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Thread: no ETs in universe

  1. #61
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    We're here, aren't we? Isn't that good enough?

    What gives you the idea they haven't been here thousands of times
    over the last billion years? There is absolutely no reason to think
    that they haven't.

    Why would they be here? What would they do here for a billion years?
    Sit around playing pinochle while they wait for an intelligent species to
    arise? Tease the native animals? Evolve into something else? What?

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
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  2. #62
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    Jeff: well one of the possible logical conclusions is that they are indeed here already, but they are keeping themselves secret, or are keeping us in a cosmic zoo etc. However if we discuss those we will find ourselves banned no doubt.

    I'm willing to admit that there is a small possibility of ET's existing. If we posit that the probability of a technological civ arising is extremely small, it is just about conceivable that we are amongst the first few technological civilisations in the galaxy.

    That situation could have arisen by chance, but it's only reasonable to think this only if the prior probabililty is extremely low. It's not very scientific to conclude this either, because it is not the path of maximum likelyhood.

  3. #63
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    I haven't the slightest doubt that the galaxy has many, many civilizations
    older than ours, interested in and capable of spaceflight. But I don't think
    there is any galaxy-wide interstellar civilization, and I don't think there are
    any ET's here currently. Interstellar travel is terribly difficult, terribly
    expensive, and takes an awfully long time to do. It may have scientific
    value, aesthetic value, and spiritual value, but it takes too long to have
    any commercial value. So it may be very difficult for ET to afford it.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  4. #64
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    Quote Originally Posted by kzb View Post
    If the development of a technological civ were in any way common, or even inevitable, the evidence for these ancient civilisations would be obvious.
    That is not a valid conclusion. We would not now be detecting a twin to our civilization at a nearby star. You have to make a lot of assumptions about what we should be seeing to conclude that we can rule out other civilizations now or in the past.

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

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  5. #65
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    Quote Originally Posted by Van Rijn View Post
    Quote Originally Posted by kzb View Post
    ...If the development of a technological civ were in any way common, or even inevitable, the evidence for these ancient civilisations would be obvious. But we don't see any.
    That is not a valid conclusion...
    Generally agreed. the best we can say is that we see no evidence of the types of advanced technological civilizations that we imagine ourselves becoming in the future, even within the next few millenia, yet alone millions or billions of years from now. Other types of technological civilizations may exist, we simply have no compelling evidences or indications that they do.

  6. #66
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    Quote Originally Posted by Van Rijn View Post
    That is not a valid conclusion. We would not now be detecting a twin to our civilization at a nearby star. You have to make a lot of assumptions about what we should be seeing to conclude that we can rule out other civilizations now or in the past.
    But it is statistically unlikely to be a twin to our civilisation. In fact the probability that they are within even a few centuries of our technological level is remote.

    Furthermore, the first civilisations have now HAD to vacate their home systems. In the same way that Earth will be uninhabitable in a few hundred million years, the same would have happened to their star.

    So development of interstellar travel is not optional in the long term. You have to develop spaceships or die.
    Last edited by kzb; 2011-Oct-01 at 04:43 PM. Reason: grammar

  7. #67
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    What interests me the most about the idea of life outside of Earth is the science behind discovering how life begins in the first place. When and how does an object turn from non-living to living? What is the formula and biology behind it? Did we really evolve from a pool of Amino Acid, or some other way? I'd rather not bring God into this because that's a whole 'nother discussion altogether. At what point did materials on Earth make the transition from non-living to living? Once we discover this, it will make it much easier for us to evaluate the possibility of life elsewhere in the Universe.

  8. #68
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    Quote Originally Posted by kzb View Post
    But it is statistically unlikely to be a twin to our civilisation. In fact the probability that they are within even a few centuries of our technological level is remote.
    Yes, alien civilizations would likely be different, which again points to the fact that we cannot assume they would be obvious to us with the limits of our current observational capability.

