Photon Theory V4.0: Photon as the Physical Carrier of the Fourth Dimension and the Emergence of Time

This paper presents Photon Theory V4.0, a self-consistent, complete, observationally consistent and strictly falsifiable framework in fundamental physics. The core conclusions are: Time is not the fourth dimension; the photon constitutes the physical ontology and carrier of the fourth dimension; and time is a macroscopic emergent quantity generated by photon propagation along the cosmic optical axis. This framework does not contradict any experimentally confirmed phenomena, provides a unified explanation for the invariance of the speed of light, spacetime geometry, cosmic evolution, relativistic effects and quantum behavior, and forms a logically closed system.