I enjoy a good space opera and have always wanted to write my own, but at the heart of most space operas, even the relatively “hard” sci-fi ones, lurks the FTL drive. Plots just don’t advance well without them. But if relativity is correct, then FTL is the same thing as time travel, which leads to paradoxes and the death of causality. (There are two main flavors of fictional FTL drives: Those that travel FTL through normal space, and those that jump instantaneously from one place to another. For the purposes of what I'm discussing here, you need only consider the second kind, the "jump drive") Because I’m unwilling to let go of causality but unable to ignore relativity, I would need a method of FTL travel that couldn't be used to time travel. But as I understand it, there are precious few options for this, and they are: Parallel Universes, Consistency Protection, Restricted Space-Time Areas, and Special Frames. The above link explains each of these better than I can. Of the four, I definitely like Special Frames the best, especially the barely-touched-upon case where the FTL traveler must take on a specific frame of reference as it begins its FTL trip. I understand that this would contradict the relativity concept of all frames being equivalent, but I have a thought on that, which is what brings me here. My thought is that a pseudo-special frame of reference could be created. If a beacon sent out a constant radio signal at a specific frequency, a ship with knowledge of the frequency should be able to utilize the Relativistic Doppler Effect to determine the frame of reference of the beacon and change velocity to match frames (I have difficulty visualizing this, so it may be the case that multiple beacons and signals would be necessary for it to work on all axes). If instead of a radio signal, the signal sent was a signal “somehow” vital to the FTL drive (not simply for navigation, but for its very function), it should eliminate the potential for paradoxes by forcing all FTL travel to occur in the same frame of reference. A potential problem I see with this design is that if the frame of reference of the object emitting the signal should change (which would almost certainly happen at some point), relativity demands that the new frame of reference signal allow for FTL travel as well. A ship could then use the new signal to travel FTL to a region of space still receiving the old signal, and use the old signal to travel back, recreating the time travel paradox. So in addition to the limitation of needing to match frames with the signal origin, the drive must also only be able to connect regions of space currently receiving identical signals (“currently” relative to an object that has matched frames), and without crossing any regions of space receiving signals from different frames of reference. With all these limitations in place, the FTL system has an interesting dynamic. First of all, ships can’t travel to regions of space that haven’t yet received a signal. If the object emitting the signal gets bumped, changing its frame of reference, a “new” signal is effectively sent out. Ships in a new signal's light cone would be unable to travel into or through the old signal's light cone, though ships in an old cone would still be able to enter the expanding new cone via the progression of time. So if a big ship was preparing to make a historic FTL journey to a distant star system that finally came into range, and terrorists bumped the signal emitter, as soon as the light cone of the new signal passed the ship, it couldn't travel beyond the edge of the new signal. It would create an incentive for a civilization utilizing such a system to continuously expand outward to ensure that the opportunity to travel further didn’t get snatched away from them. My question is simply, does the above sound right? It's all fictional, of course. But I'd be disappointed to learn that I've missed some glaring design flaw, or worse, the potential for a paradox.