    Furthermore, the first civilisations have now HAD to vacate their home systems. In the same way that Earth will be uninhabitable in a few hundred million years, the same would have happened to their star.
    You seem to be assuming a civilization would continue for several hundred million years. That is an extraordinary assumption - species don't last that long.

    However, if there are organizations that have continued for hundreds of millions of years in this universe, they probably would have had to long since come to terms with limits to growth, and would have already taken steps to focus on long term survival. With careful management, an organization could plan to continue for trillions of years - but wouldn't necessarily be a profligate energy waster, or builder of megastructures. Again, we can't know we would be able to detect such.

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

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

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  9. #69
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    Quote Originally Posted by neilzero View Post
    Perhaps they cannot even tell that our solar system has a third planet,
    What you are talking about? We, meager humans, are literally on verge of detecting Earth-sized planets around other stars in habitable zone (in fact, we already have unconfirmed reports about it thanks to Kepler), and I expect having preliminary colonisation list (not that we would fly there any time soon, mind you...) for our neighbourhood (say 100 ly) in my lifetime. Advanced technologically ET would know about Earth (and pretty much every planet in entire galaxy) long, long ago.

    Planetary detection is relatively low tech in comparison to other technologies concievably possible for sufficiently advanced aliens.

  10. #70
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    The two techniques we have for detecting extrasolar
    planets which have yielded all or nearly all discoveries
    so far -- Doppler shifts of light from the parent star and
    eclipsing of the parent star -- both depend on the planet
    being in an orbit edge-on to us. Technology and luck
    are both essential.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  11. #71
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    I don't believe we can yet determine by statistical means or probabilities whether life exists any where else in the galaxy, or possibly the universe.

    So far, our only evidence is that life began and thrives on this planet and this planet alone (remember it is our ONLY evidence so far). Therefore our sample consists of one - Earth.

    We can talk lots about the POSSIBILITY of life elsewhere, but not the probability. There is a subtle and significant difference between the two.

    Now, should the Mars probes begin to find real evidence of some form of life there, or maybe other probes finding somehing on, say, Europa, THEN perhaps we can begin to create statistics and talk about probabilities etc.

    My personal view is that there is quite possibly some other forms of life out there, and maybe even intelligent ones. However, with our current understanding of physics, we seem to find that there is a universal constant - the speed of light - which means any interstellar travellers would be in for a long haul shoud they be able or wish to attempt it! There COULD be changes ahead in physics (possible very recent experiments may.... or may not ... show this), but this is certainly our current understanding.

    Our civilisation has only really grown up through mankind rising over perhaps 2 to 5 million years, with the last 10,000 or so being the real town and city dwelling part of it. This has driven developments in technology, warfare, agriculture, and the arts over perhaps 5000 or more years, culminating where we are now. Huge advances within that have happened in only the last 200 years or so (industrialisation, transport, electricity, computers, space, and of course nuclear).

    This timescale within that of the galaxy is just a moment in time, and practically nothing at all in the context of the universe. Some other similar (ish!) intelligent species could be one million years ahead of us and we may have no understanding of their technology or communication methods. One million years would be nothing in the scope of the universe's history, just a blink of an eye ....

    I am just showing the possibility that if we are not the only intelligence around, it COULD be that any other one may be at a COMPLETELY different place along that life evolutionary scale and we may never know.....

  12. #72
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    Quote Originally Posted by Van Rijn View Post
    ...You seem to be assuming a civilization would continue for several hundred million years. That is an extraordinary assumption - species don't last that long...
    Non-technological species, of the form of life we are aware of,..."don't last that long."

    Speaking of technological species, and potentially, life as we don't know it,...this assertion seems a pretty big assumption on its own.

  13. #73
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    VAn Rijn wrote:
    Yes, alien civilizations would likely be different, which again points to the fact that we cannot assume they would be obvious to us with the limits of our current observational capability.

    But the whole galaxy should be colonised. Or at least run by superintelligent AI beings, who keep all the intelligent biota as pets.

