3 ms·

This is your daily reminder that if we do indeed discover life so close (~120 LY) to Earth, it's an incredibly bad sign for us. This is an exercise in Bayesian

by jmyeet 2y ago

This is your daily reminder that if we do indeed discover life so close (~120 LY) to Earth, it's an incredibly bad sign for us. This is an exercise in Bayesian reasoning. Imagine there are 2 planets in the Milky Way where life has developed. The odds are incredibly low they're next to each other, assuming a random distribution. So it's way more likely that there are more than 2. Imagine a sphere of radius 60 LY (120/2). Our Earth is the center of one. This planet is another. That's a volume of 10^6 LY^3. The Milky Way volume (from Google) is ~17T LY^3 so there'd be roughly 170M such spheres in our galaxy. Now imagine if the odds of simple life becoming intelligent life that we could detect and could become spacefaring is 1 in 1 million. There'd be ~170 such civilization in the Milk Way. We have absolutely no evidence of this So simple life is a lot less common, intelligent life is a lot less likely or, and this is the scary part, something tends to wipe out sentient civilizations and that's likely in our future. In Fermi Paradox terms, we call this a Great Filter.

thangalin 2y ago
On a related note, Birth-Death Formalism connects Jaynes' Prior Probabilities in a paper, "Do SETI Optimists Have a Fine-Tuning Problem?" https://arxiv.org/abs/2407.07097 https://arxiv.org/abs/2407.07097 One of the authors posted an approachable video explaining how the ideas connect: https://www.youtube.com/watch?v=b6-9Hq8dV_4 https://www.youtube.com/watch?v=b6-9Hq8dV_4
awb 2y ago
There’s no evidence yet, but we also haven’t looked very carefully or in very many places. And we only know to look for planetary life as we know it. The middle of the galaxy could have a wildly different composition and habitat for life than the outer reaches where we are. Time is also another factor. Maybe the galaxy is perfect for complex life, we just happen to be early on the timescale and in another billion years or two life will be clearly abundant everywhere. For some perspective, if you take the size of the Milky Way (100k light years) and relate it to the size of NYC (~30 miles), then 120 light years ends up being ~190 feet in NYC, or less than a city block.
- jmyeet 2y ago
  The middle of the galaxy is unlikely to be conducive to forming intelligent life simply because it's not stable enough for long enough. In our part of the galaxy, the mean distance between stars is around 4-5 LY (at a guess) in terms of nearest neighbours and ignoring binary (and up) systems. At the galactic center it's a few light days. We've had many events that have caused mass extinction. There are many more that could end all life as ew know it (eg gamma ray bursts, a sufficiently close supernova. We have ~10 stars within 10 LY of us. Imagine if that were millions instead. I find it hard to believe conditions would be stable enough for the millions or billions of years necessary to create and sustain complex life. As for our galaxy being "perfect" this touches on a coupole of concepts, notably the Anthropic Principle. But again we return to Bayesian reasoning. If there was going to be 1000 spacefaring civilizations in our galaxy, what are the odds that we are first? And while the Sun is <5B years old, there are stars up to 14B years old. There's been a ton of extra time for civilizations to develop elsewhere.
kypro 2y ago
If you assume life is very likely then the Great Filter has to be an almost perfect filter to explain the Fermi Paradox. With fewer civilisations in the galaxy (<50) you might be able to assume that if 95% of them destroy themselves it would be unlikely we'd ever find life. If we assume 170 civilisations then the great filter would have to be something akin to a natural law. My gut says that the Great Filter is real but probably doesn't filter more than 99% of civilisations. Were I to guess complex life is uncommon, and intelligent life very uncommon. The majority of planets which do develop intelligent life destroy themselves fairly quickly.
- frogeyedpeas 2y ago
  There's only the fact that we probably just CANNOT perceive extremely advanced civilizations. An insect crawling around a 75 year old brick house that is covered in ivy and moss will have NO idea that the object it is walking upon is NOT part of it's natural environment. That brick house seems as natural to the environment as the grass, and trees, and rocks, and streams nearby it -- to the bug at least. Similarly we take our telescope out and see what looks like a natural organic universe with organic galaxies and normal looking stars etc... Because we don't have solar system sized brains and billion year life spans we are absolutely hopeless to realize that theres' a lot of massive artificial structures in this universe. We're too bug-like to even be able to perceive them from our natural environment. *we do know of massive cosmic structures like filaments, voids, and the great wall. So it is possible we as humans are starting to notice the "house" in the woods since our theories of physics cannot really explain why these structures exist at these massive scales (we would expect uniformity at those scales). See [here](https://en.wikipedia.org/wiki/List_of_largest_cosmic_structures#List_of_largest_structures https://en.wikipedia.org/wiki/List_of_largest_cosmic_structu...)
  - UltraSane 2y ago
    extremely advanced civilization would be living around black holes because they are perfect heat dumps (they get colder as you add matter!) and would enable fundamentally better technology.
  - jmyeet 2y ago
kjkjadksj 2y ago
A lot of assumptions are made here about intelligent life with the great filter ideas. Intelligent life is not a fundamental phase of matter. It took a random walk over billions of years to end up there, with any point potentially leading to a deviation and entirely different outcome. Take the number of bacteria dividing over the last 4 billion years on earth to one and there’s your rate of intelligent life in the universe based on what we’ve seen on earth. Are there even that many planets or bodies in the galaxy for what a billion to the power of a billion to one odds or whatever absurd number this is?
AIPedant 2y ago
Now imagine if the odds of simple life becoming intelligent life that we could detect and could become spacefaring is 1 in 1 million. Why not assume the odds are 1 in 200 million, so that there's only one such planet in the whole galaxy and there's no Great Filter to worry about? It seems just as valid, except "200 million" is slightly less aesthetically pleasing. We already know that human-type technological civilization is extremely unlikely, since the planet was full of somewhat intelligent bipedal dinosaurs for about 100m years, yet none of them seemed to engage in mining, large-scale construction, severely disruptive extinctions, nuclear power... (humans will leave a thick geological layer of concrete and pollution, along with plentiful unique minerals coming from slag, plastic, etc.) I really have no patience for this sort of p(doom) nonsense. If you make up numbers you can come to any quantitative conclusion you want. Mildly tweaking totally unfalsifiable odds makes the Fermi "paradox" go away entirely.
- vimax 2y ago
  Anything that acts to lower the odds by 200x so that we're the only likely intelligence in the galaxy is the definition of a "great filter".
  - aradox66 2y ago
    That's not right, the great filter comes after the development of intelligence
    - awb 2y ago
      A Great Filter could come before or after intelligence. For example, predation could be a Great Filter. We made it past the threat of predation, but perhaps most life forms in the universe don’t. In this example, life could be pervasive in the universe but it’s optimizing for defensive attributes like speed and armor rather than intelligence. That could explain why we don’t see aliens colonizing the galaxy. With the Great Filter behind us, nothing would be stopping us from colonizing the galaxy ourselves, we just might be among the first to do it. Putting the Great Filter in front of us postulates that many life forms have achieved our same accomplishments but haven’t colonized the galaxy. It could be because of doom and gloom scenarios like war, aliens, cosmic catastrophes, etc. Or it could be a beneficial Great Filter like enlightenment and the lack of desire to propagate and consume endlessly, or the ability to survive in deep space, leaving stars and planets untouched.
j_timberlake 2y ago
This argument is fairly dated now, we no longer need alien ruins to prove that humanity will probably destroy itself.
nanna 2y ago
> it's an incredibly bad sign for us. No reason to expect other lifeforms to be as bellicose and destructive us humans.

