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RE: starship-design: FTL travel
I've finally gotten around to posting a contribution to the recent
discussions. As I understand it, when we talk about 'faster-than-light'
travel to the stars, we are doing so from our reference point here on Earth.
To summarise the previous discussions briefly: if a spacecraft was launched
towards the nearest star (call it 4 light years away), and travelled there
and back (assume instant turn-around time!) in less than 8 years, we would
say that it has travelled faster than light. I'm assuming it hasn't used a
wormhole or other such shortcut.
However, say the spacecraft travels at the 0.894c mentioned in previous
posts. Then to us observers here on Earth, it would return after about 8.944
years. To the crew on-board, the journey would only last about 4 years. So,
as far as the crew are concerned, they have effectively (but not actually,
to us) travelled faster than light - because of time-dilation.
The point I'm thinking about is that if you're purely an explorer, and don't
care about being able to sensibly communicate with people back on Earth,
then it doesn't matter if you can't employ FTL travel as long as you can
travel very close to 'c'. For, due to time dilation, you can comfortably
cover vast distances in what seems like a reasonable amount of time to you
(as the crew in Poul Anderson's "Tau Ceti" did). You have, in a sense, your
FTL ship. You get to travel round the universe and see a lot of sights in
your lifetime :)
Thinking along more practical lines though, such interstellar travel is more
likely to be funded by a corporation of some kind rather than a very wealthy
(and lucky) individual who gets the chance to do the aforementioned jaunt.
The point being that the corporation is going to want some kind of financial
return in the foreseeable future for stumping up the cash to begin with.
They're going to want a *true* FTL ship - something that can travel from
Earth to a destination hundreds of light-years away and back within a decade
(say). They don't care that travelling at a mere 0.9999c will make the trip
seem considerably shorter for the crew if they don't get their investment
back for a several centuries.
To sum up: we're discussing FTL travel from the point of view of being on
Earth. Travelling four light years at 0.89c and having the *crew* think
they're burning along at 2c (due to time dilation) isn't FTL.