Is existence subjective or objective? There are two observers, Alice and Bob, in a de Sitter cosmology with a positive cosmological constant. Both coast along their geodesics with some initial spatial separation between them. Soon, the de Sitter geometry will push each of them out of the causal horizon of the other observer. According to the causal patch hypothesis, past the point of no return, Alice will conclude she exists, but Bob no longer does. Bob will conclude the exact opposite. Unlike black hole complimentarity, no one will face a certain impending doom at a singularity, which would complicate matters.
Who is right about questions of existence? If there is a transcendental arbiter/judge to decide, we can go along with it. But what if there is no higher arbiter? Or what if there is a higher arbiter, but it (or "god") is not universal or fair, and it makes ad hoc judgments? Does each observer have their own reality? If there is continual two-way communication between observers, we may combine them into a single larger observer creating a mutual consensus reality, but what if such a communication channel breaks down with no global perspective? Are we condemned to postmodernism then?
The naive correspondence theory of truth and existence breaks down without a global perspective of a god, or objective reality. What then is truth or existence?