A Five-Dimensional Spacetime Model Based on Event Branching

A unified five-dimensional spacetime model is proposed in which the fifth dimension encodes event branching. Instead of treating branching worlds as disconnected possibilities, the model embeds them within a single higher-dimensional manifold, where each component denotes a distinct four-dimensional spacetime branch. Within this framework, 5D spacetime is interpreted, for a fixed time slice, as the structure containing the possible event branches available at that moment, whereas a given 4D branch represents one realized spacetime history experienced by an observer. On this basis, a Lorentz-invariant branching metric, a five-dimensional proper-time relation, a branch light-cone structure, an extended Lorentz transformation, and a five-dimensional Einstein field equation are introduced as elements of a formal geometric framework. The theoretical aim is not to claim a completed unification of relativity and quantum theory, but to formulate a geometric language in which branching structure can be represented explicitly. The model is positioned relative to Kaluza–Klein theory, string theory, and the Everett many-worlds interpretation by treating the fifth coordinate as a branch index rather than as an ordinary compact spatial direction. In this sense, the construction can be read as a speculative but systematic attempt to give the many-worlds picture a Lorentz-covariant five-dimensional embedding, while leaving observational consequences and phenomenology as qualitative directions for future work. This work is a speculative theoretical construction rather than a completed physical theory, and all observational implications are presented as qualitative directions for future study.