If you are far enough, the quality of information you detect essentially degrades because it is quantizied by E=hf "bits". So, if on planet X you receive less quanta per antenna area per second than the signal content (in bits/sec), you will not be able to distinguish content from noise even if antennas are covering entire planet. Simple calculations show that our Earth's becomes practically radioinvisible from distances of a few light-days only. Account for Sun's background radio-noise makes it even less visible. Accounting for inherent detector noises -even less.

There is technical possibility to beam very little information - small number of bits per second (like a Morse code) to a few light-year distances IF YOU KNOW WHERE EXACTLY TO DIRECT NARROW RADIO-BEAM (to where certain planet will be in several years when the beam will arrive). Also,I wonder, will it have much sense to communicate with the speed of few bits per second anyway? How much info can we send and receive?

And still what to do with 1000s years delay in getting answer if indeed civilisations are scattered over large distances? (Actually, 1000 light years is quite optimistic - it basicly means that there is about 10^4 civilizations in it at any given time. Most likely, the # of civilisations is much less, so mean distance between them is in 10^4 + light years range.

At such distances radiocommunication is likely impossible at all.

• I meant 10^4 civilisations in Milky Way. - alexander - December 18, 2001 - 20:47 UTC
  • Can you have civilizations near the center of the galaxy? - harvey1 - December 19, 2001 - 04:35 UTC
    • Article in Sept Scientific American - yanniru - December 19, 2001 - 15:28 UTC
      • Yes, that was it - harvey1 - December 19, 2001 - 16:18 UTC
        • Still not nesesserary (only in the ring). - alexander - December 19, 2001 - 17:41 UTC
  • this pretense of precision goes against principles of chemistry - spazcon - December 19, 2001 - 06:55 UTC
• Then we are wasting lot's of money on SETI - yanniru - December 19, 2001 - 14:48 UTC
  • US government stopped supporting SETI long ago. - alexander - December 19, 2001 - 17:44 UTC
    • You are correct - yanniru - December 21, 2001 - 00:26 UTC
      • I agree (with incompetence of government). - alexander - December 23, 2001 - 16:24 UTC
        • The law of sacrifice - yanniru - December 23, 2001 - 18:55 UTC
        • CarefulUniverse's Law of Development of Civilization - carefuluniverse - December 24, 2001 - 06:01 UTC
  • Richard, radioastronomy does NOT deal with alien radiosignals. - alexander - December 19, 2001 - 17:49 UTC