Billy Brown wrote:
>
> IMO, the picture isn't that simple. Early nanotech won't be able to burrow
> that well - remember, there is nothing preventing us from using 100 MT
> warheads instead of the puny <200 KT devices currently in fashion. Later
> nanotech could do it, but by then you're facing multi-gigaton weapons.
> Mature nanotech could protect you from anything reasonable, but by then I
> would expect all threats to be pretty unreasonable. For a good level of
> security, you really need a good anti-missile system and enough room to use
> it.
>
If we are willing to believe that nanotech permits at least some way to
build large structures using multi-generation assembler production techniques,
then it should be possible to send arobotic probe to the Oort cloud and find
a very large comet or a bunch of smaller comets, aggregate them into a
large mass, add reaction engines, and direct the resulting mass into a
cometary orbit that intersects the earth. Just how do you intend to defend
against this? There are a great many alternative attacks: this is just
the first one I happened to think of.