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B How far outward can we rule out intelligent life?

  1. Feb 9, 2016 #1
    Let's assume there is a planet out there with life equally intelligent as humans that is putting in the exact same amount of effort to detect alien life that we are. Their science and technology also developed in line with human technology. Given that we're looking and they're looking, what is the closest this planet could be to us given that we don't know about them (yet)? Any guesses?
     
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  3. Feb 9, 2016 #2
    How long have we had the technology to detect them? and from how far away?

    The lesser of the detection limits of our technology or distance in light years equivalent to how long we've had the technology seems reasonable to me..

    If we were to broadcast a message to them now, but they're 10 light years away, it would take 10 years before they knew of our existence.. if they got the transmission.
     
  4. Feb 9, 2016 #3

    russ_watters

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    That's a really difficult to answer question because of how strict "rule out" would be and how similar (or not) such life's technology would be to ours.

    If we narrowly constrain the issue to focus on omnidirectional radio broadcasts, if there were any within a few tens of light years away, we probably would have noticed by now. It is possible to calculate a detection threshold based on transmission wattage and receiver (radio telescope) sensitivity.
     
  5. Feb 9, 2016 #4
    My guess is they can be anywhere outside the SOL System. The universe is about 13.7 billion years old. Light reaching us from the earliest known galaxies has been traveling, therefore, for more than 13 billion years. So I assume they have the same information as well. In fact the farthest satellite reach from earth is only outside our System. They can be within our Galaxy and their probe still about to leave their system. There so much information and data that we should consider for this.
     
  6. Feb 9, 2016 #5
    So you think if there was human-equivalent intelligent life on a planet or moon of Centauri or Sirius we may not have noticed this yet?
     
  7. Feb 9, 2016 #6
    I'm not saying just right there in our Backyard. I'm saying that they might be existing beyond our Solar System.
     
  8. Feb 9, 2016 #7

    Chronos

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    This is reminiscent of the Fermi paradox - where are they - If intellligent life is rampant, why have we not already detected their radio signals? The most likely answers are 1] radio communication is rare, 2] intelligent beings are rare. If we choose to dismiss option 2, then we must come up with a reason for the lack of radio detection. Contenders include 1] the universe is too vast for radio signals to be detectable beyond short distances; 2] we are the crown jewel of intelligent beings within radio detection distances; 3] we are too moronic to recognize an intelligent signal; 4] we are the only ones dumb enough to paint a radio bullseye on ourselves in a universe teeming with exploiters and predators. Our ability to generate radio signals detectable across many light years allows us to rule out option 1. Option 2 can be eliminated on anthrocentric grounds. That leaves my personal favorites, options 3 and 4, as the most reasonable explanations
     
  9. Feb 9, 2016 #8
    3 I would say more likely than 4.
    If the Universe is actually full of exploiters and preditors it's not likely that all of them will have conspired to co-operate under a total radio silence agreement.
     
  10. Feb 11, 2016 #9
    I think species with advanced technology are rare. That doesn't mean we are the crown jewel of intelligent beings. There are countless intelligent species out there but how many survived to have the knowledge and capability of modern civilization? How many species out there have automated manufacturing? Just about zilch. Our species is the best hope for the planet and we have an obligation to act better. I think we have little to offer a higher intelligence unless we get along better with other species first; the earth could be a great school if you take the best civilization has to offer. We can study manned space missions but shouldn't be spending big money planning them unless they are sensible, and they're not. For that kind of stuff developing robotic space planes is better for now.
     
  11. Feb 12, 2016 #10
    We may or may not be the most intelligent beings in the universe. The point of creating this thread was to determine how far outward from the earth/sun scientists would feel safe about saying there is no human-equivalent intelligent life. I was hoping to get some more specific answers, even if merely based on intuition. The observable universe has a diameter of some 90 billion light years.

    What if there were humans just like us living on a planet 100 light years away from Earth (with the same telescopes and radios and satellites) who were also interested in finding alien life? Would we have detected them by now?
     
  12. Feb 12, 2016 #11
    I disagree, I would think that radio to them is like smoke signals: outdated technology. Also, a radio laser would not be detectable unless you were in the beam. The concept that the galaxy should be dominated by some apex predator is practically Darwinian. I think it's the only possibility in the long term, the only question for me is whether or not there has been enough time yet, 13 billion years is a long time, but in terms of the universe's scale, we're still infants.
     
  13. Feb 12, 2016 #12

    russ_watters

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    Probably yes.
     
