The Philosophy of Time Travel

Sparrow opens by naming the two universes of her cosmology: the Primary Universe we live in, and the unstable Tangent Universe that can branch off it when the Fourth Dimension of Time is corrupted. Left alone, a Tangent Universe collapses within weeks and destroys everything.

The two elements of time travel. Water forms the portals between universes; metal forms the Artifact that must be carried back through them. Every water and metal image in the film — the flooded school, the axe in the bronze mascot, the jet engine — belongs to this chapter.

The Artifact is the metal object that appears out of nowhere at the start of a Tangent Universe. In the film it is the jet engine that lands in Donnie's bedroom on October 2 — the engine nobody can trace to a plane, because the plane it belongs to will not lose it for another 28 days.

Donnie is the Living Receiver: the one person chosen to return the Artifact. The chapter explains his powers (the axe in the mascot, the flooded school, the fire at Cunningham's house) and his torment (Frank, the visions, the sleepwalking) as symptoms of the role rather than of schizophrenia.

Everyone around Donnie — his family, Gretchen, Kitty Farmer, Jim Cunningham, Ms Pomeroy, Dr Thurman, even Seth and Ricky — is one of the Manipulated Living. Their strange, exaggerated behaviour is explained as unconscious help in returning the Artifact.

Frank and Gretchen both die inside the Tangent Universe, which makes them the Manipulated Dead: able to travel through time and contact Donnie through water. Frank's countdown, his instructions and Gretchen's death are the Ensurance Trap that guarantees Donnie returns the Artifact.

The final chapter explains the last two minutes of the film: the montage of characters waking on October 2 with a memory of something they cannot name. Cunningham weeping, Kitty, Dr Thurman, Frank touching his eye, Gretchen waving at Rose — the Tangent Universe survives only as a dream.