This paper constructs a three-threshold cyclic universe model based on black hole critical evolution and spacetime phase transition mechanisms. By defining the minimum collapse mass of stellar black holes as the fundamental quantization unit of spacetime, the model establishes a complete evolutionary framework featuring bidirectional reversible transitions between classical general relativity and quantum gravity regimes. The core finding of this study is that general relativity and quantum gravity are fundamentally compatible rather than contradictory. The two physical theories dominate distinct phases of cosmic evolution and can naturally transform into one another through spacetime phase transitions triggered by the accumulation of black hole equivalent units. Three physical thresholds — cosmic capacity threshold, domain-switching threshold, and cosmic rebound threshold — govern the whole cyclic process: classical spacetime gradually transitions to quantum gravitational spacetime as black hole units accumulate, and reversely returns to the classical regime when the quantum system reaches saturation and rebounds. This model demonstrates that compatibility between the two gravitational theories is achieved through phase alternation and mutual transformation, instead of forced mathematical unification. Within established physical frameworks, it provides a new self-consistent explanation for cyclic cosmic evolution and offers an alternative perspective to resolve the long-standing compatibility puzzle between classical and quantum gravity.
Jingheng Lin (Sun,) studied this question.