Re: starship-design: One more try...

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

L. Parker wrote:
>Ken,
>> There are four classes of journeys one can even consider making.  

>> A) Within your forward time cone (All STL and light-speed falls in here)
>> B) Out of your forward light cone, but still (from Earth's perspective) 
>> forward in time.
>> C) With your backwards time cone (Staying in the same place but travelling 
>> backwards in time.
>> D) Our of your backwards light cone, but still (from Earth's perspective) 
>> backwards in time.

>> The first point is that there is no difference between B and D.  They are 
>> both FTL and they are both identical.  The only distinction is made from 
>> Earth's perspective, so it is not a real distinction. For those of you who 
>> think that B-type FTL journeys are okay and D-type are not, that is an 
>> artificial separation that can only be true if there is a preferred 
>> reference frame.  You can't outlaw D without outlawing B, and therefore 
>> outlawing all FTL.

>Awww, Gee, all I really wanted for Christmas was B...

Then maybe you want a special frame of reference, and for that special
frame of reference to be that of Earth (?!?!!!).  But we can't always
get what we want.

>C is a matter of slight of hand, if you can move back to the same point in 
>your space line and backwards to an earlier point in your time line then it 
>doesn't really matter how many permutations in time and space it took to 
>get there. Only the end result will count.

Yes, and what's important to note is that the examples of using FTL
from time travel only depend upon the end result in B type travel.
It doesn't matter what permutations it took to get there, so long
as you get there (and Earth's frame of reference isn't a special
frame of reference).

>> This is obvious; A D-type trip away from Earth, followed by a D-type trip 
>> back to Earth, will add up to a C-type trip.  Other examples include Adding 
>> a B-type and a D-type trip to get a C-type.  There are lots of ways to go 
>> backwards in time once FTL (B and D) is allowed.

>No it isn't obvious, you've defined TWO cases A and B, C is a subset and 
>D is simply B- NOT the other way around. To say that B isn't possible 
>because D isn't is the same thing as saying the square root of one isn't 
>possible because the square root of minus one isn't possible.

Wrong, to say B isn't possible because D isn't is the same thing
as saying the square root of -9 isn't possible because the square
root of -1 isn't possible.  It's skipping a lot of steps, but the
two situations _are_ basically the same.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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