SETI again

a few problems with this idea.

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.

2) if these people are anywhere close to human, they will end up
with wars and such which will slow things down and would likely cause
it to take thousands of years before they could start to colonize a
new planet.

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

4) any kind of natural disaster could happen to knock them back to
the stone age, and then it would be milieus before they even think of
heading to the next star.

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.

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.

the point is that the figures for expansion is very optimistic

--- In spacesettlers@yahoogroups.com, "Lucio de Souza Coelho"
wrote:
>
> On 7/21/06, Robert wrote:
> (...)
> > why would they have to be billions of years ahead of us. why
would
> > it necessate them taking over and colonizing the entire universe
if
> > they are ahead of us. that would assume that they found a way
past
> > light speed. if it cant be beaten, then they would be limited to
the
> > distance they could travel.
> > our galaxy is 100000 light years in diameter.
> (...)
>
> You don't need FTL to colonize a galaxy in a few million years. The
> numbers that I'll show here are from a diffusion model that I saw
> years ago:
>
> 1) Assume that you have colonization ships able to travel at 10% of
lightspeed.
>
> 2) Assume that you send some of those ships to a handful of systems
> close to your own. Taking an average distance of 8 ly between stars
in
> the galactic periphery, they would take about 80 years in average to
> reach those systems.
>
> 3) Assume that 500 years upon arrival in the new systems, the
> colonists are now developed enough to send their own new colony
ships
> to nearby unoccupied systems.
>
> 4) Repeating this again and again and again, you basically have a
rate
> of expansion of the colonization sphere about 8 ly every 580 years.
> This way, even a civilization in the border of the galaxy would
> colonize the whole Milk Way in 7.5 million years.
>
> Now you can say that the assumptions are too optimistic and assume,
> say, ships travelling at 1% of lightspeed and a time of 1,000 years
of
> developing of a civilization in a new system before sending
colonists
> to another one. Even though Milk Way would be full in 22.5 million
> years.
>
> However, one interesting point in your analysis is the pretty
> reasonable assumption that after some time - who knows, ten
thousand,
> one million years, whatever - the civilization in a given system
gets
> extinct. In that way, in fact the expansion sphere would be an empty
> shell, with a thick layer of thriving systems in the surface and a
> grim hollow of extinct systems inside. Those would be systems were
the
> resources used by the civilization, whatever they are, got
exhausted,
> and so the systems would not be recolonized.
>
> However, after millions or billions of years, those systems could be
> "recycled" by natural phenomena. For instance, systems were all
> asteroids had been consumed when it was home to a space habitat
> civilization could in time produce new asteroids by means of new
> planetary collisions and the like. Systems with old stars would
> eventually die and their matter would someday form new systems
across
> the galaxy. And so on.
>
> So, I would not think inconceivable that perhaps Earth is inside one
> of those "hollow shells". Although, if that is the case, our system
is
> pretty well recycled already, and ripe for supporting *our*
expanding