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

  1. #901
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    Quote Originally Posted by Colin Robinson View Post
    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.
    Yeah, that gets into the assumptions I was talking about a few posts back.

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    Quote Originally Posted by Colin Robinson View Post
    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.
    I don't take that as a given. A "tech savvy" species, I assume, means one that can colonize beyond their star system. (And by that definition we are not tech savvy.) So the alien civilization spreads out to other stars. Does it necessarily follow that they will continue to do so forever, until reaching the galactic limits of growth?

    Humanity has been predicted to do so with Earth. Now it seems, as our societies develop economically and socially, population growth has begun to slow. We may not continue to replicate as bacterially as at our peak breeding speed. A base assumption about ourselves has not held up in practice, defying all predictions. So it may be with the spread of an intelligent species. What would drive such a frenzied spread over such difficult distances? It's not like population pressure could do it, if they live in space they must have some means of controlling their reproduction. Fiction to the contrary, Moties would not exist for long as a civilized society capable of maintaining a space habitat. What, then, would lead to continually paying the cost of an interstellar journey to an uncertain situation? What would you have there that would not be available at home? Certainly a whole star system has enough volume for any isolationist to get lost in.

    And yes, it's been done on Earth, with sailing ships, but for reasons that would not apply to an advanced technological culture under completely different conditions. Sailors could catch fish and breathe air in any ocean.

    It may be that interstellar travel is a young species' game. Something to be outgrown, sowing one's wild oats before settling down. We can't even predict what post-humans would do or what motives they may have. How can we guess how aliens might do things?
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    Quote Originally Posted by Van Rijn View Post
    Yeah, that gets into the assumptions I was talking about a few posts back.
    Robin Hansen's argument is that living (evolving) species have a general tendency to expand where they can...

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    Quote Originally Posted by Colin Robinson View Post
    Robin Hansen's argument is that living (evolving) species have an general tendency to expand where they can...

    Under natural conditions, sure. Interstellar travel is hardly a natural occurrence. It's a costly decision entailing a considerable risk, a major investment or energy and effort.
    "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
    I don't take that as a given. A "tech savvy" species, I assume, means one that can colonize beyond their star system. (And by that definition we are not tech savvy.) So the alien civilization spreads out to other stars. Does it necessarily follow that they will continue to do so forever, until reaching the galactic limits of growth?
    And assuming known physics, exponential growth over a galaxy is impossible. A society must be able to control population quite early or overshoot resources and collapse.

    Humanity has been predicted to do so with Earth. Now it seems, as our societies develop economically and socially, population growth has begun to slow.
    One idea is that Earth would become something like Asimovís Trantor or Star Warsí Coruscant. That is, the entire surface (including the oceans) covered with buildings and farms for food until it reaches a stable maximum capacity. With exponential growth that would happen very quickly compared to the age of the world. Personally, I strongly hope humanity can reach a stable population and limit use of the planet to something below theoretical limits.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." ó Abraham Lincoln

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    Quote Originally Posted by Colin Robinson View Post
    Robin Hansen's argument is that living (evolving) species have a general tendency to expand where they can...
    Thatís an assumption. There are a long list of assumptions when it comes to the idea of a species spreading through the galaxy, including the assumption that we would see it. After all, we canít rule out a probe landing on the Earth millions of years ago, and ultimately destroyed by natural processes, or a spacecraft in the solar system eventually destroyed by micrometeors - or not, but not discovered yet. I donít expect anything like that, but I dislike people insisting on assumptions.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." ó Abraham Lincoln

    I say there is an invisible elf in my backyard. How do you prove that I am wrong?

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    It could also be that some species did colonize the Galaxy... billions of years ago. Would their descendants necessarily still be active or visible to us now?

    Perhaps they were looking for green planets at a time when our atmosphere was still brown. Or they sought a different kind of environment entirely. Or they just died.
    "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
    It could also be that some species did colonize the Galaxy... billions of years ago. Would their descendants necessarily still be active or visible to us now?

    Perhaps they were looking for green planets at a time when our atmosphere was still brown. Or they sought a different kind of environment entirely. Or they just died.
    They may have died, yes. It may be that colonies have a lower life expectancy than home-grown ecosystems. Then it wouldn't be strange that Earth has a home-grown ecosystem but no sign of having been successfully colonised (in the sense of colonists leaving biological descendants)...
    Last edited by Colin Robinson; 2020-Dec-23 at 04:06 AM.

