From: Olie Lamb (olie@vaporate.com)
Date: Mon Oct 10 2005 - 23:35:55 MDT
(On a separate note, has anyone else noticed that some of the
post-numbers in the SL4 archives are distinctly off from the index
listings? At least, clicking any indexical link tends to take me at
least 3 messages away from my intended destination for August this
year... haven't checked other months thoroughoghly with this in mind.)
(More)
Dani Eder wrote:
> > By the way, did anyone else who has read the book
>
>
>>also disagree with Ray's
>>conclusions on the Fermi Paradox? Page 347
>>specifically.
>>
>>
>
>Until 10 years ago, one of the factors in the
>Drake Equation, the number of planets per star,
>was a complete unknown. Since then we have
>detected about 170 extra-solar planets. This
>is a large enough sample to notice something
>interesting.
>
>
Please take note, however, that our current detection methods strongly
bias the samples: our techniques for detecting extrasolar planets are
skewed towards detecting large planets in very close orbits. Our
detection methods are not yet (at my last knowledge) anywhere near up to
detecting a planet as small as Earth at Earth-orbit distances.
(more)
> ... ... The interesting
>thing is the likelyhood of finding a planet around
>a star is strongly correlated with metallicity.
>It is something like 30 times higher for high
>metallicity stars vs. low ones.
>
>
Because of the detection-method bias, I think that the inferences we can
strongly draw need a little qualification: high metallicity stars are ~
30 times as likely to have close-orbiting giant planets. It is not
guaranteed that terrestrial planetoids are so much more likely to be
found around high metallicity stars.
Nevertheless, although the premeses are a touch inaccurate, the
conclusion of the following paragraph is still reasonable:
>High metallicity stars are generally younger, so the
>implication is that there are not many planets
>around old stars. Thus when considering the
>Drake Equation, it would be incorrect to assume
>a uniform number of planets over the history of
>the universe.
>
>This tends to make the hypothesis that we are an
>early civilization more likely. Younger stellar
>systems are more likely to have planets, but have
>not had as much time for evolution to progress.
>
(New point) This is where the Drake equation is still messing about with
unsupported conjecture. It's taken -what? - some 3 billion years to
develop from simple to complex life, and some 545 million years to get
from complex life to tool & symbol using life. Based on our sample size
of 1, it's kinda difficult to make much of a statement about whether
this is uncannily fast evolutionary progress, or pitifully slow. I
couldn't make any sort of informed statement about what rate most of
this evolution would typically take, but given that (1) a helluva lot of
evolutionary effort goes into staving off parasites (2) this doesn't get
any easier in later evolutionary periods (3) earlier organisms would
likely have less genetic material dedicated to staving off parasites;
it would seem that some complex-organism evolution /might/ be able to
work quicker in comparitively young biological groups. Restated, it
might be "easier" for complex organisms to get smart earlier in the game
than later in the game.
-- Olie
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