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Rare Earth theory?

  1. Sep 5, 2007 #1
    What is everyones opinion on this?

    How can we say life is rare in the universe when not only haven't we explored other galaxies, but have yet to even venture out of our solar system (excluding Voyager 1)???
     
  2. jcsd
  3. Sep 5, 2007 #2

    DaveC426913

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    We don't have to leave our solar system to notice the complete absence of radio or other EM signals in our sky.
     
  4. Sep 6, 2007 #3

    Astronuc

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    On the other hand, the absence may simply be due to the very low signal to noise ratio.

    I am not sure that we could detect a faint signal from the Andromeda galaxy.

    I think the power of most terrestrial systems are on the MW, and I imagine that the signals are rather feeble 1 light year away, let alone 100's, 1000's, million of ly away.
     
  5. Sep 6, 2007 #4

    DaveC426913

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    Yeah but if we're looking 2M ly away for life, I'd call that rare.
     
  6. Sep 6, 2007 #5

    mgb_phys

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    But the observable universe is 4000 Billion cubic light years!
    Still one life per galaxy would be incredibly rare.
     
  7. Sep 6, 2007 #6

    Danger

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    Of course, finding it there would mean that the civilization is at least 2M years old. A newer one wouldn't know about us either.
     
  8. Sep 6, 2007 #7

    Astronuc

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    Maybe in the Milky Way or Local Cluster, the earth is rare.

    Are stars like the Sun rare? G2V
     
  9. Sep 6, 2007 #8

    Evo

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    Looking at the recent article about how humans may not have evolved to this point except for a freak collision with that asteroid 65 million years ago, and considering how long it would take for any transmissions we might be able to detect to reach us, I'd say that it's rather naive to consider ourselves the only life.
     
  10. Sep 6, 2007 #9

    DaveC426913

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    ?

    Doesn't a freak event leading to our existence imply a lower probability of intelligent life elsewhere?
     
  11. Sep 6, 2007 #10

    mgb_phys

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    Something calling itself human might have evolved, it's just that it would have green scales and lay eggs.
     
  12. Sep 6, 2007 #11

    Evo

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    It depends on what type of life developed on the other planets. In our case dinosaurs were predominant, once they were gone, we had a chance to develop. Another planet may have never developed giant dinosaurs. We can't expect every world to develop exactly as the earth did.
     
  13. Sep 6, 2007 #12

    jim mcnamara

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    We are not making much progress on the empirical side, either:

    http://www.livescience.com/space/news/070823_mars_life.html [Broken]
     
    Last edited by a moderator: May 3, 2017
  14. Sep 6, 2007 #13

    DaveC426913

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    But the logic here is that, in the only example of intelligent life in the known universe, it didn't come about without a _freak_ accident as a prerequisite. The implication is that the preconditions for intelligence are rare, which implies that intelligent life is a freak event.
     
  15. Sep 6, 2007 #14

    Evo

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    No, just in our case. On another planet a freak asteroid hit could wipe out what would have become intelligent life, the lack of such an accident could leave intelligent life evolving normally.
     
  16. Sep 6, 2007 #15

    jim mcnamara

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    We will become extinct. Period. There is no endpoint in evolution, and, god help us, I'm sure we are not any kind of flowering pinnacle. More like a peduncle with any luck.

    And if it matters, ants have already won the evolution cup for terrestrial animals. --- E. O. Wilson's point of view anyway. Us humans count for nada.
     
  17. Sep 6, 2007 #16

    Danger

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    Agreed. There's no reason to believe that reptiles wouldn't have achieved our level of intelligence had they been given the chance. My money would be on the small, fast ones. From what I've seen of fossil evidence, it looks as if their forepaws were well on the way to being capable of tool use.
     
  18. Sep 6, 2007 #17

    DaveC426913

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    I really don't know about that. If dinos had continued to rule the planet, would they have had any evolutionary pressure to develop intelligence? Mammals had strong pressure to evolve intelligence (I would think) as a way to stay out of the mouths of nasties.
     
  19. Sep 6, 2007 #18
    Rare Earth "theory" is about as useful as a hole in your head. So life on Earth has evolved to best make use of the planet, wow, so what does that tell us about life in the universe? Not a lot - other than perhaps how significant astronomical and geological events/processes are to evolution. Chemoautotrophs don't even need sunlight - that's a bit of a kick in the balls. The so-called "Fermi paradox" has plenty of possible solutions, so I wouldn't worry too much about lack of ETI signal detection.
     
  20. Sep 6, 2007 #19

    DaveC426913

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    No, that actually highlights the Fermi Paradox. If there are plenty of solutions, then it is more odd why we don't see life everywhere we look.
     
  21. Sep 6, 2007 #20

    Chi Meson

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    I love Wilson's work. Nevertheless, to say that humans count for nada is only true if the ants count for nada (thereby all things equally count for nada).

    Back to the OP, even if life is rare, and even if only one life-sustaining system exists for every 100 galaxies, that still means 100s of millions of life-sustaining systems. I have no doubt that there has been ,is, and will be other "earths" out there. I also have little hope that contact will ever be made. (I think that's what most of us think anyway, isn't it?)
     
  22. Sep 6, 2007 #21
    Huh? I don't follow. The way I was looking at, if there are plenty of solutions (by that I mean things that would undo the "paradox") to explain why we can't detect signals from ETI (extra-terrestrial intelligent life forms), then it should not be too revealing (as to the state of ETI in the universe) that we have not detected any (ETI signals).
     
  23. Sep 6, 2007 #22
    Maybe the ETI signals are cleverly disguised as noise so that they may spy on our activities and conduct social experiment on us by planting their own kid as leaders of the free world.

    Or not.

    I am certain intelligent life has/does exist somewhere out there.
     
  24. Sep 6, 2007 #23

    Danger

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    But so did smaller reptiles, and the small mammals that evolved along with sabretooth tigers.
     
  25. Sep 6, 2007 #24

    russ_watters

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    A few years ago it was believed that we would be able to detect alien life via radio waves. But a scant 60 years after the first high power transmissions, signal strengths are poised to drop to the point where what we emit into space accidentally would not be detectable/deciperable even just a few light years away. So even if the galaxy were teeming with intelligent life, odds are we would never detect it with our current search methods. There are other ways to detect life, and I expect that within my lifetime, new ways of searching will answer the question to the satisfaction of scientists (but not necessarily laypeople).

    So the answer to the question of why we don't detect life everywhere may simply be: how could we possibly detect life anywhere?
     
    Last edited: Sep 6, 2007
  26. Jan 14, 2010 #25
    life is rare in the universe because when life started in the earth it had to fight with environment and it developed in a complex way of life which is not possible in other planets for this you have to understand how earth created after a comet collied with it and that does not happen with every planet that's why earth developed this rare and complex life sequence.
     
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