing we could detect from a very far distance. A whole galaxy of these would be detectable from millions of light years away.
Space limits everything, and is the simplest solution to the Fermi paradox (following Occam's razor).
Source: I am a software engineer who works on cool space stuff
It also does little but derail every conversation about life in the universe into speculative science fiction.
Let's assume for a while that amino acids are everywhere in the solar system or galaxy (if not universe). Let's also assume that there are many earth-like planets.
If we found alien life on another earth-like planet, could it be possible that it too would have independently-evolved DNA? Not just DNA-like substances, but chemically identical DNA?
I guess I am wondering was DNA such an incredible fluke here on earth that we'll never see it again, or is it "the logical conclusion" for a bunch of similar amino acids in very similar environments? IIRC DNA is a chemically stable structure etc
Similarly for DNA: there are other polymers that have some of the same properties, but not to the same extent. Specifically, the ability to store information is so great in DNA. Most polymers are either regular like (-CH2-)n or random (eg lignin) while DNA (and RNA) are 'structured random', for lack of a better term.
Add to this the ability to 'unzip' double-stranded DNA into two copyable halves, its great stability, and ability to be coiled up. Like water - which is another example of something with an abundance of useful features - it's very hard to see any rival molecule that could do as many things.
Of course, you could just argue that we have not discovered or invented such a molecule yet. People have tried to make alternate compounds, and there are - as one of the other repliers pointed out - many variations in biology such as alternate nucleobases, or things like double-stranded RNA viruses, etc.
More generally, you could of course imagine distributing the properties of DNA across multiple molecules or molecular systems. That suffers from Occam's razor a little, but cannot be ruled out, I suppose.
Perhaps DNA and RNA are inevitable, or at least they are the easiest solution for they problem they solve. I guess even the same sugars and some nucleotides. The only variation on Earth is that some parts of the DNA are methylated, but it can be added and removed. There are some weird bases in the RNA for very special task, but my guess is that they will use the same main bases. I'd not be surprised if alien has DNA and RNA that is chemically identical to us (but in other order).
Even proteins are probably inevitable. Here there is more wiggling room. We use 20 amino acids, but there are like 5 more weird amino acids that are mostly modifications of usual amino acids and are made after the protein is formed. For example collagen uses a lot of proline that is a normal amino acid, and also hidroxyproline that is a modification of proline made during the creation of collagen https://en.wikipedia.org/wiki/Collagen#Synthesis I guess that the list of amino acids used by aliens will be slightly different. Perhaps between 15 and 25 instead of the 20 we use. Perhaps also some replacements. But perhaps the list has some special property we have not discovered yet. I don't expect a smoking gun here to determine if aliens are unrelated to us.
The most interesting part is the translation from DNA/mRNA to proteins https://en.wikipedia.org/wiki/Genetic_code It's a translation from the 64 combinations of 3 bases of DNA/RNA to amino acids. It's almost blocked, so there are 16 blocks with 4 options in each one. But some blocks have small changes. We know like 20 versions of the small changes. The 20 versions are very similar, they are not very different. So it's possible to make changes in this translation table. The most interesting part are the 16 blocks. As far as we know the elections it arbitrary, like a frozen random initial election that was inherited by all of living things on Earth.
So the first thing to check in an alien life is if they translate in the 16 blocks the same amino acid that we translate. I'd be very surprised if this is the case. My guess is that it's almost random, and any election is fine, and each independent alien life will have a very different initial random election.
Since we don't have access to such data, some metrics that seem useful for speculation about a property are: - How often it has evolved independently on Earth - How fast it evolved and remained dominant
That being said, there is a potential positive feedback loop going on, where most life depends on or benefits from compounds it gets from other life. Because there is an abundance of certain types of amino acids, we could hypothetically be stuck in a less optimal overall biosphere state, whereas a more fit biosphere might exist with a different composition of amino acids or other building blocks that played the same role. I'm defining fitness of the biosphere as the amount of energy from the sun that life harnesses for work.