by jmyeet 2y ago

thangalin 2y ago

On a related note, Birth-Death Formalism connects Jaynes' Prior Probabilities in a paper, "Do SETI Optimists Have a Fine-Tuning Problem?" https://arxiv.org/abs/2407.07097 https://arxiv.org/abs/2407.07097 One of the authors posted an approachable video explaining how the ideas connect: https://www.youtube.com/watch?v=b6-9Hq8dV_4 https://www.youtube.com/watch?v=b6-9Hq8dV_4

awb 2y ago

There’s no evidence yet, but we also haven’t looked very carefully or in very many places. And we only know to look for planetary life as we know it. The middle of the galaxy could have a wildly different composition and habitat for life than the outer reaches where we are. Time is also another factor. Maybe the galaxy is perfect for complex life, we just happen to be early on the timescale and in another billion years or two life will be clearly abundant everywhere. For some perspective, if you take the size of the Milky Way (100k light years) and relate it to the size of NYC (~30 miles), then 120 light years ends up being ~190 feet in NYC, or less than a city block.

jmyeet 2y ago
The middle of the galaxy is unlikely to be conducive to forming intelligent life simply because it's not stable enough for long enough. In our part of the galaxy, the mean distance between stars is around 4-5 LY (at a guess) in terms of nearest neighbours and ignoring binary (and up) systems. At the galactic center it's a few light days. We've had many events that have caused mass extinction. There are many more that could end all life as ew know it (eg gamma ray bursts, a sufficiently close supernova. We have ~10 stars within 10 LY of us. Imagine if that were millions instead. I find it hard to believe conditions would be stable enough for the millions or billions of years necessary to create and sustain complex life. As for our galaxy being "perfect" this touches on a coupole of concepts, notably the Anthropic Principle. But again we return to Bayesian reasoning. If there was going to be 1000 spacefaring civilizations in our galaxy, what are the odds that we are first? And while the Sun is <5B years old, there are stars up to 14B years old. There's been a ton of extra time for civilizations to develop elsewhere.

