A Spacetime Geometric Interpretation of the Apparent Slowdown of Light in Media -- Based on the Hypothesis of Spacetime Path Decomposition

This paper proposes a geometric interpretation for the phenomenon that the propagation speed of light decreases in transparent media. Different from the traditional electromagnetism explanation that attributes the slowdown to the polarization response of media, this paper hypothesizes that light always travels at the vacuum speed of light in four-dimensional spacetime, and its apparent deceleration in media originates from the redistribution of components between spatial and temporal paths. By decomposing the actual path between the incident point and the exit point into displacement parallel to the incident direction and displacement perpendicular to the incident direction, the transverse shift quantity = S n² - 1 can be derived. This relation is consistent with experimental data of various media. This model is positioned as a testable hypothesis rather than a replacement for existing theories.