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Thread: Evidence for ET is mounting daily, but not proven.

  1. #211
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    Quote Originally Posted by Bobunf View Post
    As I pointed out before, "Visits are clearly only one way in which we would detect extrasolar ETs. Large scale engineering projects like Dyson spheres and various types of emissions, intentional and not, would also inform us of ETs existence."

    I don't understand what is so hard about that. I suppose I could say: Since there is some possibility that interstellar travel is practical, the lack of visits is another indication of a bit of evidence for a paucity of currently active, technologically advanced extrasolar civilizations.

    Note, interstellar travel - only a possibility. I don't say one way or the other. You do accept that it's a possibility? Perhaps a very remote possibility, but I don't know of any scientific principle that would rule out any possibility that interstellar travel could ever occur. Do you?

    If I say, "Tomorrow we may receive light and heat from the sun," do you want me to "show my work?" How do I know the sun may rise tomorrow? Again, assuredly you would agree that it is at least a possibility. Perhaps a very remote possibility, but I don't know of anything that would rule it out. Do you?
    Having trouble reconciling A) interstellar travel is attainable by long stand tech civilizations and B) the lack of evidence/visits/etc suggests that there are no such long standing tech civilizations. If there aren't any than how does anyone have any confidence to suggest that IF there were than they would be able to engage in interstellar travel? Is that just an extrapolation of the fact that man has made it to the moon and back?

  2. #212
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    Quote Originally Posted by Bobunf View Post
    I agree with that, and, if so, it would make the absence of ET to date more of a problem. But to satisfy Baric, one of us should show their work.
    I believe Baric was primarily concerned with the the extraordinary efforts associated with rapid interstellar transport, and the near miracle engineering associated with physical Dyson spheres. If he would like more information regarding slower transit ventures or Dyson swarms I would be happy to provide it.

  3. #213
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    Quote Originally Posted by KABOOM View Post
    Is it a known fact that Sol is a 2nd generation star (vs a 3rd or 4th generation)?
    I generally see it listed as a third generation star.
    The first generation stars are the massive short-lived monsters that came about early in the history of the universe, when H and He were the only building blocks around.
    The second generation formed amid the ashes of the first gen stars, definitely more elements to work with but we get stars with thousands (to hundreds of thousands) times less metallicity than our own Sun.
    Third generation stars tend to be metal rich by definition.

  4. #214
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    Quote Originally Posted by KABOOM View Post
    Having trouble reconciling A) interstellar travel is attainable by long stand tech civilizations and B) the lack of evidence/visits/etc suggests that there are no such long standing tech civilizations. If there aren't any than how does anyone have any confidence to suggest that IF there were than they would be able to engage in interstellar travel? Is that just an extrapolation of the fact that man has made it to the moon and back?
    LOL, well, perhaps not quite so big a leap, but yes, there is an element of that.
    We can't know what we don't know, but, the steady progression of technological
    development would eventually lead to a point where the understandings and
    hardware required for such efforts are available. We can't speak to the will to employ
    these technologies, but the extrapolation is reasonable.
    Last edited by Trakar; 2011-Jan-12 at 07:25 PM. Reason: double word correction

  5. #215
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    Quote Originally Posted by IsaacKuo View Post
    If interstellar travel is impossible, then there could be billions of civilizations out there which light beam radio communications at us and no reason to fear interstellar communications. So the question is--where are the signals? (Obvious answer--most or all of them could be so far away that it would be expensive and seemingly pointless to send signals at us. So maybe there are only a hundred civilizations in range, and it just so happens that none of them feel like doing it.)
    That answer may be obvious and easy, but is it plausible? If there were a hundred technologically advanced civilizations within, say, a thousand light years of Earth (5 million stars), they would be aware of:

     Earth’s temperature, size, orbital stability, and the presence of oceans and land
     abundant life on Earth from methane and ozone out of thermal equilibrium
     intelligent life from the effects of pervasive agriculture, extensive metal working and coal burning
     they might be able (from their far more sophisticated understanding of biological and social evolution, and industrial pollutants) to determine our state of technological development.

    These are capabilities we will begin to deploy perhaps in this decade, and the full extent of which are conceivable within a century.

    For there not to be any deliberate attempts at communication would require monolithic behavior within all the groups within all 100 civilizations. Such attempts would not be expensive for such a civilization. The Arecibo radio telescope in Puerto Rico, has a one megawatt radio transmitter which could be picked up an Arecibo sized receiver at 320 light years. The observatory has a budget of about $10 million per year. I would be pretty surprised if we could not send a considerable more powerful transmission at considerably less cost by 2200.

