nemesis <nam### [at] gmailcom> wrote:
> carbon-based life.

  Has any form of (intelligent) complex life which is not based on chemistry
similar to our own, and/or which is not heavily dependent on water, been
even seriously conjectured?

  Complex life (ie. anything more complicated than something resembling a
virus) requires certain molecular structures, which in turn require certain
chemistry and certain chemical elements to appear in certain proportions.

  For example, anything even remotely resembling proteins requires molecules
with certain structures and certain elements to be stable and feasible. If
these elements are not abundant enough, such complex molecules simply cannot
form.

  AFAIK, it's physically impossible to get anything even remotely usable
for forming complex life from hydrogen and helium alone. This rules out
most star systems on the outer edges of galaxies, as well as most stars
in galaxies of certain type, for instance.

  Also even non-carbon-based life won't survive a collision with an
enormous celestial body. No matter how exotic your lifeforms are, they
will most probably not survive if their planet collides with a star. Thus
star density in the galaxy is a key factor. (While direct collisions might
be less likely, close encounters may well fling the planet out of its orbit,
dooming any potential life to a slow death. You most probably can't have life
at 3 kelvin.)

-- 
                                                          - Warp

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