![Embarrassed :oops:](./images/smilies/icon_redface.gif)
Anyway, let's say you have a low-tech species that relies on sound and has nothing that travels faster than sound. One day, they develop a supersonic jet, or weapon, or whatever. To them, it appears that it just broke all the rules on causality - it arrived before the sound of its passing did. Yet to our eyes it didn't.
Now put humans in the place of the above species: they somehow develop an FTL starship (no fancy hyperspace or anything, just normal space), and launch it from Mars to the Earth. The ship, very obviously, travels between the two points, and takes time to do so (it's not that fast
![Razz :P](./images/smilies/icon_razz.gif)
Also, consider the point of view of 3 observers, one at the start, finish and middle of the route:
-The first sees the ship at Mars. A moment later, and it disappears. A short while later (depending on how much faster than light it travels), the light from the ship above Earth reaches him. Because the light from the ship takes time to go from Earth to Mars, he will always see it in this order. No problem here.
-The second sees the ship at Mars preparing to leave. A moment later, before it has appeared to leave Mars, it is visible in orbit over Earth. Rather than time travelling however, the ship simply outran the last image of itself from Mars, and arrived first - even though nobody saw it do so. Here apparently is the problem, at least as I understand it.
-The third observer, being equidistant from Mars & Earth, and because the trip from one to another takes time even for the FTL ship, observes the ship departing Mars orbit before arriving in Earth orbit. No problem here.
My point is why it's not possible to say that "ok, the thing travelled faster than light, therefore it appeared to travel through time". Granted you might not be able to tell a time traveller from an FTL traveller but that wouldn't matter because the traveller would know:
-Assume that I can travel at 100c between star systems, and want to arrive at Tau Ceti in time for lunch in a particular city. I check the distance from Tau Ceti to Earth, work out how long light takes to travel from one to the other, and look through a telescope to see where the inhabited planet is. Factor in time to travel there at 100c, the length of the orbit etc, and off I go.
-Once I arrive on Tau Ceti III or whatever we call it, I go about my business. A few years later, my ship can be observed leaving Earth. Have I time travelled? Of course not - if you could magically teleport from Tau Ceti to Earth instantaneously, my ship would not be in orbit there, and I would have left in time to have arrived at Tau Ceti when I did.
As I see it, the only problem is that it probably requires some sort of universal frame of reference. I suppose for me this is the actual position of the matter at any one time - those last 3 words being the problem. However, because observers can interact and exchange information, is this really a problem? When I see you walking, I can watch your position move from A to B to C - or to be more precise, your position a minute fraction of a second ago. However, because we can communicate - even touch - we can figure out where we are (or were, perhaps) in relation to one another. So why can't we scale this up to encompass say, interstellar distances? Can you not maintain causality yet appear to break it from one point of view*?
* Perhaps an "apparent" and "actual" causality - the former would be the point of view of any one observer, the latter should they get together and work out what happened (or had a universal frame of reference, FTL sensors or somesuch). Would this work, and if not how badly?
Finally, on a (mostly) unrelated note, what happens when you introduce to a universe:
-A speed limit above that of light for information (eg your good old telepathy)?
---Obviously picking up signals might be a problem given how fast they'd go through something as small as a human head or satellite dish, but what else?
-A scanner that can observe without in any way interfering with the observed?
---What effect would it have if I could, say, determine precisely the position and momentum of a particle? How would quantum physics work (or not) with such tools?