    There might be hundreds of thousands of entities in each of the 100 postulated advanced civilizations that would be capable of spending the equivalent of a few million dollars per year on such a project. It seems most implausible that, amongst these millions of entities, none would send messages, perhaps to all nearby planets that have identified technological civilizations.

    There could be innumerable motives for such an undertaking: academic curiosity, altruism, spreading the Good News, sending their obituary, for instance. Some might be delusional and think they are communicating with their ancestors.

    Whatever, it seems far likelier that a bunch of these entities would send us a message rather than maintain stony and boring silence. It only takes one.

  6. #216
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    Quote Originally Posted by baric View Post
    That is correct.
    Which aspect are you most interested in? There is value in this discussion in relation to the subject but we have to be careful to keep the discussion relevent to this thread's topic and not just wander into a more general discussion of interstellar transport. As background material, here are a few related considerations of relevence:

    "The Fermi Paradox: An Approach Based on Percolation Theory" - Geoffrey A. Landis - http://www.geoffreylandis.com/percolation.htp

    Stephen Hawking: Why Isn't the Milky Way "Crawling With Self-Designing Mechanical or Biological Life?" - http://www.dailygalaxy.com/my_weblog...ical-life.html

    "An instrument-based method to search for extraterrestrial interstellar robotic probes" - http://www.sunstar-solutions.com/sun...BIS-SETV01.pdf

    "The search for extraterrestrial intelligence" - http://www.bioinf.uni-leipzig.de/~il...gy_nature5.pdf

    Temporal Aspects of the Interaction among the First Galactic Civilizations: The "lnterdict Hypothesis" - http://www.users.globalnet.co.uk/~mfogg/fogg1987.pdf
    [table one is of interest - I know it is oft repeated, but this provides a good RoT guide for common considerations of how long galactic colonization takes]

    "The Grand Analogy: History of the Idea of Extraterrestrial Life" - http://www.bigear.org/CSMO/HTML/CS05...ll.htm#cs05p02

    Not anything that is required reading for further discussion, just some basic background reading/reference considerations for this general thread.

  7. #217
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    Quote Originally Posted by Trakar View Post
    Which aspect are you most interested in?
    Some legitimate arguments about the viability of interstellar travel as opposed to simply presuming it is inevitable.

    Quote Originally Posted by Trakar View Post
    "The Fermi Paradox: An Approach Based on Percolation Theory" - Geoffrey A. Landis - http://www.geoffreylandis.com/percolation.htp
    From this article:
    The analysis is based on two key assumptions. First, it is assumed that interstellar travel is possible, but difficult, and thus that there is a maximum distance over which colonies can be directly established.
    They did not show their work!

    Quote Originally Posted by Trakar View Post
    Stephen Hawking: Why Isn't the Milky Way "Crawling With Self-Designing Mechanical or Biological Life?" - http://www.dailygalaxy.com/my_weblog...ical-life.html
    This is just a brief list of some possible explanations for the Fermi Paradox which have all been discussed in this thread. There's not a lot of meat in it!

    Quote Originally Posted by Trakar View Post
    "An instrument-based method to search for extraterrestrial interstellar robotic probes" - http://www.sunstar-solutions.com/sun...BIS-SETV01.pdf
    From the article:
    Once an advanced ETI civilization has overcome certain major technological challenges, like practical interstellar travel, what might the probe missions invovle and what behaviors might be observed?
    Once again, beginning with an assumption of interstellar travel and then proceeding onward. They did not show their work!


    Quote Originally Posted by Trakar View Post
    "The search for extraterrestrial intelligence" - http://www.bioinf.uni-leipzig.de/~il...gy_nature5.pdf
    Not really relevant to my concerns. Interesting article, though!

    Quote Originally Posted by Trakar View Post
    Temporal Aspects of the Interaction among the First Galactic Civilizations: The "lnterdict Hypothesis" - http://www.users.globalnet.co.uk/~mfogg/fogg1987.pdf
    [table one is of interest - I know it is oft repeated, but this provides a good RoT guide for common considerations of how long galactic colonization takes]
    Almost pure fantasy, imo. This link was the richest of all. Not only did they not "show their work", they dismissed the requirement to show their work out of hand (with a single reference to a 1984 paper), proceeded as if interstellar travel was a given fact and all that was left to debate was the rate of expansion. Balderdash!