    You seem to be assuming a civilization would continue for several hundred million years. That is an extraordinary assumption - species don't last that long.

    If not one civilisation has managed to stay in existence long enough to colonise the galaxy, that is a so-called "Bleak Future" scenario. Logically, by the principle of mediocrity, that means we also are doomed to stay forever in the solar system and our civilisation collapse, in at most a million years or so. It also means that no interstellar-capable AI is ever developed, by us or any other race.

    With your last paragraph, you seem to assume that any civilisation is some centrally-planned, target-driven organisation. What is more, if they are becoming resource-limited when they have the entire galaxy at their disposal, would that not take us back to square one, that is, their presence would be obvious?

  14. #74
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    There is a paper discussed on this topic over at the Centauri Dreams blog site. Scroll down to the Lost in Time and Space entry, dated 29-September-2011.

    http://www.centauri-dreams.org/

    Quote (emphasis mine):
    And the median age of all civilizations is also the median age of our nearest neighbor. There’s a fifty/fifty chance it will be either younger or older than that, but there’s a 90% chance it will at least be 10% of the median, which means that in all likelihood our nearest neighbor will be hundreds of millions of years older than us. And, if you want to find an ETC of approximately our own age, say within a thousand years of ours, you will on average have to pass by a million older to vastly older civilizations.

  15. #75
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    Quote Originally Posted by kzb View Post
    ...There’s a fifty/fifty chance it will be either younger or older than that, but there’s a 90% chance it will at least be 10% of the median,...
    Does he give a link to his actual paper?

    I'd be extremely curious as to how he derives a standard deviation without more than one data point.

  16. #76
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    Quote Originally Posted by kzb View Post
    But the whole galaxy should be colonised.
    Why? Why must the ENTIRE galaxy be colonized?

    If not one civilisation has managed to stay in existence long enough to colonise the galaxy, that is a so-called "Bleak Future" scenario.
    I don't see why "Not colonizing the galaxy" = "bleak future."

    With your last paragraph, you seem to assume that any civilisation is some centrally-planned, target-driven organisation.
    No! I'm not even sure what "civilization" is supposed to mean when you're talking about hundreds of millions of years. It would certainly have to be a very different thing than what we think of today as civilization. I'm just pointing out that this is a very long time period. How, in this universe, would a "civilization" continue for such periods if it doesn't have a long term strategy? Things happen, and resources must be managed.

    What is more, if they are becoming resource-limited when they have the entire galaxy at their disposal, would that not take us back to square one, that is, their presence would be obvious?
    The evidence is that star travel is expensive and takes a long time. It doesn't appear impossible, but galactic empires based on cheap fast travel do.

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

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

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  17. #77
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    Van Rijn wrote:
    I don't see why "Not colonizing the galaxy" = "bleak future."

    Well certainly our planet will not remain habitable for ever, and neither will any other planet with a sun-like star. Any long-lived civilisation will have to cope with this problem sooner or later. This will inevitably drive interstellar travel to take place.


    I suppose you could argue that civs with a red dwarf star can carry on quite happily where they are, ever since the first habitable planets formed. However by the principle of mediocrity some civs must have had sun-like stars and some of these have long since (billions of years) ceased to be habitable.

    Why? Why must the ENTIRE galaxy be colonized?

    I think once you are interstellar capable, and have been for 100 million years, it's inevitable.

    Trakar wrote:

    Does he give a link to his actual paper?

    I'd be extremely curious as to how he derives a standard deviation without more than one data point.


    No, no link, and Google Scholar does not find it either. However if you go to the Centauri Dreams site it does give quite a bit of detail. I've asked over there if there is a link but I've not had time to return since.

  18. #78
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    I think that fungus has existed for well over 100 million years, yet
    there are still plenty of plants around that haven't been consumed
    by fungus. Do you think that civilizations are more thorough at
    consuming planets than fungi are at consuming plants?

