The post-determined block universe

Abstract

A series of reasons to take quantum unitary evolution seriously and explain the projection of the state vector as unitary and not discontinuous are presented, including some from General Relativity. This leads to an interpretation of Quantum Mechanics which is unitary at the level of a single world. I argue that unitary evolution is consistent with both quantum measurements and the apparent classicality at the macroscopic level. This allows us to take the wavefunction as ontic (but holistic), but a global consistency condition has to be introduced to ensure this compatibility. I justify this by appealing to sheaf cohomology on the block universe. As a consequence, Quantum Theory turns out to be consistent with a definite four-dimensional spacetime, even if this may consist of superpositions of different geometries. But the block universe subject to global consistency gains a new flavor, which for an observer experiencing the flow of time appears as "superdeterministic" or "retrocausal", although this does not manifest itself in observations in a way which would allow the violation of causality. However, the block universe view offers another interpretation of this behavior, which makes more sense, and removes the tension with causality. Such a block universe subject to global consistency appears thus as being post-determined. Here "post-determined" means that for an observer the block universe appears as not being completely determined from the beginning, but each new quantum observation eliminates some of the possible block universe solutions consistent with the previous observations. I compare the post-determined block universe with other proposals: the presentist view, the block universe, the splitting block universe, and the growing block universe, and explain how it combines their major advantages in a qualitatively different picture.