    It amazes me how easily skeptical some people are with regards to abiogenesis (an established occurrence) but then throw that scientific attitude completely out the door when the topic of interstellar travel arises (an unproven possibility).

    Quote Originally Posted by Trakar View Post
    "The Grand Analogy: History of the Idea of Extraterrestrial Life" - http://www.bigear.org/CSMO/HTML/CS05...ll.htm#cs05p02
    That's a nice summary article, but doesn't really touch upon the issue of interstellar travel.

    Not anything that is required reading for further discussion, just some basic background reading/reference considerations for this general thread.
    No, thank you for the links! I find the topic fascinating.

  8. #218
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    Quote Originally Posted by KABOOM View Post
    Is it a known fact that Sol is a 2nd generation star (vs a 3rd or 4th generation)?
    It is known to be 4.5 billion years into its life... of about 10 / 12 billion years. It could be a third generation star. Most likely a second generation star if you factor the universe is 13,7 billion years old. How short was its previous stellar parents life ? No. I do not know that.
    What we do know is that some of the mater found on earth are not from the solar mass of sol.

  9. #219
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    Quote Originally Posted by Trakar View Post
    I generally see it listed as a third generation star.
    The first generation stars are the massive short-lived monsters that came about early in the history of the universe, when H and He were the only building blocks around.
    The second generation formed amid the ashes of the first gen stars, definitely more elements to work with but we get stars with thousands (to hundreds of thousands) times less metallicity than our own Sun.
    Third generation stars tend to be metal rich by definition.
    Thank you for the response.

    Is the chemistry/physics well known as to how stars initially comprised of just Hydrogen and Helium upon their Supernova'd deaths gave rise to new elements who in turn upon their demise gave birth to further new types of metals?

    Will 3rd generation stars like Sol (or bigger ones) upon their deaths continue this trend of spawning still further heretofore unknown metals? If so, does this somehow increase the going-forward (yes billions of years downstream) potentiality for life in the universe as the presence of metals increases?

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    Yes, it might...

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    Why isn't the Milkyway teaming with life ? or where are the aliens ? Can only be answered by approximation's of facts unknown.
    I think the 'best' answer still is... It might be. We have not seen any sign of it yet does NOT suggest its not. Does it ?

  12. #222
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    Quote Originally Posted by KABOOM View Post
    Is the chemistry/physics well known as to how stars initially comprised of just Hydrogen and Helium upon their Supernova'd deaths gave rise to new elements who in turn upon their demise gave birth to further new types of metals?
    It's physics, there's no chemistry involved in nucleosynthesis, and I think it is very well known.

    Quote Originally Posted by KABOOM View Post
    Will 3rd generation stars like Sol (or bigger ones) upon their deaths continue this trend of spawning still further heretofore unknown metals?
    No unknown metals will be produced.

  13. #223
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    Quote Originally Posted by IsaacKuo View Post
    If interstellar travel is possible, then there could be one civilization which has dominated our region of the galaxy. So the question is--why is this one civilization not obvious to us? (Obvious answer--it's just one civilization, so maybe they just didn't care to colonize our star system.)

    So, the question of whether interstellar travel is possible changes the problem, but either way there are easy answers to the Fermi Paradox.
    Maybe easy and obvious, but plausible?

    Under this circumstance (one galactic civilization), it’s required, for us not to be aware of ETs existence, that they not only do not colonize, but do not visit (even with robotic agents), do not communicate, do not have any visible engineering projects and not enough energy leakage anywhere and anyway so as to be obvious. It also assumes monolithic behavior within the civilization. They would be spread across millions, maybe billions, of worlds, separated by tens of thousands of light years and time, and they would all act the same. That does not seem likely.

    Each world could have hundreds of thousands of various types of groups and entities that could spend the equivalent of a few million dollars a year on communication with worlds identified as having a technological civilization. Across the galaxy there could easily be trillions of such entities. And they all act the same. That does not seem likely.

    Some such entities might also send visitors—robotic or staffed—from motives of altruism, curiosity, enlightened self-interest, from religious, ideological, philosophical and other enthusiasms

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    Quote Originally Posted by baric View Post
    The Zoo Hypothesis doesn't really make any sense when you examine it, especially when you look at geological timescales.
    Here's a paper which you might broaden your perspective: Brane Worlds, the Subanthropic Principle and the Undetecability Conjecture.

