On 11-09-24 01:58 AM, Kyle Mcallister wrote:
[ ... ]
It should be pointed out that there are formulations of relativistic transforms
(Tangherlini, Selleri, etc.) which allow some form of absolute reference frame,
and therefore absolute simultaneity. There is a distinct 'past' and 'future'.
These various formulations are indistinguishable from conventional special
relativity up to C. Above C, they give wildly different predictions; with
special relativity, you run into causality violations.
I believe I alluded to something like this earlier.
In a universe which adheres in general to the SR model, you can, none
the less, allow instantaneous information transfer in a single,
distinguished "universal rest frame" without leading to any causality
violations.
It's when you allow the "instantaneous" transmitter to move at an
arbitrary velocity, and send information to an arbitrary receiver in the
same inertial frame as the transmitter, with arrival time being
"instantaneous" in the (arbitrarily selected) rest frame of the
transmitter, that you run into trouble.
The causality violations happen when you send information FTL in one
frame (frame #1), relay it to someone in another (carefully selected)
frame (frame #2), and send it back to the starting point in the that
other frame. When it comes back in frame #2, it's going backwards in
time in frame #1, and it ends up at the same spatial coordinates it
started at in frame #1, but at an earlier time.
Note well: Time travel is just fine (entails no contradictions) as long
as the destination is outside the backward light cone of the starting
point. It's getting the destination into the backward cone of the
starting point which requires the frame hopping. This becomes clear if
you try to draw the "contradiction" on a space time diagram. You can
move from certain positions which are outside the backward light cone of
an event to inside it, if we allow "single-frame" FTL travel, but to
move from the event to a position outside either of its cones from which
you can still get to a point inside its backward cone, you need to
frame-hop.
To put it another way, two events which are separated by a space-like
interval can occur at (nearly) any relative times you like in any
particular inertial frame. To get the contraction, you need to travel
across one or more space-like hops, and end up with a time-like
separation from your starting point -- and the separation must be in the
"wrong direction".
(I hope this made at least a little sense...)
If an assumed absolute frame is present,
Which, BTW, is the case according to at least some modern theories of
cosmology.
Any model in which you can see yourself if you look far enough out into
space has an implicit absolute frame in it. As I recall, there was a
major search, using Hubble, for just such a situation a while back (no
luck, tho, the universe may still be open for all that experiment showed).
