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Thread: What do you think is the most likely explanation for the Fermi paradox?

  1. #871
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    Quote Originally Posted by Colin Robinson View Post
    Have you heard of the planula hypothesis? It's the theory that all animals with bilateral symmetry, including tree-climbers, are descended from a cnidarian (jellyfish family) larva that failed to grow up.
    That's certainly an interesting hypothesis, and I had never heard of it. That's one cool thing about this forum, that you get exposed to interesting things, whether they turn out to be true or not.
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    Quote Originally Posted by Colin Robinson View Post
    So, when you said



    You actually meant: "Nothing that isn't related to a jellyfish is going to climb a tree." ?
    An organism evolved to climb a tree is no longer in any way recognizable as a jellyfish, any more than a primate is a lungfish. It would require adding far too many genetic and selective differences. But that was arguing with your specific example, not with my main premise; which is that common ancestry will not be shared with alien life, and so the very specific factors that led to cephalization in one very specific line of development in Earth life will not be shared.
    Last edited by Noclevername; 2020-Jun-30 at 05:01 PM.
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    Quote Originally Posted by Noclevername View Post
    An organism evolved to climb a tree is no longer in any way recognizable as a jellyfish, any more than a primate is a lungfish. It would require adding far too many genetic and selective differences. But that was arguing with your specific example, not with my main premise; which is that common ancestry will not be shared with alien life, and so the very specific factors that led to cephalization in one very specific line of development in Earth life will not be shared.
    So when you wrote, "If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree," you didn't mean that a jellyfish would never evolve to climb a tree, but rather that if it did evolve, we would no longer call it a jellyfish? That seems like a pretty obvious point to me. I can't imagine why anyone would argue the opposite, that if one organism evolves into another, we would still use the same name...
    As above, so below

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    Quote Originally Posted by Jens View Post
    So when you wrote, "If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree," you didn't mean that a jellyfish would never evolve to climb a tree, but rather that if it did evolve, we would no longer call it a jellyfish? That seems like a pretty obvious point to me. I can't imagine why anyone would argue the opposite, that if one organism evolves into another, we would still use the same name...
    The context was, I was responding to what Colin Robinson said about ecological niches. Why do people keep fixating on the jellyfish part of that post?

    Quote Originally Posted by Colin Robinson View Post
    In an organism which occupied a comparable ecological niche, wouldn't you expect comparable adaptions?
    Quote Originally Posted by Noclevername View Post
    If there were the existing genetic potentials to support that adaptation. No jellyfish is going to climb a tree.
    The niche is not simple. It is a complex interaction of many species and environmental factors in a complex ecosystem. So a non-terrestrial biosphere would not contain the same niches as the present lines of evolution on Earth. It would comparing apples to fnordsperk*.

    The substrate that parallel evolution is built on is the organism's genetic structure; a dolphin and a large shark are both similar in niche and general body plan, but no shark has lungs and no dolphin has gills. ET life might plausibly evolve large, complex mobile life forms, but they will not be Animalia. There would be no reason to expect Nature to find the same solutions to survival (including cephalization) every time. Natural selection of random mutations is not deterministic. It is a Rube Goldberg device of mistakes that sometimes work out well enough.


    * Know what a fnordsperk is? Nope, because we've never seen one. It's alien.
    Last edited by Noclevername; 2020-Jul-01 at 06:39 AM.
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    Quote Originally Posted by Noclevername View Post
    The context was, I was responding to what Colin Robinson said about ecological niches. Why do people keep fixating on the jellyfish part of that post?
    Perhaps because the jellyfish (with its kinship to other Animalia) is a relevant and fascinating case of how evolution actually works.

    The niche is not simple. It is a complex interaction of many species and environmental factors in a complex ecosystem. So a non-terrestrial biosphere would not contain the same niches as the present lines of evolution on Earth. It would comparing apples to fnordsperk*.

    The substrate that parallel evolution is built on is the organism's genetic structure; a dolphin and a large shark are both similar in niche and general body plan, but no shark has lungs and no dolphin has gills. ET life might plausibly evolve large, complex mobile life forms, but they will not be Animalia. There would be no reason to expect Nature to find the same solutions to survival (including cephalization) every time.
    If they are large, complex and mobile, that's 3 important characteristics they have in common with many of Earth's Animalia. If that much is plausible, why isn't it plausible that they'd have other features in common with Animalia as well?

