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

  1. #811
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    Quote Originally Posted by Roger E. Moore View Post
    A new paper on the Great Filter.

    https://arxiv.org/abs/2002.08776

    Observational Constraints on the Great Filter
    Jacob Haqq-Misra, Ravi Kumar Kopparapu, Edward Schwieterman
    (Submitted on 18 Feb 2020)

    The search for spectroscopic biosignatures with the next-generation of space telescopes could provide observational constraints on the abundance of exoplanets with signs of life. An extension of this spectroscopic characterization of exoplanets is the search for observational evidence of technology, known as technosignatures. Current mission concepts that would observe biosignatures from ultraviolet to near-infrared wavelengths could place upper limits on the fraction of planets in the galaxy that host life, although such missions tend to have relatively limited capabilities of constraining the prevalence of technosignatures at mid-infrared wavelengths. Yet search-ing for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolution--the Great Filter--is probably in our past. But if we find that life is commonplace while technosignatures are absent, then this would in-crease the likelihood that the Great Filter awaits to challenge us in the future.
    IOW We're still extrapolating from a sample size of one, but now we can be more pessimistic about it!

    No, if we find find (a BIG if) life is common and easily detectable tech isn't, it only means that life is common while easily detectable tech isn't.

    Perhaps it just means life does not always produce the kind of intelligent tool use leading to interstellar-ly visible Dyson spheres "technosignatures at mid-infrared wavelengths", and that's the whole "Great Filter" maybe possibly?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  2. #812
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    Quote Originally Posted by Roger E. Moore View Post
    A paper is out that says "life in the universe could be common, but not in our neighborhood". Now, what they mean by "our neighborhood" is the entire observable universe. WHAT? So we're essentially alone, you're saying?

    https://phys.org/news/2020-03-reveal...ghborhood.html

    "RNA is a polymer, meaning it is made of chemical chains, in this case known as nucleotides. Researchers in this field have reason to believe that RNA no less than 40 to 100 nucleotides long is necessary for the self-replicating behavior required for life to exist. Given sufficient time, nucleotides can spontaneously connect to form RNA given the right chemical conditions. But current estimates suggest that magic number of 40 to 100 nucleotides should not have been possible in the volume of space we consider the observable universe.... Indeed, the observable universe contains about 10 sextillion (10^22) stars. Statistically speaking, the matter in such a volume should only be able to produce RNA of about 20 nucleotides. But it's calculated that, thanks to rapid inflation, the universe may contain more than 1 googol (10^100) stars, and if this is the case then more complex, life-sustaining RNA structures are more than just probable, they're practically inevitable."
    As Van Rijn said, they're leaving out any intermediate steps between randomness and fully formed biochemistry.
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  3. #813
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    Quote Originally Posted by Noclevername View Post
    As Van Rijn said, they're leaving out any intermediate steps between randomness and fully formed biochemistry.

    also leaving out the effect of evolution (it sounds like a creationist argument that life is virtually impossible).

  4. #814
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    Quote Originally Posted by Noclevername View Post
    As Van Rijn said, they're leaving out any intermediate steps between randomness and fully formed biochemistry.
    See, I think you've got a point as there's this article and others talking about RNA evolving, essentially.

    https://www.newscientist.com/article...lop-into-life/
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  5. #815
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    Quote Originally Posted by Roger E. Moore View Post
    See, I think you've got a point as there's this article and others talking about RNA evolving, essentially.

    https://www.newscientist.com/article...lop-into-life/
    Self-assembly is a noted property of many complex molecular patterns.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  6. #816
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    My favorite analogy is the box of paperclips. Shaken up, the clips will usually hook on to each other and form long complex branching chains. A good example of adding energy to a chaotic system and getting order out of randomness.

    I think comparing self-organizing organic chemistry and biogenesis to winning a lottery is a misleading analogy. One in a million chance of winning, but if you have a billion players playing a million times each, the odds of no one winning at all are vanishingly small.

