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204143Re: Universal language for communicating with space aliens

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  • Leonardo Castro
    Jul 26, 2014
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      2014-07-23 20:30 GMT+02:00 Warren D Smith <warren.wds@...>:

      > The "rare earth hypothesis" is discussed here:
      > http://en.wikipedia.org/wiki/Rare_Earth_hypothesis
      >
      > I personally am unconvinced of its truth or falsity.
      >

      And how could anyone be convinced of either of them?


      >
      > There are too
      > many uncertainties which are too large. It seems clear that advocates
      > of both this hypothesis and its opposite have, historically, made
      > large errors. Many of the claims that have confidently been made were
      > just wild guesses which probably were quite wrong. I find it
      > possible that Earth's might be the only life in the entire universe,
      > or that intelligent life might be pretty common, with a
      > million places in our galaxy harboring it; and everything in between.
      > It has been estimated, based on extrapolating from planet-hunter data
      > to estimate all the planets we did NOT see
      > (planet hunting techniques can only detect planets a small fraction of the
      > time;
      > those fractions can be estimated a posteriori) that 22% of stars have
      > an Earth-size planet in their "habitable zone." In fact, by
      > correcting for detectability biases they attempt to understand the
      > whole distribution of planet sizes, etc. That is explained in
      > http://www.pnas.org/content/110/48/19273
      > http://www.pnas.org/content/110/48/19652.short
      > (click "Full Text").
      > It would however, be more convincing if we actually had detected a few...
      >
      > Catalogs of over 1000 known planets:
      > http://exoplanet.eu/catalog/
      > http://exoplanetarchive.ipac.caltech.edu/
      >
      > Also, the whole idea that Von Neumann machines are going to do this or
      > that faces the objection that nobody has ever built one, and perhaps
      > they just can't both exist and work very well. I do not know the
      > answer to that either. Life itself is a Von Neumann machine which,
      > even 3Gyr ago was far more capable than anything we can build, and in
      > 4 Gyr it has not managed to spread beyond Earth as far as we can tell,
      > nor has it even managed to do anything impressive in (say) current
      > Antarctica -- which compared to the Oort cloud or Mars seems a very
      > hospitable place...
      >

      Aren't penguins impressive?

      Até mais!

      Leonardo
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