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    Quote Originally Posted by Colin Robinson View Post
    If they are large, complex and mobile, that's 3 important characteristics they have in common with many of Earth's Animalia. If that much is plausible, why isn't it plausible that they'd have other features in common with Animalia as well?
    I'm not saying it's not plausible that they do. I'm saying there are also an indefinite but very large number of other ways they could go.
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    Any sufficiently advanced technology is indistinguishable.

    Could we even identify something a billion years ahead of us, let alone communicate with them? They might send nanotech probes we can't even see; they'd be easier to propel across light-years, for sure. Or be watching us with gravitational-wave radar. They might have encoded their minds in ice crystals or meteoric iron or neutronium, and ignore the boiling hell of liquid-water planets. They might be the size of a galaxy with cosmic strings for neurons and neutrinos for impulses. Or they might be in cozy Matrioshka Brains that look outwardly just like all these brown dwarfs we keep seeing everywhere.... Hmm.

    There's no telling just what a billion year old form of intelligence may be capable, of or would want to do. We have no frame of reference for such beings.
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    Quote Originally Posted by Noclevername View Post
    Any sufficiently advanced technology is indistinguishable
    from magic... Yes, but maybe, like magic, technology has a way of backfiring on those who try to do too much with it... I'm thinking of the old story about the sorcerer's apprentice.

    We evolved in a biosphere which is complex and diverse. One that self-regulates in ways which have kept it relatively stable over geological time.

    Right now, that biosphere is changing fast, due to us.

    Perhaps scientific knowledge, plus co-operativeness and common sense, will make it feasible to develop a long-term sustainable mode of living here on Earth… Or maybe not…

    … even if we can do that, will we be able to develop a long-term sustainable mode of living outside of the biosphere we evolved in?

    Perhaps that isn’t feasible, and will never be feasible.

    Which would be a Great Filter at least as plausible as any I've seen suggested.
    Last edited by Colin Robinson; 2020-Nov-15 at 01:03 AM.

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    Can the SETI Paradox be avoided?


    https://arxiv.org/abs/2010.04089

    Mutual detectability: a targeted SETI strategy that avoids the SETI Paradox

    Eamonn Kerins (Univ. Manchester)

    As our ability to undertake more powerful Searches for Extraterrestrial Intelligence (SETI) grows, so does interest in the more controversial endeavour of Messaging Extraterrestrial Intelligence (METI). METI proponents point to the SETI Paradox - if all civilisations refrain from METI then SETI is futile. I introduce Mutual Detectability as a game-theoretic strategy aimed at increasing the success potential of targeted SETI. Mutual detectability is embodied by four laws: mutuality, symmetry, opportunity and superiority. These laws establish how SETI participants can engage each other using game theory principles applied to mutual evidence of mutual existence. The law of superiority establishes an "onus to transmit" on the party whom both SETI participants can judge to have better quality evidence, or common denominator information (CDI), thus avoiding the SETI Paradox. I argue that transiting exoplanets within the Earth Transit Zone form a target subset that satisfies mutual detectability requirements. I identify the intrinsic time-integrated transit signal strength as suitable CDI. Civilisations on habitable-zone planets of radius Rp/R⊕≲(L∗/L⊙)−1/7 have superior CDI on us, so have game-theory incentive (onus) to transmit. Whilst this implies that the onus to transmit falls on us for habitable planets around L∗>L⊙ stars, considerations of relative stellar frequency, main-sequence lifetime and planet occurrence mean such systems are likely a small minority. Surveys of the Earth Transit Zone for Earth-analogue transits around sub-solar luminosity hosts, followed up by targeted SETI monitoring of them, represent an efficient strategy compliant with mutual detectability. A choice to remain silent, by not engaging in METI towards such systems, does not in this case fuel concerns of a SETI Paradox. Rp/R⊕≲(L∗/L⊙)−1/7 have superior CDI on us, so have game-theory incentive (onus) to transmit. Whilst this implies that the onus to transmit falls on us for habitable planets around L∗>L⊙ stars, considerations of relative stellar frequency, main-sequence lifetime and planet occurrence mean such systems are likely a small minority. Surveys of the Earth Transit Zone for Earth-analogue transits around sub-solar luminosity hosts, followed up by targeted SETI monitoring of them, represent an efficient strategy compliant with mutual detectability. A choice to remain silent, by not engaging in METI towards such systems, does not in this case fuel concerns of a SETI Paradox.
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    Speculations on what the Great Filter might be, and how hard it is to cross it.

    https://astronomy.com/news/2020/11/t...-fermi-paradox
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by Roger E. Moore View Post
    Speculations on what the Great Filter might be, and how hard it is to cross it.

    https://astronomy.com/news/2020/11/t...-fermi-paradox
    I thought it was going to tell us what the great filter is most likely to be ! No such luck.

