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Supercavitation is a phenomenon by which an object travels almost frictionless with high velocities inside a gas bubble surrounded by a liquid [1]. So far, supercavitation has mostly been applied to military use.
Whereas folklore claims that relativity theory excludes any sort of ether, the general theory of relativity [2,3] and quantum field theory [4] conceptualize entities, often called ``ground state,'' ``vacuum,'' or ``empty space,'' which resemble the pre-relativistic ``mechanic'' ether in many respects. Thus it is not totally unreasonable to speculate that an analogous phenomenon might also occur in the quantum field theoretic vacuum.
The main issues of supercavitation seems to be to (i) reach and (ii) maintain this state, with the additional desideratum of (iii) flight, in particular direction, control. Let us therefore first discuss conceivable options for the formation of ``bubbles of exotic vacuum,'' and then proceed to their maintenance and guidance.
As regards the initial stage of reaching an environment which might be capable of supercavitating, one candidate would be the formation of a Casimir vacuum between conducting plates [5], which, due to boundary conditions, lacks certain modes of the electromagnetic field. As a consequence, the radiative corrections and the associated renormalized physical entities such as mass, anomalous magnetic moment [6] and the index of refraction [7] are modified. The refractive index n(w) < 1 (w indicates dependence on photon frequency) decreases relative to the refractive index in unbounded space (taken to be unity here), making possible velocities of light v=c/ n(w) > c higher than the speed of light in unbounded vacuum c.
Another possibility would be to consider a squeezed vacuum, or an environment which is characterized by superluminally ``moving'' charge-current patterns; i.e., synchronized arrays of charges acting similar to phase array radar systems. Maybe also certain divergences of rotating electromagnetic fields could be utilized [8].
The maintenance and steering of supercavitation in the quantum ether remains an open question. In the case of a cavity in which a Casimir vacuum is confined it is unclear if this cavity can be engineered to become a dynamical one. So far, mostly static problems have been considered; with perfectly conducting, fixed walls. It may happen, though, that, due to mirror charges or other effects, the boundary of this cavity can become a dynamical interface.
It is an often heard belief that superluminal transfer of information or travel of objects and agents would result in time paradoxes; since then it would be feasible in certain relativistic coordinate frames to ``reverse the flow of time,'' to ``travel to the past,'' and what not. Yet, many chronology protection schemes and remedies of different sorts have been proposed for these scenarios [9,10,11,12], which may make such concerns less troublesome.
A caveat: Let me, instead of a summary, reiterate that this note is very speculative and contains remotely conceivable options for supercavitation in the quantum ether. I am aware that this appears to be impossible to realize with today's scientific and technological means. Nevertheless, if our ancestors had never dreamed of possibilities of sailing faster then the wind or rafting quicker than the currents, then we might not be able to cross the continents, let alone to leave our planet.