Potential energy was the energy from possible futures; Ace stated that potential energy flowed between every point in the multiverse. (AUDIO: A Life of Crime)
The Weeping Angels fed on the potential energy of an individual, though some used other sources. (TV: The Time of Angels/Flesh and Stone) A Weeping Angel would touch someone, sending them to the past while feeding on the lives they might have had. This led the Tenth Doctor to describe them as "the only psychopaths in the universe to kill you nicely," since their method of killing was to let their victims "live to death". (TV: Blink) During World War I, however, the Weeping Angels found themselves starved as their victims came from a "lost generation" whose lives were cut short. (COMIC: The Weeping Angels of Mons)
Similarly, the Oroborus turned the planet Centauri into a black hole by "siphoning off its future", as Alistair Gryffen said. (TV: Oroborus)
Peter Hutchings explained the theoretical impossibilities of a time-space corridor, since vanishing from the material universe would cause a vast energy discharge due to conservation of energy. Time travel would be impossible unless somebody could harness a black hole, somehow storing up all the potential energy debt incurred and letting it leak out of the event horizon as slow dollops of Hawking radiation, which was also impossible. (PROSE: Timewyrm: Revelation)