Warp Drive Speed

No true paradoxes, but there might be some interesting things that seem like paradoxes. Though, pole-barn paradox is in the same category, so that's probably what you are thinking of.

The biggest conceptual "problem" with FTL travel is that it violates causality. Causality is a local concept in GR, which is why Warp Drive can exist, but it's a bit hard for people to wrap their mind around global causality violations.

Look at the same pole-barn paradox. It seems like a paradox because order of events appears to switch. But in order for this to happen, the two events must be space-like separated. In other words, closing of the first barn door cannot be the cause of second door opening. If you rig the second door to open only after the first one closed, the pole will ram into the second door in every frame, because the signal required to open the door has not had time to propagate. This is effectively how pole-barn paradox is resolved. Yes, order of events is frame-dependent, but effect always follows cause in every frame.

But if instead of the light beam signal from first door to second I send information with a tiny warp drive ship, the information can actually arrive in time. I can have the second bar door open as response to first door closing, and do so in time for the pole to go through. Now the situation becomes truly bizarre from pole-bearer's perspective. He knows that the second door will only open after the first one closes, but he observes the second door opening before the first door closed. The effect precedes the cause.

That's the sort of "paradoxes" that we can expect with a warp drive.

Notice that these still don't cause any real contradictions. Yes, causality is a frame-dependent concept now. But even though there is a frame of reference in which you can have results of the lottery drawing before the drawing took place, there is no way to make use of that information.

Of course, GR also allows time travel, so apparently, knowing results in advance and being able to act on it would not be a problem either. But that's a separate discussion all together.

Of course, GR also allows time travel

In the space described by Eq.10 there is a region within
one of the bubbles, both in the primed and unprimed coordi-
nates, in which the ‘‘forward’’ light cone runs backward in
time, and CTC’s occur. Suppose a passenger leaves S1 on a
spaceship traveling in the unprimed bubble, starting at
t=t'=0, moving along the line y=y0, and arriving at S2 at
t~=0, t'=T'~=-yBD, at which point the spaceship has
come to rest and the bubble has disappeared. He now travels
the short distance to y=-y0 at subluminal speed through
flat space, and accelerates to sublight velocity B, so as to be
at rest in the primed coordinates. [We assume that this pro-
cess requires negligible time since y<<D and, from Eq. ͑7͒,
B may be small when A is large.] The passenger can then
board a second spaceship bubble and travels back to S1 in the
primed bubble, arriving at t=T1=-BD, thus arriving home
before starting by a macroscopic time interval and carrying a
newspaper reporting on events which have not yet occurred.
This, of course, raises the problems with paradoxes always
associated with closed causal loops. It would appear pos-
sible, e.g., to arrange a mechanism which ensures that a
spaceship will depart from S1 at t=0 if and only if no news
of such an event has arrived from S2 at t<0. This does not
mean that a model of the type introduced in MA is ruled out
as being logically inconsistent, but it does mean that in such
a model there are restrictions placed on the initial conditions.
That is, apparently if superluminal travel through some
mechanism similar to that discussed in MA could actually be
realized, it would imply that the laws of physics include a
principle of consistency, as discussed by Friedman et al. ͓7͔,
which constrains the initial conditions on spacelike surfaces
at times subsequent to the creation of closed timelike curves,
so as to ensure in some way that no contradiction arises; for
example, the initial conditions might guarantee the failure of
the mechanism by which the previous arrival of news of the
spaceship’s departure prevents its later departure from occur-
ring. While not logically inconsistent, such theories appear to
enforce correlations which are certainly counterintuitive.

I think I found the answer to my question in the paper "Warp drive and causality" by "Allen E. Everett": http://adsabs.harvard.edu/abs/1996PhRvD..53.7365E (http://exvacuo.free.fr/div/Sciences/...0prd950914.pdf)



So, it seems that if these "warp drives" are at all possible and if you can freely use them to travel between arbitrary points then you *can* use them to create real paradoxes just like any other FTL method and so this relies on contrived "consistency maintaining" methods existing in the universe, just like any other FTL method. Am I missing something?

Am I missing something?