 What does \(J^-(p)\) reveal about the rest of spacetime? In classical GR, we would not expect the physical state on \(J^-(p)\) to determine that of other regions of spacetime—even the causal past of a point just to the future of  \(p\).[19]  There are some models in which \(J^-(p)\) does reveal more: “small universe” models are closed models with a finite maximum length in all directions that is smaller than the visual horizon (Ellis &amp; Schreiber 1986). Observers in such a model would be able to “see around the universe” in all directions, and establish some global properties via direct observation because they would be able to see all matter that exists.[20] 