    The scale in time and places of the trial and error mixing and matching of molecules on early Earth, means that lots and lots of one in a billion chances actually happened. I'm not saying self replicating molecules were inevitable, just that in some form or another, they were probably not as unlikely as one event.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  7. #817
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    What is the probability of there being other communicating intelligences, and how far away are they?

    https://arxiv.org/abs/2004.03968
    The Astrobiological Copernican Weak and Strong Limits for Extraterrestrial Intelligent Life
    Tom Westby, Christopher J. Conselice
    (Submitted on 8 Apr 2020)
    We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent civilizations (CETI) in our Galaxy by utilizing the latest astrophysical information. Our calculation involves Galactic star-formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in Habitable Zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist - on our own planet. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so. We investigate the possible number of CETI based on different scenarios. At one extreme is the Weak Astrobiological Copernican principle - such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Condition in which life must form between 4.5 to 5.5 Gyr, as on Earth. In the Strong Condition (a strict set of assumptions), there should be at least 36 (+175/−32) civilizations within our Galaxy: this is a lower limit, based on the assumption that the average life-time, L, of a communicating civilization is 100 years (based on our own at present). If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most 17,000 (+33,600/−10,000) light-years away, and most likely hosted by a low-mass M-dwarf star, far surpassing our ability to detect it for the foreseeable future. Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M-dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within our Galaxy based on variations of our assumptions.
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    Maybe the problem is that Earths are far rarer than we had thought.

    https://arxiv.org/abs/2004.05296
    Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars
    Michelle Kunimoto, Jaymie M. Matthews
    (Submitted on 11 Apr 2020)
    We present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0.5-16 R⨁ and orbital periods between 0.78-400 days, orbiting FGK dwarf stars. We base our results on an independent planet catalogue compiled from our search of all ~200,000 stars observed over the Kepler mission, with precise planetary radii supplemented by Gaia DR2-incorporated stellar radii. We take into account detection and vetting efficiency, planet radius uncertainty, and reliability against transit-like noise signals in the data. By analyzing our FGK occurrence rates as well as those computed after separating F, G, and K type stars, we explore dependencies on stellar effective temperature, planet radius, and orbital period. We reveal new characteristics of the photoevaporation-driven "radius gap" between ~1.5-2 R⨁, indicating that the bimodal distribution previously revealed for P < 100 days exists only over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, we provide several estimates of the "eta-Earth" value -- the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0.75 - 1.5 R⨁ orbiting in a conservatively defined Habitable Zone (0.99 - 1.70 AU) around G type stars, we place an upper limit (84.1th percentile) of < 0.18 planets per star.
    Do good work. —Virgil Ivan "Gus" Grissom

  9. #819
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    Quote Originally Posted by Roger E. Moore View Post
    Maybe the problem is that Earths are far rarer than we had thought.
    We only know that Earth itself has produced complex life, a likely prerequisite for technological intelligence. But the open question is, are Earth conditions the main/only types of worlds that can lead to such complexity, or just one of many paths?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  10. #820
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    Quote Originally Posted by Noclevername View Post
    We only know that Earth itself has produced complex life, a likely prerequisite for technological intelligence. But the open question is, are Earth conditions the main/only types of worlds that can lead to such complexity, or just one of many paths?
    This would mean the Drake Equation is not one equation but many additive ones: the chance of intelligent technological life developing on the surface of an Earthlike world, PLUS the chance of intelligent technological life developing in a subsurface ocean planet, PLUS etc. All the various ways a planet could have life would be added together as the Drake Equation was really just built for us.

    This would seem to make it more likely for there to be intelligent life, but maybe not--life undersea might not develop technology, just intelligence, and certain types of lifebearing planets might be very rare.
    Do good work. —Virgil Ivan "Gus" Grissom

  11. #821
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    Quote Originally Posted by Roger E. Moore View Post
    This would mean the Drake Equation is not one equation but many additive ones: the chance of intelligent technological life developing on the surface of an Earthlike world, PLUS the chance of intelligent technological life developing in a subsurface ocean planet, PLUS etc. All the various ways a planet could have life would be added together as the Drake Equation was really just built for us.