    Abstract: In the recent article ‘Conflict between anthropic reasoning and observation’ (gr-qc/0303070) Ken D. Olum, using some inflation-based ideas and the anthropic premise that we should be typical among all intelligent observers in the Universe, arrives at the puzzling conclusion that ‘we should find ourselves in a large civilization (of galactic size) where most observers should be, while in fact we do not’. In this note we discuss the intriguing possibility whether we could be in fact immersed in a large civilization without being aware of it. Our conclusion is that this possibility cannot be ruled out provided two conditions are met, that we call the Subanthropic Principle and the Undetectability Conjecture. The Subanthropic Principle states that we are not typical among the intelligent observers from the Universe. Typical civilizations of typical galaxies would be hundreds of thousands, or millions, of years more evolved than ours and, consequently, typical intelligent observers would be orders of magnitude more intelligent than us. The Undetectability Conjecture states that, generically, all advanced civilizations camouflage their planets for security reasons, so that no signal of civilization can be detected by external observers, who would only obtain distorted data for disuasion purposes. These conditions predict also a low probability of success for the SETI project. We also argue that it is brane worlds, and not inflation, what dramatically could aggravate the ‘missing-alien’ problem pointed out first in the fifties by Enrico Fermi.
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

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    What I find strange is the reluctance to consider abiogenesis as fact. Are we unconsciously allowing for a theistic origin of life on Earth, which in turn allows for no natural abiogenesis? Either it happens and is a natural process or it does not and is not.

    The difficulties with the Fermi paradox, if one accepts abiogenesis as fact, relate to interstellar travel, mean distances between advanced civilizations, and so forth. If, say, there is only one advanced civilization per galaxy, we may never have experimental proof nor contact, but that does not disprove abiogenesis.

    Life's around out there, somewhere.
    For each man, according to the measure of his intelligence, must speak what he can speak, and do what he can do. - Alfred, King of Wessex
    Calm down, have some dip. -George Carlin

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    Quote Originally Posted by Hlafordlaes View Post
    What I find strange is the reluctance to consider abiogenesis as fact. Are we unconsciously allowing for a theistic origin of life on Earth, which in turn allows for no natural abiogenesis? Either it happens and is a natural process or it does not and is not.
    Of course it is only theists who do not accept abiogenesis as fact, it being a natural consequence of the universe. For the rest of us, the question is whether or not it occured on Earth. There are plentiful contending theories as you may know, and because of this theists persist with god-of-the-gaps arguments.

    The difficulties with the Fermi paradox, if one accepts abiogenesis as fact, relate to interstellar travel, mean distances between advanced civilizations, and so forth. If, say, there is only one advanced civilization per galaxy, we may never have experimental proof nor contact, but that does not disprove abiogenesis.
    Life's around out there, somewhere.
    Yes, whether or not we attain proof of advanced ETs, it is clear our universe is naturally geared to produce life, and it likely happened as soon as the right ingredients were available.
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

  17. #227
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    Quote Originally Posted by A.DIM View Post
    Here's a paper which you might broaden your perspective: Brane Worlds, the Subanthropic Principle and the Undetecability Conjecture.

    Abstract: In the recent article ‘Conflict between anthropic reasoning and observation’ (gr-qc/0303070) Ken D. Olum, using some inflation-based ideas and the anthropic premise that we should be typical among all intelligent observers in the Universe, arrives at the puzzling conclusion that ‘we should find ourselves in a large civilization (of galactic size) where most observers should be, while in fact we do not’. In this note we discuss the intriguing possibility whether we could be in fact immersed in a large civilization without being aware of it. Our conclusion is that this possibility cannot be ruled out provided two conditions are met, that we call the Subanthropic Principle and the Undetectability Conjecture. The Subanthropic Principle states that we are not typical among the intelligent observers from the Universe. Typical civilizations of typical galaxies would be hundreds of thousands, or millions, of years more evolved than ours and, consequently, typical intelligent observers would be orders of magnitude more intelligent than us. The Undetectability Conjecture states that, generically, all advanced civilizations camouflage their planets for security reasons, so that no signal of civilization can be detected by external observers, who would only obtain distorted data for disuasion purposes. These conditions predict also a low probability of success for the SETI project. We also argue that it is brane worlds, and not inflation, what dramatically could aggravate the ‘missing-alien’ problem pointed out first in the fifties by Enrico Fermi.
    Sounds very "just so" with very little in the way of positive confirmatory data in support of their speculations, overall it is well called a "speculative opinion article" rather than a scientific paper of considerations and finding.

  18. #228
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    Quote Originally Posted by astromark View Post
    It is known to be 4.5 billion years into its life... of about 10 / 12 billion years. It could be a third generation star. Most likely a second generation star if you factor the universe is 13,7 billion years old. How short was its previous stellar parents life ? No. I do not know that.
    What we do know is that some of the mater found on earth are not from the solar mass of sol.
    First Gen stars only have a lifespan of a few million years. big huge monsters that burn through their fuel quickly and detonate in blasts visible across the universe forming black holes.
    (note - it is technically possible for a first gen star to form right now, it just has to form in a region that hasn't picked up the ashes from stellar evolution through the last 13 Billion years or so)

    Second Gen stars are much like Third gen stars, in that they come in a variety of sizes and life spans, the primary difference is in proportion of elements heavier than H/He. There is no definitively clear second/third gen dividing line, and this is one reason the Sun is occassionally still listed as a 2nd gen star. (as noted above, second gen is more of a composition issue than a time of formation issue)

    We know that our Sun formed about 5 billion years ago, and at that time it was probably among the earliest stars with its level of metals to form (not the earliest, but among the early examples of this type of star). Star metallicity, however, may well be a double edged sword with too little and too much both being potential negatives with regards to the potential for life to arise among their planetary systems.

  19. #229
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    Quote Originally Posted by Hlafordlaes View Post
    What I find strange is the reluctance to consider abiogenesis as fact. Are we unconsciously allowing for a theistic origin of life on Earth
    Being a theist would still allow for an infinite number of originations of life, with or without abiogenesis.

    Being an atheist would still allow the possibility that abiogenesis is very improbable; say the reciprocal of the number of stars in the observable universe. Or even the reciprocal times 10^ -9. Either probability would handily explain the Fermi paradox.

    That examples of more than one abiogenesis have not been found on Earth or anywhere else in our solar system suggests that the probability of abiogenesis occurring may not be high.

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    Quote Originally Posted by A.DIM View Post
    it is clear our universe is naturally geared to produce life, and it likely happened as soon as the right ingredients were available.
    I don't see how you can say that abiogenesis is likely. You have one example of it occurring, and some evidence that it didn't happen very often in our solar solar system. You have no idea how abiogenesis works.

    How is it possible to draw probability conclusions from one example and within a very limited and incomplete theoretical structure?

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    I was away since Christmas eve until today, so I'm replying to a
    post from December 27. I see that others have replied to it, but
    I haven't read those replies yet.

    Quote Originally Posted by CaptainToonces View Post
    Quote Originally Posted by Jeff Root View Post
    There is no reason to expect that we would see any evidence of
    intelligent ET life even if it is extremely common.
    Yes, there is. If intelligent ET life were common we would see
    evidence of it everywhere.
    There is no reason to think that.

    You personally might expect to see evidence of intelligent ET
    life in many places if it were common, but even you would not
    expect to see it "everywhere". You did not say what you
    actually meant. You meant that you would expect to see
    evidence in many places. I do not share that expectation,
    since there is no good reason for it.

    Quote Originally Posted by CaptainToonces View Post
    In fact, we probably would've been born into subservience of
    such life rather than randomly evolved in a lonely corner of the
    universe.
    I interpret that to mean you think life on Earth would probably
    have originated elsewhere and have been brought here rather
    than originating here. I disagree. There is no reason to think
    that the relative commonality of intelligent ET life would make
    independent origin and development of life on Earth improbable.
    Given that the evidence we do have suggests that life did
    independently originate and develop on Earth, we can surmise
    that the same has happened elsewhere. We cannot surmise that
    its happening elsewhere made it unlikely to happen here.

    Quote Originally Posted by CaptainToonces View Post
    But that anthropomorphic line is a little philosphical and not my
    main point anyway. The main point is based on the observation of
    how quickly human intelligence is developing, on geological time
    scales. For God's sake man we have only been writing words for
    4,000 years. If you have any hope for our ability to one day bridge
    the vast gap between star systems, do you think we could do it in
    100 million years?
    I agree that human intelligence developed to its current level
    very quickly, and that human technology has developed to its
    current level even more quickly. I do have hope that humans
    will be able to communicate with and maybe even travel to
    other star systems. I have no idea how long it will take, if it
    ever comes about. First contact may have been made today,
    and we'll find out all about it in the morning news. Or we might
    give up looking and never make contact.

