What FTL models are appropriate given my constraints?
I'd like to have faster-than-light travel (and communications) be an late-game option for a video game I am working on. The extent of the playable universe is approximately 4 million light years in all directions, and this area will have at least 1 spiral galaxy in it, plus whatever other features I can contrive to make it look as realistic as possible. Probably a few dwarf galaxies and globular clusters as well, something that looks similar to the Milky Way and its immediate vicinity.
In-game, the passage of time will be 1 megasecond per 15 minutes of real-time, or about 3 years per real-day. I suspect that this rate will allow for significant exploration possibilities with advanced sublight propulsion (mmo, players might take real-weeks to send ships to destinations if need be).
I'd like to describe the FTL technology sufficiently so that players feel as if this is a real thing. I know that this can't be a science-based or hard-science question (FTL isn't those things at all), but I still want some suspension of disbelief.
There are quite a few science fiction tropes to choose from (or I could even choose multiple models I suppose), but many have issues that make them less than ideal.
Which FTL models could fit my requirements?
- It shouldn't allow instantaneous travel, even at the highest level of miniaturization/efficiency/whatever
- It should be compatible/consistent with an associated FTL communications concept, at the very least not ruling that out entirely
- Ideally, it also shouldn't directly imply FTL communications either, so that communications/propulsion might be independently discovered, in either order
- It should be ship-based, either requiring space vessels or that being the most practical way to utilize it
- Vessels shouldn't be easily interfered with while in transit, no photon-torpedoing the Borg while they're chasing you at warp speed, though technologies that prevent the FTL from functioning in a large area or make it less efficient aren't ruled out entirely
- Effective speed is still limited such that it might take several game-years (minimum) to cross the entire playable universe even in the very late game
Science fiction tropes, fringey pseudoscience, and any other concepts are all welcome. Answers that suggest more than one distinct concept to be available are also welcome. I'm modestly well-read on science fiction, but please include both author and title for those concepts I might be unfamiliar with so that I can google them if need be. Answers that suggest more than one concept also welcome.