    This would seem to make it more likely for there to be intelligent life, but maybe not--life undersea might not develop technology, just intelligence, and certain types of lifebearing planets might be very rare.
    And there might be totally alien conditions that don't happen on Earth or in our Solar System at all, that somehow give rise to ETI life. But we have no knowledge of such, and currently no way to acquire knowledge of such. And those alien circumstances might be more or less common than Earthlike. Mid-sized planets for instance are not found locally, but Sub-Neptunian and Super-Earth exoplanets are abundant.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  12. #822
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    We can invoke an "Anthropic Principle"; Earth and Sol and the Milky Way seem to have had a number of advantages over the average planet and star and galaxy as far as allowing for the conditions required to allow for development of complex, thinking life. We evolved for the specific conditions of this world and this space and time, and so it all seems ideally suited to us, when in fact it's we who are suited to it. As with Geocentrism, Anthropism is a self-centering philosophy. But we are the water conforming to the shape of the pond.

    Earth is rare because it possesses stability. Most places that we have observed, do not share this elusive quality to a large degree. Galactic cores are active, suns flare, axial tilts slew about at random. Even in those neighborhoods were metallicity and orbit and temperature and radiation all fall into ideal slots, stability is often wanting. Even if life existed on all those worlds, it might be difficult to reach the complexity required for beings that can build civilizations and technology.

    We pass through galactic arms less than most stars, we have a fairly quiet Sun, our Moon keeps our tilt at a manageable consistency. Our spinny core generates a nice magnetic shield. Jupiter may have led us to the Goldilocks Zone and slung away a lot of asteroids and comets. All these things lessen the frequency of mass extinction events that favor simple, hardy forms of life over the luxury of big brains and higher functions beyond basic survival. Imagine a Dino Killer or a Gamma Ray Burst every couple of million years. Think we'd have evolved if that were the case? Not to mention the unquantifiable chance of photosynthesis, oxygenation, eukaryotes, and consciousness.

    We are in a position of privilege, and like all privileged, we ourselves have trouble realizing it. We tend to take our place in things for granted.

    We are the result of astronomical luck... in both senses of the term.
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  13. #823
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    I suspect that life might be common, and intelligence life possible, even technological intelligence, BUT space travel and space communication, very very rare. Underground ocean life never gets above ground, high-gravity super-Earths restrict space travel, etc. We did get lucky here.
    Do good work. —Virgil Ivan "Gus" Grissom

  14. #824
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    We might not have considered how long a planet remains habitable before its sun expands into a red giant stage or worse. A lot of planets, and I think that's a LOT of planets, just get toasted before life can develop anywhere worthwhile on an interstellar or interplanetary stage. O, A, and B stars won't hack it, and F stars are dicey.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by Roger E. Moore View Post
    We might not have considered how long a planet remains habitable before its sun expands into a red giant stage or worse. A lot of planets, and I think that's a LOT of planets, just get toasted before life can develop anywhere worthwhile on an interstellar or interplanetary stage. O, A, and B stars won't hack it, and F stars are dicey.
    Yes, and common M stars have their own problems; Tides and flares, close orbits and cool temperatures.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    Yes, and common M stars have their own problems; Tides and flares, close orbits and cool temperatures.
    I’ve seen arguments that K dwarfs would be the best on that score: Longer time on main sequence than our G dwarf, orbits not as close as for M dwarfs, reasonably well behaved once they age a bit, and more common than G though less than M

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    Quote Originally Posted by Van Rijn View Post
    I’ve seen arguments that K dwarfs would be the best on that score: Longer time on main sequence than our G dwarf, orbits not as close as for M dwarfs, reasonably well behaved once they age a bit, and more common than G though less than M
    I've seen those papers, too.

    I was trying to think of all the non-SF ways in which intelligent alien life is supposed to be able to arise, maaaybe. Different forms of the Drake equation, basically.

    1. Just like us, walking on the surface of a terrestrial planet.
    2. Swimming under the planetary (frozen) crust in a subsurface ocean.
    3. Flying around in the upper atmosphere of a Jovian giant or a brown dwarf.
    4. Help me out here, I have brain damage.
    Do good work. —Virgil Ivan "Gus" Grissom

  18. #828
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    Quote Originally Posted by Roger E. Moore View Post
    3. Flying around in the upper atmosphere of a Jovian giant or a brown dwarf.
    Jovians have stormy atmospheres which tend to create large downdrafts, sweeping organic molecules into the destructive depths. Upwellings of them, like the Red Spot, are short lived compared to the time thought needed to form life. And any life that does crop up, would face the same problem.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  19. #829
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    Another potential rarity regarding our Solar System:

    https://arxiv.org/pdf/2005.01401.pdf
    The Sun is less active than other solar-like stars

