--- Robin van Spaandonk <[EMAIL PROTECTED]>
wrote:
<SNIP>
> In short, causality isn't really violated, it only
> appears that way to an observer relying on EM signal
> transmission for his/her information.
> [snip]
This could be argued from a certain point of view in
the one way FTL sense. But if we allow round trip FTL
signals, we find that according to the relativity of
simultaneity and thus the equivalence of all inertial
reference frames, as given by SR and later GR, that we
can allow events to happen which not only appear to go
backwards in time, but really do in measureable ways.
Such as, frame A, not moving, can send an FTL signal
to frame B, moving at some high fraction of c. Frame B
will, according to his view of things (which according
to relativity is just as valid as A's) receive the
message before it is sent from A. Now, if he sends an
FTL signal in reply fast enough (this is nowhere near
infinity, just for clarification), frame A will see
this signal arrive before A ever sends the first
signal. So what if A decides then not to send the
signal? A reply from nowhere, literally.
These are serious consequences of mixing FTL and
relativity theory as it is currently held to be true.
However, there is a nice solution to this, it involves
modifying the transformation equations so that
simultaneity is not relative, but absolute. Therefore,
there is an underlying ordering of cause and effect,
and no time travel paradoxes occur...the FTL signal
just gets there very fast, but never before it is
sent.
Note that this is perfectly acceptable and compatible
with observed relativistic effects, such as Lorentz
contraction and Larmor retardation (commonly called
time dilation). The only necessary changes involves
the distance-related term in the t' transform, thus
removing the time 'desynchronization' from our
results. The work of Tangherlini and Selleri
demonstrates this nicely.
--Kyle
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