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Existance of extraterestrial form of life

  1. Oct 22, 2012 #1
    Do you beleive in existance of extra-terrestrial beings? why/Why not?
  2. jcsd
  3. Oct 22, 2012 #2
    Yes, I believe that extra-terrestrial beings exist.

    I do not have evidence for this fact, so I acknowledge that I can be wrong, however, the chances that they exist seem pretty large to me.
    I do not believe extra-terrestrial beings visited earth. That just seems silly.
  4. Oct 22, 2012 #3
    Why so?
  5. Oct 22, 2012 #4
    Other people can explain it better than me:


  6. Oct 22, 2012 #5

    Why, because of probability, even though the following is a quote and webcomic, the combination between the two of them accurately depicts my opinion.

    Space is big. Really big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. -Douglas Adams
    Also: xkcd.com/1123/ All you need is H and time.

    As for why we haven’t heard from good old ET take a look at http://en.wikipedia.org/wiki/Drake_equation
  7. Oct 22, 2012 #6


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  8. Oct 22, 2012 #7
    I've heard people say that probability states that likelihood is high, but how is this worked out?

    From what I can tell of extraterrestrial life probability, we can't judge how common it is when the only point of reference we have is ourselves. Currently we're trying to judge how many things are in a room with no lights and without a torch. Are we the only things in the room? We'll only find out when we find it.
  9. Oct 22, 2012 #8


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    Did you follow the link above to the wiki on Drake's equation?
    There are of course a number of unknowns in that equaion, but we are getting better data. We e.g. now that that there are planets in a very large proportion of solar systems, and there was no data at all about this when Drake first wrote down his equation.
  10. Oct 22, 2012 #9
    Yes I did and I find it insufficient to suggest that we are entitled to state likelihood is anything but pitiful no matter how much we want to think life out there is likely - this is wishful thinking, not science.

    How many have we found that can support life? How do we know it can support life with any degree of certainty? Surely any planet is capable of supporting life until we know what all life of all varieties is and isn't capable of surviving. We only have an idea of the upper and lower limits on Earth and even then we often find a new record breaking living organisms.

    So far, we only know of one, Earth, out of hundreds of planets. Drake's Equation goes on to civilisations... we're still stuck at "well, we haven't found anything microbial yet." in which case, probability is looking pretty low.

    EDIT: Sorry I guess I wasn't clear. What I meant by "how is this worked out?" was "how can people come to such an optimistic conclusion?"
    Last edited: Oct 22, 2012
  11. Oct 22, 2012 #10
    The problem with this argument is that if even one of the factors in Drake's equation is unknown, then the entire equation fails. I don't mean to say that the equation is entirely useless, only that it fails to predict whether or not we are alone. Here are the factors.

    R = the average rate of star formation per year in our galaxy
    fp = the fraction of those stars that have planets
    ne = the average number of planets that can potentially support life per star that has planets
    fℓ = the fraction of the above that actually go on to develop life at some point
    fi = the fraction of the above that actually go on to develop intelligent life
    fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
    L = the length of time for which such civilizations release detectable signals into space
  12. Oct 22, 2012 #11


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    Whilst space is big and old and we know that life is possible we have no real idea of how likely it is. Earth could be a one in one google chance, or it could be far lower. At the moment we don't know.

    Without a comprehensive theory of abiogenesis we're in the dark on this one.
  13. Oct 22, 2012 #12
  14. Oct 22, 2012 #13


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    I agree. But the point I was making was that we at least know more now than we did 50 years ago. We a getting close to having good estimates for R, fp and if we limit ourselves to life "as we know it" we could presumably also estimate ne (planets with liquid water etc). I suspect most astrobiologists would agree that fl is a farily large number. What is missing is good estimates for fl and fc (we can use ourselves as an example to put a lower bound for L, lets say at least 100 years).

    Even fairly pessimistic estimates tend to put he number of detectable civilizations in our galaxy to be larger than 1.

    Also, the question was extraterestial LIFE -not neccesarily intelligent- in which case the last four factors disapear. This means that the only uncertainty is fl; which -as mentioned above- should be prettly large.
  15. Oct 22, 2012 #14
    But knowing about planets doesn't really count for anything. If we walk past a house in the street, we can say with a good level of probability someone lives in it, because it was purposely built to have someone live in it. Planets on the other hand, it doesn't matter how inhabitable they are, they could be what we would call a paradise, but if they don't have any life on them then it's all pretty futile, right? Why is "knowledge of average pre-discovery life" (ie life we know exists at the moment) not get factored in? You could count a million planets are that inhabitable, but if only one has provable life on it, surely each new inhabitable but lifeless planet decreases the likelihood?

    How many of the planets that we have found, have been super-Earths, earth-like, hot jupiters or earths so close to their parent star they're screwed?

    "tend to"? I'm assuming that every estimate has to be larger than one, due to the amount of civilisations on Earth.

    I agree, I wouldn't bother with above f for the time being, I think achieving this will be a mountainous task.

    I think it would be very interesting (understatement of 2012) to find life off of Earth and I want there to be something. I think a lonely existence in the universe would be a bit of a downer (runner up understatement of 2012). However, we have not found anything that comes really close to Earth yet, have we? An interesting perspective is the idea of the seed. There must be life out there because where did our life come from if abiogenesis turns out to be unfeasible? (even if it happened on Earth, doesn't mean it will happen elsewhere). We could turn this on its head - maybe we are the seeding life for the universe?

    Sorry if I come across as aggressive or argumentative in this post, f95toli, it's not my intention, I was just trying to be clear cut with my criticism. If I'm entirely wrong on the premises of my points then I'll be happy to concede.
  16. Oct 22, 2012 #15


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    My thoughts exactly !
  17. Oct 22, 2012 #16
    true, they exist and they may be looking for extra-terrestrial beings too.
    Last edited by a moderator: Oct 22, 2012
  18. Oct 22, 2012 #17
    Anyway, I wonder if ET speculation is science, as in using the scientific method (Mm's Feynman lecture). Here is the hypothesis: intelligent ET exists/does not exist. Compute - Drake's equation; compare to nature, now what? Fail or are we too impatient and should we listen another million years?

    Also why is Venus not much more like earth while it's close to the Goldilocks zone?
  19. Oct 22, 2012 #18
    fℓ is rather a large problem is it not? If N is the number of candidate planets in the universe, that is, planets that could support life, then this is what we have discovered so far.

    [tex]\frac{1}{N} \le fℓ \le 1[/tex]

    In other words, we haven't learned anything we didn't know when we were living in caves. As I said, if you don't know even one of the factors of Drake's equation, then it provides no answer to the question at hand.
  20. Oct 22, 2012 #19


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    You should read the forum rules. Definitive statements of fact have to be ones that can be backed up by citations. CLEARLY this statement cannot be validated.
  21. Oct 22, 2012 #20


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    I feel there is life out there, but have no valid arguments for my position.
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