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Observing the Ancient Times

  1. Feb 19, 2009 #1
    Hi,

    If there has been a civilization (aliens etc.) that is some 2400 lightyears away from our world that has the same technology we humans have, would it be possible for them to observe Plato lecturing in Academia ?

    If this is not possible, is it because the shortcomings of the technology (if so what are they ?) or is it fundamentally (eg. absorption of light, light source issues, issues regarding the earth's atmosphere etc.) not possible (if so why) ?

    I am curious especially about the fundamental side actually.
     
  2. jcsd
  3. Feb 19, 2009 #2
    I guess in theory they could see Plato lecturing in Academia if it occured about 2400 years ago (I'm not sure when it happened)...if they had the technology. If they had the same technology as we do, I don't think they could see an individual person. I don't remember hearing that we have telescopes that can see that well.

    If our planet is moving away from their planet, I think it would take longer for the light to reach them. (This gets into SR, which I'm not 100% sure about so don't take this as fact.)
     
  4. Feb 19, 2009 #3

    Nabeshin

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    I can't think of anything (other than obscuring dust) that would fundamentally limit observation of our own planet.

    However, an individual person subtends an arc of roughly 10^-16 arcseconds as seen from a distance of 2400ly. The angular resolution of a telescope, then, must be on the order of 10^-16 arcseconds, which, viewing at optical wavelengths, would require a telescope with a diameter of about 10^13m, or about .001ly.

    So, I guess it's POSSIBLE....
     
  5. Feb 19, 2009 #4

    russ_watters

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    ....well, I think you just argued for a fundamental limit due to resolution! Also, guys - if you follow the news at all, discovery of extrasolar planets gets reported every now and then. If our technology allowed us to image planets in the kind of detail you're looking for here, you'd most certainly have heard about it!
     
  6. Feb 19, 2009 #5

    Nabeshin

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    Well what I'm saying is it's POSSIBLE. There's nothing that precludes it from happening, it's not as if you cannot achieve a resolution necessary, it's merely ridiculously infeasible. For all intents and purposes though, it is impossible.

    As far as imaging exoplanets is concerned, we can barely even resolve them (the entire planet) right now, let alone at 2400ly away.
     
  7. Feb 21, 2009 #6

    Chronos

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    It's also unlikely. Half the energy any such civilization had evailablle would have been required to launch and find a suitable planet to colonize. Space travel in enormously expensive without a theory to replace relativity.
     
  8. Feb 21, 2009 #7

    Vanadium 50

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    There's also the light collection problem. It there's 1 W of reflected light per person, that's ~ 3 x 1018 photons/second, or 5 x 10-22 photons/s/m2 at 2400 ly. Even with the .001 ly mirror, it would collect roughly one photon from Plato every 7 years.
     
  9. Feb 21, 2009 #8
    Wow....I am really amazed by your math aptitude!....myself is more philosophical....but I always think good math is amazing....
     
  10. Feb 21, 2009 #9

    Vanadium 50

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    Well, it's not so much the calculation as knowing what question to ask. For most astronomical observations, it's not the magnification that limits you: it's the light collection ability.
     
  11. Feb 21, 2009 #10

    Nabeshin

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    Correct me if I'm wrong here but a .001ly mirror has a radius of about 10^12m, which yields a collection area of ~10^24m, which is about 100 photons per second.
     
  12. Feb 22, 2009 #11

    Vanadium 50

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    You're right. I missed a square.

    Even so, of course, this is a very small number. (Just not quite so small) One could take a photograph of Plato, but not make a movie.
     
  13. Feb 22, 2009 #12
    No one has mentioned atmospheric effects yet. An extremely, extremely large telescope could image the Earth, but atmospheric changes would still keep the image too fuzzy to see individual humans.

    So, where Nabeshin mentions you get 100 photon per second, you still haven't accounted for atmospheric effects, which would reduce that number.

    Cheers,
    --Jake
     
  14. Feb 22, 2009 #13

    Nabeshin

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    Good point. I forgot that the atmosphere limits seeing when you're looking out from it and out into it. Not sure how this effect propagates into any kind of calculation though.

    Point is, ain't nobody seeing Plato.
     
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