Two events are simultaneous if they occur at the same time. For events at the same location, this is unambiguous — all observers agree. For events at different locations, the situation is more complex.
Einstein’s 1905 thought experiment — two lightning strikes at the ends of a moving train — demonstrated that simultaneity depends on the reference frame of the observer. An observer at the midpoint of the embankment sees both strikes simultaneously. An observer at the midpoint of the moving train does not.
This is the relativity of simultaneity, and it is a genuine physical consequence of the second postulate — the invariance of the speed of light.
The question this theory addresses is: does the relativity of simultaneity require length contraction? In Special Relativity, the answer is yes — the two are linked by the Lorentz transformation. In the revised framework developed here, the answer is no. Simultaneity remains frame-dependent, but the framework that produces this frame-dependence does not predict any contraction of physical lengths along the direction of motion.
This is the central claim of Part II, derived formally from the postulates without additional assumptions.