On a typically cloudless day in Mountain View, Calif., Google engineers are brainstorming feverishly, making emphatic notations on a whiteboard. Arcane tech problem? New business plan? Latest twist in the plot to rule cyberspace? No, these engineers are arguing the relative merits of superhuman powers. The choices? Invisibility versus flight, invisibility versus teleportation, flight versus teleportation, and the power to kill from 200 meters versus the power to move people with your mind.