An Open Universe Hypothesis: Dark Energy and Dark Matter as Environmental Effects of a Branching Multiverse Gravitational Wave Background

I propose an open‑universe hypothesis in which dark energy and dark matter are not independent, self‑contained fields, but macroscopic manifestations of the gravitational influence exercised by a branching multiverse whose structure and dynamics are governed by kinetic‑impact fractal branching of the inflaton field. The observable universe is interpreted as an open subsystem continuously shaped by a coherent, long‑wavelength gravitational wave background generated by neighboring cosmological domains that evolve, interact, and periodically collapse via kinetic‑impact events in the inflaton landscape. This environment acts as a unified external forcing term that generates the effects we empirically describe as the cosmological constant and dark matter, while leaving the standard Einstein and Friedmann–Lemaître equations unchanged. The guiding hypothesis is that several persistent cosmological anomalies—the Hubble‑constant tension, anomalous galactic rotation curves, and the KBC local void—can be understood as correlated projections of the same branching‑multiverse environment, rather than as independent internal failures of the standard model. The framework is formulated so that it is directly falsifiable via cosmological surveys, galaxy‑scale observations, and future gravitational‑wave observatories. Connections to the kinetic‑impact fractal branching mechanism are explicitly discussed in the companion paper [Ref. 1].