Let me geek out on you (I love science) and explain to you the science (I love science) and why this had previously been confined to the pages of science fiction (I am a nerd; and oh Dear Sweet Bunsen-Burner Lighting Lord, do I love science). So it's a pretty firmly established principle that every act causes, and requires, an equal and opposite reaction. If I understand this right (did I mention I love science?), this means that any space vessel will have to carry with it an enormous amount of reaction mass. You can't -- we think, or thought...