On Monday, October 01, 2001 8:29 AM Robert J. Bradbury email@example.com
> I thought the article was very weak.
I found it just okay for a popular level article. I usually don't like
_Scientific American_. Case in point with this one. They dismiss
counterarguments much too skimpily, IMHO.
I kind of brought it up to shift focus away from the terror attacks.
> 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).
That's always possible. Plus, we don't know the parameters for life in
general. Perhaps complex life of our sort might not be able to survive
under radically different conditions, but who knows about what the range of
complex life is?
If we had some defensible minimum time to evolve intelligent life, perhaps
we could better settle this, but that would seem to involve actually getting
many samples of such. So far, we only have one.
> 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.
Well, it is a bacteria. Bacteria overall are much hardier than most more
complex organisms. This doesn't utterly refute your point, but what applies
to bacteria shouldn't be extrapolated to higher life to readily.
> 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.
You might be right here.
> Finally, it contains no discussion of what happens if technological
> civilizations evolve to our stage and beyond (through the singularity).
Well, I think you have to have the conditions for evolving such life first.
> 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.
Maybe not. I suspect it might be a matter of how much time such
civilizations need to go from the kind of communication technology we could
detect -- and thereby we'd be able to find out about them -- to stealthing
for whatever reason -- even unintentionally. My belief is, if everything
goes right, this might be a matter of decades. (Imagine a counterfactual
history of Earth, where humans come up with all the neat tech, but avoid
wars and such that represent setbacks. Imagine also that most humans are
dedicated to technological progress and don't put any irrational roadblocks
in its path.)
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