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  19. #79
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    http://www.centauri-dreams.org/
    And the median age of all civilizations is also the median age of our
    nearest neighbor. There’s a fifty/fifty chance it will be either younger
    or older than that, but there’s a 90% chance it will at least be 10%
    of the median, ...
    I don't know much statistics, but those two points seem okay to me,
    as long as I interpret "median age of our nearest neighbor" to mean
    "the median expected age ..." obviously. The second point should
    only be significantly incorrect if the rate of civilization births/deaths
    has been changing significantly.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  20. #80
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    Quote Originally Posted by Jeff Root View Post
    I think that fungus has existed for well over 100 million years, yet
    there are still plenty of plants around that haven't been consumed
    by fungus. Do you think that civilizations are more thorough at
    consuming planets than fungi are at consuming plants?

    -- Jeff, in Minneapolis
    I can confirm that all plants that were alive 100 milion years ago have indeed been eaten by fungus, or something else that got there first.

  21. #81
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    Quote Originally Posted by kzb View Post
    I can confirm that all plants that were alive 100 milion years ago have indeed been eaten by fungus, or something else that got there first.
    Untrue. Note the existence of the coal industry.

    --- and as for relevance: The existence of coal demonstrates that not all plants were worth exploiting by the fungi and animals of the time. Similarly, it's plausible that not all star systems are worth exploiting by aliens (if they exist).

  22. #82
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    Quote Originally Posted by Jeff Root View Post
    http://www.centauri-dreams.org/

    I don't know much statistics, but those two points seem okay to me,
    as long as I interpret "median age of our nearest neighbor" to mean
    "the median expected age ..." obviously. The second point should
    only be significantly incorrect if the rate of civilization births/deaths
    has been changing significantly.

    -- Jeff, in Minneapolis
    Most statstical analyses would require at least 3 data points to get
    anything like an acceptable StDev calculation. I'm just interested in
    the methodology used to derive the stated results. If the author
    didn't mean to imply strict calculations and standard mathematical
    applications, I'd be curious as to why he used the terms that imply
    such.

  23. #83
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    Quote Originally Posted by IsaacKuo View Post
    Untrue. Note the existence of the coal industry.

    --- and as for relevance: The existence of coal demonstrates that not all plants were worth exploiting by the fungi and animals of the time. Similarly, it's plausible that not all star systems are worth exploiting by aliens (if they exist).
    All the plants would've been attacked by microorganisms including fungi as they lay rotting. Maybe this is even a required part of the coal-making process !

    Unlike plants, it's highly likely that some stellar sytems are not worth exploiting I agree. But it's just the nagging conviction that a set of billion-year old civilisations should have left an obvious trace in the galaxy. It just does not seem reasonable to me that things are so "pristine", as described above.

  24. #84
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    Trakar:
    he does not have ANY actual observations, let alone three. What he has done is calculate various expectation values based on different models and possibilities.

    The statistical predictions then follow from the numbers.

  25. #85
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    Quote Originally Posted by kzb View Post
    But the whole galaxy should be colonised. Or at least run by superintelligent AI beings, who keep all the intelligent biota as pets.
    "Should be" in this case seems to indicate only opinion, not a predictive and falsifiable hypothesis based on observation. It "feels" like it should be true; This is not a useful viewpoint in science. Why assume that older civilizations are more expansive than young ones?
    I'm a cynical optimist. I think the only way out is through, but once we get through it'll be better. Very different, but better. Howard Tayler

    It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change. Charles Darwin

    "It is the duty of the writers to seduce me into suspending my disbelief!" Paul Beardsley

    Power, Lord Acton says, corrupts. Not always. What power always does is reveal. Robert A. Caro

  26. #86
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    Quote Originally Posted by kzb View Post
    All the plants would've been attacked by microorganisms including fungi as they lay rotting. Maybe this is even a required part of the coal-making process !