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    Quote Originally Posted by Colin Robinson View Post
    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.
    IF a Galaxy can be colonized. IF a tech savvy species even desired to do so in the first place. IF a tech savvy species kept up the drive to do so for many millennia and hundreds of generations.

    "Colonize the Galaxy" is like saying "Drink the oceans dry". It's a mathematical abstract that ignores scale and innate difficulty and impracticality. No, I think that's not a well reasoned argument.

    I can buy that a species might want to colonize nearby stars, with great effort. But the whole Galaxy? No. By the time they reached the end of their Arm the last travelers would have become culturally, and probably genetically, unrecognizable to the society of origin. Who would also have changed drastically over their old culture.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Perhaps they got caught in a nearby supernova and now consist only of presolar grains.

    Or, space is huge and interstellar-level intelligence is rare.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    OR... Our solar system has been "colonized"; or "seeded"; and we don't even realize it...
    Last edited by Grant Hatch; 2020-Dec-23 at 05:34 PM.

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    One thing is for sure.... we are relative late comers to the scene and it seems that life arose almost as soon as the planet was no longer molten. Then wiped out and arose again as the planet went through the late heavy bombardment. At least according to paleo geology..... This would seem to indicate that life is a natural part of our universe... at least "locally". We may find that it's CROWDED out there. Intelligence would also "seem" to be a natural consequence of evolution, though we only have a sample of one to extrapolate from.
    Last edited by Grant Hatch; 2020-Dec-23 at 05:58 PM.

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    Quote Originally Posted by Grant Hatch View Post
    OR... Our solar system has been "colonized"; or "seeded"; and we don't even realize it...
    Any terraforming efforts would likely focus on making a home for intelligent life, which would require a source of energy greater than anaerobic life in a reducing atmosphere could provide. IE, some source of oxidation, or advanced photosynthesis. There's no evidence of such on early Earth. The environment of the planet back then, just could not support complex multi-celled creatures with brains.

    In addition, known science seems to indicate that the earliest ancestors of current life were very genetically simple proto-bacteria. If aliens seeded Earth with life, then we're evolved from the most primitive life they could find... or accidentally leave behind with their garbage!
    "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
    One thing is for sure.... we are relative late comers to the scene and it seems that life arose almost as soon as the planet was no longer molten. Then wiped out and arose again as the planet went through the late heavy bombardment. At least according to paleo geology..... This would seem to indicate that life is a natural part of our universe... at least "locally". We may find that it's CROWDED out there. Intelligence would also "seem" to be a natural consequence of evolution, though we only have a sample of one to extrapolate from.
    Nope. You're drawing conclusions about commonality from a sample of one! Commonality is inherently comparative. It requires multiple examples. Indeed, nothing can be common, rare or unique without a spectrum of possibilities to choose from.

    We might be average, common, or a total fluke. Without other life bearing planets to measure the occurrence of, we just don't know!
    "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
    Any terraforming efforts would likely focus on making a home for intelligent life, which would require a source of energy greater than anaerobic life in a reducing atmosphere could provide. IE, some source of oxidation, or advanced photosynthesis. There's no evidence of such on early Earth. The environment of the planet back then, just could not support complex multi-celled creatures with brains.

    In addition, known science seems to indicate that the earliest ancestors of current life were very genetically simple proto-bacteria. If aliens seeded Earth with life, then we're evolved from the most primitive life they could find... or accidentally leave behind with their garbage!
    OR.... the seeding took place (long)? after the oxygen atmosphere was created. What of the pre-cambrian explosion? Perhaps entirely natural, perhaps not?
    Last edited by Grant Hatch; 2020-Dec-23 at 06:15 PM.

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    Quote Originally Posted by Noclevername View Post
    Nope. You're drawing conclusions about commonality from a sample of one! Commonality is inherently comparative. It requires multiple examples. Indeed, nothing can be common, rare or unique without a spectrum of possibilities to choose from.

    We might be average, common, or a total fluke. Without other life bearing planets to measure the occurrence of, we just don't know!
    True enough. But I was thinking the multiple times of the genesis of life here might give us a larger sample size...

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    Quote Originally Posted by Grant Hatch View Post
    OR.... the seeding took place (long)? after the oxygen atmosphere was created. What of the pre-cambrian explosion? Perhaps entirely natural, perhaps a little help?
    I've seen that movie.

    But if ET life was introduced to our world, we'd see the separate genetic origins of it. All the life we've ever found is branches off a single tree. Alien life would be from a totally different tree.
    "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
    True enough. But I was thinking the multiple times of the genesis of life here might give us a larger sample size...
    What multiple genesis?

