# Re: Re: starship-design: FTL idea

```KellySt@aol.com wrote:
>In a message dated 8/25/97 12:29:41 PM, jimaclem@juno.com wrote:

>>Sorry I have'nt posted in a while, been busy getting children ready to
>>start school and sick family members.  I've been perusing this thread on
>>FTL travel, and I have a question.  My relativity is'nt what it should
>>be, but all this talk of causality violations brings to mind objects
>>travelling faster than sound.  Now I know that this is'nt quite the same
>>thing, but, could these causality violations just a result of limited
>>sensing ability, ie, our sensors work only a light speed, but our (ships,
>>torpedoes, comm systems) work FTL.  Kind of like seeing an explosion
>>before you hear it.  Help me out here.

The problem is more serious, and it's not so easy to explain without
pictures of space-time diagrams why FTL travel, relativity, and a
flat/convex space implies time travel.  Suffice it to say that
assuming these three factors, you can go back in time and meet

>Kind of depends on your point of view.  Obviously to those in the FTL ship
>time seems to go in the same direction.  Just the outside seems to going
>backwards until they slow down.

Actually not.  Assuming you're not warping space-time ala wormhole
or Alcubierre metric, you're in a true FTL frame of reference.
It is NOT OBVIOUS that time seems to be going in a normal direction
to you!  Why?  Because time won't seem to be going in any normal
direction.  You can define your own subjective time in a bunch of ways,
but they all basically boil down to time being what's measured by
a "clock" (whether that clock is a digital or analog, biological,
or chemical, in sublight frames of reference they all agree).

The problem with an FTL frame of reference is that "clocks" don't
work.  Even the simplest of theoretical clocks, Einstein's
hypothetical light clock (two mirrors with a photon bouncing
between them) doesn't work right.  At some angles, the clock
will operate, but not always at the same speed!  At other
angles, the clock won't operate at all.

More complex clocks made out of atoms can't even exist in an
FTL frame of reference--atoms just can't be constructed in
the bizarre topology of an FTL frame of reference.

This is a point which few people seem to note--I attribute
this to the popularity of 2D space-time diagrams.  In the
case of a 1D universe, FTL frames of reference _do_ look
normal, just with space and time flipped.  However, with
a 2D or 3D universe, FTL frames of reference are absolutely
bizarre.
--
_____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
__|_)o(_|__
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi

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