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

  1. #1321
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    Quote Originally Posted by 7cscb View Post
    And, regardless, we will likely expel much mass in our interstellar travels, which is not Closed.
    Mass expelled from an interstellar vessel will be propellant, not from the life supporting biosphere. A separate system entirely. We don't use the breathing oxygen inside an airplane cabin to run the jets.

    Now, any sealed chamber is imperfect. There will be some material losses from inside the starship biosphere, that's inevitable, and replacement volatiles will have to be carried. But the more closure the builders can achieve, the better for life supporting purposes. So they'll aim high.

    For an orbital habitat replenishment is easier, because there's asteroids and comets to mine, but high degrees of closure of the internal material cycles is still a significant goal, especially as the habitats are being established.
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  2. #1322
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    Even with VERY conservative assumptions the galaxy fills within one eon:
    https://www.centauri-dreams.org/2021...ic-settlement/
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  3. #1323
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    Quote Originally Posted by Tom Mazanec View Post
    Even with VERY conservative assumptions the galaxy fills within one eon:
    https://www.centauri-dreams.org/2021...ic-settlement/
    Zero is a conservative estimate

    I have already discussed here why I don't believe the colonize-a-whole-galaxy scenario is plausible, let alone a default assumption. A number of posters have come back with "but it only takes one!". My response is, it only takes none to explain what we see. We know we have not detected any technosignatures; Occam's old saw says "there's no technosignatures to find" would be the most likely reason for that.

    IF there's another species with minds, and IF they do get out of their home star system, there's still no particular reason to settle every single star in any galaxy. Yes, "life spreads"... in nature. But by definition a civilization that achieves star travel is an artificial construct that does things on purpose, they need not stick to blind imperatives.

    Also, life growing in a glacier or desert sand does not need to expend massive amounts of energy to adapt; but the physics of relativity and motion necessitate that all forms of interstellar travel will require the commitment of vast power and resources. Especially in-person travel with the intent to colonize. That's always going to be expensive, probably even to a star-system-wide economy.

    A generation ship or "slowboat" would be cheaper in energy but basically require a portable civilization. That also seems like a nontrivial commitment of resources. Either way, fast or slow, it's not ever going to be something a society does casually or without good cause at any tech level. And it almost certainly won't be a priority for a colony system still bootstrapping its industries.
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  4. #1324
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    Quote Originally Posted by Noclevername View Post
    Zero is a conservative estimate

    I have already discussed here why I don't believe the colonize-a-whole-galaxy scenario is plausible, let alone a default assumption. A number of posters have come back with "but it only takes one!". My response is, it only takes none to explain what we see. We know we have not detected any technosignatures; Occam's old saw says "there's no technosignatures to find" would be the most likely reason for that.
    Agreed.
    Stepping even further into the evidence-based speculative realm, (for unclear reasons), one can argue that 'aliens' actively attempting to attain the goal of visiting/reaching/making contact with Earth, firstly requires their detecting the existence of the Earth from their light-year distance viewpoints.

    There are seven star systems that can detect Earth transiting the Sun, (ie: the 'Earth Transit Zone'), which are themselves, known to host one or more exoplanets.
    Given the possibility that there may be more systems having exoplanets which we haven't yet detected, there are 1,715 star-systems known, which could have possibly 'spotted' Earth's so-called 'bio-/techno-signatures', since human civilization took off (about 5,000 years ago).

    Over the past 10,000-year period, 117 objects are known to have been within about 100 light-years of the Sun and 75 of these objects have been in the 'Earth Transit Zone' since commercial radio stations on Earth began broadcasting into space, about a century ago.

    This post is more a reality check on the current state of closer-to-fact based knowledge and, along with the fact of the lack of detected technosignatures to date, could be used for useful statistical estimation type discussions.
    It will be interesting to monitor the development of this closer-to-fact based knowledge set, as I think it is unlikely to dramatically change over our not too distant future (JWST observations notwithstanding .. maybe).

    Reference:
    Past, present and future stars that can see Earth as a transiting exoplanet

    Video here.

