actually, according to spoiler statements about
dimension book 9, PPE and the popular image of zero point energy (that of energy extracted from space itself) are related. tapping such energies would require either magic artifact making knowledge or advanced math and high end physics, mechnical, and electrical skills. or both.
in physics zero point energy is an energy state, basically the smallest energy state something can exist in. much like how if you take a bit of matter and break it down you get atoms, which are made of subatomic particles, which in turn are made from quantum particles. quantum particles are in turn just 'packets' of energy.
zero point energy is the same kind of principle allied to the
fundamental interactions of the universe. basically those forces at their most basic forms and on the smallest scales possible. they're subject to things like the heisenberg uncertanty principle and other such oddities of quantum mechnics, which is why no one has been able to create a grand unified theory explaining how they work one way at the quantum level but another on the classical (atoms and up) levels.
the zero point feild is the expression of electromagnatism at this level, and there is strong experimental evidence that it governs the inertia aspects of mass. the inertial mass manipulation is based on proposals derived from the mathmatics explaining how this works, basically with the right electromagnetic feild you can change how your matter interacts with the ZPF and thus make the inertia think you have less mass than you really do.
the tachyon aspect i drew from hypothetical faster than light quantum particles..combined with the parts of string theory which tell us the universe has additional compact dimensions of measurement which we cannot perceive. there is strong experimental evidence for this, although string theory is incapable of fully bridging the gap between the quantum and the classical. (one of the reasons brane theory was developed..which is basically string theory with a few extra compact dimensions and some extra sanity-reducing math. and it still doesn't explain everything)
one of the possibilities predicted when string theory (or brane theory) got combined with zero point feild studies is that with a strong enough EM feild interacting with the ZPF, a ship could translate to a version of the universe where one or more of those compact dimensions isn't compact, where speeds greater than the convnetional speed of light are possible.
sounds like a home to tachyons to me, so i tossed it all together and kicked it up a notch. Bam!
i basically pulled all the other attributes out of my rear..mainly for game balance sake. i tried to pick restrictions that made sense and flowed from the initial assumptions. like the fact gravity doesn't block it. it's an electromagnetic based interaction with the fabric of space, not gravity based. so it became a literal 'go anywhere drive'...but since that would allow the ship to potentialy try and come back to 3d space, the problems of 'what happens then' come up. and so on. the bit about the geometric increase in power required to go faster, and the mention of the feild being self-powering to an extent is a handwave to overcome the real world problem of needing absurd amonts of power in the EM feild to pull off the FTL bit.. you'd basically have to funnel the entire earth's yearly power output int othe EM feild every second to make it work. so instead i handwaved the 'self-powering' version where outside power has to be added to keep things stable (in order to not excessively violate the laws of thermodynamics..there is no such thing as a free lunch in physics). the cool upside? with DB9's revelation about the PPE/vacuum energy connection, the drive now counts as techo-magic!