kypro 2y ago

If you assume life is very likely then the Great Filter has to be an almost perfect filter to explain the Fermi Paradox. With fewer civilisations in the galaxy (<50) you might be able to assume that if 95% of them destroy themselves it would be unlikely we'd ever find life. If we assume 170 civilisations then the great filter would have to be something akin to a natural law. My gut says that the Great Filter is real but probably doesn't filter more than 99% of civilisations. Were I to guess complex life is uncommon, and intelligent life very uncommon. The majority of planets which do develop intelligent life destroy themselves fairly quickly.

frogeyedpeas 2y ago
There's only the fact that we probably just CANNOT perceive extremely advanced civilizations. An insect crawling around a 75 year old brick house that is covered in ivy and moss will have NO idea that the object it is walking upon is NOT part of it's natural environment. That brick house seems as natural to the environment as the grass, and trees, and rocks, and streams nearby it -- to the bug at least. Similarly we take our telescope out and see what looks like a natural organic universe with organic galaxies and normal looking stars etc... Because we don't have solar system sized brains and billion year life spans we are absolutely hopeless to realize that theres' a lot of massive artificial structures in this universe. We're too bug-like to even be able to perceive them from our natural environment. *we do know of massive cosmic structures like filaments, voids, and the great wall. So it is possible we as humans are starting to notice the "house" in the woods since our theories of physics cannot really explain why these structures exist at these massive scales (we would expect uniformity at those scales). See [here](https://en.wikipedia.org/wiki/List_of_largest_cosmic_structures#List_of_largest_structures https://en.wikipedia.org/wiki/List_of_largest_cosmic_structu...)
- UltraSane 2y ago
  extremely advanced civilization would be living around black holes because they are perfect heat dumps (they get colder as you add matter!) and would enable fundamentally better technology.
- jmyeet 2y ago

kjkjadksj 2y ago

A lot of assumptions are made here about intelligent life with the great filter ideas. Intelligent life is not a fundamental phase of matter. It took a random walk over billions of years to end up there, with any point potentially leading to a deviation and entirely different outcome. Take the number of bacteria dividing over the last 4 billion years on earth to one and there’s your rate of intelligent life in the universe based on what we’ve seen on earth. Are there even that many planets or bodies in the galaxy for what a billion to the power of a billion to one odds or whatever absurd number this is?

AIPedant 2y ago

Now imagine if the odds of simple life becoming intelligent life that we could detect and could become spacefaring is 1 in 1 million. Why not assume the odds are 1 in 200 million, so that there's only one such planet in the whole galaxy and there's no Great Filter to worry about? It seems just as valid, except "200 million" is slightly less aesthetically pleasing. We already know that human-type technological civilization is extremely unlikely, since the planet was full of somewhat intelligent bipedal dinosaurs for about 100m years, yet none of them seemed to engage in mining, large-scale construction, severely disruptive extinctions, nuclear power... (humans will leave a thick geological layer of concrete and pollution, along with plentiful unique minerals coming from slag, plastic, etc.) I really have no patience for this sort of p(doom) nonsense. If you make up numbers you can come to any quantitative conclusion you want. Mildly tweaking totally unfalsifiable odds makes the Fermi "paradox" go away entirely.

vimax 2y ago
Anything that acts to lower the odds by 200x so that we're the only likely intelligence in the galaxy is the definition of a "great filter".
- aradox66 2y ago
  That's not right, the great filter comes after the development of intelligence
  - awb 2y ago
    A Great Filter could come before or after intelligence. For example, predation could be a Great Filter. We made it past the threat of predation, but perhaps most life forms in the universe don’t. In this example, life could be pervasive in the universe but it’s optimizing for defensive attributes like speed and armor rather than intelligence. That could explain why we don’t see aliens colonizing the galaxy. With the Great Filter behind us, nothing would be stopping us from colonizing the galaxy ourselves, we just might be among the first to do it. Putting the Great Filter in front of us postulates that many life forms have achieved our same accomplishments but haven’t colonized the galaxy. It could be because of doom and gloom scenarios like war, aliens, cosmic catastrophes, etc. Or it could be a beneficial Great Filter like enlightenment and the lack of desire to propagate and consume endlessly, or the ability to survive in deep space, leaving stars and planets untouched.

j_timberlake 2y ago

This argument is fairly dated now, we no longer need alien ruins to prove that humanity will probably destroy itself.

nanna 2y ago

> it's an incredibly bad sign for us. No reason to expect other lifeforms to be as bellicose and destructive us humans.