  5. #1325
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    Quote Originally Posted by Selfsim View Post
    Agreed.
    Stepping even further into the evidence-based speculative realm, (for unclear reasons), one can argue that 'aliens' actively attempting to attain the goal of visiting/reaching/making contact with Earth, firstly requires their detecting the existence of the Earth from their light-year distance viewpoints.
    Unless they had sent out probes and/or colonists that had reached nearer or more angled stars, giving a broader view.
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    Quote Originally Posted by Noclevername View Post
    Unless they had sent out probes and/or colonists that had reached nearer or more angled stars, giving a broader view.
    .. adds more untested hypotheticals .. relies solely on theory and lacks demonstrations of practical feasibility.

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    Quote Originally Posted by Selfsim View Post
    .. adds more untested hypotheticals .. relies solely on theory and lacks demonstrations of practical feasibility.
    Space probes lack demonstration of practical feasibility? Yeah, sure. Interstellar space probes are obvious technological extrapolation over current human demonstrated capability, no new physics needed. Whether there are ETs to send them is the question.

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  8. #1328
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    Quote Originally Posted by Van Rijn View Post
    ... Interstellar space probes are obvious technological extrapolation over current human demonstrated capability, ..
    Obvious or not, 'technological extrapolations' ​are untested predictions projected from hypotheses.

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    Quote Originally Posted by Selfsim View Post
    Obvious or not, 'technological extrapolations' ​are untested predictions projected from hypotheses.
    But, we do have tested predictions? we currently send out probes to visit other planets already, we just don't currently have the capability to send them to other solar systems fast or efficiently enough for any useful reconnaissance.

    I think its reasonable to assume, based on our own current development, that probes are a sensible and economical solution. Obviously doesn't mean that ET is out there sending probes, just that it's a sensible possibility based on our own experience.

  10. #1330
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    If you guess a probe speed at 30,000 m/s that probe takes 10,000 years to travel one light year. (Earth escape velocity about 11,000 m/s). Human visual observation, less than 10,000 years, human radio observation and broadcast, about 100 years.

    We are being impatient to expect the neighbours to call yet.

    We could consider making pyramids to show we were here, perhaps.?
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    Quote Originally Posted by profloater View Post
    We are being impatient to expect the neighbours to call yet.
    Absolutely, and this assumes that they are existing within these tiny time frames (human existence), relatively short distances (local in cosmic terms) and capable of detection from other planets.

  12. #1332
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    Quote Originally Posted by profloater View Post
    We are being impatient to expect the neighbours to call yet.
    Are we?

    The stars which could have seen Earth, (via the Transit method), when life started to evolve, are a different set to the ones which can spot signs of life on our planet now .. compared to those which will see it transit in the far future. The high proper motion of such star systems, moves them into and out of the vantage point of seeing our Earth block the light from our Sun, on the scale of only several hundreds of years.

    Given that life started here about 3.8 - 3.5 billion years ago, that's quite a few star systems which could have potentially known our position for a long time (as their first step in them attempting to make contact).

  13. #1333
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    Quote Originally Posted by Selfsim View Post
    Obvious or not, 'technological extrapolations' ​are untested predictions projected from hypotheses.
    Uh, huh. So you won’t consider even obvious technological extrapolation. In your view, we shouldn’t discuss IC chips with higher commercial densities because that involves untested predictions. Let’s just forget about the Europa Clipper mission - it’s untested. Same for landing people on Mars, or permanent lunar bases. Any technological extrapolation is untested by definition, so shouldn’t be taken seriously, right?

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  14. #1334
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    Quote Originally Posted by profloater View Post
    If you guess a probe speed at 30,000 m/s that probe takes 10,000 years to travel one light year. (Earth escape velocity about 11,000 m/s). Human visual observation, less than 10,000 years, human radio observation and broadcast, about 100 years.

    We are being impatient to expect the neighbours to call yet.
    See the discussion in the other thread:

    https://forum.cosmoquest.org/showthr...-sciam-article

    I make no assumptions about ETI existing, but if they do, it is plausible that they could leave probes in systems with complex life. It isn’t that they would send probes now, but that they might well have put them here on a long term basis.

    We could consider making pyramids to show we were here, perhaps.?
    There are a lot of signs of Earth technology that a hypothetical probe could have detected.

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  15. #1335
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    Quote Originally Posted by Selfsim View Post
    .. adds more untested hypotheticals .. relies solely on theory and lacks demonstrations of practical feasibility.