    Quote Originally Posted by CaptainToonces View Post
    And if you can spread successfully from one star system to
    another, you could spread to many many star systems.
    There are an enormous number of assumptions behind that
    assertion, most of which you know nothing about.

    Quote Originally Posted by CaptainToonces View Post
    So if civilizations like our's were common, that is to say
    INTELLIGENT life, would it not be common for some of those
    civilizations to last millions of years and spread through
    hundreds, thousands, millions of worlds?
    Completely unknown.

    I'll repeat that: It is completely unknown how long a
    civilization can last or is likely to last, and completely
    unknown what a civilization can accomplish, will accomplish,
    or is likely to accomplish during its existence.

    Quote Originally Posted by CaptainToonces View Post
    Would that not reveal some sort of evidence? Any sort of
    evidence?
    You tell me. What sort of evidence? I am not aware of any
    sort of evidence that we should have seen if intelligent ET
    life is common.

    Quote Originally Posted by CaptainToonces View Post
    We clearly have had an impact on the Earth.
    Yes, I agree. We have affected the Earth in many ways.

    Quote Originally Posted by CaptainToonces View Post
    Someone observing our solar system (not even saying that have
    to be doing it from another star) would clearly see the impact of
    intelligent life on this planet's surface.
    Not if they didn't come to Earth. Evidence of intelligent life on
    Earth is easy to see from low Earth orbit. From the distance of
    the Moon, or farther, radio transmissions are probably the only
    detectible evidence of intelligent terrestrial life. At the distance
    of Mars, those radio signals are incredibly difficult to detect.
    At the distance of Proxima Centauri, there is almost no hope at
    all of detecting intelligent life on Earth. Just detecting that the
    Earth exists would be an impressive accomplishment.

    Quote Originally Posted by CaptainToonces View Post
    So why would we not see evidence of intelligent life throughout
    the galaxy if it were, as you say, "common"?
    Why would we see evidence? You have given no reason
    at all for your expectation.

    What evidence would you expect to see? You have given
    no indication, which suggests that your expectation is based
    on nothing.

    Quote Originally Posted by CaptainToonces View Post
    These potential civilizations have had billions of years to appear.
    I agree. There has been time for many civilizations to appear and
    also to die off. I think intelligent life is probably quite common in
    the Universe and in our Galaxy. I hope that definitive evidence of
    it will be found in my lifetime, and I'll do what I can to make that
    happen. It certainly won't happen if people stop working on 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

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    Quote Originally Posted by Bobunf View Post
    I don't see how you can say that abiogenesis is likely. You have one example of it occurring, and some evidence that it didn't happen very often in our solar solar system. You have no idea how abiogenesis works.
    We have learned that pre-biotic molecules are quite common in interstellar clouds. We know that complex organic molecules can form in environments like Titan. We have found a wide variety of organic molecules aboard meteorites. Due to their ubiquity, I do not think it's a stretch to say that the existence of complex organic molecules is inevitable in the vast majority of the billions of planetary systems in our galaxy.

    The gap between what we know is common and what remains unique has been shrinking noticeably over the past few decades.

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    Quote Originally Posted by baric View Post
    We have learned that pre-biotic molecules are quite common in interstellar clouds. We know that complex organic molecules can form in environments like Titan. We have found a wide variety of organic molecules aboard meteorites. Due to their ubiquity, I do not think it's a stretch to say that the existence of complex organic molecules is inevitable in the vast majority of the billions of planetary systems in our galaxy.

    The gap between what we know is common and what remains unique has been shrinking noticeably over the past few decades.
    I perceive the opposite. We have gone from anywhere we have liquid water, a source of energy and time, to a situation where even in the most unusual but optimum conditions, life, and especially complex life, may be a hit or miss proposition.

    The Implications of the Early Formation of Life on Earth - http://arxiv.org/PS_cache/arxiv/pdf/...807.4969v1.pdf

    Conclusion
    The fact that life arose surprisingly early after the formation of the Earth can be used as evidence
    for the hypothesis that abiogenesis is easy, and hence supports the conclusion that life is common
    in the universe. However, the evidence is not as conclusive as has been claimed. Specifically,
    this study has highlighted the fact that knowledge of the early abiogenesis time on Earth is still
    compatible with the following hypothesis: that life is extraordinarily rare in the universe, perhaps
    even only on Earth, and we observe early abiogenesis due to chance (we’d have to be moderately
    lucky, but not obscenely so). This conclusion differs from Lineweaver & Davis (2002) because they
    unwittingly made overconfident prior assumptions. Hence, unless there is a direct detection, the
    answer to the perennial question “are we alone” remains “nobody knows”.

