User blog comment:PitaKang/Funday Monday 3: What would an interstellar civilization look like?/@comment-4758513-20130430022547/@comment-3218619-20130430234048

I skimmed through the article and think I know what it's saying. The second paragraph says that it needs matter with negative energy density, which, like tachyons with imaginary mass, have never been proven. May or may not exist.