SETI again

On 7/21/06, Robert wrote:
(...)
> 1) it assumes that all the planets are easily usable. imagine someone
> trying to use mars for colonization. it would be hard to expand with
> things as is on it, and would take much of that thousand years to
> make it where you could expand quickly. even if they used the
> asteroids to create habitats it would take a long time before they
> could be able to build them on their own.

I was preferably imagining space habitats. A civilization that for
some reason limits itself to planets will likely spread more slowly -
because a system with the "right" kind of planet is likely to be rarer
than *any* system with any kind of rocks around (habitats are not
picky with planetary systems).

(...)
> 3) if they build space habitats there would be little reason to head
> out to the next star for much longer than 1000 years.

Perhaps, but as I hinted even if you raise some of the assumptions but
one or two orders of magnitude the galaxy would be colonized in a
cosmically small time. Cosmic time is *really* beyond human scale.

(...)
> 5) after 500 years they will likely have forgotten that they came
> from a different star, with only legend to tell them where they came
> from. If they send out another colonizing ship, they would be as
> likely to send it to a star that had already been colonize as not.

Frankly I think that you are overestimating the capacity of people to
forget history. Last time that I checked I had not forgotten that
Brazil was discovered by Portuguese navigator Pedro lvares Cabral,
506 years ago. ;-)

Anyhow, in a long enough timescale - guess, 10,000 years - that is
likely to happen. But at a time like that I think that any such system
would be well inside the expanding shell of colonized systems, and
therefore they would not matter for SETI estimations.

> 6) mutations would occur fairly quickly in new environment, meaning
> the ones that left might not seem at all like the ones that arrived.
> IF there are much like humans they will likely consider the mutations
> as an affront, and treat them like lower class citizens leading to a
> war between races. If the do end up sending a ship to a star already
> colonized, it would likely be a situation of two alien races meeting,
> with the likelihood of war.

Again, this makes no difference for a SETI estimation of contact with
a truly alien civilization, for those warring groups mistakenly
thinking of each others as "aliens" would also be well inside the
expanding shell of colonized systems.

> the point is that the figures for expansion is very optimistic
(...)

Perhaps, but again even if you grow the numbers you end up with
cosmologically small times.

Also, you are perhaps being overly pessimistic if I am correct in
understanding that you suppose that *always* something will go wrong
with every colony. Lets picture another scenario in the first step of
the expanding shell. And I will use planets instead of habitats
because the chance of isolated, gravity welled planets going wrong is
far higher.

Suppose that in a not so distant future Earth finds (using
supertelescopes and the like) 12 nearby systems (yes, I am watching
too much BSG ;-) with somewhat colonizable worlds. By "somewhat
colonizable" I mean something at least as good as Mars, appropriate
for Zubrin-style colonization. Now lets see what happens in this
scenario - and beware, I will use some dramatic but not-so-plausible
pulp space opera cliches: ;-)

- Shortly after sending the ships, Earth itself reverts to the Middle
Ages thanks to a virus that kills 90% of Humanity, disintegrating the
network of knowledge and products that maintains our technology.

- Colony #1 is never reached because the ship going there hits a
meteoroid at thousands of kilometers per second and is destroyed.

- In Colony #2 they found out that remote estimation of resources in
the planet was far from accurate and everyone dies a few years after
landing there due to a shortage of the most basic elements for human
life.

- In Colony #3 the colonists successfully conduct a terraforming
process across a 200-years period. Unfortunately the system has too
much asteroids and one of them hits the planet. They revert to a
pre-historian civilization. Also, since the terraformation was not
that perfect, they quickly start to suffer adaptations developing
spidery legs and arms due to low gravity, barrel-chest for huge lungs
able to breath the thin atmosphere and huge black eyes able to see
well in the dim red light of their sun.

- A social engineer on board of the ship for Colony #4 purposely
erases all records of Earth history and invents some bullshit about
the ship being created by God to populate a new world. People in
Colony #4 develop a burgeoning civilization with the rest of knowledge
supposedly given by "God", and a thousand years later they send
spaceships to new worlds fulfilling God's plans of being fruitful and
multiply. However, they end up sending ships to Earth and Colony #3,
where the colonists conduct a genocide of those sentient creatures
that surely are sons of *Satan*! Specially those bug-eyed men from
Colony #3, not even human!

Even though, you still have eight healthy colonies that will thrive
and eventually colonize new systems. (I guess that Colony #4 sent some
ships to them to, but luckily they had the good sense to nuke those
pesky zealots still in outer space.) Heck, even Colony #4 *is*
contributing to the expansion of the shell (in their own twisted way)
if they sent ships in other directions.