X-Message-Number: 11211
Date: Mon, 1 Feb 1999 08:53:21 -0800
From: "Joseph J. Strout" <>
Subject: Re: probably not GRB

In Message 11203, Robert Ettinger () writes:

>Suppose it takes, on average, half a billion years for a civilization to
>develop after a GRB.

That's actually a pretty reasonable supposition -- the great mass
extinction at the end of the Precambrian, just before the Cambrian
Explosion (which resulted in most major phyla existing today), was 545
million years ago.

>Randomness should assure a variation on the order of at
>least 10 million years, so there should be at least one that is several
>million years ahead of us, thus should have reached us by now.

Well, that's the crux of Fermi's paradox, isn't it?  But normally the mean
time to develop is assumed to be something like 5 or 10 billion years,
which if we assume a similar coefficient of variation, suggests a much
wider distribution of development times.  I ran some numbers under those
assumptions once, and found that in order to not have aliens in your back
yard, you'd have to be one of the first 1 or 2 (out of thousands) of
civilizations to evolve in the galaxy, and the probability of that is well
below the 0.05 level.

But if we assume a standard deviation of 10 million years -- well, I
haven't run the numbers, but I'll bet any of the first 20% or so
civilizations to develop would not see any aliens before they reached our
technological level.  And supposing that we're in the top 20% is not so far
fetched.

>One other point: If the GRB only lasts a few seconds, and underground life
>would be spared, then eradication of the advanced civilization seems unlikely.

I wasn't suggesting that a GRB would eradicate an advanced civilization.
Even for us, it would be only a massive holocaust -- probably humanity
would survive.  I was only suggesting that, as long as you get a GRB every
few hundred million years, life won't be able to get to the civilization
stage in the first place.

>The simplest explanation seems to me the most likely--we haven't seen advanced
>aliens here because they aren't here, and they aren't here because they aren't
>anywhere.

But why aren't they anywhere?  The most likely explanation I've heard so
far is that they are too frequently killed off by GRBs.  To suppose that
Earth is so special that it's the only habitable planet in the galaxy seems
much more far-fetched to me.  Could be true, but I doubt it.

Anyway, our understanding of GRBs is brand new and I'm hoping that we'll
get some more answers in the coming decades.  If there was a GRB at the end
of the Precambrian, I hope it will have left some evidence behind that
we'll learn how to read.  Barring that, we'll eventually find out what's
what when we get out to other stars, find some with the right conditions
for life, and see what's there.  (A mass extinction there at the same time
as one of Earth's would clinch the theory, I believe.)  So both of our
theories are falsifyable.  But we may have to wait a very long time for the
results.  ;)

Cheers,
-- Joe
,------------------------------------------------------------------.
|    Joseph J. Strout           developer: MacOS, Unix, 3D, AI     |
|                 http://www.strout.net              |
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