NASA Breakthrough Propulsion Physics Project (no longer funded) has an introduction to space travel which covers FTL and reactionless drives – Warp
Drive- When? The only suggestions for Faster Than Light travel that appear to have scientific credibility (for very lenient values of "credibility") are Wormholes and the Alcubierre drive (original paper here), both of which rely on Exotic Matter (matter with negative mass). Exotic matter probably gives us reactionless drives as well, like the diametric drive (cool name). Now, if only we could find some…
For an SFish treatment of these concepts, the Orion’s Arm project has nice entries on Wormholes and Reactionless Drives.
