OK, this is goofy, but I just had a dream about a method of exotic propulsion that has a kind of half humorous, half intriguing aspect.
As you might recall, there's been talk of the Planck length Quantum Foam
that might compose the
smallest yet known environment, in which fluctuations, or turbulence in the quantum field create a type of foamy surface.
The propulsion in my dream used a component of the Casimir Effect
to flatten out this foam, and
when the foam rebounded to this energetic foam configuration, prodigious quantities of energy were released.
In addition, tachyons were released and condensed and these pulses enabled the 'drive' to exceed faster than light speeds (at which tachyons exist).
Then, the strange part. I log on to Wiki and it turns out that tachyons do condense
least in one exotic theory.
See, this is what happens if you spend too much time here.
Incidentally, in this dream, this 'quantum foam' drive was discovered as the mode of travel in a craft that was found in a deep cavern and
attributed to a race of 'Ancient Ones'.
The drive was 'explained' to me in even greater detail, which included some kind of 'grabbing' like a ratchet in a rapidly spinning water wheel,
which enabled the drive to have an 'inertial damping' effect, resulting in the ability to hit FTL speed and then return to 'impulse' speed, almost
instantaneously. Tapping into this used the energy inherent in the 'fabric' of the quantum universe, so it did not require tremendous acquisition of
energy to propel physical craft. I won't go into the 'Tachyon Tunneling' details and stuff because, well, it's already silly enough.