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View Diary: Who can own the future? (262 comments)

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  •  Even if so, where are the radio signals? (1+ / 0-)
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    I can believe that physical interstellar travel could be effectively impossible, or so difficult and expensive as to be vanishingly rare.

    But sending radio signals across interstellar distances is easy. We've been doing it (unintentionally) since the invention of centimeter-wavelength radar in the 1940's. A civilization with our own modest level of technology would be able to pick up our VHF/UHF/microwave emissions from radars and TV broadcasts across dozens of light years (once they got there, that is). These signals have unmistakable "artificial" signatures that distinguish them from anything created by natural processes.

    Even if ET can't travel to us, even if she/he/it isn't deliberately trying to talk to us, if other tech civilizations were at all common, we should still be picking up their incidental electromagnetic chatter. SETI has certainly looked for it. But it doesn't appear to be there.

    The only conclusion that seems plausible is if other technological civilizations exist at all, they aren't anywhere nearby ("nearby" defined as within several hundred light years.) That seems to imply that they must be very rare - or as Mark hypothesizes, very short-lived.

    •  How long? (2+ / 0-)
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      rodentrancher, bartcopfan

      It comes back to the problem of time...How long are civilizations communicative via radio?  It is quite possible that the radio signals of another civilization swept over earth 200,000 years ago and bathed our planet in radio signals for 65,000 years.  But we couldn't hear them.  135,000 years ago we didn't have radio.  Heck 135 years ago we couldn't have heard them.  

      The probability of us listening while another civilization is transmitting are very small.  Factor in the inverse square law and the chance of hearing a signal and it's very possible that there are 0 civilizations transmitting (that we can hear) while we are listening.  

      Those who cannot remember the past are condemned to repeat it. George Santayana

      by RAST on Sun Jul 14, 2013 at 10:47:18 AM PDT

      [ Parent ]

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