Abstract: Cognitive rhythm represents a fundamental yet largely unexplored dimension of human AI interaction.This paper presents a formal theory that describes how cognitive synchronization, phase shifts, and resonance shape the way humans and artificial intelligence learn, think, and create together. We introduce a mathematical model:RC(H, A, t) = f (ΔΦH(t), ΔΦA(t), S(t), R(t)) where:• ΔΦH(t) = variation in human cognitive phase at time t• ΔΦA(t) = variation in AI cognitive phase at time t• S(t) = level of synchronization at time t• R(t) = quality of resonance at time t Through conceptual and simulated case studies, we demonstrate how this framework can inform the design of more effective and adaptive collaborative AI systems. The implications of this theory go beyond technical optimization touching on the philosophical and ethical dimensions of human–AI co-creation.We argue that cognitive rhythm is not just a metaphor, but an operational principle that can profoundly transform our understanding and design of symbiotic AI systems.