    The energetics of genome complexity - http://www.nature.com/nature/journal...ture09486.html

  24. #234
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    Quote Originally Posted by Trakar View Post
    I perceive the opposite. We have gone from anywhere we have liquid water, a source of energy and time, to a situation where even in the most unusual but optimum conditions, life, and especially complex life, may be a hit or miss proposition.

    The Implications of the Early Formation of Life on Earth - http://arxiv.org/PS_cache/arxiv/pdf/...807.4969v1.pdf
    This was a short article which spent 6 pages explaining why you can't draw a statistical conclusion when N=1. It doesn't really support the case that abiogenesis is rare, only that we don't have enough information to conclude it is common.

    The energetics of genome complexity - http://www.nature.com/nature/journal...ture09486.html
    Paywall.. I can't really comment on an abstract :/

  25. #235
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    Memo to all, let's keep the religious part out of this discussion.
    The discussion of whether or not there is a theistic bias is completely inappropriate here.
    Also, as you cannot know all theists, all general remarks can be insulting to some of them.
    All comments made in red are moderator comments. Please, read the rules of the forum here and read the additional rules for ATM, and for conspiracy theories. If you think a post is inappropriate, don't comment on it in thread but report it using the /!\ button in the lower left corner of each message. But most of all, have fun!

    Catch me on twitter: @tusenfem
    Catch Rosetta Plasma Consortium on twitter: @Rosetta_RPC

  26. #236
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    Quote Originally Posted by Jeff Root View Post
    At the distance of Proxima Centauri, there is almost no hope at all of detecting intelligent life on Earth. Just detecting that the Earth exists would be an impressive accomplishment.
    This is an impressive accomplishment of which we may well be capable in this decade. More than 500 exoplanets have already been discovered, and equipment and techniques improve almost daily. Advances in astronomical imaging such as active optics, adaptive optics, speckle imaging, aperture synthesis, lucky imaging, coronagraphy, interferometry and nulling interferometry have greatly enhanced and continue to enhance the possibilities of ground based imaging. Even more capable ground and space based instruments and techniques are under development. Within this decade we may even be able, for nearby Earth like planets, to

    > determine their existence, size and orbital parameters
    > infer the existence of oceans (bluer), continents (redder), and even vegetation (plants reflect light more strongly at near-infrared wavelengths than in normal visible light)
    > detect out of thermal equilbrium methane, oxygen, ozone and nitric oxide

    We may even be able to detect industrial gases and other pollutants, which could, not only reveal the presence of intelligent life, but allow approximations of the technological abilities of such a civilization.

    Some of this may have to wait for the next decade, the 2020s. Although cost, completion and capability estimates of incomplete or unbuilt projects are always dubious, it seems likely that many of the goals of outstanding space and astronomical projects will be met by then; especially considering all of the various technologies, funding sources and involvement of many different nations and institutions.

    If we look even a short way into the future--say the next century--we should have immensely increased capabilities in identifying the existence and characteristics of extrasolar planets, of detecting life from an analysis of atmospheric gases and other properties of such objects. We may also be able to develop a good grasp of the stage of evolution of such life based on our increasing knowledge of evolutionary biology and social development. We should be able to identify signals of agriculture, metal working and industrial pollutants.

    Based on what we have done, expect to do in the near future and should be capable of a bit further into the future, it seems to me that we should, eventually, have very little trouble detecting a technologically advanced civilization out to several hundred light years, if not considerably further.
    Last edited by Bobunf; 2011-Jan-14 at 07:15 AM.

  27. #237
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    Quote Originally Posted by baric View Post
    The gap between what we know is common and what remains unique has been shrinking noticeably over the past few decades.
    What remains in this gap is abiogenesis. We do not know how this worked. Since we don't know what happened, I think it's really hard to predict how common is whatever it is that happened to produce life. We have found many chemicals all over the place which narrows the difficulties of abiogenesis. But we also have not found a second biogenesis on Earth or anywhere else in our solar system. Which, to me, restrains the ubiquity of this happening.

