We have no idea where people go when they die; it's what makes death so scary and awful. But the sense that they obviously go somewhere—that the person in front of us, situated in the time and space we share, suddenly gets transported to another realm; that their consciousness flickers, then vanishes—also makes death incredibly inconvenient from a logistical standpoint.

This became apparent after the railroads were built. If a train engineer died suddenly on the job—poof!—he would be instantaneously swapped out for a lifeless lump of matter while the huge steel machine he'd been driving kept barreling down the tracks. To get around this problem, the railroad companies devised a "dead man's switch": a pressure-sensitive lever or pedal held down by the engineer as he drives. "If the guy suddenly plotzes," neuroscientist David Eagleman explains, "he'll release the switch and stop the train." Eagleman had this antiquated technology in the back of his mind when he sat down to write a short science fiction story called "A Brief History of Death Switches." The story begins with a familiar problem: "At the beginning of the computer era, people died with passwords in their heads."