Dimensional Buoyancy Drive

The Dimensional Buoyancy Drive is a highly advanced form of Faster-Than-Light travel used by the Eight World's Empire and Ancient Empire. Operation requires massive amounts of energy, which is used by a Drive Core. The Drive Core creates a "crack" in the border between dimensions, which the ship enters using conventional drive systems. It also projects an artificial mini-universe around the ship, allowing the ship and crew to survive the journey.

Nearly all models of the Dimensional Buoyancy drive are designed to open cracks to the fifth dimension, where space-time is compressed. Thanks to the normalized space-time pocket universe projected around the vessel, standard drives can then be used to travel to the destination, at which point the drive will open a crack back to the so-called "normal" universe. This method of travel can reach the equivalent of 100c, which causes a non-trivial delay. That's where time travel comes in.

In the fifth dimension, time as we know it is represented physically, which allows a starship to also operate as a time machine. All ships sent back in time, however, have simply disappeared (And the Eight World's Empire has never even attempted it). Of course, this oddity creates a quite interesting situation. It is standard practice for the vessel to use this phenomenon to arrive mere seconds after it left, but this does not mean the vessel is travelling instantly. It still travels at 100c to its destination, and the crew waits through the entire journey. Career Navy officers and interstellar merchants thus have "shorter" lives.