    This century we may find another abiolgenesis on Earth or elsewhere in out solar system; but I would hardly call that outcome a certainty, and I think the probability declines with time. This century we may hear from ET, but I would hardly call that a certainty. This century we may figure out how abiogenesis works; but I would hardly call that a certainty.

    If we don't find another biogenesis in our solar system, that doesn't mean that it didn't occur here or elsewhere. But such lack of evidence will constrain the probabilities.

    The other line of evidence is the Fermi paradox. That we've had no contact with ETs doesn't mean they don't exist; but it does constrain the probabilities.

    There are weak hints: life started early on Earth, complex organic molecules and extrasolar planets abound; but we haven't seen a second abiogenesis; and we haven't seen any ETs.

    In the absence of a theoretical understanding of abiogenesis, how can anyone say abiogenesis is inevitable or certain?

  28. #238
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    Quote Originally Posted by Bobunf View Post
    What remains in this gap is abiogenesis.
    Yes, I agree, but I contend that there will always be a gap there. Abiogenesis requires the existence of some extremely complex molecules that simply cannot arise spontaneously or naturally over a short period of time. Even human attempts at artificially creating life, if successful, will be tainted by the reality that human intervention is required.

    The only way to resolve this issue is to discover an undeniable instance of another abiogenesis. This is why there is so much interest in the biochemistry of Titan and also in the "shadow" evolution recently suggested by the arsenic-based chemistry recently announced by NASA.

    Abiogenesis could actually be very common yet still unique within our system. If that is the case, the gap may never be fully closed absent ET contact. I think you and I are in considerable agreement on this point.

    The other line of evidence is the Fermi paradox. That we've had no contact with ETs doesn't mean they don't exist; but it does constrain the probabilities.
    For the Fermi Paradox to be real (i.e. a paradox), you are required to accept two independent assumptions... 1) abiogenesis & intelligence are relatively common and 2) either interstellar travel is possible or technological civilizations are extremely long-lived

    There is reason to believe that 1) is true and 2) is false, thus eliminating the paradox without constraining the probability for abiogenesis.

    In the absence of a theoretical understanding of abiogenesis, how can anyone say abiogenesis is inevitable or certain?
    cogito ergo sum?

  29. #239
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    Quote Originally Posted by Bobunf View Post
    What remains in this gap is abiogenesis. We do not know how this worked. Since we don't know what happened, I think it's really hard to predict how common is whatever it is that happened to produce life. We have found many chemicals all over the place which narrows the difficulties of abiogenesis. But we also have not found a second biogenesis on Earth or anywhere else in our solar system. Which, to me, restrains the ubiquity of this happening.
    Not by much, though. There could have been many instances of abiogenesis on Earth, but we simply haven't found them because the resulting primitive life forms were wiped out by highly refined and aggressive life forms that had many millions or billions of years head start on them. It's worse than looking for a needle in a haystack. It's like looking for a food crumb in a swarm of ants. Good luck finding it before it's devoured!
    This century we may find another abiolgenesis on Earth or elsewhere in out solar system; but I would hardly call that outcome a certainty, and I think the probability declines with time.
    The probability for finding evidence of another abiogenesis event on Earth may plausibly be declining, but we have hardly even looked in the rest of the solar system. As far as we can tell, life requires liquid water and we have not looked any of the places with liquid water yet (a very difficult challenge).

    So far, our only evidence consists of Martian rocks which might have come from places where there used to be liquid water...but this is extremely limited evidence. Consider taking a random rock from Earth--chances are extremely high that it contains no fossils of any sort. So, even if life used to be abundant on Mars we would need to have been lucky to see any fossil evidence of it in our limited Martian samples.

    So, we're still at a very early stage in which our probability of finding abiogenesis elsewhere in the Solar System is increasing.

  30. #240
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    Quote Originally Posted by baric View Post
    For the Fermi Paradox to be real (i.e. a paradox), you are required to accept two independent assumptions... 1) abiogenesis & intelligence are relatively common and 2) either interstellar travel is possible or technological civilizations are extremely long-lived

    There is reason to believe that 1) is true and 2) is false, thus eliminating the paradox without constraining the probability for abiogenesis.
    What is the reason to believe 2) is false? Show your work.

    For 2) to be false, two things are required: Interstellar travel must be impossible AND technological civilizations are short-lived (by some definition of short-lived; use your own since you're making the claim).

    Thus, you need to provide two arguments--one argument that interstellar travel is impossible and another argument that technological civilizations are short-lived.

    (Note that we humans have already sent five spacecraft on interstellar journeys.)

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