X-Message-Number: 5540
Date: Thu, 4 Jan 1996 21:18:17 -0800
From:  (Eric Watt Forste)
Subject: Re: nightmares

In message #5537, Doug Skrecky wrote:
>     Frank Tipler has advanced the view that we are alone because we are
> the first technologically advanced civilization to arise in our galaxy.
> ETI's never killed themselves off because thery never existed. The
> December issue of Equinox magasine contains an article entitled "Earth:
> There's No Life Like It" written by Terrence Dickinson, which outlines a
> number of reasons why the survival of life on earth can be regarded as an
> extremely low probability fluke.

Another reason why we might be first, which I've often wondered about, but
have never seen mentioned in the literature, is the amount of time required
for a sufficient density of heavy elements (what astronomers call "metals",
but including carbon, oxygen, and nitrogen) to build up. I'm very curious
about this, but I haven't got the necessary math and astrophysics
background necessary to make even rough calculations on my own yet.

When the universe first started, it was almost entirely hydrogen and
helium, mostly hydrogen. After the first stars formed, they started cooking
heavy elements in their cores, and as they exploded (the ones that did
explode), they released those heavy elements to the interstellar medium.
Now I know that on the cosmic timescale, type O and B stars are going off
like flashbulbs all the time; their total lifetime is in the millions, not
billions, of years. However, they are very rare compared to other sorts of
stars. (The vast majority of stars are red dwarfs, which, as far as I
understand, do little or nothing to enrich the interstellar medium with
heavy elements.)

Now most of the "Where are they?" discussions I've seen *seem* to assume
that life could have sprung up just about anytime since the beginning of
the universe. But clearly, life could only have sprung up easily after the
interstellar medium reached a certain level of richness in such elements as
carbon, oxygen, and nitrogen. And the stars that make these elements and
release them to the interstellar medium are comparatively rare. I'd be very
interested in seeing any competent astrophysicist's estimates of how
metallicity of the interstellar medium (remember, astronomers call oxygen a
"metal") has changed during the life of the universe.

It may be that there were simply not *enough* heavy elements concentrated
in the universe for life to have gotten going much sooner than it got going
on Earth. This was about five billion years ago, about halfway to
three-quarters through the life of the universe, depending on whose numbers
you like. If anyone has any more information that might support or
disconfirm this idea, I'd be very interested in hearing about it.

My hunch is that we just happen to be the first on the block. I'd like to
know how the answer to this question I've raised jibes with my hunch.

Eric Watt Forste   <>   http://www.c2.org/~arkuat/


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