    Anyhow, this is a reason why searching for life on Mars and other solar system bodies is important. This could tell us if the Great Filter is behind us or is yet to be encountered.

    Really, I know this goes against the grain, but we should all be praying there is no life on Mars. Life on Mars, that is of independent origin to Earth life, means the great filter is ahead of us.

    Or at least it does if the GF is not the prokaryote/eukaryote transition, or the evolution of technological intelligence.
    .

  12. #882
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    Alternately, kzb, life originating on Mars but sent to Earth by lithopanspermia would make a Great Filter early in evolution more likely...maybe very few planetary systems have a small terrestrial to abiogenesis life and a large terrestrial for that life to travel to and develop.
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    Quote Originally Posted by Tom Mazanec View Post
    ... to abiogenesis life ...
    Abiogenerate. The verb is to abiogenerate. Please.

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    Well, I did get a C- in English...
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    Quote Originally Posted by kzb View Post
    I thought it was going to tell us what the great filter is most likely to be ! No such luck.

    Anyhow, this is a reason why searching for life on Mars and other solar system bodies is important. This could tell us if the Great Filter is behind us or is yet to be encountered.

    Really, I know this goes against the grain, but we should all be praying there is no life on Mars. Life on Mars, that is of independent origin to Earth life, means the great filter is ahead of us.

    Or at least it does if the GF is not the prokaryote/eukaryote transition, or the evolution of technological intelligence.
    .
    There may be not Great Filter at all. Just the vagaries of probability of species survival.

    If an ETI civilization with technology exists, and its progression towards space travel is anything like our own, they will face the challenges of developing a positive feedback of invention and advancement resulting in dangerous and destructive capacity. A period can exist where they have the means to destroy themselves, but not yet a corresponding means of surviving the death of one planet. We ourselves are in such an era now.

    But our end is not yet determined, there is no predestination in evolution or in life. It is entirely possible we and others might pass through such a period and go on. The Great Filter concept seemingly presumes that extinction may be unavoidable. I do not accept this concept.
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    Maybe they didn’t take care of their radio telescopes either.

    “We don’t have the quatloos, Blorg—-so quit asking”

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    Going back to the Original Post question, what is the most likely explanation for the lack of aliens...

    The Universe is a big place. It has plenty of room for anything to happen, including life, intelligence, and perhaps a star-faring civilization.

    By the same token, the Universe is a BIG place. Too big to travel or even send comprehensible signals very far. Its scale of space and time is literally unimaginable. We can label things like a billion years or a billion light-years, and make comparisons, but to truly comprehend the distances and passage of years that exist is well beyond human capacity.

    If anyone is out there, they'd have to have come into existence right in our backyard for us to notice them, let alone get visitors, and only if they or their signals get here while we walk the Earth. Think globally*, live locally. And we keep finding reasons to think that worlds whose conditions can support complex life are rare. So it seems unlikely that we'd encounter ETI within the span of human existence.


    *Globe of the sky, of course.
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    Mathematics enters the arena to calculate the number of civilizations in the Milky Way that don't kill themselves.

    https://arxiv.org/abs/2012.07902

    A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy

    Xiang Cai, Jonathan H. Jiang, Kristen A. Fahy, Yuk L. Yung

    In the field of Astrobiology, the precise location, prevalence and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial-temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: 1) the likelihood rate of abiogenesis ({\lambda}A); 2) evolutionary timescales (Tevo); and 3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the Galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult.

    QUOTE: ...we found the potential self-annihilation to be highly influential in the quantity of galactic intelligent life, suggesting another possible answer to the Fermi Paradox; if intelligent life is likely to destroy themselves, it is not surprising that there is little or no intelligent life elsewhere.
    Last edited by Roger E. Moore; 2020-Dec-16 at 01:39 PM.
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    The only way to tell how likely a n intelligent species is to destroy itself, is to destroy ourselves. That would settle the matter quite definitively.

    Otherwise, it's all guesswork. Extrapolating from an example of zero.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.

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    Well, if you think about it, in general, we are moving towards this. Let it be in the distant future and let it be by an unheard-of accident, but in the pursuit of progress and dominance even over our own species, we will destroy ourselves.

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    Quote Originally Posted by Grant Hatch View Post
    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.
    Right. We see an "absence" where no presence should be expected, then make up excuses for why the absent are avoiding us!