    Whatever, dude. Keep beating the desiccated equine skeleton.

    .

    Anyway, my point is that seeing from other angles could let hypothetical observers detect transits other than those directly visible from the stated stars.
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    Quote Originally Posted by Noclevername View Post
    Yes, "life spreads"... in nature. But by definition a civilization that achieves star travel is an artificial construct that does things on purpose, they need not stick to blind imperatives.
    On this subject it should probably be noted that, at least for us on Earth, once a civilization reaches a particular level of economic/technological advancement population growth stops and even reverses. In most of the richer countries population growth these days is negative. So it's plausible that sufficiently advanced civilizations simply stop expanding, hence why we don't see any colonizing the galaxy.

  17. #1337
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    Quote Originally Posted by caveman1917 View Post
    On this subject it should probably be noted that, at least for us on Earth, once a civilization reaches a particular level of economic/technological advancement population growth stops and even reverses. In most of the richer countries population growth these days is negative. So it's plausible that sufficiently advanced civilizations simply stop expanding, hence why we don't see any colonizing the galaxy.
    Population pressure isn't related to space expansion anyway.

    We humans explore and expand because it's what our ancestors did as hunter/gatherers, they went where the food was and thus colonized six continents. Some of us retain that instinctive drive for new frontiers. But would aliens share our wandering ways?
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  18. #1338
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    Quote Originally Posted by Noclevername View Post


    Whatever, dude. Keep beating the desiccated equine skeleton.
    If our ancestors were like this I expect we would still be hunter gatherers hunting with stick and stone tools.

    Anyway, my point is that seeing from other angles could let hypothetical observers detect transits other than those directly visible from the stated stars.
    And why focus on transits? Direct observation will be increasingly important as telescopes, especially space telescopes get larger. There are ways to block the light from the central star. Hypothetical ETs could possibly do the same.

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    Quote Originally Posted by Noclevername View Post
    Population pressure isn't related to space expansion anyway.

    We humans explore and expand because it's what our ancestors did as hunter/gatherers, they went where the food was and thus colonized six continents. Some of us retain that instinctive drive for new frontiers. But would aliens share our wandering ways?
    The Fermi Paradox assumes a growing population though, the paradox is in that - assuming a constantly growing population - any civilization millions of years older than us should've colonized the galaxy by now and should be patently obvious to see. Take away the population growth, take away the paradox. If population growth even becomes negative after reaching a certain level of economic/technological advancement (which we do see here on Earth in the developed countries) then we get a solution of the kind of "civilizations end up destroying themselves" but not with a bang but with a whimper, by slowly shrinking their population back down.

    ETA: to be clear, I'm not saying that population pressure causes space expansion, but any space expansion does require the population to expand throughout space with.

    ETA2: even if we're not talking about galactic colonization per se, other observable effects such as Dyson swarms assume a sufficiently large population to fill all those habitats making up the swarm. Continuing population growth is a necessary assumption for the Fermi paradox.
    Last edited by caveman1917; 2021-Jun-24 at 10:19 PM.

  20. #1340
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    Quote Originally Posted by caveman1917 View Post
    ETA: to be clear, I'm not saying that population pressure causes space expansion, but any space expansion does require the population to expand throughout space with.
    We have no experience with populations in space, let alone interstellar colonists. The popdrop characteristic of a First World nation can't really be generalized to all human societies, let alone non-humans.

    It's entirely plausible that those communities most interested in moving to new and untouched territories would be exceptions to the social trends of their home planet.
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  21. #1341
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    Quote Originally Posted by Noclevername View Post
    We have no experience with populations in space, let alone interstellar colonists. The popdrop characteristic of a First World nation can't really be generalized to all human societies, let alone non-humans.

    It's entirely plausible that those communities most interested in moving to new and untouched territories would be exceptions to the social trends of their home planet.
    Sure, many things are plausible. But we only have a single datapoint to work with, ourselves. And that datapoint suggests that once a society reaches a certain level of development (that allows space expansion) also gets into a negative population growth regime, taking away the basis for the Fermi paradox in the first place.

