The Philosophy of Time Travel · Chapter 2
Water and Metal
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.
Water and Metal are the key elements of Time Travel.
Water is the barrier element for the construction of Time Portals used as gateways between Universes at the Tangent Vortex.
Metal is the transitional element for the construction of Artifact Vessels.
In the film
Water
Water marks every crossing between universes in the film: the bathroom mirror ripples like liquid when Donnie's hand meets Frank's; Donnie breaks the school's water main and floods the building; the cinema screen liquefies when Frank opens a portal; the liquid spears Donnie describes to Dr Thurman flow from people's chests; and in the finale the engine passes back through the Vortex over the house.
Metal
The metal Artifact is the jet engine. Other metal objects mark the steps of Donnie's task: the axe he buries in the head of the school mascot, the gun he takes from his father's closet, the car that kills Gretchen.
Where this chapter happens on screen.