    It's like an adopted kid creating elaborate stories about his rich, famous parents, then getting upset the kid didn't inherit any of that wealth.
    Last edited by Noclevername; 2020-Dec-17 at 04:52 PM.
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    Quote Originally Posted by Grant Hatch View Post
    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.
    Yes, I’ve had this argument many times, with people making assumptions about what hypothetical ETs would or wouldn’t do if they existed, like claims ET would spread throughout the galaxy, they would build gigantic structures that could be detected across interstellar space, that interstellar civilizations supposedly would be immortal if not for that claimed “great filter” and that ET would even be here, on Earth and in the solar system. I don’t agree with the beliefs that are behind these assumptions but after going through the same debate a number of times, I usually don’t bother when I see it now.

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    Quote Originally Posted by Grant Hatch View Post
    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.
    Our biased brains may be the ultimate filter of them all?

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    Quote Originally Posted by Grant Hatch View Post
    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.
    Hello Grant Hatch,

    I don't speculate much in this thread but I check it regularly to see what others think because I think it's interesting and some important insights might be in the offing.

    I allow that Fermi's Paradox may be the modern version of counting angels on the tip of a needle but it is hardly arrogance that drives the speculation.

    You seem quite surefooted yourself. Please enlighten us on when we could humbly discuss possibilities of ETI.

    Cheers,

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    Quote Originally Posted by 7cscb View Post
    Please enlighten us on when we could humbly discuss possibilities of ETI.
    The possibility of ETI and the possibility of ETI coming here are two subjects that each need to be separately considered.

    It's not at all arrogant to think there may be life out there that thinks. It's arguably at least collectively self absorbed to imagine that their not visiting us is an omission on their part.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Think in the right direction, I agree with you!
    Last edited by EricSlater; 2020-Dec-23 at 09:31 AM.

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    Quote Originally Posted by Noclevername View Post
    The possibility of ETI and the possibility of ETI coming here are two subjects that each need to be separately considered.

    It's not at all arrogant to think there may be life out there that thinks. It's arguably at least collectively self absorbed to imagine that their not visiting us is an omission on their part.
    Hello noclevername,

    I'm not quite clear if you feel my point was arrogant.

    IMO, we are hindered in the search for ETI primarily by having very poor definitions of Intelligence. Also, our science and technology (and philosophies?) are maybe not yet up to the task. But it seems to me the discussion is normal given our desire to understand the universe and our place in it.

    In thinking of ETI, I do not preclude the possibility that we have been observed or visited. If you feel some such aspect has been ignored, please share it.

    Cheers,

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    Quote Originally Posted by 7cscb View Post
    Hello noclevername,

    I'm not quite clear if you feel my point was arrogant.

    IMO, we are hindered in the search for ETI primarily by having very poor definitions of Intelligence. Also, our science and technology (and philosophies?) are maybe not yet up to the task. But it seems to me the discussion is normal given our desire to understand the universe and our place in it.

    In thinking of ETI, I do not preclude the possibility that we have been observed or visited. If you feel some such aspect has been ignored, please share it.

    Cheers,
    It's not arrogant, but we have no specific reason to think any ETI would prioritize our world out of all the vastness of the Universe. Heck, we've only been putting out coherent signals for a few decades; signals that are weak and easily lost in the background! A tiny, barely perceptible bubble in an endless sea. Outside that tiny bubble, we may have few distinguishing features detectable over any distance.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Grant Hatch View Post
    Filter, Schmilter.... having a "Great" Filter presupposes having a great reason and great evidence for the valid creation of such a "Filter". We have neither. It was far to early to begin this discussion given the limitations of our information gathering technology, our far sensing capabilities. Our arrogance still astounds me occasionally.
    Quote Originally Posted by Noclevername View Post
    Right. We see an "absence" where no presence should be expected, then make up excuses for why the absent are avoiding us!

    It's like an adopted kid creating elaborate stories about his rich, famous parents, then getting upset the kid didn't inherit any of that wealth.
    Perhaps it's worth referring to Robin Hansen's 1998 essay where the term "Great Filter" comes from...

    It's quite well reasoned, which is why people are still talking about the "Filter" over 20 years later...

    Far from being an elaborate story about rich famous parents, Hansen is pointing out that we (probably) can't have it all.

    We can't have both a Galaxy that can be colonised in a geologically short time by a technically-savvy civilisation like us, and plenty of other technically-savvy civilisations for company.

    Because if it were true that the Galaxy can be colonised, and if it were also true that there are plenty of technically-savvy species about, someone would have colonised the Galaxy already, considering how old it is.

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