  14. Feb 12, 2016 #13
    The short answer, it's unlikely there are any ETI's with our level of development or greater within 100 light years of Earth. That's about the distance we could detect a powerful military radar with the square kilometer array.

    Edit: I now see that russ_watters answered this question above. Note that since our Galaxy is so large, there could easily be 100's of civilizations more advanced than ours, but just outside of our current range of detection. Just to elaborate, if the Universe is infinite, or even near infinite, it's probable that there would be a near infinite number of civilizations more advanced than ours.
     
    Last edited: Feb 12, 2016
  15. Feb 12, 2016 #14

    Chronos

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    Detection of a narrow band terawatt class radio signal could be accomplished with a pretty modest sized 4 meter radio dish [i.e., an amateur rig] at a distance out to about 100 light years. Earthly examples would include early warming radar systems. Broadband emissions, like TV transmitters would be almost impossible to detect beyond, or even at the fringes of our own solar system with even the largest radio telescopes currently in existence. Hopefully this fact offers some solace to those alarmed by the prospect of an Independence Day style alien species homing in on terra firma. For further discussion I would recommend this paper by NASA; http://history.nasa.gov/CP-2156/ch5.4.htm, Eavesdropping Mode and Radio Leakage from Earth, and this paper from the International Journal of Astrobiology;http://arxiv.org/abs/0707.0011, Calculating the probability of detecting radio signals from alien civilizations.
     
  16. Feb 12, 2016 #15

    ogg

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    A couple of things. First, is the OP apparently makes the contrafactual assumption that there is some absolute time frame of reference, ie that "now" is a global invariant. It. is. not. Second, there is some discussion of predation. The energy costs associated with interstellar predation makes this an excellent example of what will never ever happen. Third, there is some discussion about the size of the Universe, with various numbers such as 100 bly or ∞ being tossed about. There is effectively a zero chance of us detecting signals from 'equivalent' technologies in other galaxies. Period. Fourth, choosing an arbitrary technological level needs to be justified. Choosing a single arbitrary HISTORY of a civilization's technological development is ridiculous and completely unjustifiable. For instance, what would it mean if we learn that the expected atmospheric pressure on Earth-like planets is 10X to 30X greater than on Earth (post Theia, and if you don't know what Theia is, look it up.) What would that do to its ionosphere and radio emissions? What effect would that have on their use of Low Orbit satellites? The research literature I've seen discusses distances between 10 and 500 light years for ETI detection. The OP's original question suffers from a serious flaw in its assumption that we know enough about exo-planets, life, and technology to assume it is likely to be anything like us. Would an aquatic species use radio?
     
  17. Feb 12, 2016 #16
    Considering that most stars around Sol are moving non-relativistically relative to it, there is a practically meaningful, if somewhat fuzzy, definition of "now" when we consider possible civilizations on the planets orbiting them.

    It is a kind of assumption which may cost dearly for the civilization if it proves wrong.

    It's a thought experiment. "How far out would we see a copy of Earth with a copy of humanity on it?". You don't like the setup in this experiment, you propose a different one. Maybe in a different thread?
     
    Last edited: Feb 12, 2016
  18. Feb 12, 2016 #17
    I'll answer your question, so please answer mine (be specific). I'd like to see the copy of Earth as a planet orbiting a nearby star (Sirius). It would present a challenge to ever meet them, but it would give us ample motivation to master interstellar travel.
     
  19. Feb 12, 2016 #18
    OK, but as for intelligent creatures like us living on a planet 100 light years away from Earth the chance is slim. If there are 5000 ( a guess) suns within 100 light years of us, lets assume maybe 100 have life. But a civilization? Thats rare and its possible there's one but I doubt it. On the other hand, if each galaxy has 100 civilizations and there are say 10^9 galaxies, thats 10^11 civilizations. Regardless our species is very special and hopefully will rise above the shallow predator mentality.
     
  20. Feb 13, 2016 #19

    Chronos

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    Why assume any species would rise above a simple predatory mentality when that pretty much sums up the history of evolution on earth. Im reluctant to assume altruism is a trait that has much survival value anywhere in the universe. I naively assume life is common in the universe, but, technologically capable intelligent life is rare [only a handful in any particular era in any particular galaxy]. IMO, we only avoid predation because interstellar travel is incredibly difficult and resource intensive with uncertain rewards.
     
  21. Feb 13, 2016 #20

    phinds

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    I'm thinking, all the way up to Donald Trump's apartment door.
     
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