On 28 Mar 2019 at 18:30, Kurt Feltenberger wrote:

> I don't see any sort of time travel or other paradoxes being created
> by how Traveller handles "FTL" travel.  Jumpspace isn't normal space,
> it's something else, and the drive takes the ship and just enough of
> ourspace with it (a bubble, grid, whatever) to maintain reality during
> the duration of the jump.  For the time spent in J-space, the ship,
> its contents, and the "bubble" aren't in this reality.

The problem is that the time travel bit is a function of the geometry
of *our* spacetime. It doesn't matter *how* you from point A at time
T1 to point B at T2 (values for the distance covered and elapsed time
vary according to the reference frame of the observer).

If the interval (a value that is calculated somewhat like you
calculate distance between (X1,Y1,Z1) and (X2,Y2,Z2), but includes
the time coordinates and the speed of light) is such that light
couldn't have gotten between the two points in spacetime then the
relationship between the two events will be seen as time travel in a
number of reference frames.

That is, for some observers event 1 (the jump entry) will occur
*after* event 2 (the jump exit).

Doesn't how you get from point (X1,Y1,Z1,T1) to point (X2,Y2,Z2,T2).
All that matters is the space time co-ordinates of the two events.

On the other hand, time travcel isn't *explictly* forbidden by
relativity. It just creates some odd restrictions.

FTL
strict local casuality
relativity

Pick any *two*.

Casuality is "causes must alway preceed events". Local causality
means that it applies to any frame. *Global* casuality allows causes
to preceed effects in some frames. (I may have those backwards).

and you can swap in "time travel" for "FTL" in the above set of
choices.

relativity compliant time travel puts some really odd conditions on
time travel. Like you can't change the past. But if you don't *know*
what happened in the past, then you can do things. Mind you, you may
*think* you know what happened but be wrong. :-)

This goes clear down to the quantum level. So if you try to shoot
Hitler, *something* will prevent it. Because that is the highest
probability event.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com