Examples of convergent evolution of the most useful compunds for life on Earth. It makes sense that in a unified environment (of Earth) there is a tendency to evolve similar mechanisms to survive - on Earth.
But we just don't know what kind of other chemical environments might be out there, in the virtually infinite cosmos. As beings of Earth-based life we fail to imagine any other possibility. This is a failing of our own understanding, not of chemistry to produce life. We just don't know, so we can't really even begin to guess. All we know is, our own backyard looks pretty dead except for us.
There are many different forms that RNA takes, and some of those forms are double-stranded, but differ from DNA in certain key ways. There are even "non-canonical" forms of DNA which exist whose nucleobases differ from the traditional four bases found in most DNA.
Thus, you're premise that all DNA on Earth is "chemically identical" is flawed. But, if you expand the scope of your a bit, then the answer is a little more satisfying.
The Panspermia theory is that RNA/DNA formed there and was ejected by asteroid hits to Earth. Support for that theory is that life appears to have formed within a few hundred million years of it being possible on Earth, which seems far too short of a time for RNA/DNA to form spontaneously in an ocean Earth.
If this is all true, life may be a fluke and requiring a rather stable set of environments to work. All of this is hard to know with a sample size of one, though.
[1] https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment
Youtube: https://youtu.be/ZecQ64l-gKM
Spotify: https://open.spotify.com/episode/4U3teONvRzNh32qqtX6X2w?si=5...
There are an unlimited number of different bases that could be used to encode information, too!
The real mystery thus remains life itself. The fact that on Earth it used amino acids to express itself doesn't mean that it is necessarily limited to that single choice. It also doesn't mean that the same process would repeat in a different world, even if all the preconditions were met, i.e. the necessary for the presence of life as we can recognize it.
For all our understanding of (earthly) biology, and the tools at our disposal that we use to decide that something is alive, we still don't really know what life is, or how it begins. On another world it might as well kickstart the magic with a different medium than amino acids (e.g. more crystalline structures, some energy forms such as light or electricity, etc), with entirely different rules of replication and sustenance. It would probably make life look different to us, potentially not recognizable or even detectable.
Heck, it could happen right here, under our nose and we'd be none the wiser.
Sure, there might be (and probably is) life out there that falls so far outside our definition of "life" that we would never detect it. If it's undetectable, and maybe even incomprehensible, to us, then what's the point in even thinking about it in the context of a "search for life"? What we really mean by the question "Is there life out there?" is "Is there life out there that's similar enough to the life we see on Earth that we could recognize it as such and interact with it?"
I don't have a good way to phrase what I'm getting at without sounding dismissive - I do think it's interesting to think about other forms of "life", but it seems almost philosophical at that point and not scientific.
On the other hand, it's of course imaginable that there are beings that we would in principle consider intelligent agents, but who exist in a way that in practice we have no hope of recognizing as such. Again to pick a somewhat trivial example, if galaxies were in fact intelligent beings that take billions of years to form a single thought, we may both in principle be very interested in communicating with each other, but in practice could never even hope to recognize each other as sentient beings, because of the intense difference in time scale.
But I guess science is stubborn too, so let's see where we get.
https://en.wikipedia.org/wiki/Murchison_meteorite#Nucleobase...
In it. Not "on it". A very important distinction. You'd expect to find all kinds of bio stuff on pretty much any solid object.
Are we sure it doesn't just mean the compounds were already sitting on Earth for the same reason they're sitting on the asteroid? I guess maybe if literally all of them were cooked to death in the Hadean and had to be refreshed from space, but then how do they avoid being cooked to death in asteroid impacts?
https://www.science.org/content/article/scientists-may-have-...
https://en.wikipedia.org/wiki/Abiogenesis#Homochirality
…is the chirality of the molecules we’ve found on comets and meteorites. The amino acids and sugars out in space match what we find in Earth biology. That in way proves that some of the building blocks of life on Earth were generated in the Solar System, but at least it’s a plausible link.
Not because they have any unique lifeforming property.
