From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Wed Jul 07 1999 - 21:51:00 MDT
> From: Damien Broderick <d.broderick@english.unimelb.edu.au>
>
> At 09:27 PM 7/07/99 +0200, Anders wrote:
>
> >It also shows that nearby supernovae aren't necessarily
> >planetkillers. As far as I know there was no major extinction the last
> >million years.
This seems correct. The atmosphere functions as a pretty good shield.
However, if you wait long enough one will occur close enough to you
that the atmosphere doesn't help much. [That is a good reason why
SIs aren't located in close proximity to us unless they are actively
defusing the larger nearby stars. But more on that later...]
The current theories on Supernovas, I believe has them forming
as a result of gravitational waves triggering large gas cloud
compressions and bursts of large star formations. These rapidly
evolve into supernovas. There was something about the rotation of
the galactic arms causing such waves/star formation bursts/SNovas
at periodic intervals. So your neighborhood may be comfortable for
quite a long period of time and then get really nasty.
There is also the theory that the Sun's orbit crossing through the
galactic plane causes the disruptions in the Oort cloud/Kuiper
Belt that then results in increased bombardment for short periods.
Plus you have the problem of stars randomly orbiting close to our
solar system causing orbital disruptions. Think about all
those stars with those big planets in very strange orbits...
So in the "windows of opportunity" you need to evolve to the point
where you can anticipate, plan for and survive these catastrophes.
>
> No, but if you're inside a relativistic starship (or time-machine, in my
> fanciful version in DREAMING DRAGONS), that's a lot of compressed sleet all
> at once... I get more and more worried about the hazard of travelling
> fast. Nano streams catapulted to near c, the front-runners taking the
> ablation shock (but maybe, alas, adding to it in secondaries), sounds like
> maybe the only plan that's safe against wear&tear.
>
There were several articles in JBIS regarding the problems of high
velocity travel back when people seriously considered things like
this. A simple little H-atom packs a heck of a lot of energy at .99c.
The particles are difficult to deflect and really do a number on any
nanomachinery. Sure you can stick a big Tungsten shield out front
but that makes your starship/nanoprobe heavy and drives up your
acceleration costs. Ignoring the fact that all that energy you spend
to get to those high speeds could better have been spent "thinking" while
you were going slow.
I believe Robert Freitas is planing to do a more in-depth analysis
of the radiation damage problem on nanomachinery in Volume II
of Nanomedicine (expanding significantly on Eric's rather brief
treatment). Unfortunately we will have to wait a year or two to
get it.
Robert
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