Theres a good thread over here: https://www.physicsforums.com/showthread.php?t=613210 I don't want to derail it. But if energy is "poorly defined" globally in GR as explained in that thread then let's exploit it. Let's devise a "machine" that creates energy. I pose this in such a provocative way to underscore the point- its not enough in todays physics to say that global energy conservation isn't well defined. We should either lead this notion into a contradiction or start figuring out how to manufacture energy with it.