    I've never heard of any sign of that.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    As with all other ideas, we must go where the evidence takes us. And right now it leads nowhere. We have many "possible" explanations for a problem we made up (let's be clear, here.) But there's no aliens, no current ET life let alone starship-builders, no recognizable communication, and no (reliably documented) visitors. We're not going to make progress on this matter until one or more of those voids in our knowledge is filled.
    "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
    What multiple genesis?

    I've never heard of any sign of that.
    As I understand it there are gaps in the presence of life in the geologic record of the early earth?

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    Quote Originally Posted by Grant Hatch View Post
    As I understand it there are gaps in the presence of life in the geologic record of the early earth?
    And...?
    "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
    I've seen that movie.

    But if ET life was introduced to our world, we'd see the separate genetic origins of it. All the life we've ever found is branches off a single tree. Alien life would be from a totally different tree.
    OR.... DNA is a common "natural" result among several possiblities in the genesis of life everywhere. In which case the Aliens had a bag of tricks to draw from...

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    Quote Originally Posted by Grant Hatch View Post
    OR.... DNA is a common "natural" result among several possiblities in the genesis of life everywhere. In which case the Aliens had a bag of tricks to draw from...
    What? I don't understand this post.
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    Quote Originally Posted by Noclevername View Post
    And...?
    Some scientists have concluded, perhaps erroneously, that life generally follows quickly when the conditions allow it.

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    Quote Originally Posted by Grant Hatch View Post
    Some scientists have concluded, perhaps erroneously, that life generally follows quickly when the conditions allow it.
    Citations, please.

    It sounds too much like "God of the Gaps" to me. Imagination can fill those blank spaces with anything.
    "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
    What? I don't understand this post.
    You were talking about the "tree of life" which uses DNA to propagate itself. I was saying that it's quite possible Earth is not the only place life uses DNA to propagate. While there may be other mechanisms of propagation they are likely limited in number due to the requirements (energetic, chemical etc.) of such information transmittal and the life it engenders ... In other words, a limited number of "trees of life".

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    Quote Originally Posted by Grant Hatch View Post
    You were talking about the "tree of life" which uses DNA to propagate itself. I was saying that it's quite possible Earth is not the only place life uses DNA to propagate. While there may be other mechanisms of propagation they are likely limited in number due to the requirements (energetic, chemical etc.) of such information transmittal and the life it engenders ... In other words, a limited number of "trees of life".
    Well, modern genetics can quantify the divergence from our common origin. We have many genes in common with other life forms, all the way down to the most basic microbes. An alien tree of life might use DNA or something chemically similar (though there's no particular reason why it should, there's plenty of alternative amino acids to make it happen), but they will not share the same genes in common.
    "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
    Citations, please.

    It sounds too much like "God of the Gaps" to me. Imagination can fill those blank spaces with anything.
    https://researchoutreach.org/article...ed-life-earth/

    https://www.pnas.org/content/pnas/80/10/2981.full.pdf
    Last edited by Grant Hatch; 2020-Dec-23 at 07:13 PM.

  29. #929
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    It's a long article. Can you please tell me which are the relevant passages and citations?
    "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
    IF a Galaxy can be colonized. IF a tech savvy species even desired to do so in the first place. IF a tech savvy species kept up the drive to do so for many millennia and hundreds of generations.

    "Colonize the Galaxy" is like saying "Drink the oceans dry".
    Considering that all living things do drink, in the sense of taking in water, it is reasonable to ask why they haven't drunk the oceans and rivers dry...

    The answer is that there's a balance between the water living things take in and the water they emit, e.g. as urine and as exhaled water vapour.

    I can buy that a species might want to colonize nearby stars, with great effort. But the whole Galaxy? No.
    But if a species wants to colonise nearby stars, and succeeds in doing so, and if its colonies then want to colonise stars which are nearby to them, doesn't that mean the species steadily spreads through more and more of the Galaxy until and unless something stops it?

    By the time they reached the end of their Arm the last travelers would have become culturally, and probably genetically, unrecognizable to the society of origin. Who would also have changed drastically over their old culture.
    Robin Hanson mentions that point: "Without FTL travel to mediate conformity, we would also not be surprised by a great diversity among the different parts of an explosion, and especially among different explosions... We would expect, for example, different cultures, languages, and body form details. We expect much less diversity, however, regarding choices which would put a civilization or entity at a strong competitive reproductive disadvantage."

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