    ...Most of the solar-like stars with well-determined rotation periods show higher variability than the Sun and are therefore considerably more active. These stars appear nearly identical to the Sun, except for their higher variability. Their existence raises the question of whether the Sun can also experience epochs of such high variability.
    So either we lucked out to have an unusually stable Sun, allowing us to develop modern radio, telephone, power lines, and electronics without too many flare and CME events, or we lucked out by having developed modern electrical lines and electronics within an unusually stable period of solar activity. Either way, the more common conditions of sunlike stars might place a damper on the development of a technological spacefaring civilization.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  20. #830
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    Quote Originally Posted by Noclevername View Post
    Another potential rarity regarding our Solar System:

    https://arxiv.org/pdf/2005.01401.pdf

    So either we lucked out to have an unusually stable Sun, allowing us to develop modern radio, telephone, power lines, and electronics without too many flare and CME events, or we lucked out by having developed modern electrical lines and electronics within an unusually stable period of solar activity. Either way, the more common conditions of sunlike stars might place a damper on the development of a technological spacefaring civilization.
    I think we'd just keep trying, if the Carrington event came in 1970 or so; we'd start over and armor the electronics.
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  21. #831
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    Quote Originally Posted by Roger E. Moore View Post
    I think we'd just keep trying, if the Carrington event came in 1970 or so; we'd start over and armor the electronics.
    Assuming it happens that late in our tech development. If it happened early or often, we might not put in the effort to pursue what might look like a dead end.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    I get a little dark sometimes in my head, so I don't have any trouble assuming that civilizations destroy themselves as a rule. After all, the default state of all life on the planet is to consume. We are exceptionally good at it. But I try remind myself that is an assumption. There are so many ways we could go extinct, it doesn't have to be by our own hands.

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    Quote Originally Posted by jascryan View Post
    I get a little dark sometimes in my head, so I don't have any trouble assuming that civilizations destroy themselves as a rule. After all, the default state of all life on the planet is to consume. We are exceptionally good at it. But I try remind myself that is an assumption. There are so many ways we could go extinct, it doesn't have to be by our own hands.
    We very well might self destruct (or a hypothetical alien society very well might). Many species end. But we also may go on, adapt, evolve, and grow into a variety of lifeforms, as happens in nature since the beginning of life on Earth.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    We very well might self destruct (or a hypothetical alien society very well might). Many species end. But we also may go on, adapt, evolve, and grow into a variety of lifeforms, as happens in nature since the beginning of life on Earth.
    Agreed. I hope for that outcome. It would be a shame for the collective accumulated knowledge of humanity to disappear. How else is the universe gonna observe itself? Your point that we are here at all is very well taken. I will add that to the list of things to remind myself.

  25. #835
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    Quote Originally Posted by Roger E. Moore View Post
    I was trying to think of all the non-SF ways in which intelligent alien life is supposed to be able to arise, maaaybe. Different forms of the Drake equation, basically.
    "Supposed to be able" and "non-SF" are both problematic. We just don't have enough information to rule anything out. Hypothetically, any environment with the right chemistry, temperature, and energy might host life.

    But how often those conditions occur outside the environments you list is a big unknown; how often the potential for life actually becomes life, is an even bigger unknown.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    There might be a lot that we don't know. Maybe we should add 10 more terms to the Drake equation and set each to 10% as an estimate for the stuff we don't know yet.

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    Quote Originally Posted by Chuck View Post
    There might be a lot that we don't know. Maybe we should add 10 more terms to the Drake equation and set each to 10% as an estimate for the stuff we don't know yet.
    Why set them to any percent? We can mark all the unknown factors as "unknown".
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    Why set them to any percent? We can mark all the unknown factors as "unknown".
    The answer would be unknown, not very appealing to lots of people. The addition of percentages was developed to assume a likely amount of places where intelligent life may exist.

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    Quote Originally Posted by bknight View Post
    The answer would be unknown, not very appealing to lots of people. The addition of percentages was developed to assume a likely amount of places where intelligent life may exist.
    But they are unknown. Assigning arbitrary numbers to fill the gaps and calling them "likely" just smacks of false advertising to me.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    I was keeping with the spirit of the original Drake equation by guessing wildly.

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