>CurtAdams@aol.com wrote:
>
>> retroman@tpk.net (Michael Lorrey) writes:
>> >Once we've
>> >expanded past the limit of possible extinction, then any such
>> >catastrophe thereafter is simply a stumble in our march across the
>> >skies.
>
> >Depends on how fast we can expand, which isn't yet clear.
>We could expand at a rate of 0.50% of light speed in all
>directions (.005 C) and still have the ability to allow 50% of all of
>humanity to escape destruction, assuming they are still human in a
>million years.
That would be fine, but .005 C is 1,500 km/sec, which is really fast for
something big enough to function for the 1000 or so years it would need to
get to a nearby star (5 ly).
But, to be fair, if we have on average 100,000,000 years and need to travel
1,000 ly, 1/100,000 of the speed of light will do (3 km/sec). If deep-space
colonization is possible at all, that is certainly doable. So I guess
gamma-ray bursters aren't a serious problem for any deep-space civilization
bigger than one burst.
>Given the vastness of space, it will hardly be like the evactuation of a
>city. Even using salt mines would suffice for planetary protection,
>while with space, there are plenty of comets to go around in the Kuiper
>belts of most stars.
The limiting factor for survival is not cubic volume, but infrastructure.
That's bound to be in limited supply, and because building burst-hardened
infrastructure is very expensive, there will be very little built to survive
a burst unless we have plenty of warning and a fair amount of determination.
>Even at a slow rate of human expansion, the
>population density will still be less than one person per cubic AU or
>even small fractions of that.
Population density will be much higher for inhabited space, obviously. In
any case, it's irrelevant, as space and the things in it need a lot of work
before they are suitable for human occupation through a 100-year flare of
hard radiation.
Hey, where's my reference? I want to read up on those technectium deposits.