Based on the axiomatic system of Time Field Theory (TFT), this paper strictly derives the velocity composition law in inertial frames. Using the conservation of total speed, spacetime decomposition, flat spatial geometry, and covariant conservation, the one-dimensional and three-dimensional velocity composition formulas are obtained. The derivation is first-principles, self-consistent, and compatible with experimental observations. The framework maintains flat Euclidean space and scalar time field without additional assumptions.
Huowang Huang (2026) studied this question.