The Infinite Self-Similar Multiverse (ISSM): A Minimal and Falsifiable Framework for Causal Fragmentation and Quantum Nucleation in an Accelerating Cosmos

We present the Infinite Self-Similar Multiverse (ISSM), a minimal cosmological framework in which all universe proliferation emerges from two established physical mechanisms: (i) causal horizon fragmentation in accelerating spacetime with posi- tive cosmological constant, and (ii) quantum vacuum decay via Coleman-De Luccia tunneling. Without introducing new particles, forces, or dimensions, ISSM demon- strates that an infinite A-dominated universe necessarily evolves into a self-similar hierarchy of causally disconnected spacetime regions, each capable of further vac- uum transitions. The framework is grounded entirely in general relativity, quantum field theory in curved spacetime, and the scale invariance of infinite sets. We derive a quantitative bound on observable bubble collisions and explicitly state falsifica- tion criteria. ISSM is testable through cosmic microwave background observations, gravitational-wave experiments, and late-time expansion measurements.