Re: ET: Scientific American article on GHZ

From: Robert J. Bradbury (
Date: Mon Oct 01 2001 - 09:29:21 MDT

I thought the article was very weak. While it may be true
that we currently live in the "habitable zone" it doesn't
make a good case as to why it is impossible that an advanced
technological civilization could not have evolved a few
hundred million to a billion years earlier than us somewhat
closer to the galactic center (where the metalicity is higher).

Articles like this always cite the radiation hazard, but any
radiation level below that which vaporizes the oceans of
a planet is somewhat suspect IMO. We know from Deinococcus
radiodurans that it is perfectly feasible to evolve life
forms that have *much* more robust radiation tolerance than that
the average species on this planet has. A reasonable argument can
also be made that higher radiation levels and/or cometary
impacts would actually accelerate evolution. Yes, you can
get to the point where you keep reducing life to dust faster
than it can complexify but we have no good feel for whether
we are in the middle of the galactic hazard function or
either end of the distrubtion.

Finally, it contains no discussion of what happens if technological
civilizations evolve to our stage and beyond (through the singularity).
The Fermi Paradox rests on the assumption that travel and/or colonization
by life forms like us is a worthwhile persuit. I'd argue that
civilizations capable of interstellar travel are going to be much
more interested in "harvesting" brown dwarfs or dense molecular
gas clouds than planets like Earth. But we have been over all
of this ground before so it probably isn't worth the bandwidth.


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