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    Quote Originally Posted by Van Rijn View Post
    Uh, huh. So you won’t consider even obvious technological extrapolation. In your view, we shouldn’t discuss IC chips with higher commercial densities because that involves untested predictions. Let’s just forget about the Europa Clipper mission - it’s untested. Same for landing people on Mars, or permanent lunar bases. Any technological extrapolation is untested by definition, so shouldn’t be taken seriously, right?
    I didn't mention any of that .. and none of that particular strawman changes the fact that 'technological extrapolations' ​are untested predictions projected from hypotheses.

  23. #1343
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    Quote Originally Posted by caveman1917 View Post
    The Fermi Paradox assumes a growing population though, the paradox is in that - assuming a constantly growing population - any civilization millions of years older than us should've colonized the galaxy by now and should be patently obvious to see. Take away the population growth, take away the paradox. If population growth even becomes negative after reaching a certain level of economic/technological advancement (which we do see here on Earth in the developed countries) then we get a solution of the kind of "civilizations end up destroying themselves" but not with a bang but with a whimper, by slowly shrinking their population back down.

    ETA: to be clear, I'm not saying that population pressure causes space expansion, but any space expansion does require the population to expand throughout space with.

    ETA2: even if we're not talking about galactic colonization per se, other observable effects such as Dyson swarms assume a sufficiently large population to fill all those habitats making up the swarm. Continuing population growth is a necessary assumption for the Fermi paradox.
    I’ve made a similar argument about population growth. Assuming no new physics (like FTL travel) and even being optimistic about development of space habitats, exponential population growth time is very limited. In our system, perhaps a few more centuries of growth would be possible in system, but ultimately we must learn to control population growth at some point or face collapse. Exponential growth cannot continue with interstellar colonization. Among other things, the speed of light limits expansion, but in practice, energy and mass limits are more important.

    Given that a civilization must learn to control population relatively quickly compared to timespans to develop an interstellar civilization, that removes a major argument for expansion.

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    Quote Originally Posted by Van Rijn View Post
    And why focus on transits? Direct observation will be increasingly important as telescopes, especially space telescopes get larger. There are ways to block the light from the central star. Hypothetical ETs could possibly do the same.
    Because transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life.

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    Quote Originally Posted by Selfsim View Post
    I didn't mention any of that .. and none of that particular strawman changes the fact that 'technological extrapolations' ​are untested predictions projected from hypotheses.
    You implied it and are doing it again.

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  26. #1346
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    Quote Originally Posted by Selfsim View Post
    Because transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life.
    For now, but that will change as we develop larger space telescopes.

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    Quote Originally Posted by Noclevername View Post
    Anyway, my point is that seeing from other angles could let hypothetical observers detect transits other than those directly visible from the stated stars.
    Its a valid point .. can you quantify how much difference it would make? (Ie: what's the benefit vs the cost?)

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    Quote Originally Posted by Van Rijn View Post
    I’ve made a similar argument about population growth. Assuming no new physics (like FTL travel) and even being optimistic about development of space habitats, exponential population growth time is very limited. In our system, perhaps a few more centuries of growth would be possible in system, but ultimately we must learn to control population growth at some point or face collapse. Exponential growth cannot continue with interstellar colonization. Among other things, the speed of light limits expansion, but in practice, energy and mass limits are more important.

    Given that a civilization must learn to control population relatively quickly compared to timespans to develop an interstellar civilization, that removes a major argument for expansion.
    It's not even that a civilization must control population growth, population growth in developed countries on Earth is already negative without any explicit control. This idea that populations grow exponentially without external controls is simply wrong.

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    Quote Originally Posted by Van Rijn View Post
    For now, but that will change as we develop larger space telescopes.
    Could you please provide references?

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    Quote Originally Posted by caveman1917 View Post
    It's not even that a civilization must control population growth, population growth in developed countries on Earth is already negative without any explicit control. This idea that populations grow exponentially without external controls is simply wrong.
    Like Noclevername, I don’t want to assume too much from the short period of time we have had civilizations with widespread availability of birth control but (generally) access to sufficient food, reasonably good public health measures, etc.

    For instance, in the long term, I could see cultures that promote large families outcompeting cultures that are fine with limiting family size. It isn’t clear to me if voluntary action will be sufficient in the long term.

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