[ExI] No mirrors, was Deceleration mirrors

[BillK]

On 21 September 2015 at 09:20, Anders Sandberg  wrote:
<snip>
> We have looked both at the laser launch and in-flight damage
> deflection/repair. Some cool problems there (interstellar hydrogen becomes a
> proton beam when you move fast enough).
>

Two conflicting problems there.

If the ship travels slow, then interstellar debris can be shielded
against, but travel time takes centuries. This system is OK for AI
exploration. (So why aren't they here already?).  :)
By the time humanity is considering interstellar travel we may be AIs
ourselves, so we might be happy to travel slow. Flesh bodies really
don't behave well during long-term space travel.

If the ship travels fast (substantial fraction of lightspeed), then
interstellar debris becomes a major problem. Possibly even a
show-stopper. It is not just hydrogen. There is dust as well, some of
which might be significant bits of rock, cosmic radiation, etc. So the
ship needs a good shielding system.

The trouble is that the interstellar medium is not evenly spread.
Average calculations might look OK until you hit a denser cloud, then
the ship becomes more interstellar dust. It would be a big help if we
could map routes first by AI ships and report back to earth. They
might even be able to sweep routes clear of dust, but over the time
scales involved the routes may become clogged again.

I have the feeling though that (excluding magic physics) interstellar
travel will prove to be too expensive / dangerous / difficult and civs
find more preferable things to occupy themselves with.

BillK