I've not thought too much about it, but it seems to me, on a cursory analysis, that not *all* FTL communication breaks causality. If one is only dealing with relative velocities that are substantially subrelativistic (and similarly "tame" masses etc.) it seems that one could have "sufficiently slow" FTL, albeit non-instantaneous, communications that still preserve causality. In particular, in a world where the maximum relative velocity of any pair of quantum farcasters is v_max < < c, having QE communication at a speed no larger than something of the order of 2c^2/v_max^2 (which is still much larger than c) should be unable to violate causality.
If that were the case, we could slightly fix the physics of EP QE communications (e.g. saying that large inertial shifts slightly "distort" the entanglement slowing down communication between the two qbits) in such a way that:
1) they do not allow time travel, satisfying the physics geeks among us, but
2) they are still in practice "instantaneous" for all practical *game* purposes.
Consider this. If you move your qbits using any ship slower than 300Km/s (that's several times faster than what you can get using mainly gravity assists, and it does allow you to reach the outer edge of the Kuiper belt in about a year), you can have communication between any two naturally orbiting bodies at the opposite outer edges of the Kuiper belt with a round-trip delay of about a tenth of a second - that's better than what you get from most telephone calls today. Use fast couriers running at top speed, and this degrades to about a dozen seconds (which is not *much* worse than what I've occasionally experienced with skype...), or again a fraction of a second within the inner system.
Pandora gates probably ruin your QE, but I do not see that as particularly problematic *in*game*terms*. Of course, if you throw Pandora gates into the mix, causality starts to face serious trouble (from the wormhole, rather than the QE) but not necessarily unfixable (see e.g. http://www.aleph.se/Trans/Tech/Space-Time/wormholes.html) - and in any case, if you are talking about Pandora gates, you are handwaving so much that a little more shouldn't hurt.
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Fixing QE to preserve causality AND faster-than-light communication
Thu, 2010-09-09 19:54
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Fixing QE to preserve causality AND faster-than-light communication
root@Fixing QE to preserve causality AND faster-than-light communication
[hr] This one has an easy solution from my point of view. The first step it to grant the arrow of time the status of having it's own dimension, and therefore it's own string. What q-bit communications do is wait for 2πT[sup]11[/sup] seconds, where T is the total length of time in the universe in seconds. When the entangled q-bit is racing up on itself again, it already knows how the flip will turn out, so it can "instantaneously" choose which way it needs to flip.@-rep +1
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[hr] "This means absolutely nothing, in case anyone was wondering."@-rep +1
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