Glossary
Fourth Dimensional Construct
The medium, made of water, through which the Manipulated Dead contact and manipulate the Living Receiver.
The bathroom mirror scene is the clearest illustration: Donnie touches the glass, it ripples like water, and Frank is on the other side. The liquid spears and the flooded school are further signs of the Construct at work. Sparrow refers readers to Appendix A and B, which the film shows only as diagrams.
Defined in The Philosophy of Time Travel