Re: poly: polymath digest for 16 Dec 97

From: d.brin <>
Date: Tue Dec 16 1997 - 19:40:34 PST

Hi folks. I love this discussion! But do step back and consider that the
Great Silence can have an entire array of potential explanations. (For
absence of apparent ETIC in our light cone.) In my paper
(Q.Journ.RoyAstronSoc. 1983) I survey the range of morphological
explanations in Zwicky-space.

It seems that the 'Uniqueness Crowd' (Tipler, Hart etc.) emphasize
solutions to this quandary that limit or reduce 'early' factors in the
modified Drake equation.

For example, Hart limits N(e) the number of Earthlike worlds, using logic
that has since been demolished by atmospheric scientist Kasting. (It seems
that Sol's 'life zone' is pretty wide, though our Earth does seem to skate
its very innermost edge.) Other uniqueness folks would reduce F(l) or
F(i) (The fraction of species that achieve intelligence) to explain the
apparent scarcity.

The Drake-Sagan crowd nearly all choose 'late' terms to de-emphasize.
Recall the nuclear winter scenario? That had its origins in Sagan's need
for a mechanism to cull violent and expansionary species (since simple
radiation and blast from a nuke war would not do it alone.) By thus
reducing average value of 'L', he was able to posit that only gentle (and
presumably non-expansionary) races would survive, thus explaining the
absence. (They aren't here yet, and they are nice, so we'd better be too.)

Other Contact Optimists emphasize other late Drake Equation terms, eg. ship
speed. Many of them give it a value of zero, reducing the expanded Drake
Equation to the Classic Drake Equation, wherein all species stay where they
evolved. This also solves the absence question.

Finally, some use the Approch-avoidance cross section. (We would not
notice a space civ that loved living on comets and communicated by

See my paper for the full scan of concepts. (Alas, there has been no
substantial work since, except for Robin's discussion of the Great Filter

The best explanations are those that are compulsory (impose themselves,
creating a relatively stable equilibrium condition). By 'best' I do not
mean nice, though. 'Malign Probes' is a scenario that fits -- VonNeumann
machines that seek potential competitors and destroy them.

The nicest scenario is 'Water Worlds'. (No, I don't mean Costner's
movie... though I do recommend the Postman!)

This scenario launches from the fact that Earth skates the VERY inner edge
of Sol's life zone. Our atmosphere must be virtually transparent in order
to shed enough heat to avoid calamity. Co2 levels must remain minuscule.
(If Earth were now at Mars's position, it would have liquid seas, having
achieved a Gaia balance with dense CO2. Small size is what killed Mars.)

This makes Earth potentially exceptional, even more so than its big moon.
Suppose the vast majority of life worlds out there have MORE water than
hot/dry Earth? We have more land to develop walkers with hands who can use
fire. More free oxygen for high metabolisms.

This is the compulsory/plausible explanation that I love the best, because
it means there are tons of beautiful worlds out there, some with
philosophical sea beings, but almost no hands-fire potential competitors.
We will be the travellers who bring star drive. We will set the tone.

We will be the postmen.


Of all the explanations, it's the most favorable I've seen.

Received on Wed Dec 17 03:32:40 1997

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