From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Thu Jan 23 2003 - 08:55:18 MST
On Wed, 22 Jan 2003, Anders Sandberg wrote:
> On Wed, Jan 22, 2003 at 08:10:36AM -0500, Eliezer S. Yudkowsky wrote:
> > Anders Sandberg wrote:
> > >Some good news:
> > >
> > >http://www.sciencedaily.com/releases/2003/01/030122072843.htm
> > >
> > >Scientists at NASA and Kansas University have determined that the
> > >supernova would need to be within 26 light years from Earth to
> > >significantly damage the ozone layer and allow cancer-causing ultraviolet
> > >radiation to saturate the Earth's surface.
Their results (at least in terms of time scales) *do* seem to be in
conflict with the Dar and Dr Rujula results with respect to times
between gamma ray bursts.
(So we may not have to worry about supernovas, but we may have to worry
about GRB which are far worse if your planet happens to be in the
"cone of extinction" (side ref to the infamous "cone of silence"
which people who watched TV in the U.S. in the '60s may get).
> > >*One* thing less to worry about.
Loss of the ozone layer from supernova's I can deal with (so I wasn't
worried in the first place). The GRB on the other hand make for a really
really bad couple of days.
I think the loss of the ozone layer and an increase in UV radiation is
*very* overblown. Back when I was studying biology, the conventional
wisdom was that humans didn't even have a photolyase enzyme to repair
UV induced DNA damage (I'm unsure if they have found one or more in
the process of the HGP). If we can survive reasonably well without
that then UV tolerance isn't *that* important to our survival.
For heaven's sake -- humans could simply go back to living in caves
(many of us spend much of our time without exposure to the sun as it is).
I'll admit that there may be problems with cows or sheep going blind
prematurely but the long term evolution of our species should be in
the direction of eliminating them as food sources anyway.
We don't have any good benchmarks for how rapidly species could up-regulate
or develop more robust DNA repair in the face of an increase in the amount
of UV radiation -- we do however know (from Deinococcus) that it *is*
feasible to be very UV radiation tolerant.
Eliezer noted:
> > No, this is *poor* news, because it eliminates one of the *less* forboding
> > explanations for the Great Filter.
As I state above, I think surviving the loss of an ozone layer and/or
dealing with an increase in UV flux is something most technological
civilizations could manage. So the NASA results don't significantly
impact the GF situation IMO. Even if one knocks "life" back to the
Deinococcus level every half-billion years, there still seems to be
a reasonable amount of evidence one can make it back up to our level
(multiple times in the lifetime of a star like the sun).
Now, *I* at least would not consider a GRB "sterilization event"
as "non-forboding".
Anders notes:
> I have always considered the supernova argument for the GF unlikely. They
> are relatively rare compared to the likely timescales of intelligent
> evolution and technology, making the variance in the number of novas
> during the critical period before sufficiently strong technology large
> enough to let quite a few civs through the filter.
I would tend to agree. As I've argued (though most don't seem to get
it) the answer to the GF seems to be in the evolution of technological
civilizations -- replication becomes hard (expensive) and potentially
self-defeating and so should be discontinued as a behavior. One only
has to read Malthus or Dyson and think about this a bit to realize
that at some point one has to regulate ones growth.
Robert
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