The actual statement in the episode is, "Space-time can be interpreted as the surface of an n-dimensional superfluid." There is no reference to bubbles, spheres, negative-energy, etc. The references is to a "surface"; superfluids have highly idiosyncratic surface properties. The idea is taken seriously within physics, tho only barely, in that light traveling across vast distances is seen as having less energy loss than would be expected, were space-time a normal fluid. Not, however, if it were considered as a superfluid. The adjective "n-dimensional" (or nth-dimensional) may, or may not, have been thrown in to complicate the issue.