    Unlike plants, it's highly likely that some stellar sytems are not worth exploiting I agree. But it's just the nagging conviction that a set of billion-year old civilisations should have left an obvious trace in the galaxy. It just does not seem reasonable to me that things are so "pristine", as described above.
    Not sure that "pristine" is an appropriate qualification, especially at our own level of development. It is entirely possible that our solar system is fully colonized by multiple byo civilizations, we are just not advanced enough to detect/recognize the colonies and signs of their presence. My arguments come down more on the side of the understanding that if there are a handful of byo tech civs in our galaxy, then there should be millions if not billions of tech civs roughly approximating our own level of development in our galaxy. It is the apparent absence of these more proximal tech civs which should be producing traces that we should be able to detect, that lead to my perspectives about technological ET.

  27. #87
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    Quote Originally Posted by kzb View Post
    All the plants would've been attacked by microorganisms including fungi as they lay rotting. Maybe this is even a required part of the coal-making process!
    No. The plants that turned into coal started off by falling into an anoxic water environment. This lack of oxygen prevented microorganisms from consuming their chemical energy. This chemical energy would eventually be available to us in coal form.

    (The reason the water environment was anoxic in the first place was because of excessive microorganism activity. Peat forms in conditions where lots and lots of dead plant material builds up in water. Initially, this abundance of food produces a burst of microorganism growth, but this ends when they use up all of the oxygen.)

    Unlike plants, it's highly likely that some stellar sytems are not worth exploiting I agree. But it's just the nagging conviction that a set of billion-year old civilisations should have left an obvious trace in the galaxy. It just does not seem reasonable to me that things are so "pristine", as described above.
    I am not so sure that things are "pristine". There are a lot of things out there, and alien signatures could be staring us in the face.

  28. #88
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    Trakar wrote:
    ....if there are a handful of byo tech civs in our galaxy, then there should be millions if not billions of tech civs roughly approximating our own level of development in our galaxy. It is the apparent absence of these more proximal tech civs which should be producing traces that we should be able to detect, that lead to my perspectives about technological ET.

    When engaged in thinking about these things, we have to appreciate the deep time aspect of the argument.

    The first habitable planets in the Galaxy should have formed about 8 billion years ago according to models. The median habitable planet is about 1 billion years older than Earth.

    The situation should actually be the opposite of what you say. There are not a handful of byo civs, and thousands of civs around our age. It is the other way round: there are thousands of very old civs and just a handful around our age. This is precisely the point of the paper.

  29. #89
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    Quote Originally Posted by kzb View Post
    Trakar wrote:
    ....if there are a handful of byo tech civs in our galaxy, then there should be millions if not billions of tech civs roughly approximating our own level of development in our galaxy. It is the apparent absence of these more proximal tech civs which should be producing traces that we should be able to detect, that lead to my perspectives about technological ET.

    When engaged in thinking about these things, we have to appreciate the deep time aspect of the argument.

    The first habitable planets in the Galaxy should have formed about 8 billion years ago according to models. The median habitable planet is about 1 billion years older than Earth.

    The situation should actually be the opposite of what you say. There are not a handful of byo civs, and thousands of civs around our age. It is the other way round: there are thousands of very old civs and just a handful around our age. This is precisely the point of the paper.
    That is indeed backwards. Why would the universe be becoming more hostile and less conducive to the formation of life? Either you are misunderstanding the paper, or I have multiple serious disagreements with author's thesis.

  30. 2011-Oct-07, 03:34 PM

  31. #90
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    Quote Originally Posted by Trakar View Post
    That is indeed backwards. Why would the universe be becoming more hostile and less conducive to the formation of life? Either you are misunderstanding the paper, or I have multiple serious disagreements with author's thesis.
    I don't think I've misunderstood the article. It does not imply the universe is becoming more hostile to life, that is not the reasoning.

    For the sake of the argument, imagine civs appearing at a constant rate over the past 5 billion years. Say one per million years on average, and they last forever. Because we have only just appeared, it stands to reason that almost all civs are substantially older than us.

    It's basically as simple as that.

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