Somebody Else's Problem field
The SEP field is a fictional technology from the Hitchhiker's Guide to the Galaxy "trilogy" by Douglas Adams. It is a cheaper alternative to an invisibility field.
The letters stand for "Somebody Else's Problem". An SEP field can be erected on, or projected around a bizarre and unbelievable scene so that the unconscious minds of the observers instantly abdicate responsibility for its existence, assert that it's "somebody else's problem", and therefore don't perceive it at all. The primary example of this was given in the third book Life, the Universe and Everything, when a UFO (a spaceship powered by the Bistromathic drive owned by the character Slartibartfast) landed in the middle of a cricket ground during a match, and the assembled crowd failed to notice it.
The SEP field requires much less energy than a normal invisibility field (a single flashlight battery can run it for over a hundred years) due to the natural propensity of humans to see things as Somebody Else's Problem. This is very close to the idea suggested by Terry Pratchett (who has often been compared to Douglas Adams) that people do not see what they are sure cannot be there (such as Death).
See also: bystander effect, cognitive dissonance
