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B Earth's radio bubble

  1. Dec 18, 2016 #1
    I've been reading about this interesting topic today. So the first radio signals emitted from the Earth are about 110 light years away from Earth now. Most authors point out that an advanced alien civilization only 125 light years away would have no idea of our existence.
    Fair enough, but the assumption here is always that any intelligent life out there is far more advanced than we humans are.
    Let's say for argument's sake that there is a humanoid species living on the newly discovered Centauri planet just four light years away and that this civilization has achieved the level of technological advancement that humans on Earth had achieved in the year 1850. Am I correct to presume that neither civilization would be aware of the other's existence?
     
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  3. Dec 18, 2016 #2
    Well first any radio signal that originated from earth by the time it reaches the nearest star would be too weak
    that it would probably below the level of background noise therefore not detectable. I supposed you could beam
    a signal strong enough to reach the nearest stars but I assume you will need a pretty high energy beam.

    Theoretically I think there is no reason why a nearby civilization couldn't reach us given they have the technological mean.
    I guess you can go by the old fashion way by just going as fast as you can.
     
    Last edited by a moderator: Dec 18, 2016
  4. Dec 18, 2016 #3
    The idea of there being a civilization (humanoid or not) as close as our nearest neighboring star system is wildly improbable, though it can't ruled out.
    As close as that they would certainly be able to detect curious radio signals if they had the technology to do so.
    Jupiter might pose a problem for them though, it's very radio noisy, so the Earth signal would need to be extracted from within a louder radio hiss being emitted from there.
    Anything beyond 10ly the signal is probably well buried in background noise and wouldn't show up unless the aliens were actively looking for it.
    Any aliens dedicated to such an effort though would have no special reason to examine Earth in particular among thousands of other possible candidates.
     
    Last edited: Dec 18, 2016
  5. Dec 18, 2016 #4
    That's precisely the point. An intelligent species 4ly away at the level of 1850 humans would not have the technology to detect our signals.
    Furthermore, if one of the Voyager probes ever passes by a planet inhabited by intelligent life, they would probably need to be more advanced than humans in order to detect the probe in time and then be able slow it down and capture it.
     
  6. Dec 18, 2016 #5

    Drakkith

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    Several posts have been removed for rules violations. Please stay on topic and within the realm of current science.
     
  7. Dec 18, 2016 #6

    mfb

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    You can easily extend this to 1950, signals emitted before that were too weak to be detected with our current technology.

    After that, it is a matter of luck: The strongest radar signals emitted by Earth are for radar astronomy: we let them reflect off planets or asteroids to measure their distance, size, shape and rotation. The directions are given by the objects in our solar system, it is purely an accident if some star is in the same direction. Listening is also spot-like: radio telescopes, especially the most sensitive ones, point to various sources of radio waves and look for emissions in some frequency bands. We don't scan the whole sky in all frequency bands all the time. Alpha Centauri and Proxima Centauri got more attention recently in the context of exoplanet searches, chances are good someone spent a bit more telescope time on listening in that direction. Once both know there is something, establishing a radio contact with 1950 and 2016 technology would be easy.
    But, as rootone mentioned: Being within ~100 years in research progress, after a few billion years of evolution, would be extremely unlikely.
     
  8. Dec 18, 2016 #7
    That reminds me of a really good sci fi novel, can't remember the name of it but think it was written by Isaac Asimov.
    The plot was that an AI controlled probe sent from some other civilization was detected passing through the solar system.
    We humans made some effort to capture the thing but failed, it had defense systems to stop that.
    However before it departed from the solar system we had managed to gather some clues of where it might have come from.
     
  9. Dec 19, 2016 #8
    If an alien civilization sent a Voyager-like probe past the Earth at the same speed, would we humans really be able to capture it? Just think of the resources that would need to be expended to do this. I suppose we'd have to try, as it would mark one of the most important discoveries of all time.
     
  10. Dec 19, 2016 #9

    Drakkith

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    Probably not, unless the probe was actively transmitting signals that we could detect.
     
  11. Dec 19, 2016 #10
    Which Voyager doesn't. Assuming we did detect it whizzing past Earth at 14 mps, think of how long it would take to launch a recovery vehicle and how far away the probe would be by then. The recovery vehicle would probably need to be carrying a lot of fuel to brake the probe once it catches up.
     
  12. Dec 19, 2016 #11

    Drakkith

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    It would only need to slow the probe down enough to capture it into an orbit around the Sun. Then we have all the time in the world to put together a missions to retrieve it. I honestly don't know how much fuel it would take.
     
  13. Dec 19, 2016 #12

    mfb

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    We probably wouldn't see it, and even if we did, capturing it would be quite a challenge. I made some toy estimates a few months ago. We would need a spacecraft with capabilities significantly beyond those of existing spacecraft, sitting around waiting for a launch.
     
  14. Dec 19, 2016 #13
    Without getting into the mathematics of it, how would we go about bringing a probe like that into orbit around the sun?
     
  15. Dec 19, 2016 #14
    I guess by attaching a powerful enough rocket motor to provide a braking force to slow it down.
    Or it might be easier not to directly attach to it, but use some kind of net, dragged along by several small rockets.
     
  16. Dec 19, 2016 #15
    Seems like putting the probe into orbit and coming back a second time would be more of a hassle than just getting it the first time.
     
  17. Dec 19, 2016 #16

    Drakkith

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    It depends on how much time you have and how much fuel and equipment you need to slow the probe down. If it takes more weight than we can currently launch, then we cannot do it it one step. We would have to make multiple launches and assemble the vehicle in orbit, or make a single launch with just enough fuel to slow the probe down into a solar orbit and come back for it later.
     
  18. Dec 19, 2016 #17
    We might be able to detect them, but not the other way around. We're starting to be able to analyze the atmospheres of nearby exoplanets. It'd be possible to detect a species' pollution through spectroscopy in some circumstances. It depends on exactly what kinda of pollution they are creating and in what quantity. In 1850 the hints of industrialization were there, though probably not detectable yet.
     
  19. Dec 20, 2016 #18
    They'd need to look in the right spot. The pollution in 1850s London was horrible. It should also be kept in mind that large parts of the southern hemisphere of the planet Proxima Centauri b would never to visible observers on Earth.
     
  20. Dec 20, 2016 #19
    It can't just be pollution, it has to be a certain kind of pollution that can not be made by natural processes and be abundant enough to be seen from another star. You can't really look at any once places specifically, the resolution isn't that good. Astronomers look at the planet as a whole mostly.
     
  21. Dec 20, 2016 #20

    mfb

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    That's what I calculated in the linked thread. Once the probe is captured in a solar orbit, everything else is easy compared to catching it.

    We are lucky if we can get some data on the atmospheric composition in general. We cannot look at individual spots, not with current telescopes and not even with the most optimistic proposals for future telescopes. Also, pollution detectable from space is not necessarily what we call pollution in the streets. You won't see smog from far away - it is just like dust. Chlorofluorocarbon, on the other hand, is not too hard to spot (if you have enough of it), but it gets distributed evenly over the globe so you don't have local areas with higher concentration.
     
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