Glossary
Artifact
The metal object that marks the start of a Tangent Universe and must be returned to the Primary Universe to end it. In Donnie Darko, the jet engine.
The engine falls into Donnie's room on October 2 and cannot be traced to any aircraft - because it belongs to the plane that will carry Rose and Samantha home from Los Angeles on October 30. In the finale Donnie tears it from the plane and sends it back through the Vortex, closing the loop.
Sparrow notes that Artifacts "are often linked to religious iconography" because their appearance defies explanation. The FAA agents who cannot identify the engine are the film's version of that bafflement.
Defined in The Philosophy of Time Travel