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Re: starship-design: FTL idea - Steve

Steve VanDevender wrote:
>Timothy van der Linden writes:
> > Well, the calculations I did where compared to another (rest)frame. What
> > worries and confuses me is that the event reversal only happens in certain
> > frames and not in all frames.
> > But I'll accept this as one of the oddities of relativisics.

>You can't have another "rest" frame.  If you're going to declare a
>particular frame to be the "rest" frame, you need to work the problem
>consistently with reference to that.

>The point, which you now seem to understand better, is that if events
>are connected by a spacelike (FTL) worldline, then not all observers
>agree on their time ordering, as opposed to the case of events connected
>by timelike or lightlike worldlines where all observers do agree on a
>time ordering.  I'm not sure what you mean by "the event reversal
>happens in all frames".  For any spacelike relation of events there are
>always some observers who see one time ordering and some who see the
>other time ordering.

Absolutely wrong.  Any string of events where any pair of events is
within the light cones of each other will have a time ordering which
_all_ (sublight) observers will agree upon.  In particular, the time
ordering of events happenning to any sublight moving entity will be

Now, with FTL communication, you can typically set up a signal which
is sent to yourself earlier in time.  Thus, the event of receiving
the signal in your past is within the light cone of the event of
your sending the signal.  This results in a signal sent backwards
in time, and _all_ (sublight) observers will agree upon the fact
that it went backwards in time.

Note I'm talking about "sublight" observers.  What about FTL observers?
Don't even talk about FTL frames of reference.  Some of you may have
played around with space-time graphs and Lorentz transformations in
the 2D case (1 dimension of space, 1 dimension of time), and gotten
the impression that FTL frames of reference are pretty normal, even
though they're "flipped" a bit.  This is utterly wrong!  FTL frames
of reference in any higher dimension (we live in the 4D case) are
exceedingly bizarre.  Unless your familiar with the mathematics of
topology, I'm afraid you probably can't comprehend how bizarre they
are.  Suffice it to say that there's no way to construct an atom,
any sort of orbit, any sort of camera, or any sort of person in such
a frame of reference.  The topology is such that particles and light
travel infinitely fast in some directions, at finite speeds in others,
and _can't_ travel in other directions.  If you _could_ exist in such
a frame of reference, and were sitting in a room, you'd find that
you could see some of the walls, but not others.  If you got up and
walked around your chair, you'd be able to see it from some angles,
but not from others.  An ftl frame of reference would be like this
from the microscopic level to the global level.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi