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How far did the signal of life in earth travelled yet?

  1. Nov 21, 2011 #1
    If someone in a distant stars is watching for signals of life coming from other planets, how far did the signal of life in earth travel yet, in a cosmological context?
  2. jcsd
  3. Nov 21, 2011 #2


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    In terms of just life on our planet? About 4 billion years ago, give or take a few hundred million years. If you wait for a few billion years, the organisms begin to significantly alter the atmosphere of the Earth, creating a signal that could potentially be recognizable to alien entities. Perhaps 2 billion light years?

    In terms of intelligent life signals, we started broadcasting messages ~100 years ago, so ~100 light years would be the maximum travel for these signals.
  4. Nov 21, 2011 #3


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    Broadband radio signals would be virtually undectable by the time they left the solar system, so it is unlikely ET is watching 'gilligan's island'. Narrow band signals could be detectable across many light years, depending on power and frequency. We are, however, talking about a lot of power - in the terrawatt range. We have historically emitted few signals with this kind of power. It is simply overkill for almost any known practical purpose. Hence, there is little reason to believe ET would routinely generate signals of this strength. Of course, if money were no object and you were obsessed with SETI, it is certainly possible [albeit unlikely to enjoy long term public funding].
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