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Fwd = Shostak: Galaxies home to many advanced societies

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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl (Frits Westra) URL: http://msnbc.com/news/773228.asp?cp1=1 Original Date: Sun, 30 Jun 2002 14:35:29 +0200
    Message 1 of 1 , Jun 30, 2002
      Forwarded by: fwestra@... (Frits Westra)
      URL: http://msnbc.com/news/773228.asp?cp1=1
      Original Date: Sun, 30 Jun 2002 14:35:29 +0200 (CEST)

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      SETI Institute astronomer says hotly debated
      topic should be decided by evidence, not opinion
      By Seth Shostak

      June 27 -- When it comes to alien activities, visiting Earth seems to
      be pretty high on the "to do" list. But does that make sense?

      APPROXIMATELY HALF the U.S. population suspects that
      extraterrestrials have come to our planet. This is such a
      controversial (and emotional) topic that its mere mention in one of
      these articles is usually sufficient to guarantee a storm of Web chat
      and high-voltage e-mails. In the end, of course, the matter of alien
      visitation will be decided by the evidence, not by the intensity of
      opinion. While I certainly expect that the Galaxy is home to many
      advanced societies, the quality of the evidence has so far failed to
      convince me that any of them have emissaries on our planet. But let's
      back off to our neutral corners for a moment and consider an
      intimately related question: why would aliens be visiting now?

      According to the most popular view of this matter,
      extraterrestrial craft have been flitting across our skies since 1947.
      That's 55 years in a planetary history of 4,600,000,000 years. If we
      assume for the moment that these claims are real, this chronology
      tells us immediately that either:
      * 1. We are the beneficiaries of an enormously rare event (one chance
      in 100 million, or if you want to argue that no aliens would visit
      until they detected oxygen in our atmosphere, one chance in 40
      * 2. The aliens routinely visit Earth.
      * 3. Our activities (nuclear tests, environmental degradation, etc.)
      have attracted the aliens' attention, and encouraged them to drop by.

      The first possibility, that we just happened to luck out (being
      around for the first and only alien encounter), is less probable than
      that you - not someone, but you - will win next month's lottery
      jackpot. It strains credulity, to use polite vernacular.
      The second possibility, that Earth hosts extraterrestrials on a
      routine basis, and therefore a visit during your lifetime is not
      particularly improbable, deserves a bit more scrutiny. The question
      is, how often do they visit? If it's only once in a few tens of
      millions of years, we're back to the first possibility, and the odds
      are highly stacked against you being one of the lucky visitees. But
      some folk claim that aliens have glissaded to Earth in historical
      times (five millennia ago, when the pyramids were built, or one
      millennium ago, when the Nazca Indians elected to decorate the
      Peruvian desert floor with glyphs of turkeys and other of their
      favorite fauna). If any of this is true, it argues for visits at least
      once every 1,000 years or so. The problem with this is that - barring
      some reason for them to visit humans in particular (a possibility we
      consider below) - it implies that there have been millions of
      expeditions to Earth!
      We may send the occasional anthropological research team to
      Borneo, but we don't send millions. And it's a lot easier to get to
      Borneo than to traverse hundreds or thousands of light-years. This,
      too, seems to be an unlikely explanation for visitors now.

      Finally, we consider door number three - we have enticed the
      aliens with human activity. Let's set aside the question of whether
      advanced galactic societies would have the slightest interest in our
      wars, our pollution problems, or our reproductive systems. The real
      question is, how would they know about us at all?

      In fact, there's only one clear and persistent "signal" that
      Homo sapiens has ever sent to the stars: our high-frequency radio
      transmissions, including television and radar. The Victorians (let
      alone the Egyptians or the Nazca Indians), despite all their technical
      sophistication, could never have been spotted from light-years away.
      Humans have been making their presence known to the universe only for
      the last 70 years or so.
      And that's a problem. It means that even if, after receiving an
      earthly transmission, the aliens can immediately scramble their
      spacecraft and fly to Earth at the speed of light, they can't be
      farther than 8 light-years away to have arrived by 1947. There are
      four star systems within this distance. Count `em, four. We're back to
      winning the lottery.

      What about warp drive? Maybe the aliens can create wormholes
      and get here in essentially no time. It doesn't matter. Our signals
      travel at the speed of light, and this means that even with infinitely
      fast spacecraft, the aliens can't be farther off than 15 light-years
      to have reached our lovely planet by 1947. The number of star systems
      within 15 light-years is about three dozen. There would have to be 10
      billion technically sophisticated societies in the Galaxy to have a
      reasonable chance of finding one camped out among the nearest three
      dozen stars. That's optimism of a high level indeed.
      It's nice to think that either Earth or its human inhabitants
      have not only attracted the attention of galactic neighbors, but
      encouraged them to visit. But frankly, the numbers don't give much
      support to this somewhat self-indulgent idea.

      © 2002 Space.com. All rights reserved.

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